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Old 02-09-2012, 04:26 PM
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Aidan (Aidan)
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Sun and Sun spots

Greetings,

I have an old star explorer SE114900 telescope (lens aperture of 114mm, focal length 900mm).

Is it safe to use this to project the sun onto a sheet of card. Or am I likely to melt something (internal). I am not overly fussed what happens to the scope as it has a big brother now.

Are there any safety concerns outside of looking into the eyepiece and setting my retina on fire? Or the screen?

Any tips and pointers would be greatly appreciated.

I had a brief play with the idea today and was able to project a reasonable image, although i have not figured out how to get clear shots on a white background with the digital SLR. Although i was able to make a quick sketch.

Aidan
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Old 02-09-2012, 04:42 PM
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Merlin66 (Ken)
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IMHO the safest and best way to do white light observing of the sun is to use a Baader Solar Film filter over the front.
Easy to make your own and 100% safe when securely fitted.
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Old 02-09-2012, 04:44 PM
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Thanks

Ozscopes has it for 34 dollars in this a good price?

Aidan
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Old 02-09-2012, 05:42 PM
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sheeny (Al)
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Yes, got to agree with Ken.

I was about to reply with a similar suggestion but got interrupted.

$34 sounds OK for a pre-made filter.

Al.
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Old 02-09-2012, 06:19 PM
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Awesome...

will do

thanks again.

Aidan
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Old 04-09-2012, 11:58 AM
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When I want to look at sunspots I just use my Tamaya Jupiter sextant, which has a set of shade-glasses specifically designed to filter the sun's harmful rays out and pass enough visible light for decent observations. Using the 7X40 telescope and resting the frame on a fixed object allows rapid quantitative observation.
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Old 04-09-2012, 12:54 PM
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Hi Aidan, I would see little problem with projecting using a 4 1/2 inch scope. I've regularly observed the Sun using the projection method with a 5 inch and 8 inch reflector for a great many years, and never broken or damaged any equipment as a result. I'd recommend not using a favourite, new or expensive eyepiece for the job, just in case the worst happens, as the greatest risk is with the concentrated light at the focus at the eyepiece end. I don't think there's any risk to your primary mirror or objective lens. You'll not set anything on fire unless it's very close to the eyepiece: by the time you've spread the light (by projection) out into a broad disk it's not hot enough to ignite the paper. For lurkers, it goes without saying to never ever look through directly of course - the damage threshold to a retina is a lot lower than a piece of paper!
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Old 05-09-2012, 05:38 AM
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ZeroID (Brent)
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I have used a cheap 60mm refractor for projection with a cheap EP just in case. Worked quite well.
You could also cap the aperture of the reflector and have a smaller (offset) hole to reduce the risk. Most scopes come with a cap with that already built in.
The Baader film works best though.
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Old 05-09-2012, 04:53 PM
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Quote:
Originally Posted by andyc View Post
Hi Aidan, I would see little problem with projecting using a 4 1/2 inch scope. I've regularly observed the Sun using the projection method with a 5 inch and 8 inch reflector for a great many years, and never broken or damaged any equipment as a result. I'd recommend not using a favourite, new or expensive eyepiece for the job, just in case the worst happens, as the greatest risk is with the concentrated light at the focus at the eyepiece end. I don't think there's any risk to your primary mirror or objective lens. You'll not set anything on fire unless it's very close to the eyepiece: by the time you've spread the light (by projection) out into a broad disk it's not hot enough to ignite the paper. For lurkers, it goes without saying to never ever look through directly of course - the damage threshold to a retina is a lot lower than a piece of paper!
Projection seems to be the go, I have some Baader film on the way, which is going to fun to try.

I have been making a larger disc as not to completely concentrate the light (magnifying glass style).

thansk again for the advice
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