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Re: [OM] Auto focus for OM?

Subject: Re: [OM] Auto focus for OM?
From: "Hans van Veluwen" <hcvanveluwen@xxxxxxxxx>
Date: Wed, 27 Jun 2001 11:41:49 +0200
: There were a few of this type of lens made about 10 years ago by third
: party lens makers when the major manufacturers were going AF. They're not
: common because they were pricey and possibly a bit slow compared to a true
: AF camera - a good idea but a marketing failure. The only ones I've seen
: are tele zooms - I think I've seen a Tamron as well and that was bulkier
: than this Sigma. Everything is in the lens - motor, batteries, focussing
: sensors - I don't know how reliable or accurate they are.

I have this Tamron Adaptall AF lens, bought out of curiosity and because it 
wasn't
expensive. I've never actually used it, only played with it. It's a 70-210mm/F4
Internal Focus lens, meaning that its length does not change while zooming or
focusing. This, and its constant F4 aperture make it an interesting design.
Problems with such lenses (including the Olympus stand-alone 35-70mm/F4 AF 
lens) is
not reliability or accuracy, but sensitivity and speed. They don't work in low
light or low contrast conditions, and auto focusing is rather slow. Its typical 
AF
lag is 1~1.5 sec. Compared to the iS-3000, which focuses in a fraction of a 
second,
this is slow and can be a problem. The lens has three focusing modes: MF, 
Single AF
and Continous AF.

hnz



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