M8 Rangefinder Infinity Adjustment

From Leica Wiki (English)
Jump to: navigation, search

lac4tricro

Required Materials:
2mm Allen wrench
A target

One Method for Testing Adjustments

After turning one of the adjustment cams (see links below), you need to establish some protocol to determine whether the adjustment makes things better, or worse. This trial and error method works if you are having problems close up, e.g., 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.

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 (see link below). 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.

  • 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.

That's it. Now go shoot wide open and forget about focus issues.


Focus Shift

Some lenses at close distances show focus shift when you stop down. The Noctilux especially has focus shift; in other words, after this adjustment 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.



Photosshowing how to make the adjustment

FAQ on DIY rangefinder adjustment

Chart and instructions for doing a focus test

Noctilux article discusses focus shift