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Old 02-06-2013, 11:00 PM
04Stefan07 (Stefan)
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Standard Eyepiece FOV

Does anyone know what a 1.25" 25mm eyepiece FOV is that comes standard with a new telescope?

I have a super angle long eye relief one that came with a Skywatcher telescope. I am entering all my equipments information into AstroPlanner and I have no idea what the FOV is for this 25mm.

Thanks!
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  #2  
Old 03-06-2013, 08:09 AM
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Merlin66 (Ken)
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Try starting with a 50 degree AFOV for the eyepiece. The final actual FOV will be AFOV/magnificantion.
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Old 03-06-2013, 08:53 AM
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Today most "standard" EPs that come with scopes are plossl's. These have a typical AFOV of 50 to 52deg in the 1.25" format like Merlin mentioned, but not always.

There is a way of actually determining both the AFOV if it is not mentioned on the EP, or to verify the actual value. Aim at a star that sits along the equatorial line in the sky, or close to it. What you want to do is time its drift takes to span the FOV of the EP. You will end up with a figure in seconds (1min 20sec is 80seconds). Then divide this time value by the magnification given by the EP. This will give you the TFOV in decimal value. The AFOV is then given by manipulating the equation Merlin gave:

AFOV = TFOV X magnification

Not all EPs in a given series will have the exact AFOV mentioned. As an example a series of EP that states 68deg could have EPs that vary plus or minus a few degree, but the average is 68. The timing method is a quick & easy way to determine this.
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Old 09-06-2013, 10:01 AM
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Hi Stefan, agree, they are typically Plossls, to keep costs down. But your statement of 'super angle long eye relief' suggests it may be something different. Can you post a picture of it and maybe a better guess might turn up... Cheers Fox
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Old 09-06-2013, 06:00 PM
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If these are the ones that look a little like an XW thats been living on the wrong side of the tracks I think there 50 degrees or so .
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