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Equipment Discussions >> Classic Telescopes

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jwaldo
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Loc: Simi Valley, CA
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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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
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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neotesla
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Reged: 11/18/10

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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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jsiska
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Reged: 07/12/06

Loc: NW Ohio
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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Jon Marinello
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Reged: 09/21/10

Loc: Santa Barbara, CA
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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Jon Marinello
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Reged: 09/21/10

Loc: Santa Barbara, CA
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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Jon Marinello
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Loc: Santa Barbara, CA
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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Jon Marinello
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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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jsiska
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Reged: 07/12/06

Loc: NW Ohio
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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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
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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Jon Marinello
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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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Datapanic
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Reged: 10/17/09

Loc: Tucson, Arizona
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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Joe Cepleur
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Reged: 03/18/10

Loc: Dark North Woods
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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Joe Cepleur
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Reged: 03/18/10

Loc: Dark North Woods
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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Carl Kolchak
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Reged: 08/02/06

Loc: Northeast, Florida
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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Jon Marinello
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Reged: 09/21/10

Loc: Santa Barbara, CA
Re: Use of vintage eyepiece sun filters... Why not? [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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Jon Marinello
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Reged: 09/21/10

Loc: Santa Barbara, CA
Re: Use of vintage eyepiece sun filters... Why not? [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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Jon Marinello
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Reged: 09/21/10

Loc: Santa Barbara, CA
Re: Use of vintage eyepiece sun filters... Why not? [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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Jon Marinello
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Reged: 09/21/10

Loc: Santa Barbara, CA
Re: Use of vintage eyepiece sun filters... Why not? [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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Jon Marinello
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Reged: 09/21/10

Loc: Santa Barbara, CA
Re: Use of vintage eyepiece sun filters... Why not? [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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