Protecting Optics (not eyes) During Solar Observing

[mishima]

Hi, I don't have much experience with amateur astronomy, but I was going to try and take a few shots with my Canon EOS 20d mounted on my 6" Ritchey-Chretien astrograph this Monday. The telescope was manufactured by Orion, and was a few hundred dollars so probably not the highest quality. Since I'm a teacher, I'm planning to have it setup for most of the occultation's 3 hours for students to check out.

My concern is heat. Should I worry about adhesives on the optics? What about the CCD in my DSLR? I'm really in the dark about solar observing with a telescope. I do not want to damage my scope.

My only filter is a single layer of mylar.

edit: Extra question, I will have to unmount my telrad because that specifically had a warning against solar observing. Recommendations for a simple replacement for easy centering? Its just an alt/az mount without tracking or autoguiding, etc.

 

[fresh_42]

You should be more concerned about your eyes. These cannot be replaced, optics can. It's really dangerous. Why don't you ask the company you got your telescope from about special filters for this event? Maybe an IR filter to protect the telescope from overheating and UV filters to protect your eyes.

 

[mishima]

I'm not planning to use an eyepiece at all, just the DSLR. I received a pair of eclipse goggles from the AAPT because of my subscription to the American Physics Journal, so not worried there. Also the school bought goggles for the entire student body.

edit: but yes, its a little too late for manufactured solutions from the telescope supplier. Is the IR that damaging? Thats dissapointing if so.

 

[davenn]

My only filter is a single layer of mylar.

nowhere near enough <--- I can't stress that enough

you need to stop down the aperture from 6" to around 2" using a cover plate over the front of the scope with that 2" hole in it

THEN ... over that 2" hole use at least 2 to 3 layers of mylar

Dave

 

[mishima]

That can certainly be done. But what exactly is the hazard? I'm just trying to understand. What does solar observing do to a telescope with a DSLR on it? Should I make efforts to cover the primary every instant its not in use? Like I said it will be sitting out there for a good 3 hours.

 

[davenn]

What does solar observing do to a telescope with a DSLR on it?

burn the crap out of the optics and insides of the scope

 

[davenn]

Should I make efforts to cover the primary every instant its not in use? Like I said it will be sitting out there for a good 3 hours.

if it's not pointing at the sun it doesn't matter
but safer to keep it covered to save a moment of non-thinking carelessness and pointing at the sun without protection

 

[mishima]

burn the crap out of the optics and insides of the scope

Sorry, I don't mean to sound like an idiot, but what do you mean? The reflective lining on the primary will get so hot a hole shall be scorched in it, or what? The CCD's noise will go to infinity?

 

[davenn]

do you not understand what the word burn means ?

enuf heat to crack glass optics and burn/melt any plastic parts etc etc

 

[mishima]

Wow, alright, well...that was what I was fearing I guess.

 

[rbelli1]

enuf heat to crack glass optics and burn/melt any plastic parts etc etc

And then proceed to crack/melt/burn the inside of the camera.

Forcing the magic blue smoke out with external means is just as damaging as letting it out though internal means.

BoB

 

[mishima]

Wait, I've seen some transit setups without any filters at all where projection was used. Can that only be done with pure refractors?

 

[mishima]

I think I could do something like that fairly easily. Looking at my secondary, there is only about 1.5 in clearance, and the only dill bit for circular holes I have on hand is a 15/16".

So, I'd be stopping the aperture down to 15/16", with 3 layers of mylar. Is that enough? Should I throw a layer of glass or polycarbonate in there as well? I think the only plastic parts in my scope are the baffle down the main tube. But I'm not sure about the adhesives and as mentioned the IR effects on the mirror/CMOS sensor is pretty scary.

My field of view is .94 x .62 degrees. Probably the longest time pointing directly at Sun would be during focusing.

 

[DarioC]

If that is your 6 incher there I would humbly suggest that the hole is too big. I have a factory cover for my 5 inch with a smaller hole and it is just enough to make a bright moon comfortable to look at. Just a suggestion; Why not make some smaller holes in pasteboard for example and tape them over the hole that you have. Start small and work up carefully. Of course you need to use a very dark filter over the hole as mentioned above. I am using two lenses from old fashioned welding goggles.

 

[mishima]

That pic is not my telescope, but that off-axis solar filter is what I'm trying to make. I think I will drill 15/16 inch hole then cover with various pasteboard holes a bit smaller as you say, thanks for the tip.

 

[fresh_42]

I've just found the following article, maybe it helps.
http://www.sciencealert.com/here-s-how-to-photograph-the-solar-eclipse-without-damaging-your-camera

 

[mishima]

Thanks, fresh.

I've got my aperture stop all constructed with a 15/16" hole. I'm starting to think the best idea would be to just cut my eclipse goggles in half and use that. Each eye has a 1.5" by 1.5" of the material.

 

[mishima]

Think I've got something that will work. Here's a few quick shots and a horribly off-center showing color for Sun.

Just need to rig up a good aiming solution and think I'll be set. :)

 

[mishima]

Found a great solution to targeting! I just put the other cut eclipse goggles eyepiece on my Telrad's glass plate. Check this out:

First pic is outside, you can see the Telrad reticle with actual Sun orange spot far off to the top left.

 

[davenn]

Wow, alright, well...that was what I was fearing I guess.

look for the smoke ...

 

[mishima]

Well, I didn't destroy my cam or scope. :)

1002 images taken, 8 GB. Was doing 1/4 second shots.