AF hard stopping on DSLR

lotech · 12-29-2018, 12:26 PM

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 ?

Adam · 12-29-2018, 12:32 PM

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.

lotech · 12-29-2018, 12:47 PM

I think you are probably right, I can feel the torque of the motor when I grab the focus ring by mistake during AF.

**BigMackCam** · 12-29-2018, 01:03 PM

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.

**TwoUptons** · 12-29-2018, 03:29 PM

Short answer: they slam around on film cameras, too

-Eric

lotech · 12-29-2018, 06:30 PM

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.

12-29-2018, 12:26 PM	#1
lotech Pentaxian Join Date: Apr 2012 Posts: 1,312	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
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	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. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

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12-29-2018, 12:47 PM	#3
lotech Pentaxian Join Date: Apr 2012 Posts: 1,312 Original Poster	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
BigMackCam Digitiser of Film Join Date: Mar 2010 Location: North East of England Posts: 20,670	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
TwoUptons Loyal Site Supporter Join Date: Nov 2015 Photos: Albums Posts: 4,213	Short answer: they slam around on film cameras, too -Eric

12-29-2018, 06:30 PM	#6
lotech Pentaxian Join Date: Apr 2012 Posts: 1,312 Original Poster	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.