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Old 19-02-2008, 12:51 PM
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dugnsuz (Doug)
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Lightbulb ??????Increasing ED80 magnification????????

Hello all,
I'm currently using the ED80 at prime focus for imaging, and love the results.

One aspect frustrates though, small objects such as my recent Jewel Box image have to cropped mercilessly to get a useable final image.
http://www.iceinspace.com.au/forum/a...4&d=1203378210

Is there any way to increase the magnification of the scope without compromising quality and using Eyepiece projection!?

I had thought of using the Canon 1.4 or 2x Tele convertor between scope and camera to up the magnification

Would/Could this work!?
Cheers
Doug
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Old 19-02-2008, 01:08 PM
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[1ponders] (Paul)
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You can Doug, but at the sacrifice of f ratio. For every doubling of magnification you will increase your required exposure time by 4. You can use a 2" 2X (or higher - 5X 25X exposure length) barlow or powermate (negative projection). You will just need a T thread to 2" adapter.

The other way is to use a good quality eyepiece and try positive eyepiece projection, as you have already mentioned.

Realistically though to get a reasonable size image in a respectable time you need big aperture and long focal length. i.e 12" newt @ f5 = ED80 x 2.5 and less exposure.
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Old 19-02-2008, 01:36 PM
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iceman (Mike)
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Get an ED100 or ED120, or an 8" f/4 newt, or 10" f/5 newt

That's next on my DSI list - get more focal length with an 8" f/4 newt.
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Old 19-02-2008, 01:51 PM
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Quote:
Originally Posted by [1ponders] View Post

Realistically though to get a reasonable size image in a respectable time you need big aperture and long focal length. i.e 12" newt @ f5 = ED80 x 2.5 and less exposure.
Quote:
Originally Posted by iceman View Post
Get an ED100 or ED120, or an 8" f/4 newt, or 10" f/5 newt

That's next on my DSI list - get more focal length with an 8" f/4 newt.
Great, Thanks Gents...
That's what I needed to know.
Cheers
Doug
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Old 19-02-2008, 02:09 PM
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iceman (Mike)
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Focal length = image scale.

You need the longer focal length without significantly increasing your focal ratio, otherwise, as Paul said, you need longer exposure times for the same amount of light input.

I want to image at around 1000mm focal length as my next DSI scope, and for me, that will be an 8" f/4 newt. So it will be faster than the f/6 480mm ED80 (with reducer) i'm imaging with now.
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Old 19-02-2008, 03:25 PM
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[1ponders] (Paul)
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If you are going that far Mike you might as well look at going for a 10" f4 SN to give you the 1000mm you want.
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Old 19-02-2008, 05:44 PM
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This is the reason I ended up with an 8" f4 newt, apart from the miserable side of me. I too find occasionally that a little more would be good, so am contemplating either a 2x barlow, or a butchered tele-convertor from a camera system. If you beat me to it, let us know how please.
Gary
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Old 19-02-2008, 10:53 PM
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I have an ED80 and until the burgulars took off with my 2x teleconverter, I used it very successfully with the ED80.

However I probably should have bought the ED100 or similar instead to give me a longer focal length. Unfortunately when I got the ED80, there were no ED100's available and being the impatient type....

Really the ED80 is a great little 'scope - light, portable and fits in a suitcase no problems. The ED100 is really too long to take on many holidaze. Having said that, I would still like a long focal length scope. When I was at uni, there was a 6" f15, making the whole thing about 2.5 m long. It needed two people to handle it and any breeze would sent it a'wobbling, but the views of the planets was amazing.
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Old 27-02-2008, 09:28 AM
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If you are imaging stars, focal ratio theoretically makes no difference and in practice makes hardly any difference, so for things like the jewel box, use any method you find good to increase the focal length. It is only for imaging extended objects--nebulae, galaxies, planets etc that you need to worry about focal ratio.
Geoff
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Old 27-02-2008, 10:14 AM
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Quote:
Originally Posted by ghsmith45 View Post
If you are imaging stars, focal ratio theoretically makes no difference and in practice makes hardly any difference, so for things like the jewel box, use any method you find good to increase the focal length. It is only for imaging extended objects--nebulae, galaxies, planets etc that you need to worry about focal ratio.
Geoff
Exactly right!
You will find little difference in the stars recorded even with a 2x extender but diffuse objects, the all important focal ratio makes a difference. The faster the better I reckon! Also remember the seeing and focus and guiding all have to be spot on to appreciate the extra scale.
If you are after a convertor go for a genuine canon one as the cheap ones arn`t very good showing coma and CA in the corners. Mine cost close to $200 and is rubbish for astro work.
cheers Gary
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Old 27-02-2008, 02:30 PM
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Cheers for the info all
Doug
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