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12-29-2018, 12:26 PM   #1
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AF hard stopping on DSLR

I got couple film lenses to play with my K3, namely the Tamron 28-200, the FA 80-320 and the FA 28-90 or 24-90 I forgot. I found they have something in common, they all have AF hard stopping, the motor stops like hitting the wall, unlike my non SDM 55-300 that stops smoothly. Since I don't have a AF film camera to test I can't tell how the lenses actually perform on a body they designed for, or hard stopping was how old AF lenses work ?

12-29-2018, 12:32 PM   #2
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The motor on the K-3 (and newer models) is more powerful than those on film cameras, so the hard stop effect feels more pronounced. Newer lenses sure are nice in that they don't have such behavior.

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12-29-2018, 12:47 PM   #3
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I think you are probably right, I can feel the torque of the motor when I grab the focus ring by mistake during AF.
12-29-2018, 01:03 PM   #4
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It's also worth bearing in mind that most film era lenses have a hard infinity stop, whereas modern AF lenses tend to go past infinity and have drive mechanisms which simply "slip" when the end of travel is reached. Plus, I suspect the gearing in those older film lenses has less reduction.

12-29-2018, 03:29 PM   #5
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Short answer: they slam around on film cameras, too

12-29-2018, 06:30 PM   #6
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Talking about gear reduction I found my 2 film lenses work quite differently, the Tamron 28-200 which is macro capable has a very short focus throw not so MF friendly, but the FA 80-320 has a quite far MOD of 1.4m has near a full turn this is weird design.

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