#1
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FOV calculators?
I know there must be a free FOV (field of view) calculator somewhere that
will show what I am seeking. I want to compare and see (on a sample image) the FOV of my ETX-90 with a Nikon D40 at prime focus and also the ETX-90 with a 40 mm eyepiece with a camera (not necessarily a D40) afocally coupled. Suggestions for a suitable calculator? Thanks, SK |
#2
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FOV calculators?
Sam Kirkpatrick wrote:
I know there must be a free FOV (field of view) calculator somewhere that will show what I am seeking. I want to compare and see (on a sample image) the FOV of my ETX-90 with a Nikon D40 at prime focus and also the ETX-90 with a 40 mm eyepiece with a camera (not necessarily a D40) afocally coupled. Suggestions for a suitable calculator? Thanks, SK Is this any good Sam: http://cameraassistant.sourceforge.net/ John. |
#3
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FOV calculators?
John wrote:
Sam Kirkpatrick wrote: I know there must be a free FOV (field of view) calculator somewhere that will show what I am seeking. I want to compare and see (on a sample image) the FOV of my ETX-90 with a Nikon D40 at prime focus and also the ETX-90 with a 40 mm eyepiece with a camera (not necessarily a D40) afocally coupled. Suggestions for a suitable calculator? Thanks, SK Is this any good Sam: http://cameraassistant.sourceforge.net/ John. Or this: http://www.nto.org/whatusee_en.html John. |
#4
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FOV calculators?
On 2008-06-29, Sam Kirkpatrick wrote:
I know there must be a free FOV (field of view) calculator somewhere that will show what I am seeking. I want to compare and see (on a sample image) the FOV of my ETX-90 with a Nikon D40 at prime focus and also the ETX-90 with a 40 mm eyepiece with a camera (not necessarily a D40) afocally coupled. Suggestions for a suitable calculator? The imager on a Nikon D40 is 15.6 mm by 23.4 mm. The focal length of the ETX-90 is 1250 mm. The field of view in degrees vertically is approximately 57.3 times 15.6 divided by 1250, or 0.715 degrees. The field of view horizontally is 57.3 times 23.4 divided by 1250, or 1.07 degrees. For afocal photography it gets a little complicated, because you have to be concerned with the field of view of the eyepiece, the field of view of the camera lens and the fact that the camera lens might not see all of the field of view. The 40 mm Meade Super Plossl, for example, has an apparent field of view of 43 degrees. On an ETX-90 that eyepiece gives a magnification of 31 times and an apparent field of view of 1.4 degrees. Based on the CCD diagonal of 28 mm, a 35 mm focal length lens would cover a field of view of a little more than 43 degrees, if you can match the exit pupil of the eyepiece to the entrance pupil of the lens. Pocket digital cameras come with lenses that cover more than 43 degrees. You need to match the entrance pupil of the eyepiece to the entrance pupil of the camera. What this means in practice is that you move the camera back and forth in relation to the eyepiece and adjust the zoom setting until you can see the entire field of view. You want to use a pocket digital camera that allows you to set the exposure manually. Bud |
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