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Equipment Discussions >> Classic Telescopes

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Jon Marinello
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Reged: 09/21/10

Loc: Santa Barbara, CA
Use of vintage eyepiece sun filters.
      #4610823 - 05/30/11 11:36 AM Attachment (193 downloads)

I'm sure this will start a small skirmish but here goes. I have always known that you should never ever use the old vintage solar filters that screw into the bottom of a .965 eyepiece. I have never heard why though. I assume its that they might be old, cracked, dried up or otherwise fail to provide adequate shielding from the sun's rays that would be focused at or near the plane of the filter.

Well I decided to give them a try as I wanted to see what all the concern was about. I have also always had a hard time with authority. I have several of these old filters and so I picked one in new condition and inserted it into a 60mm sears scope and pointed it at the sun. First I waited for it to start smoking. It didn't. So I slowly and carefully inched my eye up to the 18mm Tak LE ep and voilŕ. There was the sun. No heat, no blinding light. The only complaint is the false coloring. That was yesterday. Today I tried it with the same Tak ep but on my 4" AstroTelescope. Much nicer view as you would expect and it worked again without a hitch.

So the question is why shouldn't we be able to use these inexpensive filers? I'm sure there is a large collective of experts on this forum who will "school me" on the errors of my ways!

All of this said... I am not advocating that you try this at home.

Edited by RLTYS (07/17/11 08:18 AM)


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4610839 - 05/30/11 11:43 AM

LOL, right after posting this I went back out to view the sun and what do you know. The little filter had developed a small crack and was letting a small amount of the sun's bright light through. That said this didn't happen with the 60mm yesterday. But with a larger scope it failed. In any case, the risk is there.

So there you go! If you leave these filters in a scope pointed at the sun for an extended period of time THEY WILL CRACK!


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Preston Smith
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4610844 - 05/30/11 11:46 AM

Hi Jon!

First of all, Happy Birthday!

The sun filters work great however, they heat up and can crack or shatter. When this happens, it happens very fast. If you are observing and it cracks, there is a high probability that you will have highly magnified sunlight coming directly into to your eye - and there is no time to react. Some of the members of this group have personally experienced this.

The only time it is safe to use a sun filtera is if it is used in conjunction with a Hershel Wedge which redirects most of the heat before it gets to the filter.


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Preston Smith
The Travel Scope Guy
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Reged: 04/24/05

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Preston Smith]
      #4610851 - 05/30/11 11:50 AM

There ya go! You obviously posted your second post while I was typing mine.

I think we should get more comments in this thread and then ask our moderator to make this a permanenet thread at the top of our forum. If it saves just one eye then it is worth having at the top of the forum


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Preston Smith]
      #4610852 - 05/30/11 11:51 AM

Hi Preston,

Thanks for the birthday wishes. See my other post as the filter did crack. Fortunately when I was not looking through it.

jon


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Preston Smith]
      #4610858 - 05/30/11 11:53 AM

Sounds like a great idea Preston.

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grendel
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4610957 - 05/30/11 12:39 PM

therin lies the problem, if you are looking through one when it cracks your problems may b twofold, one is the magnified sunlight which can render you blind in an instant - or the infr red radiation can cook your eyeball.
or when it cracks small slivers of glass could fly off and into your eye - neither of these is an enjoyable prospect.
when we run solar observing we always have a marshall, whose sole responsibility is to inspect each scope for safety, before and during the session. things that have been picked up vary from unfiltered finderscopes (which at best can result in burns to the forehead) to solar filters that could blow off the front of the scope. when I have performed this service in the past I carried a roll of black duct tape to make these things safe, taping the filters in place or taping over the end of a finderscope.
Grendel


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DarkSkys
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: grendel]
      #4611060 - 05/30/11 01:18 PM

Now, how safe are the solar filters criterion sold that looked like barlow's? I've seen on of them on here a while ago.

Also how do you use a hershel wedge on a newt?


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jimarshall
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4611103 - 05/30/11 01:42 PM

Some of the old classic refractors had a dust cap with a smaller hole in the center to be used in combination with the sun filter...not foolproof but it at least sounds safer. I read somewhere that Galileo made his solar observations near sunset which also would be safer.

I almost forgot...Happy Birthday!

Edited by jimarshall (05/30/11 01:46 PM)


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Don W
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: jimarshall]
      #4611116 - 05/30/11 01:51 PM

Sunset doesn't block UV rays. That's where the danger is. Not in the visible spectrum.

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Rick Woods
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Don W]
      #4611181 - 05/30/11 02:22 PM

Here's an analogy:

Picture a magnifying glass. You focus the light of the sun to start some dry brush on fire for your campfire.

Now picture the magnifying glass as your telescope objective. How hot is the glass? Probably ambient temperature, maybe a little more.
Now, picture the flaming twigs as your eye right next to the eyepiece. How hot is it there?

That's why you don't use those eyepiece solar filters.


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BarabinoSr
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: jimarshall]
      #4611209 - 05/30/11 02:46 PM

You are correct that some of the scopes had an opening in the dust cover . My 11TR Tasco does .I believe that the sun lens works best with the aperture of the telescope reduced by the opening . For example , for a 60mm I have made a cover with a 30mm diameter opening.
Sun lenses are not safe but they may be useable for short views for a few munutes . I had one split on me a long time ago using a Jason #311 60mm refractor . I saw that sliver of light and got my eye out of the way , but prior to that it heated up significantly .
I have about 6 of them and they are never used . Projecting the sun's image is much safer and many can see the image at once . G


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DAVIDG
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Rick Woods]
      #4611258 - 05/30/11 03:14 PM Attachment (154 downloads)

As stated the problem is that these filters crack. The reason is were they are placed in the optical path. When you screw them into the eyepiece they at or very near the focal plane of the telescope and of course that is were all the energy is concentrated. Many times this depends on the design of the eyepiece. If you place the filter away from the focal plane like on the front of the star diagonal then the enegery is spread out and heating becomes very much less of an issue. We all know that you can light a piece of paper on fire when placed at the focus of the telescope but move it an inch inside or outside of focus and all you do is make the paper warm.
Also one has to understand that the size of the solar image the telescope produces also is a big factor. The size of the solar image is about 0.0092 x the focal length. So you have the relationship between size and energy. The smaller the image the more energy per unit area. So a long focus scope produces a bigger image that is less of a strain on the filter. You we have ever seen pictures of the solar osberving room at Mt Wilson, it shows a white light image of the Sun that is a number of feet in diameter, yet the table that the image is project onto doesn't burst into flame.
As for the Criterion S-4 solar eyepiece, it is very well engineered unit. First it uses a barlow lens with one of the concave surfaces metallized. So the Sun light hitting this surface is divergent and can't come to focus inside the telescope. Since it's a barlow, it needs to be placed well inside the focal plane of the telescope, and not near the focal plane so it does not see any concentrated energy. Next there is a green filter similar to the ones we are discussing here. It is placed inside the focal plane of the barlow lens. So it can never see concentrated sunlight light. The green color is around 540 nm which is suppose to be the best for "white light" solar observing and this is wavelength that Baader uses in their "Continuum Filter"
If you want the best in white light solar observing, you build an instrument designed exactly for it. Here is a picture of my 4.25" f/10 Solar Newt, which uses uncoated optics and a built in Herschel Wedge.
- Dave


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Bob Myler
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4612117 - 05/30/11 11:39 PM

Dave - given that offset from the focal plane - what would be the max-size aperture that could be safely used with the Criterion S-4 barlow-filter - and for how long? Since it would be positioned in front of the diagonal on a refractor, I assume a hershel wedge would not be used here?

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jsiska
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Bob Myler]
      #4612228 - 05/31/11 02:03 AM

In 1962 I purchased a Tasco 9TE, 60mm, f = 700 refractor. It came with one of those little dark glass “SUN” filters. The dew shield cap didn’t have one of those little pop out plugs so to use the filter necessitated the use the full 60mm aperture.

I used that sun filter many times with the H12.5mm and H6mm 0.956 eyepieces that also came with the scope. In fact, I once used it every sunny day for an entire spring month for a 7th grade science project. Each day after getting home from school, I would draw the sun spots I observed in a note book. I use to enjoy the views that sun filter gave of the sun. One day, not long after turning in that science project, I decided to once again check out the sun spots. As I was about to screw the filter into the eyepiece threads, I dropped the filter on the cement sidewalk and the glass broke into little pieces. “Darn it,” I thought to myself sadly, “now I no longer have a sun filter.” I still have the body of that sun filter without the dark glass of course. Sometime in the late 1970s, I learned how dangerous those old sun filters could be and I considered myself lucky that it broke on the cement sidewalk instead of while observing the sun.

Last December, I purchased a 1960 Tasco 7TE which came with the exact same dark glass sun filter. The 7TE also came with a sun projection screen. While it’s nice for old time sake to have the little sun filter, I certainly do not plan to ever use it; however, I might try the sun projection screen someday.

I also have some that mylar sun filter material that is suppose to be safe to observe with if it is put across the front full aperture of the objective lens. I purchased it to observe and videotape an annular eclipse back in the 1990s but I didn’t like the views using the mylar sun filter as much as I remembered the views using the Tasco glass sun filter so many years ago.


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rmollise
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: DarkSkys]
      #4612334 - 05/31/11 05:57 AM

Quote:

Now, how safe are the solar filters criterion sold that looked like barlow's? I've seen on of them on here a while ago.

Also how do you use a hershel wedge on a newt?




Might be fine. Might not. The only safe filter is an aperture filter. Period.


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Giorgos
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Reged: 01/14/11

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: rmollise]
      #4612511 - 05/31/11 08:56 AM

My old Vixen 80mm f/11.4 refractor came with such a filter and the telescope cap has a smaller one on it with a label underneath "Use it when observing the sun". I considered it safe because it was given with the telescope as a standard accessory and used it many times without any accident. I consider myself lucky though!
I plan to use it to photograph the sun with a digital camera so there is no danger to make any harm to my eyesight if it breaks. The focusing can be accomplised with the aid of the camera monitor. So these filters can have another use today.


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BigC
Carpal Tunnel
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4612794 - 05/31/11 11:35 AM

The little Sun filter was designed for use with a 60mm objective (or smaller) and you overloaded it with the light from a 100mm objective!Seriously ,it was subjected to 2/3rds more heat ;there really is a lot of energy in sunlight.

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DAVIDG
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Bob Myler]
      #4612814 - 05/31/11 11:43 AM

Quote:

Dave - given that offset from the focal plane - what would be the max-size aperture that could be safely used with the Criterion S-4 barlow-filter - and for how long? Since it would be positioned in front of the diagonal on a refractor, I assume a hershel wedge would not be used here?



Criterion recommemded that you stop your telescope down to 3". With the optical design of the S-4 being a barlow, the optics have to be placed well inside the focal plane to have an image to come to focus. So by design it is difficult not to use this device correctly. Since one of the surfaces is mirrored and it used well inside the focal plane, it doesn't heat up.
You don't use it with a Herschel wedge because the solar image would be too dim.

- Dave


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Al8236
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4612857 - 05/31/11 12:12 PM

After reading this post I had to dig out one of my old Sears manuals to see what it said about the Sun filter, It does say to screw the filter into the eyepiece!
I had never realized this as I was taught back in the 60's to always screw it into the diagonal by an older astronomer friend of mine for just the reason of keeping the filter out of the focal plane to avoid over heating the filter.
40 years later and I'm just getting around to reading that part of the manual
I'm glad that I had someone to instruct me instead of just reading the manual back then.
Al


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trainsktg
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4612919 - 05/31/11 12:47 PM Attachment (70 downloads)

Quote:


If you want the best in white light solar observing, you build an instrument designed exactly for it. Here is a picture of my 4.25" f/10 Solar Newt, which uses uncoated optics and a built in Herschel Wedge.
- Dave




Ah...another solar newt!

Keith


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: BigC]
      #4612924 - 05/31/11 12:50 PM

Not the first time I have pushed things too far!

I'm going to set up the 60mm again today and run some further tests with additional sun filters I have.

I will report back the results.


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wfj
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4613228 - 05/31/11 03:20 PM

Jon, if you have a digital thermometer, you might instrument the filter to see just how hot it is getting. It might surprise us all how hot this really gets.

The reason its breaking the filter is that the thermal load is too high and the heat has nowhere to go, so it builds.

Also, the glass starts out cold, so there's likely thermal shock that's occurring.

Neither of which occurs in a full aperture situation.


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Carl Kolchak
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: wfj]
      #4613264 - 05/31/11 03:43 PM

Hi Jon

This is a good question and thanks for asking it. I do have a followup to it.

DISCLAIMER: I do not use or advocate the use of these older sun filters:

When these filters were new, '50s, '60s, '70s, and etc. were there a lot of failures? Are there a bunch of budding amateur astronomers from this era with damaged eye/eyes? Is it because of the age these filters become dangerous? Or is the warning that accompanies every post regarding these sun filters stated because folks may use the filter with larger scopes, (like Jon did) and discover that the filter will fail?

peace & clear skies,


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Bonco
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Carl Kolchak]
      #4613390 - 05/31/11 04:38 PM

Maybe it goes without saying but full aperture astro mylar filters are easy to mount and cheap. I have a more expensive 4 inch hard filter from One Thousand Oaks. Works great but is much more expensive than their mylar sheets.
My filter delivers a natural looking yellow solar disk however I think the mylars deliver a blue disk. Bill


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Don W
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Bonco]
      #4613449 - 05/31/11 05:10 PM

One of the big problem with these filters is that when you attempt to focus them the filter goes through the point of focus before the point of focus is reached in the eyepiece. When this happens, the focused heat of the sun is on the filter and the intense heat can make them crack or even burst.

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DAVIDG
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Don W]
      #4613514 - 05/31/11 05:53 PM

One of the reasons why these filter crack from the heat is that they are usually held too tight in the cell so the difference in the expansion of the glass vs the metal that is causing the failure. The usual mode of failure is that you have been observing the Sun for a number of minutes or longer and that is when they crack. Having a solar filter mounted in a black cell is also not the greatest piece of optical engineering.
If you run the experiments be sure to run one were the filter is mounted on the end of the diagonal. Also measure were the focal plane is in relationship to the end of the eyepiece you use. With many of the simple eyepiece designs that came with vintage 60mm refractors, the longer the focal length of the eyepiece, the far the focal plane of the scope was from the end of the eyepiece when it is in focus. That put the filter in position in the optical path were the energy was spread out. The shorter focal length eyepiece come to focus were the focal plane of the scope is very close to the end of the eyepiece, putting the focused image of the Sun on the filter.
I'm wondering if the cause of failure of these filters is that one first was observing the Sun with low powered eyepiece and then wanted to take a closer look at a Sunspot and switch to higher magnification and that put the filter in position were the Sun was focused on the filter.

- Dave


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: BigC]
      #4614071 - 05/31/11 11:44 PM

Quote:

The little Sun filter was designed for use with a 60mm objective (or smaller) and you overloaded it with the light from a 100mm objective!Seriously ,it was subjected to 2/3rds more heat ;there really is a lot of energy in sunlight.




Not 2/3 more, but nearly three times as much, because heat is proportional to the area of the objective.

60mm => 30mm radius; 30^2 = 900 square mm area

100mm => 50mm radius; 50^2 = 2500 square mm area

100mm objective has ~ 2.8 times the area of a 60mm objective


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MacScope
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4614093 - 05/31/11 11:54 PM

I used one of my vintage sun filters this past evening close to sunset with a 20mm Huygens eye piece in my 60mm Celestron/Vixen Cometron 910mm focal length. Nice view, green, did not view for long. Wish I could find a Swift or Tasco Herschel wedge but they are not easy to find.

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Joe Cepleur
Carpal Tunnel


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: MacScope]
      #4614156 - 06/01/11 12:43 AM

Quote:

I used one of my vintage sun filters this past evening close to sunset with a 20mm Huygens eye piece in my 60mm Celestron/Vixen Cometron 910mm focal length. Nice view, green, did not view for long.




Seems a shame to risk blindness when safe solar filters covering the entire objective are readily available, but none of us can tell others what to do. I am sure we are all glad that you enjoyed a fine view and came to no harm. Still, such good fortune does not change the thrust of this thread, nor our responsibility to educate the pubic on the safe use of classic telescopes.

Many people used this type of solar filter back in the day. Had it been 100% dangerous 100% of the time, no one would have used it. The problem is analogous to wearing seat belts. People will say, "No need; I'm not going far." Looking simply at the facts, the equations of kinetic energy have no factor representing the total time or total distance traveled prior to the crash. Only the velocity at impact matters, with consequences that may be severe. In the case of this old style of solar filter, blind is blind, regardless of how many successful viewings one has had in the past, or how fine or long the view immediately prior.


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Rich (RLTYS)Moderator
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4614363 - 06/01/11 06:18 AM

Quote:

Not the first time I have pushed things too far!

I'm going to set up the 60mm again today and run some further tests with additional sun filters I have.

I will report back the results.




I hope the filters you are testing are NOT the old fashion dark filters. You were lucky the first time, you may not be so lucky the next time.

Rich (RLTYS)


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Rich (RLTYS)]
      #4614445 - 06/01/11 07:48 AM

If Jon tests his remaining solar filters without looking through them, he may gather interesting historical data, or even open a niche field of solar photography through sacrificial cameras. I support his experiment, with the caveat that we would be responsible to convey that no readers should misinterpret the result. Suppose he showed that, over so many hours, these filters placed at the diagonal of a 60mm scope did not break, whereas one already broke promptly when screwed to the eyepiece of a 100mm scope. Given the stakes of instant blindness, the inherently flawed engineering of placing the filter after the objective, and the uncertain quality of all such antique filters of this type, it would still be unsafe to use them, and irresponsible for this forum to condone their use with live human eyes.

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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Rich (RLTYS)]
      #4614531 - 06/01/11 08:59 AM

Yes they are the old fashioned ones. But I won't be looking through them. This will just be a test to see how long they will go before breaking. I won't look through them.

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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Joe Cepleur]
      #4614532 - 06/01/11 09:00 AM

Agreed Joe.

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Preston Smith
The Travel Scope Guy
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4614558 - 06/01/11 09:26 AM

Hmmm,

DAVIDG made a very good point (as always) that the sun filters did not have thermal expansion capabilites.

What if:

A Ramsden eyepiece had an old solar filter mounted between the two elements of the eyepiece? And mounted in a manner to allow for some thermal expansion? And only used on a 60mm scope?

The filter would not be near the focal point.

Do any of you have reports of the lenses in your old eyepieces cracking from solar observing? I know that more complex eyepiece can be damaged but I have never heard of the two lens eyepieces (Ramsdens, Huygens) being damaged.


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DAVIDG
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Preston Smith]
      #4614645 - 06/01/11 10:36 AM

Eye damage is serious stuff. I've been an amateur astronomer for over 30 years and have been observing the Sun all that time. I have had a filter crack on me while I was observing the Sun and looking into the eyepiece when was I kid. Since then I have had my eye examined many times and told the Doctors what had happened and they could find nothing wrong with my eye. I did not have any lose of vision or any problem after the filter cracked. I'm still lucky to have 20/20 vision in both eyes, today.
Maybe I got real lucky but over years I have read that when these filters crack one is going to suffer instant blindness. While this is very serious, I would like to know if anyone has FIRST hand knowledge of eye damage caused by one of these filters cracking. I know that people have suffered eye damage from looking at eclipses but that is different. I do scientific research for a living and I like to see the data and seperate the facts from the fiction.
On a side note I have seen full aperture solar filter fall off telescopes and have seen the wind blow them loose so one needs to be sure that they are mounted very well. I have witness first hand when a full aperture filter came loose and it wasn't more then 3 seconds later, smoke was coming out of the telescope and a few months ago there was a newspaper article I read were a telescope was left unattended during the day and caused a deck to catch fire.

While I am not defending the use of these screw on type filters, if they crack, your letting light in thru the crack vs if you loose a full aperture filter you have much more energy at the eyepiece.
This is why I built a telescope designed for white-light solar obsevering, with many built in safety features. If any part fails, it fails safe and no image can be formed at the eyepiece.

All the Best,
- Dave


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4614656 - 06/01/11 10:41 AM

Hi Dave,

I would like to hear more about the design of the telescope you built for white-light solar obsevering, with all the built-in safety features. Can you show us pictures with lots of close ups of the features along with a detailed description? I might want to build one. Perhaps this is already documented and in that case can you just point us to that?

Thanks,

jon


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mikey cee
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4614677 - 06/01/11 10:58 AM

Well I have one solar filter maybe two but they are so hard to find for me that I will never abuse them. Between people tossing them and Jon destroying them I'll soon have a true and valuable collection!! Mike

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trainsktg
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4614778 - 06/01/11 11:52 AM

Quote:

Hi Dave,

I would like to hear more about the design of the telescope you built for white-light solar obsevring, with all the built-in safety features. Can you show us pictures with lots of close ups of the features along with a detailed description? I might want to build one. Perhaps this is already documented and in that case can you just point us to that?

Thanks,

jon




Jon,

There is a decent tutorial on how to design a dedicated solar scope on pages 43 and 44 of Sam Brown's 'All About Telescopes'. It isn't a step by step tutorial, as you will need to use the various tables to calculate the strength of the image based on the type of telescope you are designing, and then the appropriate filtration or attenuation to knock the image down to safe levels. I have yet to run across another book anywhere that discusses the construction of a dedicated white light reflector. Mine is a 4.25" f13.

Keith


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DAVIDG
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4614789 - 06/01/11 12:00 PM Attachment (73 downloads)

Quote:

Hi Dave,

I would like to hear more about the design of the telescope you built for white-light solar obsevering, with all the built-in safety features. Can you show us pictures with lots of close ups of the features along with a detailed description? I might want to build one. Perhaps this is already documented and in that case can you just point us to that?

Thanks,

jon




Jon,
You can find a couple of write ups of different solar instruments I have made over the years including my white-light solar newtonian here http://www.considine.net/dgroski/
It's a 4.25" f/10 newtonian with the primary and secondary that are uncoated. Only 5% of the light is reflected off of the primary and then 5% of that off the secondary. The light then goes to a Herschel wedge that can be rotated. So none of the surfaces ever seen concentrated solar energy. Heating and distortion of any of the optical surfaces does not occur. Since the light coming off the secondary is polarized, by rotating the Herschel wedge I can cross polarize the light and tune the brightness of the image to fit the sky conditions and magnification used. The Herschel wedge is held in place by a screw so it's not easily removed. If anything of the optical parts should fall out or some how fail no light can reach the eyepiece. If some how some one would remove the Herschel wedge and look into the 'scope they would see light that was reduced in intensity by 0.0025. The reflection off of glass or water is brighter.
The optics are held in an oversized cardboard tube and the mirror cell has a fan on the back. It allows air flow but no light from the outside to get in. The result is a very high contrast image. When the sky is clear, the area around the Sun is ink black. The grandulation on the surface of the Sun are almost always visible and Sun spots show amazing detail.
I designed this 'scope to be used at public outreach events since I know it's safe. One would have to work very hard to hurt themselves observing with it. I don't have to worry about a filter failing, a coated developing pin holes or having a kid pull a full aperture filter off the 'scope or the cap off a finderscope and looking in when I turn my back for a second.
Here is a picture of my homemade Herschel wedge. The wedge itself was sold by Edmund. This one was chipped along the edges and ground it into an ellipse. It's mounted in a PVC pipe Tee. The assembly rotates and in the picture the eyepiece is at 90 degree to the tube and in that position the images is it's dimmest because of cross polarization. When the eyepiece is parallel to the tube the image is at it's brightest.

- Dave


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BigC
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4614835 - 06/01/11 12:22 PM

That is really neat.So there is a good and proper use for uncoated mirrors.
One little note about safety: although the reflectivity of 1/4 of 1% sounds very safe,everyone should remember the scope is gathering considerably more light than the naked eye.So if the scope gathers 400 times as much as the naked eye ,then looking into the scope without the Herschel wedge would be like staring directly at the unmagnified sun.Bigger aperature scopes could be dangerous.
Wonder if one of the common cheap 76 Newts could have its mirrors stripped of coating and then be safe for solar viewing?


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4614888 - 06/01/11 12:47 PM

Quote:

Eye damage is serious stuff... I have had a filter crack on me while I was observing the Sun and looking into the eyepiece when was I kid. Since then I have had my eye examined many times and told the Doctors what had happened and they could find nothing wrong with my eye.

(O)ver years I have read that when these filters crack one is going to suffer instant blindness. While this is very serious, I would like to know if anyone has FIRST hand knowledge of eye damage caused by one of these filters cracking...

(W)hy I built a telescope designed for white-light solar obsevering, with many built in safety features. If any part fails, it fails safe and no image can be formed at the eyepiece.




Glad to hear you are okay after the filter cracked. Perhaps the outcome would have been less fortunate had it shattered?

I have to agree, I have no first-hand knowledge of instant blindness occurring. It may be an urban myth, yet seems like a realistic possibility, one easily prevented by carefully securing an aperture filter in place; or, better yet, by building or buying a dedicated, fail-safe solar telescope. I vote that we continue to teach not to use these filters. If an errant telescope can burn a deck, there is no reason to risk damaging anyone's eyes.


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roscoe
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: BigC]
      #4614894 - 06/01/11 12:48 PM

Well...... I have a cheap .965 EP drifting around here somewhere that has a plastic field stop with an arc-shaped hole melted out of it........ no news of the former owner's eyeball, but glad it wasn't me!
Russ


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: wfj]
      #4615123 - 06/01/11 02:58 PM

I don't have a digital thermometer.

The tests I want to run are:

1. Star Diagonal Test - Solar filter mounted on a star diagonal

  • 60mm
  • 80mm
  • 90mm
  • 102mm

2. Eyepiece Test - Solar filter mounted on eyepiece

  • 60mm
  • 80mm
  • 90mm
  • 102mm - The results from this test are already known.


Let me start with these tests and we can add others after we have the results. I may not have enough filters to do all the tests. If anyone has any spares they can send me that would be appreciated.

I want to run the star diagonal tests first as these tests are less likely to break the filters I have. The problem is that I can't find a .965 star diagonal that has threads in the inside of the nose piece. I need to dig out the Sears scopes and check one of them...

So I'm blocked at the moment. Clouds just rolled in too!

jon


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wfj
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4615181 - 06/01/11 03:38 PM

It would not surprise me if you had a steady supply of these filters, that if you averaged the "accumulated exposure time" at prime focus to the sun ... they would all break around the same time (plus or minus a small scatter).

You'd end up with a Gaussian distribution, and this would prove that the issue is accumulated thermal stress/strain leading to a fracture along a weakest member.

Thus all these things ever were ... a limited lifetime component with a terrible failure mode.

What's even worse was that the cost trade-off of a small piece of welders glass verses a few square inches of aluminized mylar is tiny. Probably just happened because of the cost of the vacuum equipment for doing the coatings.


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actionhac
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: wfj]
      #4615318 - 06/01/11 05:18 PM

This is probably a silly question but will the SUN filter let enough light through to project an image on the solar projection screen?

Robert

Edited by actionhac (06/01/11 09:40 PM)


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: actionhac]
      #4615319 - 06/01/11 05:20 PM

I'm only testing for the filter cracking nothing more. I won't look through it or use a camera.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4615478 - 06/01/11 07:00 PM

Jon,
It might be possible to unscrew the barrel on the star diagonal and replace it with one from an eyepiece, that is thread for filters.
Also please make a note of how tight the filter is in the cell. It should rattle slightly when you shake it. If not I would loosen it, then run your tests and then repeat the tests with the filter tight in the cell.
It's been stated that these filters might shatter. Does anyone have first hand knowledge that a filter shattered ? I have seen them crack but not shatter. It's important to seperate the facts from the fiction and understand under what conditions these filters fail and how they fail.
It has been posted that these filters fail when used with telescopes that have apertures larger then 60mm. If the filter was designed for use on a 60mm telescope and failed when used with one larger, is that the fault of the filter or the user of the telescope ?

- Dave


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Joe Cepleur
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4615540 - 06/01/11 07:40 PM

Quote:

If the filter was designed for use on a 60mm telescope and failed when used with one larger, is that the fault of the filter or the user of the telescope ?




It's customary but unfair to blame the user. The filter fits any scope with a 0.965" focuser. Realistically, what's likely to happen? Nothing stops it from being used in a scope of larger aperture. Ever notice the pump for diesel fuel will not fit the fill on gasoline powered car? That's good design, and the engineer's responsibility. Good engineering solves problems and protects people from unwitting harm. It's no secret that telescopes were often given to children, or used by adult beginners who did not read manuals

Quote:

if you averaged the "accumulated exposure time" at prime focus to the sun ... they would all break around the same time (plus or minus a small scatter)




Strictly, exposure time per unit area of objective (assuming consistent, bright sunlight). The point is the same. One filter is likely as robust (or imperfect) as the next. Whether or not blindness is a realistic risk, pain surely is, and one never knows when a particular filter will fail. 

It may sound morbid, but the army has data on how quickly a given intensity of light will blind an enemy hit with a laser weapon. A scope isn't a laser, but it intensifies light. Anyone know the facts, or care to research them?


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: BigC]
      #4615715 - 06/01/11 10:04 PM

Quote:

The little Sun filter was designed for use with a 60mm objective (or smaller) and you overloaded it with the light from a 100mm objective!Seriously ,it was subjected to 2/3rds more heat ;there really is a lot of energy in sunlight.



In my 1962 Tasco catalog, in addition to several 60mm refractors, the SUN filters also came with the Tasco 10TE Solarama 600 refractor which has a 76.2mm objective lens, and the 11TEA Lunagrosso which is a 4˝” Newtonian.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: jsiska]
      #4615796 - 06/01/11 10:55 PM

The TASCO 11TE 4.5" Lunagrosso has a lid that is a combination dust cover and light stop .It has a 2" removable cover that reduces the aperture to about 2" .G

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: BarabinoSr]
      #4615885 - 06/02/11 12:08 AM

I don't see how it is unfair to blame the user for using a filter on another telescope of larger aperture that is wasn't designed for and having it fail. Right now the data that has been posted show misuse as the mode of failure but there is very little data at all so you can't come to any type of conclusion. If the filters are provided with a 4" reflector or 80mm refractor and the instructions state to use a cap that reduces the aperture to 60mm with the filter and user fails to do this, this is failure of the user.
The original question was what is the reason why one shouldn't use these filters. We had failure when the filter was used on a telescope of larger aperture that the filter didn't come with. If the common mode of failure is misuse then we as a group need understand not to use them with a telescope they are not designed for and to also use them in correct manner on the telescope they were designed for. That is different then they are unsafe all the time. To make that determination we need data, not myths or second hand accounts.

- Dave


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Littlegreenman
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: grendel]
      #4615917 - 06/02/11 12:32 AM

Quote:

(snip)....
when we run solar observing we always have a marshall, whose sole responsibility is to inspect each scope for safety, before and during the session. things that have been picked up vary from unfiltered finderscopes (which at best can result in burns to the forehead)....
Grendel




Slightly changing the subject, I once forgot to cover the finder on a C8 while solar viewing. This would have been a 6x30 finder. My forehead started to heat up. I moved around and saw bright glare coming from the finder, thankfully off to the side.

This is one of the few blessings of thinning hair. There wasn't any hair in the path to catch on fire!

(Almost blackened) Littlegreenman


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Joe Cepleur
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Littlegreenman]
      #4615926 - 06/02/11 12:42 AM

Quote:

I don't see how it is unfair to blame the user for using a filter on another telescope of larger aperture that is wasn't designed for and having it fail. Right now the data that has been posted show misuse as the mode of failure but there is very little data at all so you can't come to any type of conclusion. If the filters are provided with a 4" reflector or 80mm refractor and the instructions state to use a cap that reduces the aperture to 60mm with the filter and user fails to do this, this is failure of the user.




It's unfair because the fault of bad engineering is then shifted to be blamed as the user's error.

If the engineering standard were that the filters would cover the entire objective, with so much absorption of light per square millimeter, then an oversized filter would in fact work fine, so long as the user found a sure means to secure it. Using an undersized might then properly be ascribed as the user's error: Duh; it didn't cover the entire objective. Fairly obviously, something intended to cover something else really needs to cover it.

A standard sized solar filter at the ocular fails this test. Any user could, not just by carelessness but by reasonable, expected human error, put the wrong filter in the wrong scope. The failure is thus the engineer's, for not designing a system that an ordinary human can use without error, every time, or risk hurting if not blinding his eyes.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4616050 - 06/02/11 04:09 AM

Hi All.
Without a Hershel Wedge in conjunction with a solar filer it is not "safe" to view the sun with any size refractor telescope. Other than that you can use a solar rejection mask that installs over the objective, but I find a Hershel wedge and a Zeiss ND filter to be the best setup for high magnification viewing of Sun spots with any size refractor. Also the optical flats that Unitron used in there solar wedges are very good and seem to work as well as Optima BC or Bader wedges.
As to taking readings of the heat generated at the focal plane of a telescope pointed at the sun. I can tell you the exact reading. Really Hot!!!
(aveman


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Rich (RLTYS)Moderator
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: actionhac]
      #4616125 - 06/02/11 06:26 AM

Quote:

This is probably a silly question but will the SUN filter let enough light through to project an image on the solar projection screen?

Robert




I wouldn't think so.

Rich (RLTYS)


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Rich (RLTYS)]
      #4616201 - 06/02/11 07:54 AM

Quote:

how it is unfair to blame the user for using a filter on another telescope of larger aperture that is wasn't designed for and having it fail




Another thought: We're asking a fair question, "Has anyone heard, firsthand, of anyone being blinded when a filter failed?" Analogously, I can say that I, personally, have never once seen a solar filter of the design in question labeled, "Use only with 60mm aperture," or, "For 90mm aperture," or "For 100mm aperture or smaller." If they were designed for differently sized scopes, they would all have different darknesses of glass, yet would all look identically opaque to the eye selecting them, and so would need to be labeled. If they were intended only for 60mm scopes, none are so labeled, nor is there warning to use an accompanying aperture mask, except possibly in a manual that should be read, but may not be. The situation invites user error, a high stakes blame game when one is engineering a telescope for viewing the Sun. The solar filters of this design that I, personally, have seen all say only, "Sun," and some of them are molded in red plastic instead of black.

Red instead of black plastic is an imperfect example of engineering for safety. With the red color (grey to the colorblind), there is less chance that the user would insert the black moon filter by mistake prior to looking at the Sun and, at the very least, risking getting hurt. The trouble is, that black moon filter would still fit. A better example would be designating dedicated solar telescopes (such as exist, some of which are mentioned in this thread), and making special focusers for them, with square solar filters that simply could not fit into ordinary telescopes.This is not perfect, because the user might still find a means for attaching the wrong type of focuser to a supposedly solar scope. Still, at least with the right focuser when it was installed, that wonderful person everyone knows who has endless curiosity about the natural world, but little mechanical ability, could never be brought to harm accidentally via an error with a solar filter.

Trouble is, putting the solar filter at or near the focus of a conventional telescope exposes it to a far greater risk of breakage due to thermal issues, so it is inherently safer simply to move it to the safest place. Where's that? Before the objective. What light does not enter the scope can not hurt anyone's eyes. Granted, as Grendel discusses, it must be mounted securely, and the finder must be blocked; but, this is still a safer situation, one engineered to evade the user's ability to err.

People take all kinds of risks for all kinds of good reasons. No one is saying that no one else should never look at the Sun through a telescope. In gymnastics, the padding at the base of the apparatus (balance beam, uneven parallel bars, and the like) must extend past where the user is likely to land to also cover the steel feet. Why bother? Isn't it user error when the gymnast falls in the wrong place? What about steel toed shoes in the workplace. Isn't it user error when the employee drops something, or steps where told not to? Why waste the money covering the drive belts in heavy machinery? Isn't it user error when clothing gets caught, pulling the operator into the belt? Why should the petroleum industry make certain that the pump for diesel fuel won't fit in your gasoline powered car? Isn't the user responsible for selecting the correct hose?

In Maine recently, a vendor's kerosene tank was accidentally filled with gasoline. This could have killed anyone who poured the fuel into a kerosene powered heater and lit it. Why the concern, with all the radio stations, newspapers, and Web sites spreading the news? Isn't it user error if someone smells gasoline instead of kerosene, and lights it anyway? What about people with no sense of smell? Aren't they responsible to always have someone else smell their fuel? In this instance, the error was caught early, so no one got hurt. It would not have occurred at all if, as with the diesel-versus-gasoline hoses for cars, the fill on the kerosene tank were engineered to be unique, so the vendor could not have made the mistake that put others at risk.

This forum is unusual in at once being a hobbyist's abode and, in the marketplace of ideas, a respected, authoritative source of information. If we say, "Use the filters," more people will; and, if we say, "Do not!" more people will not. If Jon's tests show that his remaining five or so filters do not fail under whatever conditions, that would be interesting to know, yet would not prove that no filter would ever fail out in the wild world of well intended, but possibly naive users. Given the flawed design of these old-style solar filters sitting near the focus, let alone the unknowns in the current quality of the materials in any particular filter as they all age well past thirty, forty, and even fifty years, we have a responsibility to tell the world that, as much as we love classic telescopes, we want astronomers to consign this badly engineered design to the history books and use modern filters when viewing the Sun. Equal caution and better solar filters can only result in fewer injuries, whether mild or severe.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: DAVIDG]
      #4616623 - 06/02/11 12:49 PM

My first telescope was a Tasco 66TE 50mm f/12 which came
with a sun filter, that was in 1967. Not knowing any better**,
I used it for solar observation for years, including the
eclipse of March 7 1970 which was partial from my location.
I remember it would get quite warm after prolonged use. I
also remember that the optical quality was excellent, I
could see solar granulation when seeing was good. Later,
when I made a 6" Newtonian, I tried it in that and it cracked.
Not shattered, a single hairline crack. I wasn't looking
in the eyepiece when it happened, I heard a "snap" and took
it out & saw the crack.





** I was 10 then and there were no dire warnings on the internet
about eyepiece solar filters, most likely because the internet
did not exist then.


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4616708 - 06/02/11 01:38 PM Attachment (64 downloads)

I just started test (1, 60mm) at 10:25 PST. I was able to use an eyepiece barrel threaded into the star diagonal which allowed me to then thread the sun filter into the diagonal. That was a good suggestion. I will leave it pointed at the sun for a maximum of 2 hours. I have to run to a doctor's appointment at 11:00. I will check it before I leave and after I get back. This is the test that is most likely to succeed (i.e., not crack the filter of all the tests). Will report back later today on the result.

BTW - I have included a shot of the 60mm on my Atlas EQ-G so you can see what I am using for tracking for each of the tests.


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4616714 - 06/02/11 01:40 PM Attachment (64 downloads)

The OTA for this test is a Sears Discoverer No. 4 6305-A D=60mm F=900mm. Here is a close up.

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jwaldo
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4616739 - 06/02/11 01:52 PM

This should be interesting

Speaking of EP solar filters, aside from the cracking thing, how are they for actually blocking UV/IR? On occasion I've pondered adapting mine into a sort of objective solar filter for the front of a finderscope...


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4616827 - 06/02/11 02:31 PM

Dig that Atlas mount! The question is whether the filter may crack or shatter, not whether it may explode like a hydrogen bomb....

(You must have some great scopes for such a fine mount.)

The anecdotal evidence is mounting that however reliable these filters may be when used with 60mm aperture, they break far more readily with anything larger. Looking forward to Jon's results.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Joe Cepleur]
      #4616898 - 06/02/11 03:06 PM

Interesting experiment... hopefully nothing else gets melted in the process! I have a cheap EP that was exposed to sun through a refractor, that had the solar filter taken off only for a few seconds, and it melted part of the interior lining of the lens holder. Lotsa energy in a focused beam!

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: neotesla]
      #4616964 - 06/02/11 03:47 PM

Before experimenting on a larger diameter OTA, I'd be curious to learn the results of using a 60mm refractor with the SUN filter screwed directly into an eyepiece since many old unmodified 0.956” star diagonals did not have filter threads in them. At least the two Tasco diagonals I have (1960 & 1962 – both slightly different) don’t have threads in them.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4617051 - 06/02/11 04:43 PM

Test (1, 60mm) ended at 1:40PM PST. A little over three hours. Skies are clear. The filter didn't crack.

I also took the advice of loosening the lock ring a little. I tested the temperature by touch of the filter and it was I would guess about 100-110 degrees F. I was able to hold it to my cheek (after a quick finger test) and it was hot but not so hot I had to pull it away.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: jsiska]
      #4617062 - 06/02/11 04:51 PM

Ok I will run that test next as the 60mm is already on the mount.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4617066 - 06/02/11 04:53 PM

I just started test (2, 60mm) at 1:45 PST. I will leave it pointed at the sun for a maximum of 2 hours. Will report back later today on the result.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4617229 - 06/02/11 06:53 PM

Test (2, 60mm) ended at 3:50PM PST. A little over two hours. Skies are clear. The filter didn't crack.

I tested the temperature by touch of the filter and it was I would guess about 110-130 degrees F. I was able to hold it to my cheek (after a quick finger test) and it was hot but not so hot I had to pull it away. It was hotter than test 1, 60mm but not that much hotter. The eyepiece was much hotter though as expected.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4617284 - 06/02/11 07:29 PM

Jon,

Very interesting, thank you for doing and reporting the results for tests 1 & 2.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: jsiska]
      #4617306 - 06/02/11 07:43 PM

The results of these first two tests are at once interesting and not surprising. If these filters cracked all the time, their uselessness would be clear. Instead, there are reports of people using them for years in their youth without problems, as well as verified reports of their cracking when exposed to apertures beyond 60mm. Given that Jon is testing just a few filters, not a statistically valid sample of thousands, in the end we will still have to decide whether to advise against using these antiques with live human eyes. I'll likely remain cautious (or a party pooper, depending upon one's point of view), and continue to say "No!" regardless of the results with these few filters. A well-secured, modern filter covering the entire aperture remains inherently safer, a desirable trait when the stakes are so high.

Looking forward to your continued results, Jon. Your work is a real public service, as well as good science and good fun.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Joe Cepleur]
      #4617313 - 06/02/11 07:48 PM

Agreed. My results won't be statistically significant. I will continue the tests tomorrow weather permitting.

Thanks for the encouragement!


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4617616 - 06/02/11 11:14 PM

Maybe Myth Busters would be interested in this?

Okay, so I used one of these SUN filters that came with my 60mm Towa back in the 70's and it never cracked when used with my 60mm Towa until later when I tried it on my 8" Cave, and it lasted less than a minute and I don't remember exactly what happened, but I had a 1.25" to .965" adapter and the K22mm .965 eyepiece with the solar filter was an ex-K22mm eyepiece that day. My excuse is that I was a teenager - glad I didn't burn my eyeball out! I haven't done any solar observing since...

On another sidenote - I did one time scare the ____ out of me when I was trying to find Jupiter or Venus during the day by using the Sun as a RA/Dec reference and then moving the 8" Cave tube to where the planet should be. My routine was to remove the finder and primary eyepieces from the scope, then adjust the setting circles so that when pointed at the Sun, the mount was aligned, then dial in the planet. The Sun was used as a reference for RA/Dec when pointed at the Sun and the tube's shadow was concentric. Well it worked great, but one time, I was moving the tube (with eyepieces removed) and somehow managed to pass that concentrated Sun beam across my face and one eye - the time was less than a second, but I still remember the heat, and I still have diminished vision in that eye, just a slight fault in color, blue things look green, green things look yellow, like that.

So, whether using these filters in a 60mm is dangerous or not is a myth, I sure would like to know. But surely, mis-using them is a clear danger!


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4617633 - 06/02/11 11:21 PM

This is a fine example of how scientific inquiry begins. A well designed, practical experiment determines whether a larger study of statistical significance is warranted. I like how you're raising the stakes bit by bit, so as not to destroy your few filters prior to collecting all the data you can. Despite the small sample, this will likely be the most thorough study ever conducted on this topic.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Joe Cepleur]
      #4618023 - 06/03/11 08:38 AM

Quote:

8" Cave... I was moving the tube (with eyepieces removed) and somehow managed to pass that concentrated Sun beam across my face and one eye - the time was less than a second, but I still remember the heat, and I still have diminished vision in that eye...




Amazing how many stories of near or (thankfully) relatively minor injuries are associated with accidents in solar viewing. Glad to hear you are pretty well okay, despite suspecting you'd rather still have perfect color vision in that eye.

My attitude toward safety stems from two sources. The first is extensive training in marksmanship as a child, with a superbly qualified riflery instructor. We never had any accidents on our range, but because we were disciplined, not lucky. We were taught always to treat every gun as though it were loaded. Optics during the day are like that. Every one is a potential loaded gun. Even birders must be careful, when tracking flying birds, not to pan their binoculars across the Sun. I still remember being taught that prior to being allowed to use binoculars as a child at summer camp.

Second is a quarter century of directing a children's summer camp. Wait long enough and fail to teach about safety, and any accident you can imagine will eventually occur. If not the exact accident, then a close variant that could have been prevented. Misfortune will befall not just the children, but the staff, too. Good fortune favors the well trained and thoughtful in their exercise of best practices.

This why I treat solar viewing so seriously, and believe that we modest and individually unknown star gazers -- who happen to inhabit the largest, most comprehensive, most respected astronomy forum -- have an obligation to advocate wise teaching.

I'm beginning to suspect that Jon's myth busting will show that these filters are more robust when used with 60mm objectives than I had feared. I nevertheless hold that, because we can not know the condition of any particular example of this type of solar filter, and the stakes are at least as high as avoiding Dan's class of injury, we would serve astronomy better by differentiating between what is interesting to know about these filters and what is wise to advocate in viewing the Sun.

Rock on, Jon! Let's see what it takes for you to bust your remaining filters!


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Joe Cepleur]
      #4618352 - 06/03/11 12:21 PM

Hi all

Quite by accident I came across two article/letters in the S&T archive DVDs regarding the solar filters in use at the time. I was researching the book "Make Your Own Telescope" (Allyn J. Thompson) and looking up the articles associated with it. I came across an article by David Rosebrugh titled, "Safe and Sane Methods of Observing the Sun", in the October 1956 issue. In this article he basically says to not use the filter alone. He suggests reducing the aperture, use an uncoated mirror, use a prism (not oriented for total reflection), use a Herschel wedge, or use a partially transmitting metallic film in front of the objective along with the solar filter.

In the earlier letter, "Solar Filter Problem", in the May 1950 issue page 172, by Leo J. Scanlon, he mentions "being called upon to replace dense filter caps for use on solar oculars. This indicates that in many cases serious optical damage to the observer has been averted by a small margin." To summarize the letter he advocates not using the filter alone but in conjunction with other safety measures, Herschel wedge, etc.

These were the only two article/letters I could find about solar filter problems or usage in the 50's archive.

DISCLAIMER: I do not use or advocate the use of these older sun filters

peace & clear skies,


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4618442 - 06/03/11 01:10 PM Attachment (54 downloads)

I just started test (1, 80mm (actually 76mm)) at 10:00 PST. I will leave it pointed at the sun for a maximum of 2 hours. Will report back later today on the result.

BTW - I have included a shot of my vintage (and immaculate) 76mm Sears 6339-A OTA on my Atlas EQ-G so you can see what I am using for tracking for each of the tests.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4618444 - 06/03/11 01:12 PM Attachment (52 downloads)

Here is a shot of the Star Diagonal I am using for this test. It has an EP barrel (nose) instead of the stock barrel so that I could screw the sun filter into the nose for this test.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Carl Kolchak]
      #4618478 - 06/03/11 01:30 PM Attachment (57 downloads)

I have an important update to test 2, 60mm. The filter did crack! I was looking over the filter this morning and it has a small hairline spider crack that I missed yesterday! Remember this was the test where the sun filter was screwed into the eyepiece. Note that the filter did not shatter or break in pieces. Unlike when I used on in the 102mm when it broke in two but did not shatter.

This is probably the best result we could hope for in a way. In at least one case (this one), the filter cracked when used per the manufacturer's instructions! And that was in a 60mm scope. That said the filter is really old but that's what we have to use and test these days.

It's looking like the data is pointing in a clear direction although not statistically significant.

If anyone has any extra sun filters that would help me here. I only have a couple left and I want to repeat some of the experiments. So if you can send me one or two please PM me. I will return any unused filters.

I have included a shot using my Canon PowerShot SD400 (Elf) looking directly through the cracked filter. This is the best shot I could get of the crack. It is extremely fine but you can see the visual anomaly it causes in the picture.

Thanks!

Edited by Jon Marinello (06/03/11 01:31 PM)


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4618488 - 06/03/11 01:32 PM Attachment (70 downloads)

Here is a shot of the sun filters sacrificed so far.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4618500 - 06/03/11 01:35 PM

Note that in this test, my sun filter's lock ring is a bit corroded and I can't get it to loosen up a bit. That might cause it to crack faster then if it was loose due to heat expansion.

Edited by Jon Marinello (06/03/11 01:42 PM)


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4618761 - 06/03/11 04:00 PM

Quote:

Note that in this test, my sun filter's lock ring is a bit corroded and I can't get it to loosen up a bit. That might cause it to crack faster then if it was loose due to heat expansion.




Great detail. In the real world, the quality of any given sun filter is unknown. Your noting flaws helps to show the kinds of breakages that could occur if people made the mistake of extrapolating theoretical opinions about safety into their own observing.

Neat to have already shown that even with 60mm objectives, these filters are not reliable, even if it is not yet clear how often the failures are hairline versus catastrophic (nor ever may be, with the limited number of filters available). Are you 100% sure the crack did not exist prior to your starting the test?


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Joe Cepleur]
      #4618803 - 06/03/11 04:18 PM

Yes I'm completely sure.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4618807 - 06/03/11 04:20 PM

Unfortunately, the weather didn't cooperate today. High clouds rolled in shortly after the test began. I am going out of town for the weekend so the tests will have to wait until next week.

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Re: Use of vintage eyepiece sun filters... Why not new [Re: Jon Marinello]
      #4620915 - 06/04/11 06:13 PM Attachment (77 downloads)

Case History #3745 or whatev.

Actually being a survivor of two glass sun filter failures while observing I thought I should chime in.

In 1966 in SoCal probably in February, maybe March, while looking into the soul of Sol the screw in sun filter snapped big time exposing me to a "blinded by the light" experience. I was 14 and using a Tasco 11 te 4.5" reflector. This was a scope that I only had for a few months while I was visiting the "dark side" of reflectors and soon came back to a 3" Edmund refractor. The Tasco sold for $89 and would have been da bomb except there was a collimation or secondary mirror issue. Anyway there was an offset opening as I recall in the tube cap. This was to reduce the amount of light for solar observing. I know that now but then... I was much too smart to read the instruction manual I can't say if I was viewing with reduced aperture but in any event the filter snapped leaving a pretty wide gap and a momentary exposure to unfiltered sunshine. I experienced a few minutes of panic and darkness in the exposed (left) eye. Eventually things became "normal". I can still feel the heat generated in that moment.

Being a big fan of the sun which was in a pretty intense sunspot stage I was more disappointed that the filter broke than anything else. Anyway because the Tasco 11 te never could be collimated to specs. (less than four images of Jupiter in the ep at any one time) the owner of "Optech Precision Instruments" (I bet Lew knew this gentleman) offered a deal on an Edmund 3" refractor as a upgrade/substitute. I believe the Edmund was $125 at that time and I'm quite sure we paid somewhat less. The Edmund used 1.25 ep's and I recall digging deep to purchase a solar filter with a rubber cup that fit over a 1.25" ep like a eyeguard. I was told this wouldn't break like the other kind. It must have cost a lot then... like $2.50. I used this for zillions of hours with the Edmund scope. I was hooked on sunspots and granulation and didn't let a day go by for the next few years without taking a good look at the sun. I never had a failure with this filter.

In 1995 or so I picked up an old orange C-8. I was surprised that when looking at bright objects like Jupiter or Saturn my left eye (eye for observing) gave me a mellow view and my right eye was overwhelmed by brightness unable to discern much detail. It was like my left eye was looking through a ND filter. I remembered the Tasco experience. I believe that that burst of light affected some rods for sure. The difference between what my eyes can see as far as magnitude is apparent. I don't notice this except in the eyepiece. Of course my left (primary) eye is the one that talks to what's left of my brain... I do need it!

And knowing that sun filters break but being quite risk tolerant I recently was observing sun spots once again with a 60 mm scope when the screw in filter snapped. The split was minimal the light was very bright but nothing like the first exposure back in the 1960's. I don't believe this second exposure has contributed to the dimming down of my left eye. I do like the filtered view, the orange/yellow/green (whatever) that they provide. Projection isn't really viewing for me so I don't use that technique. I actually have a device that came with an old Goto telescope that can project a solar image onto a wall for a classroom of students to see. I haven't tried it yet.

The Goto Kogaku and Nippon Kogaku scopes that I have came with solar filters that cover the eyepiece like the one that I bought for the Edmund 3". Even though the filter glass is right there at your eye surface (being on top of the ep) I don't think it absorbs much heat. The Goto Kogaku even came with a Herschel wedge/ star diagonal for sun viewing. If it ever clears here I'll try it out.

Here are some pics of how the Nippon Kogaku filters attach to ep's. They might be safer but as metioned before a full aperture filter is the best way to go.


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Re: Use of vintage eyepiece sun filters... Why not new [Re: Jon Marinello]
      #4620918 - 06/04/11 06:16 PM Attachment (77 downloads)

ep cap removes without affecting lenses

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Re: Use of vintage eyepiece sun filters... Why not new [Re: strdst]
      #4620987 - 06/04/11 06:49 PM Attachment (72 downloads)

The ep ready with filter attached.

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Re: Use of vintage eyepiece sun filters... Why not new [Re: strdst]
      #4621112 - 06/04/11 08:16 PM

Thanks for adding this type of filter to the mix. I had forgotten about these.

Unitron made a similar over the top of the EP filter for both solar and lunar versions. I have a pair of them. Does anyone else have experience with this type of solar EP filter?


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Re: Use of vintage eyepiece sun filters... Why not new [Re: Jon Marinello]
      #4623110 - 06/05/11 09:03 PM

All things being equal (glass of fhe same composition, thickness, and tint), filters fitting over the end of the eyepiece should be less likely to break than those fitting inside the barrel. Because they fit as far as possible from the focal point, heat would be less concentrated. Even so, it would still be better to filter the entire objective.

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Re: Use of vintage eyepiece sun filters... Why not new [Re: Joe Cepleur]
      #4623327 - 06/05/11 11:30 PM Attachment (56 downloads)

Jon, if you run out and your eyes survive, I have a bunch of spares for you

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Re: Use of vintage eyepiece sun filters... Why not new [Re: Steve_M_M]
      #4623359 - 06/05/11 11:48 PM Attachment (72 downloads)

I have a few as well but Jon can't have them. I'm thinking checkers or solar filter bingo markers...

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Re: Use of vintage eyepiece sun filters... Why not new [Re: Steve_M_M]
      #4623436 - 06/06/11 12:32 AM

Hey Steve,

Send them on over. I can definitely use more for this experiment. I believe you have my address.

Thanks!

jon


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Re: Use of vintage eyepiece sun filters... Why not new [Re: strdst]
      #4623440 - 06/06/11 12:33 AM

That was cold!

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Re: Use of vintage eyepiece sun filters... Why not new [Re: Jon Marinello]
      #4623447 - 06/06/11 12:38 AM

So are these filters the same type of stuff as a No/14 welders filter?

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Re: Use of vintage eyepiece sun filters... Why not new [Re: DarkSkys]
      #4623769 - 06/06/11 07:56 AM

I want to see this experiment continue so that this longstanding issue can finally be settled. More data, and more firsthand stories, would only solidify the emerging picture: these filters can indeed break when used, and although the result is not necessarily instant blindness, we have strdst's report of instantly, permanently altered vision. Clearly the engineering is inferior, in that the design places the filter at or near the the most intense concentration of heat. With better alternatives, none of which permanently alter one's classic scope, these old filters should not be used.

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Re: Use of vintage eyepiece sun filters... Why not new [Re: DarkSkys]
      #4624038 - 06/06/11 11:14 AM

Welding filters have been recommended as safe for eclipse viewing,and even for regular solar viewing if large enough to cover the objectives of a binocular.Or use one welder glass on each binocular objective.Just don't forget that the binoculars or telescope gathers more sunlight due to the bigger aperature so instead of the 2mm daylight pupil's area the sunlight from a 35,60mm or whatever lens is being concentrated and beamed into the eyeball.
Since blindness is a serious handicap to observing,I would always err on the side of caution.
Looking through some old filters that are KNOWN to be risky just seems ,well, foolish!Use a full aperature filter of proven safe design and preserve your eyesight.


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Re: Use of vintage eyepiece sun filters... Why not new [Re: BigC]
      #4624059 - 06/06/11 11:27 AM

Since the little eyepiece sun filters "color" the view anyway,I propse a welding glass large enough to completely cover the objective as a minimum safety precaution if anyone insists on trying to use the old "sun" filters.Welder's filters are available in 4x2 and 4x4 as I recall,although it has been a long time since I last struck an arc.One of the #12 welder's filters might work well as a full-aperature filter WHEN USED WITH the old eyepiece filter.The even darker #14 is recommended elsewhere for direct viewing when it is the only filter used in low magnification optics.
Please understand these are a layman's opinions ,not advice, and you do any such experiments entirely at your own risk.


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Re: Use of vintage eyepiece sun filters... Why not new [Re: BigC]
      #4625433 - 06/06/11 11:58 PM

Welding filters... interesting possibility. How bright is the Sun, compared with the flame or arc of a weld? Welding is done at no magnification, whereas a telescope concentrates lots of light from a large objective and passes it through a small eyepiece. The welding glass thus may look virtually opaque to the naked eye, perhaps even be comfortable when held blocking the Sun for the naked eye, and yet not be dark enough for viewing the Sun through a telescope. Anyone know for sure? At least we are on the right track, if we are covering the objective.

Edited by Joe Cepleur (06/07/11 12:05 AM)


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Re: Use of vintage eyepiece sun filters... Why not new [Re: Joe Cepleur]
      #4629164 - 06/08/11 10:16 PM

Does anyone know how one of these solar filters compares to an ND 3 filter?

Steve


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Re: Use of vintage eyepiece sun filters... Why not new [Re: Steve_M_M]
      #4629196 - 06/08/11 10:35 PM

Quote:

Does anyone know how one of these solar filters compares to an ND 3 filter?

Steve




A ND-3 filter reduces the light by 10^3 or 1000:1. For safe solar viewing you need 100,000:1 or a total of ND-5.
Welder's glass Shade numbers is SN = 1 + (7/3)*OD were OD is the optical density. Welders glass #14 works out to optical density of 5.57 or over 100,000:1 in the reduction of intensity.
The eyepiece Sun filters should be at least ND-5.

- Dave


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Re: Use of vintage eyepiece sun filters... Why not new [Re: Steve_M_M]
      #4629212 - 06/08/11 10:43 PM

I recall using one as a teenager with my Jason 76mm tabletop. I never let the scope stay pointed at the sun for more than a few seconds before pointing it away. I was always cautious about the potential for breakage and never had one break. Granted, I didn't use one often but was able to see my first sunspots with them. Never used them on any other scope.

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Re: Use of vintage eyepiece sun filters... Why not new [Re: DAVIDG]
      #4629248 - 06/08/11 10:56 PM

Dave,

Thank you. That is what I am looking for. So, a "sun" filter with a herschel wedge should be more than ok, right? Maybe actually too much blocking?

Steve


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Re: Use of vintage eyepiece sun filters... Why not new [Re: k2power]
      #4629268 - 06/08/11 11:05 PM

One man's opinion:

You'd have to be nuts to use one of those things! I mean, for pete's sake, look at what's at stake! Does anyone here *really* think these filters offer an acceptable risk?? Sheesh!


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Re: Use of vintage eyepiece sun filters... Why not new [Re: Rick Woods]
      #4629464 - 06/09/11 02:11 AM

Quote:

One man's opinion:

You'd have to be nuts to use one of those things! I mean, for pete's sake, look at what's at stake! Does anyone here *really* think these filters offer an acceptable risk?? Sheesh!




Not just one man's opinion. These near-focus "sun" filters need to be banned. Even in small telescopes, they have *repeatedly* been demonstrated to be a potential time bomb. You just don't know when it will fail. It could be today, tomorrow, or 20 years from now, but the risk just isn't worth it. Eyesight is precious. If you risk viewing the sun, use proper over-the-objective well-secured solar filters. I use two-component dedicated systems for H-alpha, so I don't have to worry (and I see a *lot* more than I ever did in white light). Clear skies to you.


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Re: Use of vintage eyepiece sun filters... Why not new [Re: David Knisely]
      #4629472 - 06/09/11 02:25 AM

Since I rarely dwell off the Classics Forum, can somebody tell me (and others), are these filters still made? Are they still sold with the "Department Store" scopes?

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Re: Use of vintage eyepiece sun filters... Why not new [Re: Steve_M_M]
      #4629571 - 06/09/11 06:28 AM

Quote:

So, a "sun" filter with a herschel wedge should be more than ok, right?




No; not "right." This notion shows an understanding of the intended functions of the Herschel wedge and these old solar filters that fit at the ocular, yet also more broadly misinterprets the data. While it's true that a Herschel wedge is intended to deflect 95% of the concentrated light and heat, it still fits at the ocular, whereas proper engineering requires that light and heat to be blocked where they are diffuse, before the objective. A recent post somewhere on Cloudy Nights explains how even the Herschel wedge could fail and, to work properly, still requires a reliable filter. (I'll post the link if I find it again.)

Jon's experiment with these old filters was intended to be unbiased and fair, but early failures quickly showed it to be more of a demonstration of the risks. People have a great deal of trouble evaluating risks, preferring to believe they can outsmart bad odds. It's only interesting intellectually to learn that it is, in fact, a myth that failure will surely result in instant blindness. The larger point is that while some users report years of using these filters without trouble, when strdst's filter burst, he instantaneously and permanently lost sensitivity in his eye. Nothing here proves that the next unlucky astronomer might not fare so well, instantaneously losing more vision.

We're not playing dice here and wondering how often snake eyes will appear. Vision is indeed precious. Odds must be evaluated differently when the risk is absolute to an irreplaceable part of what we are. The point is not that, on whatever odds, one may get away with using a Herschel wedge with one of these old filters, but that if you trust your vision to one of these unknown antiques, you will or will not harm your vision -- and, if you do harm your vision, it will be too late to reevaluate the odds after the loss.

Whilst a particular, fifty-year-old solar filter of unknown quality "should" be less likely to fail if set in the optical train after a Herschel wedge, the question is, "Will it?" The best answer is "maybe, but I can view the Sun while avoiding this risk by filtering where the light and heat are diffuse, before the objective."


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Re: Use of vintage eyepiece sun filters... Why not new [Re: Joe Cepleur]
      #4629577 - 06/09/11 06:36 AM

To all those out there if you have one of those filters DON'T USE THEM. You only have one set of eyes.

Rich (RLTYS)


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Re: Use of vintage eyepiece sun filters... Why not new [Re: Steve_M_M]
      #4629744 - 06/09/11 09:20 AM

Quote:

Dave,

Thank you. That is what I am looking for. So, a "sun" filter with a herschel wedge should be more than ok, right? Maybe actually too much blocking?
Steve




Steve,
That is correct. A Herschel Wedge reflects 5% of the light and these eyepiece solar filters are in the range of OD 5. If they were not close to OD 5 you couldn't look at the image of Sun since it would be too bright, when they are used without the wedge. So the image will be most likely too dim to see since you would be close to OD-7. Of course the filters are mounted after the Herschel wedge and not before it. The modern Herschel Wedges have the ND 3 filter built in.
I had a couple of commerical Herschel wedges and they come with ND-3 filter and a polarizer or a ND-3 filter and Baader Continum filter. The result is the combination is at or greater then a optical density of 5 which is safe.

- Dave


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Re: Use of vintage eyepiece sun filters... Why not new [Re: DAVIDG]
      #4629849 - 06/09/11 10:16 AM

Quote:

A Herschel Wedge reflects 5% of the light and one of these eyepiece solar filters are the range of OD 5. If they were close to OD 5 you couldn't look at the image, since it would be too bright. So the image will be most likely too dim to see
I have a couple of commerical Herschel wedges (Optica B/C. Intes and Baader) and they come with ND-3 filter and a polarizer or a ND-3 filter and Baader Continum filter. The result is the combination is at or greater then a optical density of 5 which is safe.




Optical density of 5 is, in itself, safe; but, as to the notion of experimenting with using this type of solar filter with a Herschel wedge, not exactly...

This thread is diverging into separate issues that all very well belong to the topic of safe solar viewing.

Originally, the thread discussed whether the old style solar filters mounting at the ocular were safe. Now, it adds whether commercial Herschel wedges are safe. Googling easily finds this description of Lunt's Herschel wedge, stating that it is preferable to any film covering the objective because it will give better contrast and sharpness for a better view. Here on Cloudy Nights, there is a detailed review of the Baader Herschel Prisma, explaining its safety features and how it works. Both links remind us that Herschel wedges are only for use with refractors, or with reflecting scopes using thick corrector plates. We would not want anyone jury-rigging a means to attach one to any other kind of reflecting telescope.

Lots of folks with extensive experience in solar viewing have used Hirschel wedges without incident, so let's say, for now, that, properly used, they are safe. There could still be arguments about the wisdom of filtering before the objective or the importance of choosing a well-designed Herschel wedge that properly dissipates the exhausted heat. Now, because the Herschel wedge still requires a dark or polarizing filter, the question becomes whether to use one with the type of solar filter mounting at the ocular that Jon is studying in this thread. As a practical matter, it is certainly true that, used with a Herschel wedge, such a filter will be about 100 times too dark, obscuring the view. It might also be said that, if the wedge were removing 95% of the heat, the filter would be unlikely to crack. Still, the question remains: If you were buying a Herschel wedge from a distinguished manufacturer, why would you trust that last, required 5% to a cheap, unreliable, unpredictable antique? If the filter did break, despite that it were subjected to only 5% of the heat, how would one expect the manufacturer of the wedge to reply to a complaint that, at the least, it was painful when the filter broke?

Just stumbled upon a thoughtful solution to solar viewing with a reflector, in a gallery of scopes here on Cloudy Nights. (Scroll about 2/3 of the way down the first page, to the "6" f/6.8 Dobsonian.") Note the virtues of this homebuilt scope's solar filter: While mounting before the objective, it automatically stops down the aperture and covers the finder.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4630047 - 06/09/11 12:21 PM

Just want to keep everyone posted here. This and the other tests are stalled mainly due to weather. We are socked in with SOCAL's famous "June Gloom". I also need more filters if anyone can send me their extras please PM me.

Thanks! jon


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Re: Use of vintage eyepiece sun filters... Why not new [Re: Joe Cepleur]
      #4630125 - 06/09/11 01:05 PM

All this talk about sun filters and a Herschel wedge made me think of a story that I read in one of the old ATM books many years ago. I don’t remember all of the details but it seems while the observer was viewing the sun with the wedge, only 5% of the light was reflected to the eyepiece...the other 95% was concentrated on his necktie; a situation he quickly became aware of!

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Re: Use of vintage eyepiece sun filters... Why not new [Re: jimarshall]
      #4630145 - 06/09/11 01:17 PM

That's a good one!

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4641318 - 06/16/11 12:26 AM

Still locked into the marine overcast weather pattern (during the day) over here in Santa Barbara, CA.

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Re: Use of vintage eyepiece sun filters... Why not new [Re: jimarshall]
      #4641583 - 06/16/11 08:03 AM

Quote:

All this talk about sun filters and a Herschel wedge made me think of a story that I read in one of the old ATM books many years ago. I don’t remember all of the details but it seems while the observer was viewing the sun with the wedge, only 5% of the light was reflected to the eyepiece...the other 95% was concentrated on his necktie; a situation he quickly became aware of!




This is a good example of how decisions in engineering inherently affect safety, regardless of the user's presumed responsibility to use the gear correctly.

Modern Herschel wedges have elaborate exhaust systems designed to dissipate the concentrated heat that otherwise would burn an astronomer's tie. Burning a tie may seem funny when no one gets hurt, but I recall, back in college, having a chemistry lab with a man with a broken neck. He could move, but literally not quickly enough to save his life. When he caught on fire, he might have died had his fellow students not rushed him under the shower. What might have happened had he been using an improperly exhausted Herschel Wedge alone in his back yard? Such a wedge may simply have been the standard when it was built with the assumption that the user needed to follow directions and be careful. The modern wedge avoids this particular risk at the end of the optical train, although it still concentrates the heat prior to cooling. Its advocates use it because they feel it yields a better image than a filter covering the entire objective. Is there no risk remaining? That's a topic for a different thread about errors in the use of the modern Herschel wedge, although it is evident that correcting the engineering of the exhaust radically transforms the device's safety.

Decisions in engineering include various kinds of conscious choices. One could decide to manufacture a wedge with a proper exhaust by modern standards; or, one could decide to manufacture a lower-cost version without a modern exhaust; or, one could decide to manufacture a gadget with dangerously hot exhaust in an era when no one had yet though of how to cool it safely.

The solar filters mounted near the objective relate to this by concentrating heat near the eye in a filter that was nowhere nearly as carefully constructed as a modern Herschel wedge. Baader Planetarium did not manufacture the filters in question, let alone to their usual standards. The cheapest department store scope came with one of these, a hunk of dark glass molded into a plastic housing with no particular quality control. It's no wonder that, fifty years later, Jon is breaking them one-by-one. Will they all break? Maybe not, but plenty already have, and one does not need a broken neck to be unable to move quickly enough to avoid pain or permanent harm when the time comes.


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Re: Use of vintage eyepiece sun filters... Why not new [Re: Rich (RLTYS)]
      #4647149 - 06/19/11 09:17 AM

Objectively speaking, just bought a Seymour Solar Filter on ebay for $15.14 including shipping.Listed as .330 to .390 but think that in error ;looks like 3.30 to 3.90 inches,Anyway it should be adapable by means of dewcap sleeves SECURELY fastened.Better safe than sorry.

I guess Jon is performing a public service by destroying all those unsafe eyepiece filters ,and enhancing the collector value of the increasingly rare unbroken ones!


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4649675 - 06/20/11 06:30 PM

We finally got some sun today so I have restarted test (1, 60mm) at 3:20 PM PST. Since this test failed to crack the sun filter and test (2, 60) did crack the filter I want to rerun this test to see if we can get a crack. Will end the test in a few hours. I may run it again tomorrow a little earlier if the filter doesn't crack today.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Carl Kolchak]
      #4649717 - 06/20/11 07:02 PM Attachment (40 downloads)

Quote:

When these filters were new, '50s, '60s, '70s, and etc. were there a lot of failures? Are there a bunch of budding amateur astronomers from this era with damaged eye/eyes?




I acquired a Polarex (Unitron) 4" Equatorial in the fall of 1960. It came with a solar aperture cap (basically a dust cap with a central hole about 1.5" in diameter) and a solar filter that fitted over the eye lens of the the viewing EP. It was held in place with a set screw. I attach a scan from the Unitron 1956 catalog showing the filter and the solar cap on the 4" Altazimuth model.

The filter cracked. I ordered a new one. It cracked too. I gave up on them. Not so much as a safety concern. More of an expense a young boy could not afford. I really don't recall if either cracked while I was actually looking through them. Certainly I have no recollection of anything drastic or frightening happening.

So they cracked when used as directed, with the aperture stopped down, and when brand new.

Edited by dawziecat (06/20/11 07:14 PM)


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: dawziecat]
      #4650105 - 06/20/11 10:37 PM

I wonder who designed the original eyepiece sun filter, and what his background was?
Pretty obvious failure analysis wasn't part of it.Even if because of focusing the solar energy was spread uniformly over the entire sun filter glass it still had to absorb 8 or 10 times the heat of a glass just lying in the open;plus the sun filter is poorly situated to radiate the heat .
I wonder if anyone in those days ever thought of silvering or aluminizing the surface facing the objective? Would that not have reflected a lot of heat right back out the objective?


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4650110 - 06/20/11 10:39 PM

Test ran for three hours and the filter didn't crack. I plan to re-run the test tomorrow during the middle of the day.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4650589 - 06/21/11 08:49 AM

Jon,
Are you measuring and or recording the intensity of the sun during these tests?


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: BigC]
      #4650771 - 06/21/11 10:45 AM

No I'm not. How can I accomplish that?

Cloudy again this morning. Hopefully this marine layer will burn off soon.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4650784 - 06/21/11 10:55 AM

Hi Jon:

It's really humid this week, so even though it's hot where I am (Highland Park, about 7 miles inland from downtown LA), it's probably hazy enough to attenuate the sunlight somewhat.

-Tim.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4651424 - 06/21/11 04:49 PM

Test restarted at 1:48 PM PST.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4651710 - 06/21/11 07:59 PM

Test ended at 4:58. 4 hours and 10 minutes. No crack. Tomorrow I will rerun the 60mm test with the filter in the ep which cracked last time.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4651764 - 06/21/11 08:43 PM

Perhaps a photographer's light meter could measure the intensity of ambient sunlight.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: BigC]
      #4651939 - 06/21/11 11:05 PM

The measurement would be highly specific to the meter. It seems to me that it could a relative reading from day to day. But not any absolute measure. Right?

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4653076 - 06/22/11 03:38 PM

Interesting tidbit: just received an old Optica catalog and as of 1986 they discontinued their direct view solar filters and solar diagonals.They continued to offer the "projection system" accessory,the rod and screen, described as for safe solar viewing.Wonder if there was a lawsuit or a "near miss" .This catalog is the first I ever noticed the solar diagonal which diverted 95% of the Sun's light and heat.Looks like it might be a tie lighter!
And in place of my ebay Seymour Solar Filter I received a piece of costume jewelry: a lady's monocle!


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4661653 - 06/27/11 03:30 PM

I just re-started test (2, 60mm) at 12:20 PM PST. I will leave it pointed at the sun for a maximum of 2 hours. Will report back later today on the result.

This is the second of these tests to see if I can repeat the crack.

Finally getting some clear calm skies here. Tonight should be a great night for Saturn.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4661754 - 06/27/11 04:38 PM

Quote:

...Tonight should be a great night for Saturn.




Geez Jon, do you really think you'll be able to see it through a sun filter?



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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Preston Smith]
      #4661773 - 06/27/11 04:54 PM

Preston, I guess you just aren't familiar with how clear the skies can get here. I am often forced to use a solar filter to view even DSO's.

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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4661777 - 06/27/11 04:57 PM

Still no cracks but damn that filter is HOT!

Definitely much hotter than when mounted in the star diagonal nose. As expected.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4661815 - 06/27/11 05:32 PM

Quote:

Preston, I guess you just aren't familiar with how clear the skies can get here. I am often forced to use a solar filter to view even DSO's.






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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4661989 - 06/27/11 07:52 PM

Ended the test at 4:45PM PST. That's a total time of 4:25. The filter did not crack.

This differs from the previous run of this test. The skies were very clear today and it was warm here. I was expecting a cracked filter this time. Ok so we have two different results for this test.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4662216 - 06/27/11 10:36 PM Attachment (50 downloads)

Hi everyone!

I had a Unitron or it was sold to me as a Unitron Herscel Wedge. Jon has it now. Jon, try this test with this Herschel wedge and the solar filters you got. Give us a report on it.

By the way gang, the wedge doesn't close all the way. I thought this was normal. Is it?


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Awesomelenny]
      #4662302 - 06/27/11 11:20 PM

Quote:

Hi everyone!

I had a Unitron or it was sold to me as a Unitron Herscel Wedge. Jon has it now. Jon, try this test with this Herschel wedge and the solar filters you got. Give us a report on it.

By the way gang, the wedge doesn't close all the way. I thought this was normal. Is it?




Lenny,

I believe I have an earlier version as my screws are common - not phillips. My lid does close all the way and I have a small retaining clip that holds the prism in place. THe retaining clip has two screws in it. I'll try and take a picture later.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Awesomelenny]
      #4662326 - 06/27/11 11:39 PM

Len,
Is it just me or is the prisim turned end for end?
I seem to remember the thicker end being at the bottom.
Al


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Al8236]
      #4662689 - 06/28/11 08:50 AM

Quote:

Len,
Is it just me or is the prisim turned end for end?
I seem to remember the thicker end being at the bottom.
Al




If the prism can fit either way but must fit in one correct orientation to work properly, this would be another example of bad engineering. For sake of safety, the housing should be designed not to allow any but the correct fit.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Joe Cepleur]
      #4662747 - 06/28/11 09:41 AM

Joe,
That's kind of what I'm thinking, if the prisim were reversed the cover should close properly from looking at the pictures. (at least that is the way it looks to me)
Al


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Al8236]
      #4663460 - 06/28/11 04:21 PM Attachment (49 downloads)

I flipped the prism around and it closes much better but not completely. The image is correct now so it was definitely in backwards before.

So, I setup my Meade AR6 last night and had about the best view of Saturn I have ever had. The seeing was really good for here. I was hoping to get a good view of Jupiter in the early AM. Two things stopped that; first, the clouds rolled in. second I had a very severe sciatica attack. I have never had one of these before but I can tell you the pain is excruciating. No matter if you stand, sit or lie down. It was a long night and at about 3:00 I took some aspirin and got some sleep.

Its a little better today and I wanted to continue running the tests.

Since my hind end and and left leg are in pain and out of commission I decided on this. I left the AR6 on the EQ-G and installed the Herschel wedge attaching the solar filter to the eyepiece. A 6" objective should really heat things up don't you think? Reminds me of Myth Busters.

The test started about 10 minutes ago at 1:07PM.


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4663465 - 06/28/11 04:23 PM Attachment (50 downloads)

Here is a shot of the Herschel Wedge in action. I can tell you the heat coming out the back of that wedge is intense! It could definitely fry your neck tie!

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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4663468 - 06/28/11 04:24 PM Attachment (51 downloads)

After about 10 or 12 minutes I pulled the eyepiece and felt the filter temperature. It is MUCH less hot than in the other tests. So it appears that so far at least the wedge is dissipating most of the heat.

Edited by Jon Marinello (06/28/11 05:02 PM)


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4663543 - 06/28/11 05:04 PM

Just checked the filter temperature again. It is just warm and not hot. I don't see how this will ever crack the filter. I will leave it up for a couple more hours.

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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4663691 - 06/28/11 06:39 PM Attachment (63 downloads)

At 3:35 PM I ended the current test. The filter didn't crack and was only warm. I decided to remove the current sun filter and switch to a standard Unitron solar filter. Let's see how that goes. But I expect it to work even better.

Edited by Jon Marinello (06/28/11 06:44 PM)


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4663703 - 06/28/11 06:45 PM Attachment (64 downloads)

With the filter on. It's staying very cool.

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BigC
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4669813 - 07/02/11 10:38 AM

Jon,

I have to quibble with your choice of words.

The Herschel wedge should DIVERT,not dissipate most of the heat(and light).If it is the same 95% diversion as given for the Optica solar diagonal,then even with your 6" scope the little green filter is receiving roughly one-quarter of the sunlight(and heat) of the usual 60 to 76mm scope.That should be much less stress on the glass.Using the Herschel wedge diagonal in the classic(sized) 2 to 3 inch refractor ought to mean the green glass filter would hardly become warm since it would actually receive less sunlight than if were simply lying on a picnic table.


Seems a shame the solar diagonal are apparently noonger offered new.


Put a solar cell in the path of the diverted sunlight and charge your scope batteries or power a tracking motor.How about a self-powered sun scope that use a webcam ? A Sun AVI movie from dawn to dusk could be a project that would need a fortune in equipment.


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BigC
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4669830 - 07/02/11 10:49 AM

Whoops!
I guess if the cover is kept closed the Herschel does dissipate the diverted heat.Bet that cover plate gets hot.Maybe it should have a heat sink attached.

And I did find an English firm offering new Herschel wedge diagonals,but only in the 2 inch size and priced over USD$200.


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4688725 - 07/12/11 02:00 PM

Here are the experiments I ran and the results.

Here are the results of the various test scenarios:

1. Star Diagonal [Solar filter mounted on star diagonal nose]
* 60mm (1: no crack, 2: no crack)
* 80mm (not completed due to weather)

2. Eyepiece [Solar filter mounted on eyepiece nose]
* 60mm (1: cracked, 2: no crack)
* 102mm (1: cracked)

3. Eyepiece/Herschel Wedge [Solar filter mounted on eyepiece nose combined with a Herschel Wedge]
* 152mm (1: no crack)

4. Unitron Filter/Herschel Wedge [Unitron Solar filter mounted on eyepiece top combined with a Herschel Wedge]
* 152mm (1: no crack)

Conclusions

Scenario 1
I was unable to get the filter to crack after to test runs with the 60mm scope. However, the filter did get hot. In my opinion there is a risk of a failure even with a small scope like this. The risks would increase with larger aperture scopes. The second test in this scenario wasn’t completed due to weather. Perhaps this line of the experimentation should be continued. Comments?

Scenario 2
I didn’t run all the originally planned tests in scenario 2 as I was able to get the standard sun filter to crack using the smallest scope i.e., 60mm. It is clear you should never ever use this setup or worse a larger aperture scope for looking at the sun!

Scenario 3
I started with my largest refractor in this test. Since there was no crack and very little heat generated at the filter I believe the other tests I could run in this scenario with smaller scopes are unnecessary. I believe this configuration is safe to use with scopes of this size or smaller. Larger scopes were not tested so their safety in this configuration is unknown.

Scenario 4
I started with my largest refractor in this test. Since there was no crack and hardly any heat generated at the filter I believe the other tests I could run in this scenario with smaller scopes are unnecessary. I believe this configuration is safe to use with scopes of this size or smaller. Larger scopes were not tested so their safety in this configuration is unknown.


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4694178 - 07/15/11 03:13 PM

Well things got quiet here so I will ping you all one last time on this topic.

  • Does anyone have any more comments on this?
  • Should I continue with more tests of Scenario 1? (I am willing to)
  • Do others agree with my summary and position?
  • Are there additional scenarios that should be tested?
  • Should we get this thread added to the top of this forum permanently as Preston suggested? (I think we should)


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Jim Curry
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4694775 - 07/15/11 11:00 PM

>Should we get this thread added to the top of this forum permanently as Preston suggested? <

Yes but change the title to: "Use of vintage ep sun filters...NOT"

And the one and only post should be: Don't even think about it!

Jim


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Rich (RLTYS)Moderator
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jim Curry]
      #4695153 - 07/16/11 08:15 AM

Quote:

>Should we get this thread added to the top of this forum permanently as Preston suggested? <

Yes but change the title to: "Use of vintage ep sun filters...NOT"


And the one and only post should be: Don't even think about it!

Jim




Would like to but we are limited to three tacked threads.

Rich (RLTYS)


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Joe Cepleur
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Rich (RLTYS)]
      #4695171 - 07/16/11 08:46 AM

This was a neat experiment. Thanks, Jon, for being the one to test the evidence.

The tests show that these old sun filters are unreliable, so no one should use them. Anyone who thinks it will be okay to use one at the diagonal (further from the point of focus) with a small aperture scope misinterprets the simple fact that they were not precision manufactured to begin with, and are too old to be trusted now. Several postings illustrate that guaranteed instant blindness upon failure is a myth, but instant, permanent damage to the eyes is not.

Testing with the Herschel wedge was admirably thorough, but somewhat beside the point. One would not expect cracks with 95% of the heat removed.

The ability to tack only three threads is a limitation that perhaps the pending upgrade to the site's software will change. It speaks to the need for Cloudy Nights to become not just a constantly changing conversation, but a better site for creating a vast, searchable trove of knowledge. Certainly anyone who visits should learn not to use these old filters.


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jon Marinello]
      #4695574 - 07/16/11 01:55 PM

Quote:

Hi All.
Without a Hershel Wedge in conjunction with a solar filer it is not "safe" to view the sun with any size refractor telescope. Other than that you can use a solar rejection mask that installs over the objective, but I find a Hershel wedge and a Zeiss ND filter to be the best setup for high magnification viewing of Sun spots with any size refractor. Also the optical flats that Unitron used in there solar wedges are very good and seem to work as well as Optima BC or Bader wedges.
As to taking readings of the heat generated at the focal plane of a telescope pointed at the sun. I can tell you the exact reading. Really Hot!!!
(aveman




Jon I posted my thoughts on this in the first part of the thread.
There are many way to observe the sun and over the years allot of junk has been made by companies for this purpose. I was taught by Pons and other old timers the dos and donuts. The first thing they said was this. Only use Zeiss or Baader designed ND filters that are designed to reject IR and other solar radiation. Also only use time tested and well made solar wedges like Unitron, Optima BC or other high quality device should be the only ones used. As for using Unitron Slip over filters and the other cheap ones supplied with telescopes kits I would not suggest this for long term viewing even with a good solar wedge. Get good filters made by experts if you dont want lumpy corneas!!


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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Rich (RLTYS)]
      #4695584 - 07/16/11 02:01 PM

Quote:

Quote:

>Should we get this thread added to the top of this forum permanently as Preston suggested? <

Yes but change the title to: "Use of vintage ep sun filters...NOT"


And the one and only post should be: Don't even think about it!

Jim




Would like to but we are limited to three tacked threads.

Rich (RLTYS)




RICH,
Would it be a good idea to add this to the (Useful Classic Scopes Links)?? And add a header saying DO NOT LOOK AT THE SUN! or USE SOLAR FILTERS.......Also put a side note not to look down the barrel of a gun with the bolt closed. (same thought)
(aveman

Edited by clintwhitman (07/16/11 02:05 PM)


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: clintwhitman]
      #4695823 - 07/16/11 04:33 PM

Hey Clint,

Are Zeiss ND filters still available new? If so can you point me at them with a link?

jon


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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: clintwhitman]
      #4695825 - 07/16/11 04:34 PM

That sounds like a great idea Clint. How about that Rich?

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mikey cee
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: clintwhitman]
      #4695836 - 07/16/11 04:42 PM

Quote:

Quote:

Quote:

>Should we get this thread added to the top of this forum permanently as Preston suggested? <

Yes but change the title to: "Use of vintage ep sun filters...NOT"


And the one and only post should be: Don't even think about it!

Jim




Would like to but we are limited to three tacked threads.

Rich (RLTYS)




RICH,
Would it be a good idea to add this to the (Useful Classic Scopes Links)?? And add a header saying DO NOT LOOK AT THE SUN! or USE SOLAR FILTERS.......Also put a side note not to look down the barrel of a gun with the bolt closed. (same thought)
(aveman


And never nail up a wanted "dead or alive" poster with the pistol grip! Mike

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Datapanic
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Rich (RLTYS)]
      #4695928 - 07/16/11 05:45 PM

Quote:

Quote:

>Should we get this thread added to the top of this forum permanently as Preston suggested? <

Yes but change the title to: "Use of vintage ep sun filters...NOT"


And the one and only post should be: Don't even think about it!

Jim




Would like to but we are limited to three tacked threads.

Rich (RLTYS)




Well, that's no fair! Some of the other forums have more stickies that 3! For example, Mounts has 4 and Reflectors has 5!

I think Clint's suggestion to add a link in the Useful Classic Scopes Links sticky would be good.


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John Carruthers
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Datapanic]
      #4696621 - 07/17/11 04:45 AM

a bit late but my 2p, I was taught when solar viewing to pass a hand over the eyepiece before putting your eye near it, only takes a second, might save an eye?
Hands are sensitive to IR, eyes are not.

I demonstrate toasting marshmallows with my scope to drive home the idea.


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Rich (RLTYS)Moderator
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Datapanic]
      #4696752 - 07/17/11 08:12 AM

Quote:

Quote:

Quote:

>Should we get this thread added to the top of this forum permanently as Preston suggested? <

Yes but change the title to: "Use of vintage ep sun filters...NOT"


And the one and only post should be: Don't even think about it!

Jim




Would like to but we are limited to three tacked threads.

Rich (RLTYS)




Well, that's no fair! Some of the other forums have more stickies that 3! For example, Mounts has 4 and Reflectors has 5!

I think Clint's suggestion to add a link in the Useful Classic Scopes Links sticky would be good.




Your right I checked and some forums do have more stickeys. I'll make this thread a stickey and see what happens.

Rich (RLTYS)


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Re: Use of vintage eyepiece sun filters. new [Re: Jon Marinello]
      #4780743 - 08/31/11 06:52 PM Attachment (56 downloads)

During the 1970's, in my youth, I used such a eyepiece solar filter when observing the sun with my Tasco 9TE-5 60/700mm refractor. Absolutely nobody told me how dangerous such a filter could be.... I used it more than four years, no accident so far. I remember very well to the filtered green image of the sun and enjoyed the observations of sun spots. Very interesting experience for a joungster. But I would not use again this type of filters. There are better solutions today.

Picture shows the full set of Tasco 9TE-5 accessories including the srew-in solar filter. Pure 1960's/1970's nostalgia.

Stephan


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Jason H.
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Re: Use of vintage eyepiece sun filters. new [Re: Stellarfire]
      #4863358 - 10/15/11 11:27 PM Attachment (64 downloads)

Quote:

During the 1970's, in my youth, I used such a eyepiece solar filter when observing the sun with my Tasco 9TE-5 60/700mm refractor. Absolutely nobody told me how dangerous such a filter could be.... I used it more than four years, no accident so far. I remember very well to the filtered green image of the sun and enjoyed the observations of sun spots. Very interesting experience for a joungster. But I would not use again this type of filters. There are better solutions today.

Picture shows the full set of Tasco 9TE-5 accessories including the srew-in solar filter. Pure 1960's/1970's nostalgia.

Stephan




I also remember viewing the Sun through my first telescope (a Traq scope with the dreaded Sun filter), when I was a kid. I remember feeling slightly blinded in daylight, and the Sunspot views were burned into my mind too.

This image added just to hint at the referred to green filter view of sunspots, DO NOT DO THIS! This is from this year via a Tasco green Sun filter (it didn't crack, but DON'T DO THIS!) but via a $14.95 50mm Vivitar MASKED DOWN TO 35MM. DON'T DO THIS!

Jason H.


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Bob Myler
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Re: Use of vintage eyepiece sun filters. new [Re: Jason H.]
      #4866671 - 10/17/11 09:07 PM

OK. I won't. I promise.

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Jason H.
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Re: Use of vintage eyepiece sun filters. new [Re: Bob Myler]
      #4868623 - 10/18/11 11:02 PM

Quote:

OK. I won't. I promise.




Not you! That's just a legal disclaimer.

Jason H.


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sftonkin
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Re: Use of vintage eyepiece sun filters. new [Re: Jason H.]
      #4879241 - 10/25/11 10:47 AM

In case its of interest, I videoed the "testing" of one of these filters earlier this year; I put the result on YouTube:
http://www.youtube.com/watch?v=G5xb3b-vRd4


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Bob Myler
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Re: Use of vintage eyepiece sun filters. new [Re: sftonkin]
      #4880270 - 10/25/11 09:17 PM

Impressive realtime demonstration. The flash is instantaneous - and our reflexes far too slow.

The damage is done before the blink is completed.


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greju
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Re: Use of vintage eyepiece sun filters. new [Re: sftonkin]
      #4880297 - 10/25/11 09:32 PM

Quote:

In case its of interest, I videoed the "testing" of one of these filters earlier this year; I put the result on YouTube:
http://www.youtube.com/watch?v=G5xb3b-vRd4





Good for you! It is nice to see a post in this thread that definitively states NOT to use these filters. Unlike the title of the thread and the many posts that I took to say that it was ok to use some filters some of the time. Hopefully no eyes will be ruined because someone just saw the title of this thread and did not read thru all the pages before getting to your post which shows in no uncertain terms that eyepiece sun filters should never be used. Thanks for your video.


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MacScope
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Re: Use of vintage eyepiece sun filters. new [Re: greju]
      #4881062 - 10/26/11 10:21 AM

Now to play devils advocate: the solar filter instructions I have seen state they are not for use with an objective over 60mm or as in my 80mm Vixen there is a lens cap to stop down the objective to 50 or 60mm. The above test is with a much larger objective lens I believe. NOTE: I am NOT advocating use of these filters!

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Joe Cepleur
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Re: Use of vintage eyepiece sun filters. new [Re: MacScope]
      #4881239 - 10/26/11 11:48 AM

It's true that these solar filters were intended for 60mm apertures and smaller, and also obvious that, it one wants to film a crack appearing, using a larger aperture makes a somewhat random process predictable. The anecdotal evidence we have gathered collectively ranges from tales of people using these filters for many years without problems, to stories of partial loss of vision from sudden failure. Reports include failures when used with proper aperture.

The bottom line is that these filters are of questionable quality, to due both their considerable age and the uncertainty about the quality control and engineering involved in the manufacturing of any particular example so many years ago. From an engineering point of view, filtering at a focused area of concentrated heat is crazy, at least without proper means to vent the heat, as in a Herschel wedge. There are far better alternatives, including filtering at the aperture, where the heat is diffuse.

Anyone who wants to use these filters in conjunction with cameras, go ahead. Worst happens is you destroy some cameras. Using them with the only two eyes you'll ever have is foolish. We need to take a stand and say so. By continuing to question this issue, we endanger the welfare of the many people who turn to these forums for authoritative advice.

It's past time to re-title this thread. Is there a way to change it from:

Use of vintage eyepiece sun filters

to:

Dangers of Vintage Eyepiece Sun Filters


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sftonkin
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Re: Use of vintage eyepiece sun filters. new [Re: MacScope]
      #4891377 - 11/01/11 02:32 AM

Quote:

Now to play devils advocate: the solar filter instructions I have seen state they are not for use with an objective over 60mm




I have been encountering these things for about 40 years. I do not recall ever having seen that warning on any of them.

Quote:

The above test is with a much larger objective lens I believe.




Yes, it is. A few reasons for that:
  • It's the only scope I have that is suitable for solar use without a "big end" filter.
  • I wanted the filter to fail before the camera battery ran out.


However, that said, I have, before the days of digital video, tested these things to destruction with 60mm refractors. Needs a high Sun, transparent sky, and a lot more time.

On a related note, there is a lot of incorrect knee-jerk stuff written about solar safety and it is almost inevitable that thinking people will realise that some of it just doesn't make sense so will ignore it -- that is a dangerous situation. I believe that it arises largely because most people do not recognise that there are at least three distinct mechanisms for solar eye damage. For example, most people will realise that there is insufficient heat coming through a pinhole in eclipse shades to "fry" the retina, but are probably ignorant of photochemical retinopathy, which is the mechanism for damage from the pinhole.

The only safe "short form" advice is "DON'T RISK IT", but unless we explain why correctly in the "long form", we risk having people ignore the "short form" -- that way lies potential eye damage.


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Re: Use of vintage eyepiece sun filters. new [Re: sftonkin]
      #4936475 - 11/26/11 10:14 PM

OK, I have to admit first that I haven't taken the time to read the whole thread, so bear with me if I'm repeating anything. First, I'm with those that say that these filters should be avoided at all cost. Pack it away as an artifact and use either a Herschel wedge or a modern full aperture filter. Second, with regard to these being "safe" with smaller apertures, remember that these are located very close to (or at) the exit pupil, which is an image of the objective. The power density at this point is the highest, and power density goes up as the inverse of the square of the pupil size. Doubling the magnification will raise the power density by a factor of four. The increased power density in a smaller area will make the temperature gradient across the filter steeper, and this gradient is what cracks the filter. Thus, stating that the filter is safe for a given aperture must be accompanied by what eyepiece designs and focal lengths can be used with the filter at that aperture. It's a lot easier to just use what is known to be safe.

Joe


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wfj
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Re: Use of vintage eyepiece sun filters. new [Re: Spectral Joe]
      #5256928 - 06/05/12 09:36 PM

There's one more safe use. I just held a vintage eyepiece solar filter up to my eye (no telescope) to see the Venus transit - works like a charm!

Perhaps they'd fine ... on the objective end of a telescope !


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greju
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Re: Use of vintage eyepiece sun filters. new [Re: wfj]
      #5256972 - 06/05/12 10:09 PM

Quote:

There's one more safe use. I just held a vintage eyepiece solar filter up to my eye (no telescope) to see the Venus transit - works like a charm!

Perhaps they'd fine ... on the objective end of a telescope !




Not only a bad idea but you certainly would not see the transit unless you also had bionic eyes!


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wfj
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Re: Use of vintage eyepiece sun filters. new [Re: greju]
      #5264818 - 06/10/12 02:17 PM

Wrong. I did it, and saw Venus quite easily as a disc.

Made an impact on me - I wondered if instead if Venus had been in resonance with Earth's orbit, so that Venus transits were more of a common case, then when total solar eclipses would occur, you'd tend to see a nearby planet in the sky as a naked eye disc, how we might have had a faster appreciation of the laws of gravitation prior to telescopes.

Venus was almost a minute of arc, while the sun was less than 32 minutes. Most people can make out lunar features naked eye that are a fraction of its diameter.

Doesn't take bionic eyes - duhhh. Such a joy CN senior members can be ...


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Brian RisleyModerator
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Re: Use of vintage eyepiece sun filters. new [Re: wfj]
      #5264902 - 06/10/12 03:20 PM

Guys, remember the TOS. Be Polite!

As to being able to see it with just a filter, I think that people were able to see it with the solar glasses/viewers, which would be the same as looking through an eyepiece filter hand held. It was large enough to be detectable with many standard cameras, so I suspect it was visible.
Brian


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greju
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Re: Use of vintage eyepiece sun filters. new [Re: Brian Risley]
      #5265393 - 06/10/12 10:04 PM

Since you are going to let these statemends stand I will happily respond to them.

"Doesn't take bionic eyes - duhhh. Such a joy CN senior members can be ... "

You seem to think you know my age. So what is it? And what would age have to do with it?

I will again say that holding up a small eyepiece sun filter to your eye is a bad idea, duh! It is also not a lens, you could not see the transit. And to say on a public forum that "There is one more safe use" is irresponsible at best. Looking at the sun in this manner is not "safe", no matter what age you are. Duh!

"As to being able to see it with just a filter, I think that people were able to see it with the solar glasses/viewers, which would be the same as looking through an eyepiece filter hand held."

You "think" this? And comparing "solar glasses/viewers" to a vintage eyepiece sun filter are not the same and by you seemingly condoning this are you saying this is a "safe" practice also? Oh, and cameras have lenses. I suspect that might have helped. I bet those cameras were equipped with a proper solar filter also. Not someone holding a vintage eyepiece sun filter up to the lens.


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Rich (RLTYS)Moderator
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Re: Use of vintage eyepiece sun filters. new [Re: greju]
      #5265761 - 06/11/12 05:56 AM

Come on folks lets keep this important discussion friendly.

Rich (RLTYS)


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Joe Cepleur
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Re: Use of vintage eyepiece sun filters. new [Re: Rich (RLTYS)]
      #5265864 - 06/11/12 08:33 AM

If one wanted to use a tiny eyepiece filter to look at the Sun directly, it would be safer to mount it securely behind a larger mask. Better, if one slips with one's hand, to have one's vision blocked by the mask, than to suddenly allow the Sun's rays to strike one's eye. No one has ever reported such a filter cracking due to direct exposure to the Sun (without an objective lens concentrating the Sun's rays from a larger area). Still, I would not want to advocate this use of antique filters, because it confuses the otherwise clear message not to use filters of unknown and questionable quality. That said, to play fair, at least in this case, the method clearly worked. No eyes were fried, and the experimenter unsurprisingly reports having seen the transit.

I spent $40 with shipping on a brand-new sheet of modern solar viewing film that allowed me to safely filter, at the aperture, two binoculars and a refractor -- an excellent investment for a once-in-a-lifetime transit! There was enough film left over to filter several other instruments. A club could share a sheet at a cost of five to ten dollars per person.

It's sad that the fury has obscured the comment that our sense of gravitation and celestial mechanics could have arrived much earlier in our history if Venus had a different orbit, making it visible during eclipses. That's profound.

I'll second the call for good manners. On the occasions when I have been first to make the request, I've wished others would join me.


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wfj
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Re: Use of vintage eyepiece sun filters. new [Re: Joe Cepleur]
      #5268050 - 06/12/12 12:50 PM

Digression.

Did this on a lark as I was hunting through an eyepiece bin, setting up a scope for some to see transit using eyepiece projection. Came across one from a flea market, and I noticed then it had a sun filter on it. I pick these up routinely for a buck or so, and often don't look too closely.

So I wondered, what the heck, why not check it out naked eye, as the optical density of these things are around 60. Naked eye sunspots I'd seen at sunset before.

And I wasn't knocking age, I was referring to "senior" as in large number of posts.

I remember when members of a local astronomy group were experimenting with high mag / tiny exit pupils on full aperture solar filters and comparing what they saw with pinhole projection. They were experimenting with geometric optics of a sort. Some of longer term members of the group decided this was "wrong", analogizing to the department store scopes high power thing, that they were doing a disservice to astronomy, and tried to ridicule them out of the group. Some acted as stalkers, to "police" thought as well.

Happens to lots of communities. Online as well.


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JonH
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Re: Use of vintage eyepiece sun filters. new [Re: wfj]
      #5446383 - 09/29/12 08:28 AM

Perhaps the heat in this debate is a useful and important thing.......I came to astronomy quite by chance having purchased a brass victorian parlour telescope as an object d'art. This came with three eyepieces, terestrial;astronomical and a mysterious "smoked" objective. Naturally I assumed this was for solar observation and promptly set up the scope to look for sun spots. Bearing in mind I did this in the height of summer, in Australia, with a sunglass that could have been a centuary and a half old, I was fortunate not to lose the sight in one of my eyes. Later, whilst looking for a larger tripod I came across Cloudy nights and this debate and realised the danger inherent in the beautiful brass tube work. I have kept the sunglass, but it is carefully labelled to alert any other casual viewers to its dangers. I wonder if I had'nt read this thread with its "heated" debate and occasional spots of rancour, weather I might not have experienced a moment of innattention and tried the sunglass again? I love Cloudy nights for the maturity of its correspondents but I also love it because its members are not afraid to make a noise about stuff that matters. Incidentaly, I had the brass scope out for this year's transit, stopped down and set for solar projection together with my Unitron.

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dgreyson
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Re: Use of vintage eyepiece sun filters. new [Re: JonH]
      #5560064 - 12/07/12 10:21 PM

I used to use the solar projection plate on my 60mm tasco 7te to look at sunspots back in the day when I first got it. they looked pretty cool so I took off the plate and screwed the glass sun filter into an eyepiece. Took a look and it was much better, the granularity of the spots was very interesting. I looked up for a moment to check where and what my brother was doing (he had a nasty habit of throwing rocks, broke my giant ant farm once ).

I had looked away for only a moment or so and when I turned back, before I could look again, the filter had cracked wide open. Dag! Cheap J*p junk I thought and threw the broken filter away and never looked at the sun again.

I was lucky, I could have easily been blinded. never realized that until I read this post and remembered the occasion. woagh!


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bouffetout
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Re: Use of vintage eyepiece sun filters. new [Re: dgreyson]
      #5603244 - 01/03/13 03:32 PM

I had one on my 4.25" newton ,years ago...I sat down for a break ,and the solar eyepiece shattered and little pieces of glass flew off the filter. Most of the filter was still there but cracked like I would with a hammer !
Have I stayed there watching the sun for longer,those pieces of glass would have ended in my eye...


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photiost
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Re: Use of vintage eyepiece sun filters. new [Re: bouffetout]
      #5608678 - 01/06/13 03:50 PM

With so many safe and inexpensive Glass and Mylar Solar filters available today why take ANY chance with these on your eyesight?
The BAADER AstroSolar film is my personal favorite.

If you want to observe Sunspots and have no "Safe" filter available, then eyepiece projection
(solar image projected onto a white paper) is really the only safe alternative.
.


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Jean Mario
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Al8236]
      #5778445 - 04/04/13 07:51 PM

is good for long time...

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Jean Mario
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Jean Mario]
      #5780035 - 04/05/13 04:15 PM

I have the BAADER filter it's the best a good for long time...

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Chris Lord
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Re: Use of vintage eyepiece sun filters. new [Re: Jon Marinello]
      #5808183 - 04/19/13 06:30 AM

Realise it's been a while since this thread was active, but I thought you may all like to know I've uploaded an article on this subject to my website's <FORUM> page (forum in the sense that the articles are open market and can be used by anyone gratis).

Forum article <#31> desrcibes the historical aspect to sun eyecap filters, rather than their more modern (relatively speaking) TASCO etal counterparts.

Sun eyecap filters, or "solar shades" as they were originally described, were fitted to Dollond and Ramsden refractor eyepieces (usually Huyghenians), and later Ramsden's successor Matthew Berge. They comprised a brass screw on cell with a red dyed in the mass glass filter spun tightly into the cell leaving no room for expansion. This same design was made by various refractor makers throughout the C19th and well into the C20th. I have many in my collection, made by Wray, Broadhurst Clarkson & Co. Cooke, Troughton & Simms & Ottway. They are all identical in having a 1".348 x 28TPI Whitworth screw thread. Grubb also made the same type of solar shade which was a tight push fit.

At the time nothing was known of retinal scotoma <http://en.wikipedia.org/wiki/Scotoma> caused by IR leakage. In fact William Herschel had only just discovered infra-red radiation at the turn of the C19th. The metalic gold colouring agent absorbed from blue thru' near red, but allowed deep red and infra-red thru'. They give a dull red image not because there is little light passing thru' but because there is little blue thru' near red transmitted. The eye can't see near IR, and about 2% of the deep red gets thru' presenting a deceptively comfortable image because the eye is quite insensitive to deep red light. Little IR is absorbed, so even if the filter doesn't fail it can cause retinal scotoma.

I also realise the 1950's thru' early 70's TASCO sun filters used #14 welder's type glass, giving a green-yellow image. These are slightly different in their optical properties viz a vis the retina, but nonetheless are potentially very dangerous.

The forum article describes a spreadsheet model I have created to investigate the time before failure of antique solar eyecap filters. If having read the article (a downloadable pdf) you would like the spreadsheet to play around with yourself, and if you use an Apple Mac running Appleworks, just e-mail me.

I have only ever used one of these red solar shades on a 5 draw hand held 2-inch refractor on the setting sun, for a few minutes. If you'll accept my advice, and you have a sun eyecap filter amongst your accessories, please don't be tempted to use it. It simply isn't worth the risk.

article is:
<http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/forum/EYECAP%20SUN%20FILTER.pdf>
e-mail address for spreadsheet:
<chrislord@brayebrook.demon.co.uk>


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Jon Marinello
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Re: Use of vintage eyepiece sun filters. new [Re: Chris Lord]
      #5982493 - 07/21/13 07:16 AM

Nice to see this topic is still alive and well.

jon


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mikey cee
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Re: Use of vintage eyepiece sun filters. new [Re: Jon Marinello]
      #5982798 - 07/21/13 11:16 AM

Nice to see you are as well! Mike

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brianb11213
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Re: Use of vintage eyepiece sun filters. new [Re: photiost]
      #6018583 - 08/11/13 06:44 AM

Quote:

With so many safe and inexpensive Glass and Mylar Solar filters available today why take ANY chance with these on your eyesight?
The BAADER AstroSolar film is my personal favorite.



Indeed.

Quote:

If you want to observe Sunspots and have no "Safe" filter available, then eyepiece projection
(solar image projected onto a white paper) is really the only safe alternative.
.



Safe for your eyes but not for your scope.

The concentrated solar heat can and will melt the cement in modern eyepieces. If you're using vintage eyepieces (Huyhenian or Ramsden) you'll get away with it but orthos, plossls and modern multi-element eyepieces will be rapidly damaged or destroyed if used for solar projection.

Solar projection is for use with small refractors only. The concentrated heat will damage secondary mirrors and/or their fittings and/or plastic baffles used in reflecting telescopes of all designs. Even with small refractors, it's probably best to avoid projection with modern scopes, as they may well have plastic baffles which will melt or burn if the sun strikes them whilst you're trying to centre it.


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checksum
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Re: Use of vintage eyepiece sun filters. new [Re: brianb11213]
      #6050754 - 08/28/13 01:57 PM

Personally I would not risk my eye sight with such things and would strongly encourage you all to do the same.

Clear skies, not blind eyes!


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Lindberg
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Re: Use of vintage eyepiece sun filters. new [Re: Jon Marinello]
      #6215545 - 11/25/13 04:13 PM Attachment (20 downloads)

I made this for my 75 mm Refractor

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Lindberg
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Re: Use of vintage eyepiece sun filters. new [Re: Lindberg]
      #6215553 - 11/25/13 04:14 PM Attachment (18 downloads)

And here it is I never trust a small 0.95 or 1.25" solar filter

Edited by Lindberg (11/25/13 04:16 PM)


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Joe Cepleur
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Re: Use of vintage eyepiece sun filters. new [Re: checksum]
      #6237861 - 12/06/13 06:10 PM

Quote:

Personally I would not risk my eye sight with such things and would strongly encourage you all to do the same.

Clear skies, not blind eyes!




To which "such things" does this refer? Baader solar film? The similar film from Thousand Oaks Optical? While I, too, an nervous about anything that increases the heat inside my scope, filtering at the objective is safe if done correctly. Light that never enters our scopes can't hurt us. One must always assure that the film is in perfect condition and securely attached, and that finders as well as main scopes are filtered.

Viewing the Sun is fascinating. While everyone who tries it must accept responsibility for proper use of solar viewing gear, I am against broadly discouraging this branch of astronomy. I built my first solar filter from Thousand Oaks film for the Transit of Venus, and I'm glad I did!

It is specifically filtering concentrated light at the eyepiece that this thread discourages.


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oldmanastro
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Reged: 11/17/13

Re: Use of vintage eyepiece sun filters... Why not? new [Re: Al8236]
      #6249983 - 12/12/13 09:59 PM

I used these filters back in the 60s with both my 76mm and 60mm Sears Scopes. Never stopped down the aperture and never had a cracked filter. I used to draw sunspot groups and this took sometime at the telescope. Good luck was with me those days. I don't use them anymore although sometimes i get this urge to use them for old times sake. Just a peek.....

Guido


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Karl Fabian
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: oldmanastro]
      #6294294 - 01/05/14 04:21 PM

I do not recommend using these. Most likely the reason some have been lucky with these filters is that when used with a longer focal length Huygens eyepiece the focal plane (where it is hottest) is often forward of the filter where it is not quite as hot, but still dangerous. The focal plane of a Huygens ocular is between the two lenses that make up the eyepiece. In a longer .965 focal length Huygens this would typically be about an inch from the filter when the image is in focus. On these filters the filter glass should RATTLE in the holder and not be tight to allow for expansion. I have seen many that were tightly fit in the holder. THOSE ARE ALMOST GUARANTEED TO FRACTURE! Not a good idea to use these,even the ones that rattle, especially with very affordable full aperture filters available. Anything near the focal plane has the potential to overheat. A filter over the aperture of the scope is the way to go.

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Mike E.
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Re: Use of vintage eyepiece sun filters... Why not? new [Re: Karl Fabian]
      #6388485 - 02/21/14 10:33 AM Attachment (9 downloads)

Here is an excerpt from a 105 year old Amateur Astronomy book about observing the Sun. It's interesting that danger of cracked eyepiece filters were well known back in 1909, and the alternate method of projection suggested; yet Telescscope manufacturers continued to provide these filters for at least another 70 or more years.



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SeeEmComing
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Loc: Doylestown P.A.
Re: Use of vintage eyepiece sun filters... Why not? new [Re: Al8236]
      #6424072 - 03/23/14 02:37 AM Attachment (4 downloads)

Hey Dave,

I really like your 4.25" f/10 Solar Newt, with the
herscell wedge I will download the picture and
study it more closely, Great Job! Nice work!
Here is my 3 1/2" Antique Reflector which I
restored to its original appearance

SeeEmComing

Edited by SeeEmComing (03/23/14 02:58 AM)


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