M42 Lenses on Nikon DSLRs, Restoring Infinity Focus

ltolias · Joined: 17 Feb 2012 Posts: 1

I am looking to clarify the issue of infinity focus when using M42 mount lenses on nikon DSLRs.

From what I have gathered, the problem stems from a difference of about 1mm in the flange to focal plane distances for the Nikon F mount and the M42 mount.

This problem is sometimes alleviated by using a mount adapter with corrective optics. I do not particularly like this approach.

I have also found mention scattered around a few sites on the web that it is possible on many M42 mount lenses (particularly russian lenses like the Jupiter 9 and the Helios 40), to simply unscrew the rear optical element of the lens a few turns. In these lenses the rear element is in a thread of its own that can easily be unscrewed by a spanner. Unscrewing it moves the rear optical group backwards, reducing the flange to focal plane distance. This seems to be useable as a method for accounting for the 1mm discrepancy.

I was wondering therefore, if anyone could confirm that this method of unscrewing the rear element works reliably.

In addition, after looking through many many pages of M42 lens images, it seems that all of them have a moveable rear element. Does this mean that almost all of them can be easily adapted to work perfectly on Nikon DSLRs?

martinsmith99 · Expire: 2013-11-18

I think some M42 lenses may have enough adjustment on them to use on a Nikon, but probably 99%+ will not.

Arkku · Joined: 28 Feb 2007 Posts: 1416 Location: Helsinki, Finland

Remember that it's not just the 1mm register difference of the mounts you need to make up for, but also the thickness of the adapter you are using. I doubt you will be able to reach infinity on most lenses, but do let us know if you succeed.

visualopsins · Expire: 2025-04-11

Sounds to me like it could work, but by adjusting rear group by the thickness of the adapter plus 1mm, wouldn't then the helical have to turn more to move front group (adjustment + 1mm) closer to the rear group, to achieve infinity focus? I think a helical adjustment will also be necessary.

Gurdie · Expire: 2013-02-20

Some M42 lenses can be modified to reach infinity with Nikon bodies.

Helios-44 takes some machning.
http://forum.manualfocus.org/viewtopic.php?id=12363

Here�s a link, how to remove the stop screw from a Carl Zeiss Jena 135/3.5
http://forum.manualfocus.org/viewtopic.php?id=15919

There must be many others modifiable, I believe.

philslizzy · Joined: 07 Aug 2012 Posts: 4748 Location: Cheshire, England

nick_cool · Joined: 04 Mar 2013 Posts: 5

Yes, you can move back the inner lens, and also remove the stop screw from the inside the lens.

I adapted some M42 with great success:

http://www.flickr.com/photos/nick_cool2000/6960323923/in/set-72157627250905996/

But I am still fighting with others...

Anyway I am happy with the results.

Zylkan · Joined: 08 Apr 2015 Posts: 5

Hi guys,

I realize these are all older threads but I just replied to this one here:

http://forum.mflenses.com/viewtopic,p,1445500.html#1445500

I have a S-M-C Takumar 200mm F4 that I'm trying to adapt to my Nikon body but moving just the helicoidal was not enough for me.

The rear element approach seems good to me btw. I did notice by looking at the back of my lens that there's a couple of threads in an inner "tube" to fit a spanner wrench. Maybe I could try unscrewing this a bit?

Cheers

CuriousOne · Joined: 31 Dec 2013 Posts: 669 Location: Home

Just remember, than when you adjust distance between lens front and rear part (most of them are double gauss type), you're worsening image quality, since lens inner distances were calculated in a way to cancel distortions and abberations as much as possible. When you distrupt this, you'll get more CA, coma, and sometimes geometrical distortions.

Zylkan · Joined: 08 Apr 2015 Posts: 5

Ooops...

I see your point. That just blew everything out of the water!

Damn...