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

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.

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.

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