Front focus issue ... comments please

[TonyField]

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I have an old Canadian 90mm F2 Summicron which I just received back today from Leica NJ.  The issue was that it was focusing in front of the target.  Leica indicated that it was in-spec.   Interestingly, this is the second time I sent the lens for adjustment ... the first time was for distinct back focus which they made into front focus - the lens is now "usless again" wide open but in the opposite direction.   Of course I can compensate for this to a degree ... but that is a hit-and-miss proposition..

 

Their comment was "Test shots good, mount and MTF numbers withing tolerances.  Requesting camera to test with lens.  Please contact Leica directly at ####'   Of course, I am very reluctant to send the M9 with the 90.  First of all, for the long delay turnaround (Leica is not really swift for repairs ), and secondly, if they mate the M9 and 90, will that upset the performance of the other lenses that I have (see below).

 

The sample image illustrates the problem.   The test "wire" is carefully constructed to be parallel to the camera film plane ... and the focus error can be clearly seen with the test wire "just at the edge" of the in-focus area.  The focus distance from camera to the test wire is 2.5m since, of course, I tend to shoot reasonably close to many of my people subjects.   At much greater distances, the wider DOF can still make for a slightly higher apparent "in focus".

 

The other image, just for example, with the 50mm F1.0 clearly indicates spot-on focus wide open and has the expected back-focus stopping down (as does the old 50mm Summilux). 

 

I use this test subject on all of my lenses.  My 135mm F4 Tele-Elmar, 75mm Elmarit, 50mm F1.0, 50mm F1.4 (ancient) Summilux, 50mm 1.5 Summarit, 50mm F2 collapsible Summicron, 35mm F2 (ancient) Summicron, and 28mm F2.8 (ancient Canadian) Elmarit. all have "virtually perfect" focus characteristics wide open on my M9.  In other words, my M9 seems to be in consistent and accurate alignment.

 

I am curious why Leica says my  90 is "in-spec".  Any thoughts, recommendations,  or ideas ??

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[Lenshacker]

Can you measure by how many millimeters the focus is off? Put up a ruler for the test.

 

Also try at various F-Stops. With a 90mm lens, focus shift should not be an issue, but always nice to measure it.The 50mm F1.5 Summarit is designed to front focus at F1.5, provide correct focus at F2.8.

 

This should be the version with the removable head? Make sure it is tightened in all the way into the mount.

 

- Brian

[TonyField]

I phoned Leica NJ about this problem.  After a longish technical phone call (most polite and delightful folks to chat with), I will be sending the M9 and 90mm back for adjustment.   Since my M9 works well with my other lenses, the will make the 90mm "exactly" match my M9.  After their techy explanations, certainly makes sense.

[Jeff S]

I phoned Leica NJ about this problem.  After a longish technical phone call (most polite and delightful folks to chat with), I will be sending the M9 and 90mm back for adjustment.   Since my M9 works well with my other lenses, the will make the 90mm "exactly" match my M9.  After their techy explanations, certainly makes sense.

They really won't match anything per se; rather they will make sure both are within specs, independently.  Leica asks customers to send in camera and lens to avoid any possible issues with either, and to avoid confusion and double service in case there are separate issues.

 

Jeff