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» Support Center » Knowledgebase » I want to use my spotting scope to take pictures – what’s its f-number?
 I want to use my spotting scope to take pictures – what’s its f-number?
Answer The f-number or focal ratio is just the focal length of the spotting scope divided by the aperture (diameter of the lens). It’s almost universally given as a quantity like f/5, f/2.8, etc., called the f-stop or photographic speed. These terms are used interchangeably.

Example: an 80mm spotting scope with a 480mm focal length has a f-number of 6 and its photographic speed is f/6.

Lower numbers mean the lens is delivering light more quickly and consequently shorter exposures can be used when taking a picture through the scope.

Article Details
Article ID: 2123
Created On: Nov 26 2008 12:01 PM

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