Lens calibration?

I have always had a bit of trouble with focus of my 75mm Summicron. A friend recently sent me this link: Squit Photo to a focus chart. I tried it with two lenses: a 50mm and a 75mm. I sat on a chair in almost the identical position. The 50mm is spot on accurate. The 75mm seems to focus very slightly behind what the rangefinder tells me. Is this a defect in the lens? Can it be repaired?

Hand holding the camera to test calibration is inviting error. You really need to do the testing from a tripod or optical bench. My question to you is do both lenses, when focused at infinity (the moon for instance) with your rangefinder, in fact show sharp focus (on film or your screen - depending on whether you are using a digital or film camera). The rangefinder itself has basically 2 points of adjustment, one for near and one for infinity). The lenses then can be calibrated to the rangefinder standard. My guess is that the 75 may need an adjustment, but if you're not shooting wide open, it is compensated for by the depth of field.

It can be adjusted. But I'd try the test on a tripod first. Testing the 75mm focal length (and above) can be difficult wide open - especially at f/2.

 

If you keep getting the same results, contact Don Goldberg at dagcam[at]chorus[dot]net, or Leica if the lens is still under warranty.

Thanks for the suggestions. I tried again using a tripod with delayed shutter release. The 50mm seems to be spot on. The 75mm seems to way off - more than 8cm anyway. I took exactly the same care focusing with both lenses. I have not tried infinity yet.

 

In the shots below, I used the split lines on the small circle near the 0 mark - very carefully. The result confirms the gut feeling I have had about the 75mm lens from the start. I have emailed the Leica service department.

 

The 50mm shows a very slight behind bias, so it may be that the rangefinder needs a slight tweak too, but more likely within the error bounds of my eyes:

 

The 75mm is really off:

 

 

 

Here is the 75mm deliberately focusing in front of the target:

The 75 APO Summicron can be very fickle to focus accurately. I sent mine (purchased second-hand) to DAG, who tested it, and it came back as "in-spec".

 

The focus throw is so short, and the window for error is so small, it doesn't take much. I still have mine but purchased a 75mm f2.4 Summarit to try based on so many positive remarks from users over at the Leica forum and that is the ticket at the 75mm focal length. The thing is tack sharp at every aperture, focuses to .7 meters just like the APO Summicron, is not nearly as finicky to accurately focus, is light as a feather compared to the Summicron and, not being a filter user, I prefer the Summarit's hood, which extends further and Leica includes a great cap to use with the hood mounted, so it never coming off my lens.

2 lenses aren't enough to rule out rangefinder adjustment. I am having trouble focusing M9 with my 70 year old eyes, have taken pics with all lenses and am pretty sure it's the RF, so, I guess calibrate that first. M3 used to take a lot more punishment without such issues.

I can only imagine (LOL) how almost impossible it will be focusing this new 75mm f1.25, $12,000 Noctilux when wide open.

I can only imagine (LOL) how almost impossible it will be focusing this new 75mm f1.25, $12,000 Noctilux when wide open.

+1

I suppose there's a reason they've chosen f/1.25 instead of 1.0 or .95!

I would think size. The thing is huge already. F1 or 0.95 and 75mm is probably too much for the rangefinder to handle, even with one of the magnifiers. Not to mention it probably going to $15,000.

 

The M10 and Visoflex is how I’d deal with that, in the unlikely event I ever stumbled into the opportunity to get the lens.

When they put their mind to it they can design and build lenses pretty small. All you need to do is compare a 50mm Asph Summilux-M with the equivalent SL lens. Both are f/1.4 full-frame 50mm lenses, but the SL lens is a good 3-times (or more) the size of it's M counterpart.

 

That's been an allure of the Leica M system since the very beginning.