Alley in Pisa, Italy

by Lars Kotthoff

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.

What is Effective Aperture? And how it can affect my exposure? Also how does it relate to magnification?

A question that talks about effective aperture but without details

share|improve this question
    
Same basic question, but with slightly different follow-up questions: What's the difference between real and effective aperture? –  mattdm Jul 23 '13 at 0:05

1 Answer 1

up vote 2 down vote accepted

Effective aperture is the size, in terms of diameter, of the diaphragm opening as viewed through the front element of the lens. It is the apparent diameter that is used to calculate the f-number for a given aperture setting. For instance, if you have a 200mm lens and want an aperture of f/4, the effective aperture needs to appear to be 50mm wide, regardless of the fact that due to magnification between the front element and the diaphragm in conventional designs the actual width of the diaphragm is usually smaller. This is also why it is so difficult to make a large aperture ultra wide-angle lens: the retro-focal design means the actual opening must be larger than the effective aperture.

share|improve this answer

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.