Extension of Are M lenses really interchangable

[Shootist]

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Ok I have done some more testing with my 2 M8's and the 3 lenses I have had some problems with. I wanted to do a more controlled test then Roger and I did yesterday

 

How I tested.

I made myself a new test target similar to the one found at several websites only instead of a black bar in the center with Focus Here in the center of the bar I put a series of circles horizontally and vertically and I made it 12x18 inches and printed it out on a piece of B+ (13x19) paper (If anyone want a PDF, VCD (Visual Cadd format) or DWG (AutoCad 2000 format) of it just drop me a Email).

 

I set the target on a low table and positioned my tripod and cameras at as close to a 45° angle as I could, I use the body of a combination square and a 48 inch aluminum ruler to get it as close as possible to the center of the lens mount. The tripod was positioned 44 inches from the target @ 45°.

I then took a shot of the target and move the tripod until I had the circles running as close to horizontal and verticle in the image as I could.

I places a light on a second tripod shinning down and a little from the left on the target.

I have extra bases for the M8 because I have 2 grip bases for the cameras. I have one of them fixed with a QR base for my ballhead. That base was never removed from the ballhead and the cameras were removed from the base when switching from one camera to the other.

I use the same camera for all shots with each lens then switched to the other body.

I tested with 3 lenses. 50 Cron coded New, 75 Cron APO-ASPH New and 90 Tele-Elmarit.

I started with the 90 and then to the 75 and finally with the 50.

I took 2 shots each for focus with each lens. On the first shot with each lens I would first rotated the lens to the closet focusing stop and then slowly turn it back to a point the target was in focus. On the second I would go all the way to infinty and then back to focus.

 

Conclusion for my bodies and lenses.

Since yesterday Roger and I found that on his bodies, that were at Leica AG Solms for extensive calibration, my 50mm Cron is as near to perfect as I think you will ever get and that it is just about the same on my Chrome body as it was on both of Roger's bodies I take it my chrome body is as close to perfect as his are. The small variation we got yesterday from body to body is simply user error and that the original test target is way to small to accurately focus on consistently.

With the 90 on my Chrome body it was just about perfect but it all depended on from which stop you were coming from. From the close focus stop it tended to show slight frontfocus and when coming from the infinty stop none . With the 90 on the black body it frontfocused more then on the chrome in both images.

With the 75 on the chrome body it showed backfocus of about 14-20mm on both shots. With the 75 on the black body it was back about 2-4mm.

With the 50 on the chrome body it showed a little backfocus. Just about the 1/3 front 2/3 back as it should be. With that lens on the black body the focus point was at the 14mm frontfocus mark of the target in both shots.

What does all this tell me?

That the 90 and 50 lenses are as close to perfect as I think they can be, the 75 lens has backfocus problems. The chrome body is close to perfect and the black body frontfocuses.

 

So I will be sending the black body and the 75 in for focus calibration. And I won't be sending then as a set. I want the black body to be just like the chrome and the 75 to be like the 50 and 90 are now.

If you want to see the images they are on my image sharing site.

Ed Chatlos (Shootist) : photos : M8 Lens Focus test - powered by SmugMug

 

So are Leica lenses interchangeable? I would have to say yes IF the camera and lens are properly adjusted and not specifally to each other. Whether Leica can do that the first time they leave the factory in is the air. Some times yes and other times NO.

[Guest tummydoc]

This entire subject has echoes of the Konica Hexar RF debacle.

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[c6gowin]

When we visited the Leica factory on our Leica Germany trip, I was struck by the precision and attention to detail Leica incorporated in their manufacturing process. Also, the cut-away lenses on display at the factory showed their extreme engineering and complexity. This high level of engineering and manufacturing precision seem to be a contradiction with respect to the level of focus accuracy afforded by a rangefinder system. I must say, however, that Leica's rangefinder used in the M8 is an engineering marvel in itself.

 

Mark Gowin

[glenerrolrd]

Ed Something that confused many photographers was our use of the specific chart readouts .. as someone noted 13mm is about a 1/2 inch . The original test chart was set up to provide an accurate read out at a 45 degree angle . When you measure it its about 40% larger than life size. The instructions at Focustestcharts.com explain this. Your chart is much larger than the 8 x 10 we used...so I would expect that your measurements are larger as well . If a person does this with a ruler they will get much greater numbers ? Isn t this right or did you adjust for all that with your chart. Roger

[Shootist]

Ed Something that confused many photographers was our use of the specific chart readouts .. as someone noted 13mm is about a 1/2 inch . The original test chart was set up to provide an accurate read out at a 45 degree angle . When you measure it its about 40% larger than life size. The instructions at Focustestcharts.com explain this. Your chart is much larger than the 8 x 10 we used...so I would expect that your measurements are larger as well . If a person does this with a ruler they will get much greater numbers ? Isn t this right or did you adjust for all that with your chart. Roger

 

I did the target with a CAD program and the measurement are exact in the 2D scale. I did not take into account the change of measurements along the hypotenuse. I will and change the traget.

 

Well going along the hypotenuse the 10mm mark on my original target is really 12.928932mm (call it 13mm) from the center/focus line. So that makes my orignal measurements farther off then I thought.

[ho_co]

Ed--

Very helpful, quantified data! Bravo. Making progress.

 

Curious--Why did you decide the previous thread was inadequate and an "extension" needed?

 

--HC

[Shootist]

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Ed--

Very helpful, quantified data! Bravo. Making progress.

 

Curious--Why did you decide the previous thread was inadequate and an "extension" needed?

 

--HC

 

Because of your posts and tone in the other thread.

[Shootist]

After looking at the original test target and doing some math I have found that the spacing is approximately 2.7804xxmm for each 2mm. Now that holds fairly true until the distance from the center line becomes longer or shorter.

For all intents and purposes my original target will still tell you that your RF or lens is good or bad. It just can't be relied on to give someone else exact distance that it is off.

 

I don't think Leica would even need or want to know this.

As long as everyone is using the same target the findings will be the same.

[colorflow]

Great test, thanks. Do you have a film body handy? Would be interesting to see if it shows the same results. I tested my M8 and M6 on a bunch of lenses and the results were very similar - some backfocused and a few frontfocused.

 

Alan

[Shootist]

Great test, thanks. Do you have a film body handy? Would be interesting to see if it shows the same results. I tested my M8 and M6 on a bunch of lenses and the results were very similar - some backfocused and a few frontfocused.

 

Alan

 

I plan on doing the same tests with a M3 and the same lenses. I just haven't had the time and to date I have 3 rolls of film sitting around that I haven't had time to developed yet.