Re: ATM Mel's Dob Driver and Photography?

[cshaw@ghg.net (Charles W. Shaw)]

>In a message dated 97-12-05 15:07:33 EST, Tom.Stock@gensig.com writes:
>      I'm building my Dob driver, and was just wondering if it's accurate 
>      enough for 15-20 min exposures if the field derotator is added.
>


Hi Tom,

I cannot speak to now accurately a Dob Driver works, but I have a Mel
Bartel's designed system I recently built for my 14.5"f/5 newtonian.  I also
have a field rotator I built.     The best performance I have gotten so far
was when I shot M-101 with my CB245.  I shot 21 one minute unguided
exposures (it took 30 minutes to complete the series of shots).  When I
stacked the images, the software I use (MULTI245) tracks how much the images
had to be shifted.  The last image in the stack had to be shifted 13 pixels.....

My system has pixels of about 2.2 arcsec/pixel, so that is somewhere around
30 arcsec the tracking had drifted off in 30 minutes, or about 1 arcsec/minute.

I wish I had been exposing a LOT longer for the images!!!!!!  The system
will consistantly allow me to shoot one minute exposures unguided if I do
the star alignments reasonably carefully, and then use the drift correction
feature to null any small errors.

With my focal reducer, I am shooting at f/3.9 and sky fog is actually the
limiting constraint (if there are no stars that are blooming) for exposure
durations from here is suburban Houston, Texas.  Kinda nice to have THAT as
the limit for unguided exposures!!!!!

Chuck

Chuck Shaw      

cshaw@ghg.net (Home)
cshaw@ems.jsc.nasa.gov (work)
http://www.ghgcorp.com/cshaw 

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