Focus accuracy with M3

[telenous]

As I am but another poor chap that has surrendered his soul to Leica et. al. I recently bought a nice price 1095xxx M3 to go with my M2. The price was nice but the camera needed a CLA and rangefinder recementing, so off it went to CRR Luton. It is now back in tip-top condition (incidentally, may I add in a long string of recommendations for CRR and in particular Peter Grisaffi, my own) and I have been playing with it the last couple of days.

However, just today I came to realise that the focusing of my M3 and M2 are slightly diverging. Now, when I say they diverge I mean they do so by a hair. I have been testing the two cameras side by side and when I focused on a chimney, may be 20-30 meters away the M2 focused at infinity - the M3 focused at slightly less than infinity. I am not sure what to make of this difference. Could it be the famed M3 accuracy in focusing because of its greater effective base length compared to that of the M2? I would greatly appreciate any thoughts on the matter.

This is no real worry, as the CRR provides a six month guarantee and so if there is any problem with the M3 I can still send it back for some extra calibration. Anyway I 'd still like to hear what you make of this.

 

[former member]

I'm surprised that the M2 reached infinity at "only" 20m to 30m. The M3 will hit it at ~100m. You might check them at the 5m range as well. I will double check mine later; but expect the M2 to be close to that. They were both recently CLA'd.

 

[telenous]

Thanks Brian. Why didn't I think of that, perhaps it's the M2 that is slightly off. The difference is easier for me to detect when I mount the cameras with the rigid Summicron. The indications on the barrel have a greater separation or throw between 20m -i nfinity than, say, with the Planar ZM where you go from 5m to infinity. It seems that the M2 matches the rf image at infinity while the M3 at just below infinity. Perhaps I am splitting hairs here, I am jsut wondering whether the M3 is somehow more accurate.

 

[former member]

I checked the M2 with a type I Rigid Summicron 50/2. The RF converged at about 300ft. Lots of room to go between 100ft and infinity. It looked right-on, compared with the 1x finders of the Nikons. These cameras can handle a 90/2 without problem, and some of those require focus out to that distance. I even have an RF coupled 200/4.5 Komura, and bring up the 1.5x finder of the Canon VI-t for it.

 

[waileong]

My M3 only reaches infinity at infinity... ie, the moon. I was in New York recently, taking the Staten Island Ferry and shooting the Manhattan skyline, the images aligned just a little before infinity.

 

[former member]

That might be a bit too far!
But I would not worry about it. Most slight errors are more than covered by DOF.

 

[Stu W]

Just ried my M3. I focused on an illuminated sign about 3 blocks away and it was little short of infinity. Stars are infinity. Stu

 

[Ronald M]

I set up on a star. 300 ft is insufficient.

 

[waileong]

From a purely technical perspective, lens designers use 1000xfocal length as the yardstick for infinity. Thus a 50mm lens should reach infinity focus for a target that is 1000 x 50 mm away, ie 5 km (3 miles).

 

[awilder]

Waileong is correct about "optical infinity" focus being 1000 x focal length but for a 50 mm lens it's 50 meters, not 50 km. Even 50 meters is to short too check rf accuracy as this rule probably assumes a 0.03 mm circle of confusion wihich works fine for a 3" x 5" print but not critical enlargements. To check infinity focus, the object should be at least 1 km away. This will be accurate for any RF mounted lens, even the 135/2.8, which I own and is their most distance sensitive lens in terms of rf focus. I find the moon and stars difficult to measure subtle focus errors because of overpowering contrast and internal reflections. A radio tower or building with windows works best in good haze free daylight.