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Sun Funnel and Eyepiece Damage

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#1 garyp1936


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Posted 05 May 2012 - 06:38 PM

Never having observed the sun before, I am constructing a sun funnel (described in the June S&T)to use on my Orion ST 80. The only suitable size EP I have is a Radian 10mm. Since it is not exactly inexpensive, I am concerned that using it for solar projection might damage it in some way. Is this a possibility? Should I be concerned?

#2 *skyguy*



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Posted 05 May 2012 - 09:10 PM

Do not use your Radian eyepiece for solar projection. Any eyepiece that has glued optical elements is at risk of becoming over-heated and separating. I'm surprised this wasn't mentioned in the S&T article.

This was common knowledge in the past when solar projection was the norm. Will today's modern eyepieces with advanced optical adhesives be up to the task of solar projection? I wouldn't want to take that chance!

#3 garyp1936


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Posted 05 May 2012 - 11:04 PM

If not the Radian, what type would you recommend? Would a less expensive plossl, such as the Owl Black Knight or a GSO, be a good choice?

#4 buddyjesus



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Posted 06 May 2012 - 12:06 AM

I would use a cheap chinese plossl or kellner myself.

#5 huskercr


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Posted 06 May 2012 - 10:22 AM

Would this solar projection eyepiece from Surplus Shed be useful?

#6 Spectral Joe

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Posted 06 May 2012 - 11:29 AM

Some useful info may me found here:
(Or maybe not)

#7 brianb11213



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Posted 06 May 2012 - 02:43 PM

I wouldn't use projection method with any aperture greater than 60mm, and then I'd want to use an eyepiece free from cemented elements. Either a Ramsden or a Huyghenian depending on the focal ratio of the scope.

A solar film objective filter is cheap, safe and gives a far better view in my experience.

#8 buddyjesus



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Posted 06 May 2012 - 07:53 PM

I've done years of solar projecting with my 4" refractor with no ill effects to either the 20mm plossl that I commonly use or the diagonal. I do aim away from the sun every seven minutes or so for about a minute to let it cool off. I don't even know if that is necessary as nothing feels hot to the touch. better safe than sorry I guess.

#9 Erix


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Posted 06 May 2012 - 08:24 PM

I've always used a Kellner for my projection sessions.

#10 DOTrevino


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Posted 07 May 2012 - 02:48 PM

In preparation for the upcoming eclipse and Venus transit, I tested solar projection yesterday with my 80mm scope and two inexpensive eyepieces, a Kellner and an RKE. Worked very well. I may get another kellner or MA to keep as a spare since they are very cheap.

I also have a solar filter for my 50mm scope, and while the image is great, I am expecting a group to come by and I think with the projection more people can observe the eclipse at the same time rather than standing in line to look through the other telescope.

#11 stephenramsden



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Posted 23 April 2013 - 09:20 AM

of course...I like the Ramsden eyepieces better...:)

#12 jrbarnett


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Posted 24 April 2013 - 11:13 PM

What commonly available eyepiece *doesn't* have at least one cemented optical group?

Orthos have two cemented gaps. Plossls have two cemented gaps. Kellners have one cemented gap. Same with RKEs. TMB Supermonos have two cemented gaps, etc., etc.

Only a singlet or air spaced doublet eyepiece will lack any cemented gaps. Not very common these days.



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