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07-26-2011, 12:40 PM   #46
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QuoteOriginally posted by creampuff Quote
FYI, the no-longer-made plastic fantastic Vivitar/Sears/Pentax FA 100mm f/3.5 Macro is a decent lens for the price. It offered 1:2 magnification on its own and 1:1 with the close-up diopter and this lens was made in both MF and AF versions.
Apparently it still is made and sold new ($115) under the Phoenix brand: TelephotoConversion Lenses

07-26-2011, 05:59 PM   #47
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QuoteOriginally posted by RioRico Quote
The main contradiction involves focus throw. We want AF lenses to AF quickly; this requires a short focus throw. We want macro lenses to focus precisely over some range; this requires a long focus throw. These are contradictory. The very fact that we have AF in the macro realm (1:2 and greater) where AF is unusable, where precise manual focus is necessary, is a contradiction. So designers build those contradictions into the lenses and sell them and we become used to them. But AF is still useless when shooting 1:1.
Well I have owned a fair number of DFA, DA and FA series Pentax AF macro lenses and I have not experienced the contradictions you talk about. Despite having a a very short focus throw the DA 35mm Macro for example does focus fast and accurate even up to 1:1 and it has Quick Shift to boot.

It is a fact that the longer the focal length, the longer the lens barrel has to rack away from the focal plane to achieve 1:1 magnification but even for the Pentax 100mm AF macro lenses, they focus quite a bit quicker then their manual focus counterparts. However the narrower angle of view and higher magnification does mean that there is a greater chance for an AF lens to hunt if it cannot lock focus on a clearly defined subject. But that has more to do with the shortcomings of the camera's AF and whether the subject is within the AF points than anything else. Besides, the current crop of macro lenses all allow realtime manual override or fine tuning with Quick Shift. There is definitely a place for AF when shooting 1:1 from my experience.
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