M4 front focusing - aligned rf & lenses though

[umcelinho]

Hi,

A few days ago I noticed I was getting some front focused shots with my M4 and different lenses. Since I'm travelling this Sunday I took them to the only authorised Leica tech in Sao Paulo to make sure the RF and the lenses were properly aligned. Turns out everything was aligned. I felt quite a noob and realised I must have focused in a rush, thus the occasional front focusing.

So I shot a roll last Saturday and just got them from the lab, and even though I was careful on focusing I still got some pretty front focused shots sometimes, I'm talking more than a meter off!

Like this:

monroe by Marcelo Colmenero, on Flickr

Since I'm travelling on Sunday I have no time to fix my M4.

I took a good look on the camera and thought of something. Its back plate doesnt have a cushioned feeling when closing as my M6 did, but it never bothered. I closed the back and when doing so I noticed that if I pushed the back door inwards a bit while holding the camera a slight double click could be heard, and also it goes inwards a bit.

I think I might have identified the source of the problem, but wanted to know if it makes sense or if anyone had a similar problem before I try to order a spare back plate from DAG and hope it arrives on time so I can use it on my trip.

Thanks a lot

 

[_goodtimez]

What you may do if you have an M6 is to put this M6 on a table and place an object at like 5 meter and focus on it. Take note of the precise location of the distance setting on the lens.
Then move the lens on the M4 and observe how your rangefinder is.
If all cameras set the lens distance at the same position it means both are calibrated equally and therefore you back plate may be the problem;

 

[umcelinho]

What you may do if you have an M6 is to put this M6 on a table and place an object at like 5 meter and focus on it. Take note of the precise location of the distance setting on the lens.
Then move the lens on the M4 and observe how your rangefinder is.
If all cameras set the lens distance at the same position it means both are calibrated equally and therefore you back plate may be the problem;

I've done this test with the tech, all lenses and the M4 are perfectly aligned, but I hadn't thought of the back plate possibility at the time... and I can't reach him on the phone due to holidays. I don't have the M6 anymore otherwise I'd take it, the M4 is my only film M and the camera I am going to use on the entire trip.

Considering getting a BGN M2 or M3 to be on the safe side, that was really unexpected :/

 

[sanmich]

My M4 has also a small play in the door, but I think that as long as the resulting pressure on the pressure plate is enough, it shouldn't be a problem.
You can verify your hypothesis by having a look at your camera with no lens, but I think you may have to look for the problem elsewhere.
If you have two bodies and a few lenses, you can easily set up a small experiment:
one possibility is to focus on a target, measure the exact distance to the film and see if the lens marking agrees (arguably not very precise, but when repeted on several lenses, can give you an idea)
the other one is the classic ruler at 45 degrees drill.
Just make sure to repeat the focusing exeriment several times, half of it focusing from the left, half from the right, to neutralize the "human factor".
At any rate, the kind of focus error that you describe shouldn't be very difficult to track down.
Good luck!

 

[ferider]

A loose pressure plate will result in front focus. Wider lenses will have more focus error than longer lenses. Wides are more sensitive to depth of focus variations.

If the pressure plate is your problem, you should be able to see this from the front. Close the camera, take the lens off, open the shutter on B, and see if the pressure plate is solid in place or not ....

Also, if it is the pressure plate, The M4 back door is easily replaced. You can use doors from either M2 or M3 as well.

 

[umcelinho]

Thanks a lot, ferider, that is a good hint: I've noticed that both my 50mm lenses (even the Canon 0.95) didn't show as much front focus as the 35mm and 21mm, since I had some shots with front focus (35,21) and some without (50) I assumed it would probably be just me focusing badly, but hadn't done this correlation.

I've tried what you've suggested and the pressure plate does give in a little bit (cushioned feeling) when i press it with my finger with the shutter open on B but I'm not sure if I'm putting too much pressure or not (no other M around to compare), is it supposed to not give in at all, rock solid?

I'm gonna shoot a test roll pushing the back door inwards with my thumbs and hope i can develop in time before tomorrow (highly unlikely, but..), if it works I can deal with it during the trip and have it fixed as soon as I get back.

 

[MikeL]

I've tried what you've suggested and the pressure plate does give in a little bit (cushioned feeling) when i press it with my finger with the shutter open on B but I'm not sure if I'm putting too much pressure or not (no other M around to compare), is it supposed to not give in at all, rock solid?

Marcelo, I remember the back having some give on my M4s. But the pressure plate should still be pressured against the rails. When looking at the pressure plate with the curtain open, does it move when you press on the back?

 

[umcelinho]

Marcelo, I remember the back having some give on my M4s. But the pressure plate should still be pressured against the rails. When looking at the pressure plate with the curtain open, does it move when you press on the back?

Mike, thanks. It's hard to tell, I've tried bracing the camera and then pressing the back but still the whole camera moves a tiny bit when I press it, so I can't be sure of it.

I'll share the outcome of this issue when I have it figured out, couldn't find anything similar on the web, might be of use for others.