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Equipment Discussions >> Classic Telescopes

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Steve_M_M
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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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Rick Woods
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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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David Knisely
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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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Datapanic
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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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Joe Cepleur
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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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Rich (RLTYS)Moderator
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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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DAVIDG
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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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Joe Cepleur
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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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Jon Marinello
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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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jimarshall
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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 donít 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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Jon Marinello
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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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Jon Marinello
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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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Joe Cepleur
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Reged: 03/18/10

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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 donít 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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BigC
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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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Jon Marinello
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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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dawziecat
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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 (42 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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BigC
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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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Jon Marinello
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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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BigC
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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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Jon Marinello
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Re: Use of vintage eyepiece sun filters... Why not? [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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