If you trust the focal length of the optics (and this is just a camera lens, so it should be accurate), then it's easier to just calculate the FOV numbers based on the chip size.
From <http://www.dpreview.com/reviews/canoneos40d/page2.asp> the chip size is 22.2 X 14.8 mm. Using trig (since the FOV is too wide for the small angle approximations that make this calculation easy for telescope FOV), a 22.2 mm wide chip 55mm behind the lens is an angle of 2 X arcsin(11.1/55) = 23.3 degrees ~= 1400' (since CdC wants the number in arcminutes, at least in v2.76. Or are you using v3.x, which is generally very different? Please specify the program version when asking questions). Then the height is 2 X arcsin(7.4/55) = 15.46 deg ~= 930' Given the geometric distortions common in wide lenses, you should probably take a test shot to verify those numbers. For the 200mm lens, the numbers are 2 X arcsin(11.1/200) = 6.36 deg ~= 380' wide 2 X arcsin(7.4/200) = 4.24 deg ~= 254' high -John ----- Original Message ---- > From: Sander Pool <[email protected]> > To: [email protected] > Sent: Wednesday, May 20, 2009 9:48:56 AM > Subject: Re: [skychart-discussion] Re: Finder circle for DSLR camera > > > Hi Harry, > > the official way to do step 1 is to plate solve. To be honest that's too > involved to explain here. You may want to google for it. A poor man's > plate solve is something like this: > > - take an image > - find two stars that are in opposite corners of your image > - use CdC to find the names of these stars > - use CdC to find the distance between these stars (click on one, then > the other, bring up properties window, distance at the bottom) > - use a paint program to find the distance in pixels between the stars > in your image > - do basic math to find your pixel scale > - do basic math to find your image size in arc minutes > > Then enter this size into the Display->Finder rectangle settings dialog. > > Sander > > crayonharry wrote: > > > > > > > > > > > > im not sure how to do either ... determine the field of view and also > > how to enter it in the program. > > > > > ------------------------------------ > > Yahoo! Groups Links > > >
