Converting guide adjustments from pixel to arc-seconds?

[AndyUK]

Hoping someone can help....

I used to use PHD for guiding and was able to then analyse the night's guiding by putting it through PHDLab... and through there I could could switch between guide camera pixel errors and arc-seconds.  I now use Maxim - After each session I save the log file and drop it into a spreadsheet so that I can see what was going on, but I can only seem to analyse it in pixels... There must be a formula for converting the pixel errors to arcseconds, but I drew a blank from Google (or at least I got swamped by infoglut!) - I don't suppose anyone knows the formula, do they?

EDIT:  I think I may have answered my own query - I've found  the switch in Maxim to display in arcseconds in Maxim [Embarrassed!]   I'll just have to see what it records in the log.  However, the formula would still come in handy if anyone has it

[narrowbandpaul]

Arc spec/pix = 206*p(um)/f(mm)

Where p is the pixel size in microns and f is the focl length in mm.

Eg a 5um at 1000mm would approx 1"/pix.

Multiply the pixel guide error by your arcsec/pix and bobs your uncle.

The 206 is related to the number of arc seconds in one radian

Paul

[JamesF]

Yup.  There are 206265 arcseconds in one radian.  In Paul's equation above because he has um in the dividend and mm in the divisor there's a factor of 1000 to be accounted for hence his use of 206.

James

[AndyUK]

Cheers both - Now that I see it in black and white, I do recall having seen it before... but thanks very much for getting back - I'll add it as a column on my spreadsheet

[steppenwolf]

I started off recording in 'pixels' at the very beginning and just stuck with these units as the errors are easy to 'visualize' but as you have now found there is a switch that allows you to change the display to arcseconds. MaxIm has so many switches and options - you spend days just diving into the manual!

[AndyUK]

Thanks Steve - Yes, Maxim is certainly a bit of a minefield!  As you say, imagining a pixel is much easier than imagining an arcsecond