[APML]: ST4 beginners observations

[Mark Bolton <bortech@OntheNet.com.au>]

The Astro-Photography Mailing List
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Hi All

After much sweat over an electronics bench and three weeks of continuous cloudy nights I 
finally got my ST4 working last night for the first time. I thought I'd post a beginners 
observations on the operation by someone who's never been near a CCD before. 

Firstly but is there a way to equate the correction units to movement on film. E.g. I'm 
using a 90 mm refractor with a 1300mm focal length to guide a 500mm f5 lens on a Losmandy 
GM8. Typically I'm getting corrections 3 to 4 units (0.6 to 0.8 pixels as I understand) 
but occasionally I'll get a correction of 8 or 9 units. Is this typical? I'm inclined to 
think that this amount of movement wouldn't be noticeable on the film but I'm not sure. I 
know the solution is to put the camera on and try it but it's cloudy here again and looks 
like being so for another week (and I'm curious and impatient by nature :)

After several weeks of reading the manual and articles on Chucks homepage and others I 
was dreading the focusing operation. After calibrating the drive with the default 
settings and taking a dark frame, I started by putting the scope on one of the stars in 
the Sagittarius  teapot asterism ( cause that's where I did the drift alignment) and got 
a % saturation reading and an X & Y reading straight away. It was then a simple operation 
to adjust the focus until the % saturation reached its highest level and viola the thing 
was focused (well pretty well focused I think). I then marked the draw tube of my focuser 
so I can get pretty close to good focus next time. Just a note here to anyone - make damn 
sure that your finderscope is extremely well aligned with the guidescope cause these 
chips are small. That was the hardest part of the operation getting the piddly little 6 x 
30 aligned really well.

I was getting a 69% saturation reading so I dropped the EA parameter to try and get it 
below 50% saturation but suprisingly it stayed at about 60% even with a 0.2 second (I 
think) exposure. This is probably a product of the magnitude of the star so I pressed 
track anyway and away the thing went tracking nicely.

So my point is to anyone thinking about getting one of these things - do it.  They aren't 
as difficult to operate as you might think - my lack and experience and getting the thing 
tracking within half an hour of setting it up shows just how easy it is. The idea of 
taking long exposure photos while I'm sitting in the warm, drinking coffee, is just 
fantastic.

Mark Bolton

http://www.onthenet.com.au/~bortech/