Astroart Forum

fabdev wrote: ↑

07 Feb 2019, 19:43

The current autofocus always selects the brightest star.
Maybe the focus exposure time was too short? On some fields an exposure time of 2 seconds may be necessary to get an acceptable star.
OK, I will write you by PM when ready. (But only increasing the exposure time will solve).

Thanks. I'll check the exposure time when I get back to the observatory in 3 weeks or so.

Hi Dunmunro,
If you add something like this into your script you can select the guide star you want to use for guiding! Just download the field you want to image and draw a box around the star you want to use. Then start your script!

x = Image.GetPointX
y = Image.GetPointY
Image.Close
Camera.Start(2)
Camera.Wait
Camera.Autofocus(60,x,y)

Iver wrote: ↑

09 Feb 2019, 19:42

Hi Dunmunro,
If you add something like this into your script you can select the guide star you want to use for guiding! Just download the field you want to image and draw a box around the star you want to use. Then start your script!

x = Image.GetPointX
y = Image.GetPointY
Image.Close
Camera.Start(2)
Camera.Wait
Camera.Autofocus(60,x,y)

Thanks!

Can you explain the syntax: Camera.Autofocus(60,x,y) ?

If I understand it correctly it will create an autofocuser window of 120 x 120 pixels with X, Y pixels as the window centre?

x = Image.GetPointX
y = Image.GetPointY
Image.Close
Camera.Start(2)
Camera.Wait
Camera.Autofocus(60,x,y)

Yes that's correct.
The number sets the size of the subframe used for guiding. Smaller number smaller subframe!
The X and Y are the coordinates for the subframe center!

fabdev wrote: ↑

07 Feb 2019, 19:43

The current autofocus always selects the brightest star.
Maybe the focus exposure time was too short? On some fields an exposure time of 2 seconds may be necessary to get an acceptable star.
OK, I will write you by PM when ready. (But only increasing the exposure time will solve).

I think I understand what might be happening. I've been using a guidescope to autoguide my 10in SCT. The SCT has quite a bit of mirror flop and I suspect that AA7 is using the first frame in the sequence to select the focus stars, but then uses the current frame in the sequence for autofocus, and so the selected rectangle in the current frame no longer contains the star selected for autofocus.