Back focus adjustment question.

[billh]

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I have been noticing the plane of focus appears to be behind my point of focus, so I checked it this afternoon. I used several lenses, and refocused between shots, and the error for each lens was consistent, but this back focus error varies with the different lenses. Does the camera (M8) come out of adjustment, and how do I adjust the camera for so many variations? There is a series of photos I saw on this list showing an adjustment that can be made with a 2 mm Allen key. I do NOT want to send it back to Leica again. Any ideas? Here are some (but not all) of the test shots.

 

http://homepage.mac.com/billh96007/Focus-test/PhotoAlbum205.html

 

M8 Focus test chart. I refocused for each shot. The camera was on a tripod. Mag means I used the 1.25x magnifier to focus (I actually find the M8 clearer/brighter and easier to focus without the magnifier). I checked the focus on a 30 inch monitor, using smart sharpen to see the point of most sharpness. I did not sharpen the Tifs.

 

Here is the amount of error for each lens:

 

50ASPH at f1.4, mag, 1876 backfocus 1 inch (25.4mm)

50ASPH at f1.4, mag, 1877 backfocus 1 inch (25.4mm)

50ASPH at f1.4, 1878 backfocus 1 inch (25.4mm)

 

50Noct,f1.0,1879 backfocus 3/4 inch (20mm)

50Noct,f1.0,mag,1880 backfocus 3/4 inch (20mm)

 

35ASPH,f1.4,mag,1881 backfocus 3/8 inch (10mm)

35ASPH,f1.4,1882 backfocus 3/8 inch (10mm)

 

75,f1.4,1883 backfocus 1/4 inch (6mm)

75,f1.4,mag,1884 backfocus 5/16 inch (8mm)

 

APO75,f2.0,mag,1885 backfocus 3/8 inch (10mm)

APO75,f2.0,1886 backfocus 3/8 inch (10mm)

 

28f2.8ASPH,f2.8,1887 backfocus (10mm to 14mm)

28f2.8ASPH,f2.8,mag,1888 backfocus (10mm to 14mm)

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[carstenw]

Get a 2mm Allen wrench, and stick it in the middle of the little wheel which makes contact with the lens. Turn it very slightly and re-test. Repeat. It is very easy to do, but takes patience.

[Hans Roggen]

Do you know which way to turn to move the focus further back or to the front? And isn't it easy to screw up the focussing alltogether?

 

Hans

[wattsy]

Bill, do the tests again with the lenses at F2.8 or F4. You may surprised to see that the lenses back focus even more at the smaller apertures. Both my 35/1.4 ASPH and 50 ASPH show a noticeable amount of focus shift.

[wattsy]

Get a 2mm Allen wrench, and stick it in the middle of the little wheel which makes contact with the lens. Turn it very slightly and re-test. Repeat. It is very easy to do, but takes patience.

 

I know that a number of people have used this method successfully but can anyone confirm exactly what adjustment is being made using the 2mm allen key? Is it possible to throw off the focus in another way making this adjustment? It all seems disturbingly easy and makes me wonder why it has traditionally been the job of a technician to make adjustments to the rangefinder.

[billh]

I know that a number of people have used this method successfully but can anyone confirm exactly what adjustment is being made using the 2mm allen key? Is it possible to throw off the focus in another way making this adjustment? It all seems disturbingly easy and makes me wonder why it has traditionally been the job of a technician to make adjustments to the rangefinder.

 

I sent the photos of the adjustments that were kindly posted here, and people's instruction comments to a person I know at Leica today asking about this - the M8 is going to cause all of us to become camera techs. My choice is to focus on the end of people's noses, or give this a go here. It is funny how much adversion I now have to using that huge, heavy 1Ds2.

[lovelyleica]

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My Leica M8 came with backfocus on shorter and shorter focusing distances, I mean infinity focus is perfect, short distance focus is made behind the point you adjust the rangefinder for. I tested M8 with 3 lenses 35mm f2 + 50 noct + 75 f1.4 : all 3 lenses did backfocus on short distance with perfect focus on infinity.

 

I could solve this "easily" (I did it a long time ago with M4-P wich had vert. misaligned RF + front focused RF). Here is how, but be careful, this operation can normaly only be made by a certified Leica reparator. If you do it, it is at your own risk. You could probably loose your waranty with such an operation, or even worse, damage your camera.

 

Bakfocus on short distance comes from a too short focus sensor lever. To adjust it :

 

0. before making any adjustement to the RF be sure that your lense(s) focuses perfectly on lense's (not RF) infinity (very easy to test with a digital camera). Problem in focusing precision could come from a lens whose RF barrel is not properly adjusted.

 

1. loosen just a little bit the screw which secures the lever on its shaft with a screwdriver (I modified a normal screwdriver to be oblique, so that it fits better the screw at an angle)

 

2. Turn the ring surrounding the screw by a little amount in the screwing direction, so that the lever is moved to the left.

 

3. Tighten center screw.

 

4. The effect of changing lever length is that it changes the angle of the arm with the RF lens barrel and so changes lightly infinity RF position. That's why there is a screw (allen) in the center of the focusing wheel. Adjust it to get a perfect RF infinity.

 

5. You are ready to make new tests. If it's not OK you can repeat above steps.

 

 

The amount of "move" of the lever depands of the amount of backfocusing. The best is to go with very little paths until you reach the perfect focus.

 

Again, this procedure is a micro-mechanics operation. Don't go in this procedure if you are not familiar with micro-mechanics.

[arthury]

A few observations which I am curious:

1. Why do we think that this focus test is suitable for rangefinders?
   
2. Is this test an accurate test of focus if the lens cannot focus close enough on the target line??
   
3. Perhaps, it might be more useful to enlarge that test diagram?

What do you guys think?

 

Perhaps, tilting the chart at 45 deg instead of the camera may produce a more accurate 45 deg tilt.

See this:

 

Focus Testing

[robsteve]

Bill:

 

The first step to figuring out focus is to see if the rangefinder is aligned to infinity. Find a target a mile or so away, and see if the rangefinder aligns. Take a picture with the lens at infinity and see if it is in focus. As Arthur mentiond in the posts above, I don't know if this target is the way to test a rangefinder initially. You have to make sure the far distance is set correctly before even bothering to test the near distance. The far distance doesn't need a chart, just a distant object. I think I read infinity is the focal lensth of the lens squared and multiplied by 1000. For a 50mm, it would be 250m, or 2 1/2 soccer pitches.

 

I would use the two 50mm lenses to check the infinity, trusting the Noctilux to be the most accurate.

 

If the infinity setting is not correct, you near will not be either. The infinity setting is very easy as explained in the other posts. The adjusting screw is moving an ecentric which moves the position of the roller on the follower arm.

[gesper]

Which direction (clockwise or counter-clockwise) do you turn the screw to correct backfocus?

[Tony C.]

Gesper,

 

You turn clockwise. Here's the thread that introduced the solution, and if you scroll down, you can even find pictures to illustrate the job.

 

http://www.leica-camera-user.com/digital-forum/13933-new-backfocus-thread-solution.html

 

Regards,

 

Tony C.

[billh]

A few observations which I am curious:

1. Why do we think that this focus test is suitable for rangefinders?
   
2. Is this test an accurate test of focus if the lens cannot focus close enough on the target line??
   
3. Perhaps, it might be more useful to enlarge that test diagram?

What do you guys think?

 

Perhaps, tilting the chart at 45 deg instead of the camera may produce a more accurate 45 deg tilt.

See this:

 

Focus Testing

 

Well the error is consistant (the same) with multiple shots, but this back focus issue exists in all of my photos. This is a straight on shot, and the box in focus is 1 5/8 inches behind the box in front that I focused on.

 

 

The worrying thing to me is how much the lenses differ in the amount of back focus. Is some of the problem with various lenses? If so, how can the camera be adjusted so the focus is correct with all of the lenses?

[billh]

Bill:

 

The first step to figuring out focus is to see if the rangefinder is aligned to infinity. Find a target a mile or so away, and see if the rangefinder aligns. Take a picture with the lens at infinity and see if it is in focus. As Arthur mentiond in the posts above, I don't know if this target is the way to test a rangefinder initially. You have to make sure the far distance is set correctly before even bothering to test the near distance. The far distance doesn't need a chart, just a distant object. I think I read infinity is the focal lensth of the lens squared and multiplied by 1000. For a 50mm, it would be 250m, or 2 1/2 soccer pitches.

 

I would use the two 50mm lenses to check the infinity, trusting the Noctilux to be the most accurate.

 

If the infinity setting is not correct, you near will not be either. The infinity setting is very easy as explained in the other posts. The adjusting screw is moving an ecentric which moves the position of the roller on the follower arm.

 

OK, I will try that, but the only place I notice an issue is up close. I will also stop down a bit as Ian suggested. I wonder if the depth of field might make determining the actual plane of focus more difficult? I mostly use Leica close, and for people, so this problem really shows up in my photos.

[robsteve]

OK, I will try that, but the only place I notice an issue is up close. I will also stop down a bit as Ian suggested. I wonder if the depth of field might make determining the actual plane of focus more difficult? I mostly use Leica close, and for people, so this problem really shows up in my photos.

 

The infinity focus affects the close focus too. When adjusting the infinity, you are adjusting the roller that traces the back of the lens as it moves back and forth. For the near focus to be right, the infinity also has to be right. In my experience the near focus is seldom wrong, actually for me never wrong.

 

If there is still a bad near focus problem after you have the infinity set up, it is probably a job best left for Leica. The setting up is an iterative process where the technician uses a jig and starts with the near focus setting then moves on to infinity, rechecks near, adjusts near again if a problem, then back to infinity. This process is repeated until they get it into spec.

 

From my experience with the DMR and a couple of the Leica lenses, I think the digital spec may have to be a little finer than the traditional settings for the R or M system. It may not be quality control problems, but that Leica has to tighten the specifications of setting up the lenses or rangefinders. In the case of the M rangefinder and a service manual I have for the M2, the spec was half a reticle line width for both the near and far focus settings. The reticle being the target they are focusing on. The target was not that far away and the offset of the reticals simulated the distance. It may be they need to get the rangefinder adjustment closer than this now, or go to a method/target.

[lovelyleica]

This problem is a usual one in Leica M world. I gave reason + solution in my previous post here http://www.leica-camera-user.com/digital-forum/14684-back-focus-adjustment-question.html#post153655

[lovelyleica]

Here is a picture :

[billh]

Thank you Jean-Luc. This looks like it is a fairly straightforward adjustment to make. I understand we just make an adjustment and check the focus. What do the technicians at Leica do to insure the adjustment they make i correct? Someone mentioned a “jig”, but I don’t know what they mean by that. Is it a mechanical device they align, and then assume if it is aligned correctly, the camera focuses correctly? In other words, they do not actually take a photograph and check the actual focus of a camera and lens combination?

 

This is my replacement M8 from Leica. Before it shipped they told me they did check the focus on it and it was correct. And it seemed that way until recently when I noticed this back focusing, which seems to be the worst with the two 50mm lenses (Noctilux and 50 ASPH). Probably the only thing that could drive me back to my Canons is inaccurate focusing on the M8.

 

Lastly, my 50mm lenses appear to be back focusing about 30mm at close distances, while my two 75mm lenses are only back focusing 2 to 4 mm at the close distances. Will an adjustment to the M8 bring both these lenses, with their widely varying errors, into correct focus, or will correcting the 50 mm lenses throw the 75mm lenses into front focus?

 

Thank you for your very clear explanations and photographs.

 

Bill

[arthury]

If I were you, Bill, I would bite the bullet when you can afford a downtime for the M8 and ship the M8 + all affected lenses to Leica and have them "tuned" together.

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[arthury]

Also, Bill, you sounded like the M8 was focusing fine when it arrived? Was there something that happened in between?

[billh]

If I were you, Bill, I would bite the bullet when you can afford a downtime for the M8 and ship the M8 + all affected lenses to Leica and have them "tuned" together.

 

 

Arthur, that is reasonable - but is this possible? I still do not understand how a camera is adjusted to each lens when the focus errors of the different lenses vary, unless there is also some asjustment that can be made on the lenses. If I can understand the possibilities here, I would be inclined to do exactly what you recommend.

 

Bill