Why do older camera lenses have faster F-stops?

Started Apr 14, 2013 | Discussions thread
Leonard Migliore
Leonard Migliore Forum Pro • Posts: 15,535
Look through a D800

vjk2 wrote:

Man, I really like the old viewfinders + pentaprism.

They're so much bigger, and the pentaprism makes it feel more craftsmanship-like.

Too bad you can't get them for digital. Wonder why the viewfinders of DSLR's are so small? I'm guessing the extra size of the sensor vs film requires you to reduce the size of the reflex lens. Still, I wish they'd make a "manual focus" orientated DSLR.

Crop sensor DSLR viewfinders are small because the sensor is small. The viewfinder is presenting an image of a screen that's the same size as the sensor. If you look through the viewfinder of a full-frame DSLR, you'll see something pretty similar to what you got in an older film SLR.

Back when I bought my D300, I looked through the viewfinder of a D700 and almost bought that camera instead just for the viewfinder; it was so much bigger and brighter. But I resisted because of the several thousand dollars that would have cost me by the time I got lenses for it.

One major difference is a result of autofocus. The phase detecting autofocus sensors steal about 1/3 of the light from the finder, making the image that much dimmer. To compensate for that, the manufacturers made the screens clearer. So now they're bright but you can't focus on them.

People do make their DSLR's more suitable for manual focus by replacing the focusing screens. This works best with a full-frame camera because, as I've noted, you get a decently big and bright image with them.

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Leonard Migliore

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