Plate solver precision

I’ve been using the Ansvr server for the plate solver for a long time, and it’s always been reliable and fast. I’ve been able to slew and center on any target effortlessly.

I would like to use the solver for checking my focal length, though, and I need more precision than just the two digits which appear for Scale. Can I request at least three, maybe four? The SGP log shows a ridiculous number of digits coming back from the solver, so the data is all there.

There is an explanation of the necessary calculation here (and no doubt numerous other sources):

I have a scope with quoted focal length of 480mm.
My camera is an SX814M with pixel size of 3.69 x 3.69 uM
From solver my image scale is 1.57083 arc-sec/pixel

FL is calculated as:

[Focal Length in mm] = (206.2648 x [Pixel Size in μm]) / [Arcseconds Per Pixel]

or in my case:
208.2648 x 3.69/1.57083 = 484.53181mm

Assuming you do not want to do this calculation often, I think you will have an accurate answer far mor quickly by doing a manual calculation.

Hope this helps


@FarnhamMike : I’m not sure what you’re getting at. Your calculation is the same I use, and your image scale is carried to the fifth decimal (“From solver my image scale is 1.57083 arc-sec/pixel”). This is exactly what I’m requesting: more precision in the reported image scale from the SGP solver. Your comment supports this, but it sounds like you’re recommending something else?

It seems that this is likely a fairly rare need? Would you be calculating your FL on a nightly/hourly/etc basis? Is grabbing this out of the log not adequate for what you’re after?


That’s correct, I only do it rarely, but it would be trivial for you to increase the displayed precision. Just a little usability improvement. Also, when you are tweaking your focal length you need to get a precise image scale maybe eight or ten times as you dial it in. It’s a nuisance to have to consult the log each time.