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 Post subject: A FOV question
PostPosted: Wed Jan 20, 2010 6:47 am 
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Joined: Wed Feb 21, 2007 10:32 am
Posts: 521
Location: Lincolnshire
I use a canon 350D for imaging together with a newtonian. If I want to increase the size of the FOV in order to fit larger objects into the frame, such as M31 and M42, what can I do?

Will a focal reducer work, or are they not for newts? Would a x 0.5 barlow do the trick...if anyone makes them?

Many thanks,

Andrew

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PostPosted: Thu Jan 21, 2010 10:25 am 
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Joined: Sat Jul 24, 2004 12:12 pm
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Location: Flackwell Heath, Bucks, UK
I'm not familiar with using these things, but I think that the problem with Newtonians is that you rapidly run into problems of bad coma at the edge of the field if you try to widen the field of view.

A Barlow is by definition designed to extend focal length, so a corrector lens that reduces focal length would not be called a Barlow anyway. You are right in calling it a focal reducer.

Maybe a simpler solution to wider-field photography would be to use a system with a shorter focal length, piggybacked on your Newtonian. Ideally it would be faster (ie smaller f-number) into the bargain. Hence the increased interest in small refractors for astrophotography -- effectively telephoto lenses.

Robin


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 Post subject:
PostPosted: Thu Jan 21, 2010 11:09 am 
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Joined: Wed Feb 21, 2007 10:32 am
Posts: 521
Location: Lincolnshire
Thanks for the info Robin.

I'll look into is some more (and my bank account!)

Cheers, Andrew

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 Post subject:
PostPosted: Thu Jan 21, 2010 2:25 pm 
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Joined: Thu Dec 16, 2004 5:06 pm
Posts: 1109
Location: Hartlepool
Andrew,

If you go the refractor way for astrophotography, beware.
For true colour and coma free images you'll need an Apo, or semi Apo.
The less expensive refractor, achromatic, leave horrible blue hue to everything you image

SW Equinox are maybe the better choice unless you win the lottery. Same goes for the WO range.
I went for a 80mm F/5.4 Equinox. These are crackers when used with the Canon 350D, which I have like yourself.
A 200mm lense for your camera also capture great DSO images. Just need good accurate tracking, in the Equatorial mode. It will capture M31, 32 and 110 easily.

For astrophotography I bought an AstrotracTT320X. These track the skies for upto 2 hours perfectly and are a sinch to polar align. It carries the Equinox very easily with DSLR attached.

I tried astropics through my 10" newt, but couldnot achieve enough R&P focuser travel for focusing the camera. Donot want to write an epic here. I'm not the best imager by a long shot, but this is just what I've learnt over the last couple of years whilst trying to take picies.


BRgd ....Eddie

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