Sébastien Doré

Hi Bryan,

People mention ‘setting’ the FOV.   As near as I can determine, there is no place to set the FOV directly. APPM can calculate FOV from the sensor parameters, which is supplied from FITS header, and image scale, which is set in APPM and sent to FITS header.  Is this correct?

You have already figured the following out but for the sake of other people who wouldn't have yet the FOV for ASTAP is the field height (in degrees) of the image you're trying to solve. So it is related to your "vertical" sensor size (in pixels) and your image scale (arc-sec per pixel), through the following formula:

FOV_height = vertical_height * image_scale / 3600

and can be set directly in ASTAP in the Stack Menu -> Alignment Tab. (That answers in part your above question)

For example, my ASI183MC Pro sensor which has a 5496 x 3672 pixels and used with a 70mm refractor at 338 mm FL. Image scale for this setup is 1.4646 arc-sec/pixel so FOV height to set in ASTAP will be : 

3672 px x 1.4646 arc-sec/px / 3600 arc-sec/deg = about 1.49 degree. 

That's the value ASTAP needs to work the most efficiently, all others being equal. 

With the new Beta version of APCC (, this FOV is automatically calculated from the FITS header information, as you said. And it is used by APPM when launching the ASTAP platesolving process if you have checked the new "Use FITS header for RA, Dec and Image scale" checkbox. So the need for you to provide the FOV manually to ASTAP is now gone as APPM correctly does the work for you. That assumes your imaging program includes all the required information in the FITS header in the first place (which NINA 1.11 does), of course. 

Prior to APCC v1.9.1.1, APPM forced the FOV setting to be determined by ASTAP through trial and error (i.e. not using the manually user-supplied value as seen above) which added some unnecessary time to solving each point of a mapping run. So it is a great bug-fix in the latest version in this regard, especially for those using somewhat old/slow imaging PC by today's standard.

Hope that helps understand it a bit further.


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