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spotting scope field of view

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spotting scope field of view

Postby andywand on Fri Sep 03, 2004 6:48 pm

Just glancing over some of the spotting scope models, most of the ones I see in the $200 - $400 range seem to have a field of view of around 25 ft at 1000 yrds, which to me seems a bit large. I plan to use the scope from a bay-view apartment for general entertainment, and would like to be able to see detail at a fairly decent distance. The Meade ETX 90 claims to allow one to read a license plate at half a mile, or see people walking at 2 miles, neither of which sounds likely with a field of view as large as 25ft at 1000 yards. However, the Meade doesn't give a field of view rating, and the other scopes don't make that sort of specific claim, so I am a bit confused.
andywand
 

spotting scope field of view

Postby opticsplanet.com on Sat Sep 04, 2004 12:28 am

Hi Andy

Thank you for your interest in www.OpticsPlanet.com

Field of view can be confusing to understand sometimes, especially when you begin to compare different spotting scopes in regard to this feature. Let me see if I can help explain it.

Field of view in any instrument is determined first by the magnification and second by the design of the eyepiece. A spotting scope with a zoom eyepiece typically has a field of view of about 80 feet at a thousand yards when you have it set at 20 magnification and about 25 feet at 1000 yards when it is set at 60 magnification. In other words the amount of landscape you can see when you look through the eyepiece (field of view) gets smaller as you increase image size (magnification).

Meade’s claim that you can read a license plate at half a mile or see a person at two miles is based on the magnification (image enlargement) of the eyepiece, not the field of view (how much territory you see when you look through the telescope). It is magnification that will determine whether you can read a license plate at half a mile or see a person at 2 miles. Field of view is really not a factor in this case.

Eyepiece design is also a factor in how much field of view you will have at any given magnification. For example, with the Meade ETX-90 http://www.opticsplanet.com/meade-etx90ss.html and the eyepiece that comes standard, you will have a magnification of 48x (image enlargement) and a field of view (the amount of territory you can see) of about 57 ft at 1000 yards. If you replace this eyepiece with one of the high performance, extra wide (and very expensive) eyepiece designs on the market, you can keep the magnification (image enlargement) of 48x while increasing the field of view up to 76 feet or more at 1000 yds. Image size remains the same, but you see more land or sky when you look through the scope.

To sum up, a field of view of 25 feet at 1000 yards is fairly average for a telescope or spotting scope when used at 60x. If you are concerned with reading license plates or seeing people at great distance, pay attention to the magnification, not field of view.

Hope this helps. By the way the Meade ETX-90 is a great choice in a spotting scope and one of the best buys in the price range of $200 to $400.
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