Help me estimate FOV of a scope

[luigi]

Hi All,

I'd like to know the Field of View of a very old telescope, a 9.6 inches (24.4 cm) Aprochromatic Refractor with a 4 meters tube.

It's for a silly project I have emulating how the sky would look from such a scope.

Thanks for your help!!!
Luis

[mithrandir]

Luis, you need the focal length of the scope and the camera image size (35mm, APS-C, etc) or the eyepiece focal length to work out the FOV.

[luigi]

Ty Andrew,
Ok this is going to be hard.
It's the telescope that was used at the Berlin Observatory to find Neptune. I couldn't find that information and I got no answer from the museum.
Maybe someone knows the answer...

[multiweb]

Have you tried CCD Calc (http://www.newastro.com/book_new/camera_app.php)?

[torana68]

not hard if you can do basic math, try this
http://astro.unl.edu/classaction/animations/telescopes/telescope10.html

this will give you an idea, if you want exact do the maths, estimate the eyepiece sizes to get an overall feeling. OR do some research on eyepieces available at the time to narrow it down, Id assume it was a fairly big eyepiece 20mm or more?

[DavidU]

That's a fairly tidy telescope there Luigi.

[Wavytone]

Old refractors of that size were typically f/15 - f/18.
That means a focal length around 3.5-4 metres.

At 3.5 metres, 1 degree = 61 mm across the focal plane. At 4 metres, 70mm.

You might just fit the moon in the field of some of the really big 2" eyepieces, like my LV50 mm.

[luigi]

Ty Wavytone, any guesstimate is good!