Shadowy Daisy

Shadowy Daisy
by damned-truths

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1
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3answers
85 views

tokina at-x pro 100mm f/2.8 macro for Nikon - aperture automatically changes while in manual mode

The max aperture on my Tokina 100mm at-x pro is f/2.8 but when I focus on anything closer than around 9 feet, the aperture automatically starts to close down and get progressively smaller (higher f-...
1
vote
1answer
475 views

How to calculate the focal length of cell phone cameras when none of the required parameters are available?

There are many camera phones for which the focal length, aperture size, and sensor size are not available. Is there a formula to calculate these parameters or a site which provides these details for ...
1
vote
2answers
577 views

Help me understand effective f-number

If I set a lens to, say, f/2 but my focus is set to its closest point, my effective f-number won't be f/2 any more but it will be higher by a factor that depends on focal length, image magnification ...
3
votes
1answer
197 views

What is Effective Aperture?

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
3
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2answers
1k views

What's the difference between real and effective aperture?

I understand that the simple idea that f-stop is focal length divided by aperture really applies to a simple single-glass lens, not the compound lens systems used to provide good image quality in ...
4
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1answer
2k views

Does maximum aperture change with focus distance with the Canon 60mm f/2.8 macro lens?

This site says The Canon EF-S 60mm f/2.8 Macro USM Lens loses 1/2 stop at 1:5, 1 stop at 1:3, 1.5 stops at 1:1.5 and 2 stops at 1:1 (lifesize). Can anyone confirm that at 1:5 magnification, ...
12
votes
2answers
451 views

Does focus breathing make a lens slower when close focusing?

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 ...
11
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1answer
1k views

Does focal length affect diffraction, in addition to aperture?

The reason I ask is that f/18 on a 24mm lens = 1.5mm, and f/18 on a 180mm lens = 10mm. I thought diffraction is due to the small physical size of the aperture, rather than the f-ratio, yet I only ever ...