Archived posting to the Leica Users Group, 2007/08/31

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Subject: [Leica] do it yourself back-focus adjustment..."
From: robert.rose at mac.com (Robert Rose)
Date: Fri Aug 31 23:32:54 2007

Vick,

We had a thread on this around March or so.  I had posted some  
samples and how to do it at:

http://gallery.leica-users.org/v/rjrose/focus/

I included some "proof in the pudding" pictures that the post  
adjustment photos were spot on for focus.  I have had no problems  
with focus wide open since then.

This method works if you are having problems close up.  I define  
close up as the range where you can see a focus difference in the  
rangefinder between a person's nose and their eye's.  If you are much  
farther than that, I don't think you need this.

Unless you are a real scientist about it, here is one way to do it,  
which is completely trial and error (heuristic for RIT grads), not  
especially elegant, but it will work, and should be reversible.   
There are lots more rigorous ways to do this, but this worked for me  
(as shown in my results).

1.  Shoot lots of photos wide open with your lenses.  If you think  
you are hitting the focus, keep shooting, and have some scotch to  
celebrate.  The focus will seem even less important.
2.  If you don't think you are hitting focus, get yourself a 2 mm hex  
wrench, and some more scotch.  (Just kidding about the scotch, but  
why not?)
3.  Put the camera on a tripod, and find/make a target.  There are  
lots of ideas on the web.  Maybe a newspaper on the wall, at whatever  
distance you like to shoot.  Just be consistent.
4.  Try to make the camera parallel to the wall in both x and y  
direction.  Don't go too nuts, since you are going to look at the  
center anyway.
5.  Try to have good lighting so you can use a high shutter speed.  
Use a cable release.
6.  It will help if you tether the camera to a computer using the  
camera control software.  Then you can inspect the DNG files easily.
7.  Carefully focus the lens using the magnifier if you have it.
*8.  Take a picture wide open, and be sure to keep track of it:  this  
is your control.
9.  Take a series of photos, each time slightly rotating the focus.   
It doesn't matter which way, you will repeat this going the other  
way.  Make the rotation in small increments, and take a bunch, maybe  
10.  The idea is not to be able to reproduce that position, but to  
find if you can make a better focussed picture at any position other  
than the rangefinder position.
10.  Compare the photos to the control.
11.  Are any of them any better in focus at the center?  If yes, then  
you may have a focus problem.  Repeat steps 7-10 to confirm (you  
should then also look at the new control to be sure that it looks  
like the original control), and save the best picture, as it will be  
your "target".  Now go to step 13.
12.  If not, you are not quite finished.  Repeat steps 7-10, rotating  
the lens the other way (you should also look at the new control to be  
sure that it looks like the original control).  Repeat to confirm if  
you find one of the photos is better than the control.  Save that  
picture, as it will be your "target".  If not, you are finished, the  
camera and lens is "good enough" for you and the state of your eyes.
13.  Insert the hex wrench as shown in the photos.  Take a picture of  
the camera (with another camera) so you can see where you started.   
Then turn the wrench slightly, as I describe in the photos.  Take a  
photo of wrench position.  It is probably a good idea to support the  
bottom of the wrench so that it doesn't fall onto the shutter  
blades.  (Avoid that at all costs, please)  Not much force is needed.
14.  Notice that I didn't tell you which way to turn the wrench; that  
is because some cameras differ in the direction needed.  If the focus  
doesn't get better you are going to use that photo you took to turn  
the wrench back to zero, and then go the other way.  You can start  
using my results.
15.  I don't think you will need to turn the wrench any more than I  
did in the photo.  Start with half my amount, be patient and work  
your way slowly.
16.  After each adjustment, repeat steps 7 & 8.  Are you worse than  
the original control?  If so, you are probably going the wrong way.   
Refocus and shoot another picture to be sure.  Then repeat step 13  
going the other way.  If this also makes it worse, then return to  
zero (you did save that photo, right?) and stop.
17.  If the slight adjustment made it better, keep going in that  
direction until you have a new photo that looks as good as your  
target photo.  Then stop; don't go crazy trying to get it perfect.

That's it.  Now go shoot wide open and forget about focus issues.   
All my lenses are now really great wide open, and at all distances,  
including infinity.

Oh, one more thing.  Notice that I said wide open.  Some lenses at  
close distances show focus shift when you stop down.  The Noctilux  
especially has focus shift:  http://www.imx.nl/photo/lenstest/ 
noctilux-m_11050mm.html
In other words, the focus could now actually look better wide open  
than at f/4 when you are close to the object.  You will need to  
experiment, or avoid those mid stops for critical photos.  At f/8 the  
depth of field should cover any focus shift.

*You might want to add a new step at 8 to take a control stopped down  
2-3 stops, and see whether while you improve focus wide open, you are  
not affecting focus stopped down.

I have a hunch that the factory may be calibrating the M8 for an  
average f/stop, say around f/4.

So, there you have it.  One afternoon in time, but a whole lot better  
than 6-8 weeks at the factory.  Or, you could remember to focus on  
the nose when you want those eyes to look sharp.  ;-)


Bob Rose


===============================

the Are you close to the target?
...............
Bob,

I am intrigued with this - "...do it yourself back-focus adjustment..."

Can you describe it?

I assume that this is a mechanical thing, as a given Noctilux/ 
Summilux is
supposed to be interchangeable with all M's, including the M8.  This  
would
mean that either:

1.  the lens flange-focal distance needs to be adjusted, and I can't see
doing that yourself.  I would guess it means taking the lens head off  
the
helical and adjusting its spacing shim.

2.  the lens flange-focal distance is correct, but the body flange to  
sensor
distance needs to be adjusted.  I suppose one could do this  
themselves, but
I am guessing this would involve re-shimming the lens flange from the  
body,
which would then force you to re-adjust the rangefinder arm.  Not  
impossible
at home, but the body is then matched to the one particular lens.  Then
would you hope that the adjusted body is good for all other lenses,  
or does
the DOF take care of that?

regards
Vick

Replies: Reply from vick.ko at sympatico.ca (Vick Ko) ([Leica] RE: do it yourself back-focus adjustment...")