50/1.4 ASPH front focuses only at mid distances

[2eleven]

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Hey Folks,

 

Wondering if others could let me know if this seems normal. I recently replaced my 50/1.4 ASPH with the Black Chrome edition (missed the LHSA many years ago so I jumped on this one and sold my normal version). When I got it, I noticed that mid distance shots were a little blurry because they were front focusing. I decided it was time to have all my lenses and body calibrated anyway, so off everything went to NJ. 2 months later, I get everything back, and everything focuses well except the new 50/1.4! Focus is accurate at MFD and distant objects align perfectly at the infinity stop, but middle distances are still front focusing. For an object 5 meters away, it front focuses about a half meter.

 

In the past, when I've had focus problems with lenses, if they front focused at mid distances, they would also front focus at MFD. This lens is pretty accurate at a meter (actually slightly back focuses), but is off at 5 meters, and then seems to be accurate again at infinity. That would seem to indicate that the rake on the edge of the helicoid that mates with the rangefinder is not accurate throughout its range. Does it need to be sent back to Leica and reground? Or is this just fairly normal/acceptable and I'm just encountering it for the first time?

 

Appreciate the input folks!

 

John

[Jeff S]

Not normal....I presume you've set up careful tripod tests (helps, too, if you have an M with LV).  Good practice to document and communicate clearly with Leica Service prior to sending anything in.  Better still, if you bought from a reputable dealer (always my advice), get a replacement.  Good luck.

 

Jeff

Edited August 25, 2015 by Jeff S

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[2eleven]

Thanks Jeff for the response. Yes my tests have been with a tripod and 2 viewfinder magnifiers. Also, for statistics sake, I took about a 20 shots, completely refocusing between shots. From that I figured I have a pretty good idea where the actual focus point is. I did buy from a reputable dealer, but unfortunately the black chrome edition was limited and is sold out, so a replacement is not an option.

[Jeff S]

Other option of course is to get refund and replace with a standard 50 Summilux that works properly.  

 

Jeff

[lct]

I would keep this superb lens but it needs some calibration. 

[fiftyonepointsix]

Are the actual images taken at infinity in perfect focus? 

 

If the focal length is too long it is possible for a lens to focus correctly at MFD and be off at 5m, and be off by even more at infinity.

 

If the problem only occurs at middle distances, the "index of the Cam" is not cut correctly. Most modern M-Mount 50mm lenses use a slight index in the cam, a "Cut" in it, to provide correct focus across range when the focal length is not exactly to the standard of the RF. If the middle portion of the cam is not correctly cut, it is possible to have perfect focus at MFD and Infinity, but not mid-range.

 

I made a custom indexed-cam adapter for a pre-war Sonnar 8.5cm F2- learned a bit about this process.

[pico]

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If the problem only occurs at middle distances, the "index of the Cam" is not cut correctly. Most modern M-Mount 50mm lenses use a slight index in the cam, a "Cut" in it, to provide correct focus across range when the focal length is not exactly to the standard of the RF.

 

 

This is interesting material. So is this index an indent on the ring cam? I tried to look at my 50mm Summicron cam and I'd need a runout gauge to find an index or variation, and mine is broken.

 

Aside: It looks like the 75mm Summilux V1 cam does not turn.

Edited August 25, 2015 by pico

[fiftyonepointsix]

This is interesting material. So is this index an indent on the ring cam? I tried to look at my 50mm Summicron cam and I'd need a runout gauge to find an index or variation, and mine is broken.

 

Aside: It looks like the 75mm Summilux V1 cam does not turn.

Looking carefully at the RF Cam of a 50mm lens you can see a slight cut in it as it runs from close-up to infinity. It is often a fraction of a millimeter.

[FlashGordonPhotography]

It could be one of two things. Either the cam ring in the lens isn't quite right or the RF is out. You might not see if the RF is out on other lenses depending on what they are as the 50 ASPH has a very narrow DOF and fast fall off. But it's still worth thoroughly testing all your lenses and see if there's some focus drift at mid distances with them as well.

 

It sounds like your lens is out. I'm sure that leica will get there, eventually.

 

Gordon

[thighslapper]

The floating element needs adjusting.

 

This is a complex lens and not easy to adjust for all distances.

 

Just keep sending it back and one day they will get it right ......

[jaapv]

This is a known problem with this lens. As Steve notes, it is the floating element; the mechanical tolerance there is in the order of  1/1000 of a mm. Leica can certainly  get it right, but it took them a couple of months to do so on my lens. If you are unlucky they will have to manufacture a specific part and that can take time to organize into the production process.

[2eleven]

Thanks everyone - I knew I would find the answer here. Back it goes...

[jdlaing]

Thanks everyone - I knew I would find the answer here. Back it goes...

A wise decision.

[pico]

Is it truly impossible for us to fix this issue if we can find the detent in the focus ring?