Calculating Magnification on a Telescope + Camera setup
by John Gregoriades
on
Dec 12, 2005 at 4:02:18 pm
Hi,
This is for the folks that enjoy telescope + photography.
I'm learning to use a digicam and a digi-camcorder with a telescope. I know that the magnification of the telescope is its principal focal length (1000mm mirror) divided by the focal length of the eyepiece (20mm) which works out as 1000/20=50X.
But the cameras, when zoomed a bit to avoid vignetting, add to this magnification.
Question: How does one calculate the final magnification?
The camera's zoom is from f-8mm to f-24mm (3x). The camcorder's huge (25X) optical zoom goes from f- 3.7mm to f- 92.5mm.
Is there a method to calculate what the final magnification is, at say the ends of each zoom range? (one can then interpolate in-between.)
Thank you,
John
Re: Calculating Magnification on a Telescope + Camera setup by Amish Ed on Dec 13, 2005 at 4:23:27 pm
Don't know what the calculations are, but it sounds like you're using a point and shoot. If that's the case how can you know the focal length of it's lens, let alone with any accuracy. HAve you checked out any of the astrophotography websites? What about using a camera adapter that doesn't use the scopes lens? You'll get better contrast and shorter exposures.
Amish Ed
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Re: Calculating Magnification on a Telescope + Camera setup by Jim Harvey on Jan 4, 2006 at 4:55:41 pm
In order to figure out your focal lenght you need to first know the magnification of the telescope being used. (Focal Length of Telescope divided by Focal length of eyepiece I.E. 1000mm/20mm - 50X as in your example) Knowing that, you then can multiply the focal length of the lens being used by the magnification (Camera Zoom lens at 8mm X 50 = 400mm) If you need to find the 35mm equivalent then you need to know the relationship between your sensors physical size compared to a 35mm frame. The camera manual should have this information. (I.E. and Olympus E-500 has a 150mm lens that is the equivalent of a 300mm lens in 35mm therefore 300/150 = 2. Now you can multiply your focal length by this factor to arrive at the 35mm equivalent. So in our above example we have 400mm x 2 = 800mm equivalent in 35mm)
I'd worry more about understanding the exposure values rather than the magnification equivalents if I was looking to do any serious astrophotography. It's much easier since the days of Hypered film and 3 hour guided exposures. You can dial in 3200ISO and make excellent exposures in a fraction of the time it used to take with none of the mess and bother either!
