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Re: [OM] differences in f stops

Subject: Re: [OM] differences in f stops
From: Paul Wallich <pw@xxxxxxxxx>
Date: Mon, 1 Apr 2002 10:53:23 -0500
Cc: olympus@xxxxxxxxxxxxxxx
At 7:09 AM -0500 4/1/02, ClassicVW@xxxxxxx wrote:


I do know that manufacturers are 'allowed' to be off by 10 0n their claims for both f stop and zoom range. I notice that they always seem to be off in the optimistic direction. You can see this by reading the fine print in published lens tests. I never gave it much thought if this was allowed as a 'normal' difference in manufacturing, or what. I can't see it as that; could you imagine a lens that was 'allowed' to be100ff in focusing?!

I can. In fact, I've owned at least one such lens, and I bet you have too.
It's just that the definition of "off" in focusing is generally even less
harmful than it usually is for f-stop. The design of the mirror, body and
focussing screen guarantees (ahem) that when something looks in focus through the viewfinder, it _is_ in focus on the film plane, so I don't really care what the distance scale says. And I've never believed that those markings were particularly exact. (The only time I cared was with a vivitar 19mm where the infinity stop corresponded to about 6', and even allowing for hyperfocal distance that just didn't work.)

Same thing is mostly true for f-stop. 10 0ifference isn't going to make or break any of your pictures. In fact, with TTL metering, you don't really care what the aperture is (within reason); all you care about is that each stop is half the aperture of the previous one. (All this doesn't really excuse camera manufacturers, but it should remind us what's important to making good pictures.)

paul

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Paul Wallich                                            pw@xxxxxxxxx

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