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Old 19-02-2009, 10:09 PM
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JD2439975 (Justin)
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Question 40D on 16" LB advice

Hello to all

I've been putting my wishlist together & settled on a 16" Lightbridge(aperture fever set in early) with a Canon 40D for the pretty pictures.

Tracking will be by homemade eq/platform so exposure time will be limited but image stacking should solve that problem...anyone???

A Televue Paracorr I consider a "must have" for a f/4.5 scope so that would be in the mix.
Trevor (Quark) has a thread stating the visual model can be used for imaging also, this sounds better than forking out another $600 on the imaging version.

So I guess my question is can anyone foresee any problems that might arise...achieving focus or vignetting or...??

Any help would be greatly appreciated, already learned so much from the people on this forum so thanks go out to you all.

JD
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Old 19-02-2009, 11:13 PM
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Hi Justin,

If my LightBridge is anything to go by, you won't be able to reach focus with the 40D DSLR until you shift your primary mirror up the base tube a bit (eg. 40mm). You will then want to use a 50mm extension tube on your focusser when just doing visual (rather than astrophotography).

Mind you, if you want to take long exposure images of Deep Sky Objects like nebulae and galaxies, them making a homemade EQ platform that will track accurately with something the weight of an LB 16" sounds like a significant challenge.

Good luck!

Jeff
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Old 20-02-2009, 12:13 AM
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JD2439975 (Justin)
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Thanks Jeff, that gives me something to think about.

An extension tube for visual I can live with.
I guess 3 ways to go about it...
1. spacers on the mirror cell/collimation screws??
2. cut down the mirrors tube length...yikes on a brand new scope!!
3. shift the secondary/focuser down.
Some of those options on a scope I haven't even got home yet are a bit scary but if the needs must...

JD
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Old 20-02-2009, 06:58 AM
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Checkout the following articles from the "Projects and Articles" section:

Modifying a Newtonian Tube for DSLR Photography
http://www.iceinspace.com.au/63-441-0-0-1-0.html

Astrophotography with a Dob
http://www.iceinspace.com.au/63-201-0-0-1-0.html

Folks I know who have purchased or made an Equatorial Platform for use with a large Dob have found tracking good enough for visual astronomy, but not very good for long exposure astrophotography of nebulae, galaxies etc.
- nowhere near as accurate as commercial German Eq Mounts
- lacks goto capability for helping to find faint fuzzies
- no input port for closed loop autoguiding

But it does sound like fun, and should work better on the NT than it would down her in Melb at latitude 38deg south.

Cheers,
Jeff
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Old 20-02-2009, 08:48 PM
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JD2439975 (Justin)
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Hi Jeff

The mod looks straight forward enough, just seems criminal on a new scope.
At times my middle name has been "I void warranties" so I'll no doubt be able to bring myself to do it when the time comes.

As for the platform I had originally intended it for visual use only so I could observe under high mag without having to bump the scope every 20 seconds.
Sounds like lunar & planetary should be easy enough but DSO's I'll just have to experiment to see what I can squeeze out of it.
Would love to have one of those Losmandy Titans from Bintel but at $16,000 for the tripod version I couldn't raise that sort of money if I sold my body & soul.

The platform I can put together for very little money, I could probably stretch to a Roboscope/Bartel system though I haven't researched these enough to know all that's involved, but the autoguider/guidescope setup would definitely break the bank at the moment.

It seems autoguiding is the most accurate & method of choice by many, looks like more research & save my dollars if I want to catch me some faint fuzzies.

Thanks again Jeff, most helpful.

JD
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