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Equipment Discussions >> Classic Telescopes

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photiost
professor emeritus
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Reged: 12/14/06

Loc: Montreal, Canada
Re: Use of vintage eyepiece sun filters. [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
member


Reged: 11/21/10

Loc: Québec, Canada, St-Jérôme.
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
member


Reged: 11/21/10

Loc: Québec, Canada, St-Jérôme.
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
member
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Reged: 09/26/04

Loc: Cambridge UK
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
Pooh-Bah
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Reged: 09/21/10

Loc: Santa Barbara, CA
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
Postmaster
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Reged: 01/18/07

Loc: bellevue ne.
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
Postmaster
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Reged: 02/25/09

Loc: 55.215N 6.554W
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
member


Reged: 07/20/13

Loc: Earth, Sol
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
member


Reged: 08/31/09

Loc: Skultuna, Sweden
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
member


Reged: 08/31/09

Loc: Skultuna, Sweden
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
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
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
member


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
super member
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Reged: 11/02/11

Loc: Illinois
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.
Carpal Tunnel


Reged: 01/26/10

Loc: Moonstone Observatory
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
member


Reged: 09/12/07

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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