Back focus in film shooting with M lenses.

[F456]

Parameters for this thread:

(1). Let's assume that every M body and lens I shoot with is perfectly aligned to one another, just for the sake of eliminating confusing variables.

(2). I am only shooting film -- for digital I use a different system.

(3). I understand what back focus is and that it is an inherent feature of certain lenses that is presumably nothing to do with overdue servicing or adjustment.

Questions:

(A). Am I right that a correctly factory calibrated lens will be free of focus shift at full aperture? I am thinking especially of fast lenses where focusing really is critical. That includes for me some of the lenses listed below in (C).

(B). Is there a list anywhere of the focus shift characteristics of various Leica lenses?

(C). Assuming there isn't such a list, then what focus shift -- if any -- do the following have & will it show on film: 28/2 Summicron ASPH versions and 28/2.8 Elmarit ASPH versions (i.e. clip on hood version and screw in version of each). Also 35/1.4 Summilux ASPH (previous, clip on hood version), 35/1.4 Summilux (i.e. little lens till 1990s - mine is late 70s) and 35/2 Summicron ASPH (both versions)? Finally current 50/1.4 Summilux ASPH, current 50/2 Summicron, and -- I expect this will be a tricky one -- 50/1 Noctilux, of which I have a very late example with sliding hood. I can't really test for myself as I know one or both of my M bodies needs a bit of rangefinder adjustment.

(D). Thank you for any help.

Tom

 

[Richard G]

I don't know about focus shift of different Leica lenses. But the idea that you need to send in all your lenses and camera(s) to Leica to have them calibrate the lenses to the cameras seems totally daft, despite it often being promoted here. There is a standard and the lenses need to meet the standard of the Leica bodies. Not all do, even brand new lenses. Period. My 1980 Summicron 50 had been back focussing for over 30 years before I discovered it and bothered to have it corrected. Not sure if this answers your question exactly.

 

[F456]

Back focus in shooting with M lenses

Back focus in shooting with M lenses

Richard,

Thanks for getting back to me so fast. I wasn't suggesting sending them all to Leica, just assuming everything was correctly matched so adjustment factors don't muddy the focus shift question.

The only adjustment I'll need to have done is probably to the rangefinder on one of my two bodies, because I know it is out.

But knowing the inherent focus shift characteristics of certain lenses and whether they are strong enough to affect film shooting is worth knowing, I think.

Tom

 

[brbo]

I can't really test for myself as I know one or both of my M bodies needs a bit of rangefinder adjustment.

Sure you can. You don't need properly adjusted rangefinder to do the test. The lenses will shift focus backward (or not) as you close the aperture.

 

[Sarcophilus Harrisii]

Unless the focus of a lens to the camera body register it's used with has been calibrated at an aperture smaller than its maximum, I can't see how focus shift can be an issue if a lens is used wide open. Different lenses may shift focus to a greater or lesser extent, but, until one is actually closed down, the focus can’t shift, can it?
Cheers,
Brett

 

[john_s]

I can't answer most of your questions but I can say that the 50/f1 Noctilux has huge focus shift. At f/1 on my M6 at medium distances it was spot on, actually amazing to me. At f/2 it showed really obvious back focus.

At f/2 the actual distance focused compared to what the perfectly adjusted rangefinder (or optical bench) sets at f/1 is as follows:


At f2:
2 metre: 2.12, discrepancy = 12cm = 4.7inch
3 metre: 3.28, discrepancy = 28cm = 11inch
4 metre: 4.52, discrepancy = 52cm = 20inch
8 metre: 10.45, discrepancy = 2.45metre = 8feet

This is using the focus shift figures supplied by Erwin Puts some years ago which one could probably accept as accurate given his close relationship with Leica.

The focus shift is probably covered at f/8 by DoF but that's not what Noctiluxes are for.

 

[mdarnton]

Why not do your own tests? I put a newspaper on the floor, at some distance, viewing it at an angle, the camera on a tripod, and a coin in the middle of the paper to focus on. Focus and take one shot wide open, then stop down and shoot another, without moving anything. Viewing the neg with a magnifying glass quickly shows what's going on both regarding focus shift and your/your camera's ability to focus correctly.

I was surprised to discover that some older lenses I assumed would shift did not, and also learned what I'd have to do with the shifters to compensate.

Some tests I have seen, and the discussions around them, show that not all lenses of the same description behave the same. I also learned from reading those discussions that some people who brag about their lenses (on this forum, no less) couldn't shoot an in-focus photo to save their lives and have no idea what "in focus" means, so I now believe doing my own test is the only way to get a certain answer on questions like this.

 

[Ko.Fe.]

I'm not this rich to be able to help OP. To my knowledge all M mount less glorious lenses I have tried do focus shift, including Leica made.
I tested most of them with appropriate focus chart at one meter distance, only. I can't see it at the scan on greater distances.
In real world it doesn't matter, if reason for owning these lenses on film bodies is prints.

 

[F456]

This is going to sound terrible but I'm being honest...

I can't be bothered! Too much else going on and it all takes up too much time. I'm obsessional enough without adding an extra dimension.

But I appreciate your suggestion.

Tom

 

[F456]

Initially disheartening but after reading your post a second time I realize that as I do have another Leica 50mm for more general use I really only need/want to use the Noctilux at f/1 anyway or just maybe at f/1.2. Anything else and it's not worth carrying the weight around. I will be interested to see how it performs at various distances at full or very nearly full aperture in the near future. I suspect my ability to focus precisely may be just as limiting a factor, but at least on my M7 I was far-sighted enough a few years ago to order it with the 0.85x viewfinder.

Thank you for the useful and rather alarming data!

Tom

 

[F456]

I see what you mean. I think you are saying that in the test even if the lens is not focused where I expect it to be I can see where it does focus and then compare shot by shot as the aperture and probably the point of focus move progressively.

Tom