?? Aperature question ?? (1 Viewer)

Was wanting to know what happens when the camera is set to f/2.8 and the telescope/optic I'm using is a f/4.0......

#1: Which is the aperature, the f/2.8 or the f/4.0? Or is it actually something else?
Wondering if the two seperate aperatures get added together, or if the aperature of the camera overrides that of the telescope/optic(obviously-as far as EXIF data)....... I print out a lot of the photographs I take and am wondering how much post-processing I'm going to need to do(the less the better).

#2: EXIF data does not include any afocal information..... How would I change the information to include any 'digiscoping'?




Scott (or a link to describe what I'm asking) B

First, calculate the camera aperture opening thru its zoom range. then compare that with the exit pupil of the eyepiece. Whichever is smaller is the true aperture.

For example the 30x eyepiece on the Kowa 883 has an exit pupil of 2.9mm. My FX150 camera lens has a zoom range of 6mm-21.4mm at F2.8-F5.6. So 6/2.8=2.1mm and 21.4/5.6=3.8mm. That means somewhere around the 13mm focal length, the eyepiece exit pupil becomes the "true" aperture and when fully zoomed in the lens is at F7.4.

This explains why it is generally better to increase scope magnification rather than zoom the lens if possible. That way, the camera exif value will always be the correct value.

cheers,
Rick

Thank you for the well thought out answer, and including the math helps me understand it even better!

Scott (usually takes a beating to get it) B