[Aavso-photometry] Re Alt-AZ imaging

[Roland Roberts]

Jeff Hopkins wrote:
> The big problem with using an Alt-AZ scope for photometry is that 
> photometry is best done close to the meridian. And that is where the 
> Alt-AZ mount is poor.
>
> It is always best to plan your observing (if you can) to catch the 
> object just before it crosses the meridian while it is the highest in 
> the sky (lowest air mass) and continue observing at and past the 
> meridian. A fork mounted in a polar configuration works extremely 
> well for this. This is how I do most of my photometry. In cases you 
> need to observe far from the meridian, the errors go up.
>
> I suspect tracking with the newer telescopes is not a problem, but 
> the field rotation is a pain and the median flip a problem that gets 
> old fast. I highly recommend investing in a polar mount.
>   
That's a good point.  But I think you meant "zenith" for where the 
alt-az problem is.  The meridian is not generally a problem only close 
to the zenith.  Of course, the rest of your points are still apropos.  I 
plan to sit down and figure out how the field rotation rate depend on 
zenith distance and what that means when translated into (possibly) 
discrete de-rotator motion.

We may be refinancing the house to finish off some renovation, maybe I 
can convince the comptroller to let me pad the budget and get a nice SC 
on a fork *and* a new dob :-)  If I get the Dob, I might try my hand at 
some imaging with something like a Mead DSI to see how good or bad it 
is.  If it doesn't work, I still got a new Dob....

roland

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Roland B. Roberts, PhD                             RL Enterprises
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