Not Your Everyday Banana

by Bart Arondson

submit your photo


Hall of Fame
View past winners from this year

Please participate in Meta
and help us grow.

Take the 2-minute tour ×
Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It's 100% free, no registration required.

I've heard that focal length of some lenses will become noticeably longer when focusing to a close distance, an effect called "focus breathing". Since f-number is focal length divided by diameter of physical aperture and aperture size does not change, it seems logical to conclude that such lens should become slower when focusing close.

Is that really so, or is there something I'm overlooking?

share|improve this question
    
You mean "slower," not "faster," right? –  whuber Nov 25 '11 at 19:15
    
@whuber Ah, yes, of course! –  Imre Nov 25 '11 at 19:17
add comment

1 Answer 1

up vote 5 down vote accepted

That is true, and very noticeable in macro lenses. For example a Nikon 105mm f/2.8 VR (at infinity) is f/4.8 at it's closest focus distance of 30cm or so.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.