If shooting at f/22, is a fast 1.8 lens still considered fast?

Started Apr 17, 2011 | Discussions thread
Ronj2 Senior Member • Posts: 1,195
Re: If shooting at f/22, is a fast 1.8 lens still considered fast?

noirdesir wrote:

Ronj2 wrote:

A faster lens gives a brighter view through the view finder

With todays focussing screens, you won't see much if any benefit from lenses faster than f/2.8 (or maybe even f/4 with some cameras). Just use the stop-down function on your camera and open up the lens starting from f/4, you'll probably see some brightening going to f/2.8 but little to nothing opening up further.

I can clearly see a difference between F2.8 and F4 so yes a faster lens does give a brighter view compared to a slow consumer zoom. From 1.4 to 2.8 there is no difference in my D90.

and generally gives more accurate auto focus in low light situations.

Anything faster than f/5.6 (or probably f/5) is lost on the phase-detect AF (except on some Canon bodies which have a few special f/2.8 focus points). The phase-detect AF sensor in all Nikon bodies only sees light coming from the 'f/5.6 ring'.

So it appears that phase AF only works at a slow F5.6 on Nikon bodies. Then there should be no difference in AF accuracy between a fast F2.8 like the 70-200vr2 lens and a slow F5.6 70-300vr consumer zoom in low light situations (other than focus speed). That's good to know.

One more detailed explanation is in this post:

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Ron J

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