Focus calibration: M-lenses & M-bodies

[F456]

I used to worry about the idea of adjusting and matching a Leica body to a particular lens (yes, the Noctilux is responsible for this thought). If a body were matched to one lens, wouldn't it be out with others that had always been fine?

Leica UK's Mr Herriot(t) performed a quick adjustment to my M7 and my recently-bought Noctilux yesterday and clarified the process. If I understand things right, you can match a body to a lens, in which case you cannot guarantee continued good operation with other lenses.

BUT... lenses do go out as well (contrary to what you sometimes read). If Technical Service check and adjust both the lens and the body then you should be fine with your other lenses as well, assuming they are correctly adjusted, of course.

This all sounds extremely obvious in hindsight, but I thought it was worth stating. Focus shifts or not - I couldn't even get a focused shot at full aperture; now we're ready to try again! I am using a 1.25x viewfinder magnifier with a 0.85x viewfinder, to help things along.

Tom

 

[Roger Hicks]

Dear Tom,

This has always puzzled me too. If both the camera and the lens are inside specification, you should be OK. Presumably the problem arises when both are at the limits of their tolerances -- which are INCREDIBLY small for focusing an f/1 lens at full aperture at close distances -- and either can be pulled in closer to specification. If both are brought closer to spec, so much the better.

But most people don't understand tolerances (or worse still, imagine that everything is always exactly made to its design dimensions) and don't understand how much it costs to reduce departures from design dimensions. One of the reasons why Alpas cost so much is that their tolerances are so small that one engineer said, "But you couldn't make a profit with tolerances that tight."

Cheers,

R.

 

[Livesteamer]

As a retired machinist I must add that Roger has made a very important point. Focusing an f1.0 or even f1.4 lens requires great mechanical accuracy and this does not come cheaply. Such precision is labor intensive with specialised manufacturing and inspection. This is why your Leica products cost so much and why my Alpa 6C is such a gem to use. Joe

 

[ferider]

This has been a pet-peeve of mine since a few years.

A couple of comments:

- what Roger said about lens and camera being with-in tolerances, but a certain combo not, happens as I know from personal experience, with a 90/2 Summicron v2 and M3, both CLA'ed independently, but out of spec as a pair. Don @ DAG confirmed that this can happen.

- the Noctilux is certainly an impressive and fast lens. But few people realize that many other lens/camera combos are much more sensitive to RF mis-calibration. For instance, a newer 50/1.4 Summilux, at minimum focus distance (.7m) will be MORE sensitive than a Noctilux at 1m. A Summicron 90/2 is more sensitive as well. The Leica lens requiring most accurate calibration is the 75/1.4 Summilux.

- I use lenses of various brands in LTM and M mount. What has frustrated me in the past is the obvious difference in RF calibration accuracy. Usually, old Nikkor LTM and Leica lenses of all periods are quite accurate (on the average body). I have been frustrated with the various degrees of RF calibration accuracy of some Voigtlander lenses, among others.

- Some fast RF lenses have such a short throw that they are almost impossible to focus accurarately at close distance, repeatedly. The 40/1.4 and 50/1.5 Nokton come to mind. A good way to check this visually is to look at the DOF scale. If it starts at f4, the lens might be of this category.

- When playing with LTM lenses and LTM/M adapters of obviously varying thickness (depending on manufacturer), not only is RF accuracy a parameter, but lens to film distance, too. The wider the lens, the more sensitive it is to registration distance variation (this is counter intuitive if you think of the increased DOF). For a fast wide angle, for instance, you might have picked the right adapter for RF infinity correctness, but might be out of focus because the adapter is a little off wrt thickness, and the camera lens combo doesn't match.

It's tricky. More so with longer EBL, of course. Once you have a combo of lenses and bodies that works, touch the RF alignment as little as possible ....

Roland.