My experience of focus adjustment on M2

[steve_taylor3]

This is my experience of adjusting the RF on a 1963 M2. Its a write up for my

own reference and in the hope that it helps someone.

 

I bought a 1979 Leica 50/f2 lens cheapish recently and was testing this when I

discovered my RF was off in my battered M2. Well I hoped it was this as I could

adjust this better than the lens. So I set about doing some focus checks.

 

I have a home-made focusing target (printed A3 and stuck on a bit of flat card)

with a series of vertical lines printed 10mm apart, with one of these being

thicker and marked zero. Each other vertical line is marked with the distance

from this point. There is one dotted horizontal line that goes through all the

vertical lines and the cross of this and the thicker vertical line makes the

focus target. I set this up at a 45 degree angle about a metre from the camera,

which was on a tripod. This gives a good focus target.

 

I took the back of the camera off and attached a focusing screen from a Nikon F4

onto the film rails with blu tack, making sure the flat face of the screen

touched only the inner rails. This gave a nice bright projected image on which I

could see the focusing error. At this close distance, when you adjust the focus

of the lens, you can see the zone of sharpness chase back and forth along the

dotted horizontal line. As I expected the RF and the image on the screen did not

agree.

 

I adjusted the infinity adjsutment of the RF cam so that I could get the RF and

point of sharpness on the focusing screen to coincide. I made a tool to do this

from one half of a spade fuse (the ones that go in your car fuse box). I broke a

fuse in half and this produced two connectors and the fuse bit in the middle. It

is the connectors that are of interest - one of these fits very nicely in the

slot of the RF cam. I gripped this in some forceps I had, and this made a good

tool. I also twisted the other connector so I could use it if I got near the

limits of rotation with the straight one. I made the adjustments, and got good

agreement with the RF and the image on the focus screen. Piece of cake I thought.

 

To make sure of the adjustment I ran a film through the camera and made some tests:

 

I used a number of different lenses:

 

Leica 50/2/1979 lens (the one I was testing)

 

Leica 50/2/2002 lens

 

Leica 28/2/2004 lens

 

Leica 90/2.8 lens (very old and battered - I think its about 1961 vintage)

 

CV 50/1.5

 

For each lens at wide open, 1 stop down and 2 stops down I made 3 exposures, one

focusing out (i.e. extending the lens) to get the RF to line up, one focusing in

to get the RF to line up and the third going back and forth till I was happy it

was in focus (what I do in real life). The aim of the 3 exposures was to give me

a few samples and to see if there was any pattern to the focusing behaviour.

 

The film was plus x exposed at 100 asa and developed in Rodinal 1+25 at D-20%

because I presoak with 5 inversions per minute. At today's temp it was about 5

mins dev time.

 

When I looked at the film on the light box I discovered that the focusing was

consistently too distant, i.e. the RF was indicating zero and the point of max

focus was about 30mm further away from this (this is along my 45 degree angled

scale so the actual distance was about 21mm - 30mm * 0.707). There appeared to

be no appreciable difference in the different focusing methods - all 3 of each

aperture were pretty consistent.

 

I went to the internet and found this page:

 

http://www.normankoren.com/Tutorials/MTF6.html

 

From this I gathered that the plane of focus was not only dependent on the

position of the subject and the focus of the lens, but also the position of the

film. I hypothesised that the film bulging was the cause of my focus error. I

had read about this and been advised on here in the past about film bulging.

 

So I went about adjusting the RF until the RF said the target line was focused,

but the focusing screen on the film rails said that the sharpest point was about

30mm (indicated on my 45 degree target) closer of the zero target distance.

Hopefully this would offset the error I was seeing.

 

This was not as easy as the RF other adjustment. I had to adjust the length of

the RF arm as well as the inf adjustment. This was scary and I would not have

even considered it if the camera was not so beat up. Anyway I went ahead. I

undid the screw that held the arm to the armature that goes up from the throat

of the camera into the RF, and cleaned all the surfaces so they would move

cleanly when I wanted to make adjustments. Unscrewing was the scariest part.

Once I had got it all back together I could undo the screw slightly and move the

cam and see the arm extend and contract smoothly.

 

I did an intial adjustment for infinity with the arm at a guessed length. I did

an infinity check by going outdoors and focusing on a tree on a hill about a

mile and a half away. Then I put the camera back on the tripod and did the 1m

check, which was off by miles, so I adjusted the length cam, and checked again.

I kept on repeating this process until I eventually got the focus I wanted at

infinity and 1m. This took the whole afternoon, but I did get better at it as I

went along as I got more experience.

 

Some notes on actually making the adjustments. I held the shutter open on B all

the time (with a cable release), so I could out my thumb through the shutter

opening so as to keep the arm from moving when I made adjustments. I have read

and can understand that it is very important not to stress the delicate RF

mechanism, and I certainly paid attention to this. I also took the plate with

the film loading diagram off the bottom inside of the camera and removed the

plug so I could put a screwdriver up through the throat of the camera to get to

the length adjust screw. This made things much easier. For the inf adjustments I

used my spade fuse tool.

 

Once I thought I had got the adjustment I wanted, I ran another film through the

camera (same stuff) and did the same tests with all the lenses above and some

other CV ones. In addition I did some real world tests by focusing on real

objects at 1m, 4m, 10m and inf at f2, 2.8 and 4.

 

When I developed the film I was pleased to discover that the focus at all

distances was bang on. Wahey!

 

One other thing I discovered was that even at distance (probably about 30)

correct focusing DOES matter. In these tests I focused at inf, and a chimney at

about 30m was noticeably soft at f2. I set the tripod up and did another film

test carefully focusing on the chimney using the RF. The actual rotation of the

barrel is miniscule to get the focus to come in, but when I looked at the

difference in the negs between this and focused on the inf stop the difference

was astonishing.

 

So in conclusion, I think I have seen film bulge in action. It is real, and I

don't think checking focus with a ground glass is good enough. You must do film

tests.

 

I also learned that you must focus accurately as well as doing all the other

things like keeping the camera steady.

 

Disclaimer: I am posting this as lessons I have learned in the hope that it

helps someone. I do not condone adjusting your own camera and obviously cannot

take any resposibility if anyone damages their camera as a result of reading

this! Like I said, my camera was beat up and I would have sent it in to get done

professionally if I had messed it up.

 

Hope this does help someone.

[frank_scheitrowsky1]

Thank you for this comprehensive write-up.

 

Film bulge: isn' that what the pressure plate, in conjunction with the film rails, eliminates?

[steve_taylor3]

Sorry - to be clear - from what I read in Puts and other places, I understand film bulge to be the bulging of the film away from the pressure plate, towards the lens. This was certainly consistent with my findings.

[frank_scheitrowsky1]

Perhaps film behaves differently before development, but after development while placing film strips in negative sleeves, the film edges consistently bow so that the emulsion side is concave, which when in the camera would press the film against the pressure plate, not away from it. This is my logic based on my experience which is not asw extensive as yours with measuring focus errors due to film buckling, so I may well be wrong.

[ronald_moravec1]

Leica allows for bulge in the design of their lenses. There is minor extra space in the film channel. The only way around it is a vacuum pressure plate. If there is insufficient space, film can`t move thru it.

 

There are two adjustment points, infinity and one meter from the film plane. Infinity is a star at night, not the house across the street. One meter is from the film with a 50mm lens set to i meter ,all 50 mm lenses have have a 1 meter mark. This is how to set it up.

[andrew robertson]

Film budge cannot be comprehensively accounted for, as different films do not have the

same thickness. Film will bulge away from the pressure plate unless a vacuum pressure

plate is used.

[ronald_moravec1]

No the solution is not perfect, but they compensate with an average.

 

I might note their lenses are never truely flat field, even the macro ones. The only one I never tested was my 100 APO.

 

Put a DR/rigid on an enlarger. You will see. The version 3 is better, but still not flat.

 

The 50mm enlarging lenses are not even flat except for the large front element version 2 Focotar made by Schneider. Even the supposedly super Focotar 2 needs refocusing to get the edges, then the center goes out.

 

Maybe I`ll try my new 50 2.8. The original 50 2.8 was not flat any more than the DR/rigid of the period. I used to enlarge cardboard mounted slides with any of these three as they matched the films curve much better than an enlarging lens and it was easier than remounting in glass. It was a good enough solution, but not perfect.

[Gus Lazzari]

Hello Steve, the rangefinder adjustment is purely a visual adjustment to be performed with a perfectly collimated lens. Proper adjusting can only occur with a perfect lens sample.

 

The issue of film thickness becomes moot, when using an auto collimator test instrument. This tool shoots a projected image directly in to any lens. Usually a lines per mm target that you can see reflecting back off the actual film, because this all takes place with the camera loaded with film and lens mounted. The thickness in the varieties of film is of no consequence. The film rails are just that, edges of the film are pushed up against the rails and the flat pressure plate adjusts to the thickness of any film. Hence the spring action of all pressure plates.

 

Think of it... You have a slightly off lens with an accordingly off lens focus heliciod cam. So now you adjust your visual RF and a royal mess is the result! It all begins with a perfectly adjusted lens unit first. So comfirm your best and most accurate lens before you adjust the roller cam in the body.

 

Now the body is another matter, even with the famous reputation of the robust M series bodies, if it has been subjected to excessive shock or impact, then it's possible that the lens mount or structure are off. One can't confirm a lens on that body. Another tool called a film flange test jig in conjunction with shims needs to be used to gain the factory specs again. Regards, Gus