Prime Focus

[Dude]

How do I calculate what magnification I get at prime focus with a fl of 2000 and f10 SCT?

[Ags]

Size of chip in mm times 57.3 divided by focal length in mm erquals degrees field of view (not considering vignetting).

[Capricorn]

There is no magnification.

You get an image.

That image has a size dependant on the focal length of the scope and the angle that the object subtends.

[JimStan]

I use a different method, which may not be as accurate, but seems to work for me.

In the "old" 35mm film camera days, a 50mm lens was considered to be the "normal" focal length for a standard picture. Thus a 2000 mm telescope would give a magnification of 2000/50 or 40X . Now days, it is a bit more complicated because different digital cameras have different sized sensors, but if you know what lens is considered to be the "normal" focal length for your camera, you should be able to figure out the magnification you will get with your telescope.

Close enough for me !

Jim S.

[Dude]

Hmm, it would seem the answer to the question has just confused me even more!

I use a SPC900 webcam for imaging and someone asked me the other day what magnification the images it produces are at.

Jim your answer makes the most sense to me but I have no idea what the normal focal length of the webcam lens was.

[ollypenrice]

'Magnification' is entirely meaningless in this context. Put the image on a bigger screen and it's bigger. Zoom in and its bigger still. Your scope/camera haven't changed.

The useful concept is plate scale which compares angular size on the sky in degrees, arcminutes and arcseconds on the sky with size on your chip in millimeters.

Olly