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Calculating FoV?


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I was wondering if it was possible to calculate the FoV for Explorer 130P and Skymax 127?

I have found some calculators online, but have no idea of what to input.

I needed the FoV so I can see how much the telescope will zoom in using stellarium :eek:

If there is an easier way to find out what sort of zoom I would be getting, please share! :evil6:

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Sam

You need details of a few facts to answer your question.

a) focal length of telescope - so the Skymax 127 is 1500mm F.L.

:eek: diameter of primary mirror is 127mm so its a f11.8 scope.

c) focal length of eyepiece - say 25mm which is a standard length with new kit

d) the EP will state its apparent field of view - say 50 degrees. Nagler is 82 degrees as an example

e) divide the 1500 by the 25 to get the magnification of 60

f) to get the field of view you divide the mag of 60 into the AFOV of 50 to get .833 of a degree - hence 50 minutes view through your scope with this eyepiece.

Is that ok?

Mark

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Sam

The eyepieces included with the Skymax 127 are a 25mm and a 10mm EP and I guess that the AFOV will be 50/52 degrees. The 10mm will give you a magnification of 150x perfectly ok for viewing Mars and Saturn and its rings. With this mag the FOV will only be about 20' or one third of a degree.

Mark

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Ah that all makes sense :eek:

What sort of FoV would I need to see Mars, or the rings around Saturn?

Is there any way to find out the apparent FoV?

The apparent is given by the EP manufacturer, usually 50 or 55 degrees for a Plossl.

The real FoV is, as the others said, the AFOV of the EP over the magnification you achieve with it (depends on the scope FL too).

For planets as low as you can get and seeing conditions allow, they are tiny. In other words the highest mag possible under the conditions.

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Don't get carried away with calculating and using the highest magnfication that your scopes theoretically allow (about 250x) - you will see just as much detail and get nicer views at 170x-200x on most nights.

At these magnifications the field of view will be very small as has been said so not really relevent. Field of view comes into play much more when thinking about low power views for use with deep sky objects.

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