[Aavso-photometry] Re Alt-AZ imaging

[Brad Walter]

There is another issue besides field rotation that I have noticed with any
tracking system for dob (I looked at the website in your e-mail). The alt-az
corrections are not smooth and continuous. The corrections are made in small
but clearly visible steps. This is just fine for visual work, but even with
a field de-rotator, it won't work for imaging. 


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Message: 2
Date: Tue, 17 Apr 2007 14:56:00 -0400
From: Roland Roberts <roland at astrofoto.org>
Subject: [Aavso-photometry] OT: Using alt-az for imaging?
To: "aavso-photometry at aavso.org" <aavso-photometry at aavso.org>
Message-ID: <46251840.7080108 at astrofoto.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

This is off-topic, but I've been given permission to buy a new scope 
from the "appropriates committee" :-) and since right now I've been 
using a 5-inch achromat, I'm looking for a big jump in aperture. 

And yes, I know, its complicated by field rotation, and I'm not looking 
for theoretical reasons to avoid this.  I will almost certainly be 
buying something like a Pyxis rotator soon *anyway* since it makes it 
easier to find guide stars for some images.

What I'm wondering is if anyone here has done or is doing imaging with 
an alt-az setup.  I've been eyeing the 14" Tscope (www.tscopes.com) as 
an economical way to get a big aperture with low weight.   Going over 
12" with a S-C seems to be asking for back problems :-/  And if I 
abandon alt-az as possible, I'm considering the NGT-12.5 from Jim's Mobile.

So, anyone here have any experience with using an amateur alt-az mount 
for imaging?

roland

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