let's use the french scope as an example :
I edited the Periscope_Mask_1024.dds file (stock us)
I then scaled the periscope view I had to fit the hole on the screen and redrew the lines and tick marks
the stock's hole is 540 pixels wide as far as I can tell
1) Decide a standard size of the hole, for all your optical views. I have chose 480 pixels in my mods, for example
so mine is like stock : 540 pixels
2) Tweak the cameras.dat so that you set the proper aperture angle to make that 540 pixels correspond to the 32º you want to have
how ?
3) Place the reticle markings in the hole in the proper places, with 1 degree spacing in horizontal separation
I am measuring in pixels..; how do I calculate how many pixels per degree ?
[edit] 480 pixels
240 half
240 = 16°
240/16 = 1 mark every 15 pixels right ?
[edit]

in the french scope view, there is a vertical line 175 pixels from the center with 9 divisions, so one every 19.44 pixels, I chose 19.5, and a zone without marks 95 pixels wide as half the circle is 270 pixels
if the half the view is 16° wide = 270 pixels then 1° =270/16 = 16,875 pixels
so the divisions as shown on the reticle are each 1.15°
4) Tweak all the other cameras apertures in cameras.dat to the same one as in your optics, so that the zoom proportions are correct. (Otherwise it could happen that at 6x zoom in your optics you see objects that are apparently only 2x what you see on the bridge)
?
keltos