AF with M42 Lens


tomw

Link Posted 30/05/2011 - 16:37
Hi

Just wondering if it was possible to have autofocus with a screw mount lens by using the Pentax AF Adapter, then attaching the M42 adapter on to that, then attaching an M42 lens that has a minimum aperture of 2.8 or less.

In other words the combination would be:

Pentax DSLR + Pentax AF Adapter + M42 Adapter + M42 Lens f/2.8 or less


Would it be possible?
Tom

Anvh

Link Posted 30/05/2011 - 16:57
With the Pentax AF Adapter you mean the 1.7x AF teleconverter?
Stefan


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davex

Link Posted 30/05/2011 - 17:09
Quote:
using the Pentax AF Adapter, then attaching the M42 adapter on to that, then attaching an M42 lens that has a minimum aperture of 2.8 or les

Remember that the 1.7x does not provide full range af, you need to at least manually focus the lens to about the correct area. The aperture of the mains lens does not matter, so you should be able to do what you want;
but why ?

Davex
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tomw

Link Posted 30/05/2011 - 20:27
Yes I meant the 1.7x AF Teleconverter. Silly me!

I was just wondering because apparently there was tin foil involved when you wanted to use an M42 lens with the 1.7x AF Teleconverter.
Tom

thoughton

Link Posted 30/05/2011 - 20:46
You had it right to start with, for whatever reason Pentax called it an adapter, not a TC. works fine with M42 lenses, although see davex's post. The tin foil thing is most likely only to enable catch in focus because the painted base of takumar lenses is non-conductive.
Tim
AF - Pentax K5, Sigma 10-20/4-5.6, Tamron 17-50/2.8, Sigma 30/1.4, Sigma 70-200/2.8, Tamron 70-300/4-5.6
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womble

Link Posted 31/05/2011 - 01:45
davex wrote:
... but why ?
Davex

Presumably to get AF with M42 lenses... There are some stunning M42 lenses around that produce lovely results on dSLRs, just look at the Takumar club on Pentaxforums for examples. Personally, I am happy to just use them in MF but I could see some advantages to trying this route.

K.
Kris Lockyear
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Stuey

Link Posted 31/05/2011 - 12:34
I am confused by this - by af did you mean af confirmation?

I may be wrong but whilst using manual focus you can obtain focus confirmation but no lens will autofocus unless it is specifically designed to do so and have the af screw/ af mechanism in the lens etc

I am not aware of any m42 lens with this but stand to be corrected.

Incidentally I use m42 lenses and more often than not rely on eyesight over af confirmation but either seem to work.
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Mannesty

Link Posted 31/05/2011 - 12:54
Stuey wrote:
I may be wrong but whilst using manual focus you can obtain focus confirmation but no lens will autofocus unless it is specifically designed to do so and have the af screw/ af mechanism in the lens etc

I am not aware of any m42 lens with this but stand to be corrected.

You're wrong, consider yourself corrected. To be more accurate, you are correct in saying that no M42 lens is capable of AF by itself, but it can be made to AF with the addition of this.

The SMC Pentax-F 1.7x AF Adapter is exactly that, a 1.7x magnifying auto focus adapter which makes any manual focus lens auto focus, with a few exceptions listed in the documentation. EG: It would not work with my 135-600mm lens when I had it.

An MF lens does have to be partially manually focussed first to get it somewhere near focus, then the AF adapter copes fine.

To turn a screw mount lens into an AF lens you attach the AF adapter to an AF capable K-mount body, mount the K-mount adapter to the AF adapter, then screw the lens on.

Simples.

Look at the first line under General Description here.
Peter E Smith

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Last Edited by Mannesty on 31/05/2011 - 13:04

Stuey

Link Posted 01/06/2011 - 12:39
Mannesty wrote:
Stuey wrote:
I may be wrong but whilst using manual focus you can obtain focus confirmation but no lens will autofocus unless it is specifically designed to do so and have the af screw/ af mechanism in the lens etc

I am not aware of any m42 lens with this but stand to be corrected.

You're wrong, consider yourself corrected. To be more accurate, you are correct in saying that no M42 lens is capable of AF by itself, but it can be made to AF with the addition of this.

The SMC Pentax-F 1.7x AF Adapter is exactly that, a 1.7x magnifying auto focus adapter which makes any manual focus lens auto focus, with a few exceptions listed in the documentation. EG: It would not work with my 135-600mm lens when I had it.

An MF lens does have to be partially manually focussed first to get it somewhere near focus, then the AF adapter copes fine.

To turn a screw mount lens into an AF lens you attach the AF adapter to an AF capable K-mount body, mount the K-mount adapter to the AF adapter, then screw the lens on.

Simples.

Look at the first line under General Description here.

Ok, I am surprised but for me to understand this how does that adapter turn the focus ring to acheive af from a manual focus lens

Or is it a case of you having to focus close to correct and then teh adapter alter's it's own focus to compensate
K10D, K5 plus plenty of clueless enthusiasm.

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thoughton

Link Posted 01/06/2011 - 12:44
You set the MF lens to infinity, and then the adapter has it's own lenses inside which move around when you use AF, thus bringing the MF lens' blurry image into focus. For closer objects you might have to prefocus the MF lens to somewhere close to the focus point before pressing the AF button.
Tim
AF - Pentax K5, Sigma 10-20/4-5.6, Tamron 17-50/2.8, Sigma 30/1.4, Sigma 70-200/2.8, Tamron 70-300/4-5.6
MF - Vivitar CF 28/2.8, Tamron AD2 90/2.5, MTO 1000/11
Stuff - Metz 58 AF1, Cactus v4, Nikon SB24, Raynox 150, Sigma 1.4x TC, Sigma 2x TC, Kenko 2x macro TC, Redsnapper 283 tripod, iMac 27”, Macbook Pro 17”, iPad, iPhone 3G
Flickr • Fluidr • PPG • Street • Portfolio site
Feel free to edit any of my posted photos! If I post a photo for critique, I want brutal honesty. If you don't like it, please say so and tell me why!

davex

Link Posted 01/06/2011 - 13:02
Quote:
EG: It would not work with my 135-600mm lens when I had it

I can confirm it does work with the new Sigma 150-500 OS HSM.

Davex.
K5 + 8mm-500mm zooms and primes
Please feel free to play with any images I post.
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Stuey

Link Posted 01/06/2011 - 21:27
thoughton wrote:
You set the MF lens to infinity, and then the adapter has it's own lenses inside which move around when you use AF, thus bringing the MF lens' blurry image into focus. For closer objects you might have to prefocus the MF lens to somewhere close to the focus point before pressing the AF button.

Every day is a school day
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