Diagnosing focus problem

[surfnsnow]

Hi All,

I just bought a used M 240 and a new Voigtlander CV 35mm 2.5. The focusing at close distance is off. When I focus at close range (1.0 - 1.2 m) wide open and using the rangefinder patch - I am consistently seeing the focus point in the final image 2”-3” behind where I intended to focus.

So for example, if a person is facing me at a 45 degree angle and I focus on the front eye, then check the image afterward in Lightroom, the focus point is actually on the back eye.

After noticing this in a few images, I tested it out by focusing on a ruler at 45 degrees with the camera being stationary. What I see is that when the rangefinder patch looks focused to my eye, Live View shows the focus point 2”-3” inches further away from the camera. If I then adjust the focus using Live View and look back in the rangefinder, the ghost image appears slightly to the right.

So I’m wondering if - based on this information - is there a way for me to determine if the problem is:
1. The rangefinder
2. The lens
3. User error

I don’t have another lens to test with. I’m trying to figure out if I should return the lens for a replacement - but I wouldn’t want to do that if the problem is the rangefinder or my focusing (in)ability.

Thanks in advance for any input / tips on how to properly diagnose the problem.

 

[Peter Jennings]

Check infinity. Is live view with the lens set to infinity is in sharp focus? Does focus patch show out of focus at infinity? If these answers to these questions are 'yes', then it is the camera and not the lens.

 

[surfnsnow]

Peter, Thanks for your input!

It's been a bit foggy here so I had to wait for it to clear before checking infinity 🙂

I tested with both the rangefinder patch and live view. I focused on a tree about 2200 feet away (I measured it on google maps). The rangefinder and live view both agreed that the tree was in focus.

There also happened to be a roof line about 100 feet away. Here is where they were different. Live view showed the roof line in focus, but the rangefinder patch did not. The ghost view on the rangefinder was slightly to the left.

I took 2 test shots, one at f2.5 and one at f/8. In the resulting images the distant tree was in focus in both. The roofline was in focus in the f/8 image, but slightly out of focus at f/2.5.

I checked a DOF calculator and 35mm f/2.5 2200 ft focus distance should have a close limit of about 52 ft for “acceptible sharpness”. So I would have expected the roofline at 100 ft to be in focus in both images.

Given this additional info, could one reasonably conclude if the lens or the rangefinder calibration is the issue?

 

[Peter Jennings]

Re. infinity, I live on the top floor of an apartment building in the middle of a huge city and I can look out the window and see skyscrapers over a mile away. Checking infinity is so easy for me and I sometimes forget that others don't have the same convenience.

Based on your tests, it seems it could be either the lens or the rangefinder. Sorry, I know that is not very helpful. If the lens is brand new and the camera is used, then it is more likely that the camera is to blame. Until you have another lens to compare against, I'm not sure how you can determine the true culprit. Maybe another RFFer will be able to help out.

Good luck!

 

[View Range]

Don't assume there is only one problem. It could be both lens out of adjustment and rangefinder out of adjustment. You are in SoCal and have access to camera repair shops. They can quickly check both with precision equipment.