Prime Lenses Question

Started 3 months ago | Discussions thread
Boudewijn van der Drift
Boudewijn van der Drift Senior Member • Posts: 1,218
Re: Prime Lenses Question

Boudewijn van der Drift wrote:

Joel Klein wrote:

Good morning.
What’s the reason a 50mm would cap at f/16 vs. a 2.8 zoom would close more?
Letting more light in, I understand the challenge, but why not close up to f/22?

This is about diffraction, which is different by the focal length and other parameters. Above a certain aperture number a larger portion of the light will diffract. The diafragm itself acts as a (crude) negative lenselement at its edge. Thus softening the image. It is somewhat arbitrary, I guess Nikon considers it's 50 mm so sharp that diffraction spoils the image already at f/16. Macro lenses need DOF, and extent further from the sensor at close focusing.

If that zoom includes 50 mm, it also has to cater for other focal lengths.

P.S. if you could stop down the diaphragm to pinhole size, that is what you would get, pinhole quality, notwithstanding all the expensive glass. You would need careful engineering for the blade mechanism.

A 50 mm f/22 would be 50/22 = 2.3 mm actual diaphragm diameter. And since the diafragm is closer by than 50 mm it is even smaller. Looking through the front lens enlarges it.

"Pinhole size" is a different f/number for a telelens or a wide angle. The longer lens can stand higher f/numbers. Including when it is longer due to the sensor/film format.

 Boudewijn van der Drift's gear list:Boudewijn van der Drift's gear list
Panasonic Lumix DMC-LX3 Nikon Z7 Nikon Z6 Nikon Z 70-200 F2.8 VR +2 more
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