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How do you adjust the cam in the lens?


BillCB

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My M9 focus is right on with 5 of my 6 M lenses. The lenses are sharp at infinity and the rangefinder images coincide perfectly.

 

However, while my 75 Cron ASPH focusses perfectly at the infinity mark, itt pushes the rangefinder past coincidence. In other words, the cam IN THE LENS needs to be adjusted so as not to be so "forward".

 

This is not a matter of shimming the lens because it's perfect when manually focussing using the "bowtie" against the index.

 

I've searched LUF but can't find anything about adjusting the cam in the lens - can anyone help please?

 

Bill

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My M9 focus is right on with 5 of my 6 M lenses. The lenses are sharp at infinity and the rangefinder images coincide perfectly.

 

However, while my 75 Cron ASPH focusses perfectly at the infinity mark, itt pushes the rangefinder past coincidence. In other words, the cam IN THE LENS needs to be adjusted so as not to be so "forward".

 

This is not a matter of shimming the lens because it's perfect when manually focussing using the "bowtie" against the index.

 

I've searched LUF but can't find anything about adjusting the cam in the lens - can anyone help please?

 

Bill

Actually, on this lens which works with very narrow tolerances you may find that it will have to be sent to Solms for the adjustment, as independent workshops or local Leica agencies lack the tools/parts/expertise.

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Wha are you measuring against infinity? Maybe whatever it is isn't actually far enough away - try a star.

 

That advice should be engraved in the mind. The Leica M can distinguish object focus at distances very many people would consider, intuitively, to be at or near infinity - and they are not as evinced by the rangefinder and the outcome.

 

Infinity lock is as much a pain as a benefit. Don't fix what ain't broke.

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Yes the lens IS sharp at the infinity mark on the barrel. Infinity is a white navigation light against a dark background about 8 kms from the camera.

 

But as long as the rangefinder is not coincident, it will not give me accurate focus at shorter distances. Hence the need to adjust the cam in the lens. (No point in altering the rangefinder cam in the camera - that will put the other 5 lenses out of focus!)

 

Surely the lens cam must be adjustable while keeping the actual lens elements precisely in place in relation to the sensor.

 

Bill

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Bill,

 

Don't try this at home - special tools are needed, a collimator among them..... I can highly recommend Gerry at Kindermann Canada - if he cannot do a satisfactory job, he'll tell you. The only other options will be DAG (Dan Goldberg), New Jersey or Solms.

 

Just a note from my experience - white navigation lights against dark backgrounds can produce reflections and double images in the rangefinder patch. Best is to focus in daylight, on a distant landscape object at least 5km away (i.e. telephone pole, tall building or a tall tree), so that you eliminate the risk of any secondary reflections.

 

Good luck,

 

Jan

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Thanks Jan. My "infinity marker" is perfectly effective with all my other lenses so it's not the issue. I can focus, say, my 50 Lux on the navigation light and the lens shows infinity, it is very sharp and the rangefinder image is coincident.

 

Then, without moving the camera I can put on my 21, 28, 35 or 135 lenses. All sharp, all on the infinity mark on the barrel and all have the rangefinder images coincident. So it's just the cam on the 75 Cron that's the problem. It must be adjustable without a collimator.

 

Anyway, I will try Kindermann as they're very close to where my son lives.

 

Bill

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Thanks Jan. My "infinity marker" is perfectly effective with all my other lenses so it's not the issue. I can focus, say, my 50 Lux on the navigation light and the lens shows infinity, it is very sharp and the rangefinder image is coincident.

 

Then, without moving the camera I can put on my 21, 28, 35 or 135 lenses. All sharp, all on the infinity mark on the barrel and all have the rangefinder images coincident. So it's just the cam on the 75 Cron that's the problem. It must be adjustable without a collimator.

 

Anyway, I will try Kindermann as they're very close to where my son lives.

 

Bill

 

There is an old saying that if you need to ask too closely you should not try yourself.this is a highly skilled job with a very high potential f--- up factor.the danger is turning a relatively simple job for a technician into an expensive sort out job.your kit your choice.:eek:

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Wouldn't a very cheap and reversible DIY alternative be to buy one of the codable replacement 50/75 flanges available from Ebay sellers and use that to make any modifications? Who knows it may even work properly right out of the box.The original Leica flange can then be kept safe and it would hardly matter if it all went wrong with a $10 stand in.

 

Steve

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The basic question here is .....

 

Are your images in focus at infinity at f2 when focussed using the rangefinder ?

 

If they are, you need to do nothing. The markings on the barrel are a vague guide only and I would not use them to guage whether the lens is adjusted correctly or not.

 

1/3 of my lenses are not coincident via the rangefinder when fully racked out, but after close testing the images from the camera are in focus, so the lenses are WITHIN THE TOLERANCES REQUIRED TO PRODUCE SHARP IMAGES.

 

There are problems testing wide open at infinity as you usually end up with speeds of 1/4000+ ..... and trying to do it in dull weather makes accurate focussing difficult due to the lack of contrast ...... and taking pictures of stars at night doesn't give you much to assess focus on....

 

More of an issue is focussing problems in middle and near distances. At infinity the large DOF usually makes exact adjustment unneccessary.

 

If your photos are not sharp when you are focussed on a distant object then send the lens for adjustment. You need an optical workbench and experience to do it properly..... I've done plenty of daft things but even I'm not mad enough to dismantle a Leica Asph lens....

 

I have sent 2 50/1.4 to Solms for adjustment and both are still off at infinity on the rangefinder..... but the images are now pin sharp.

 

Unless it's a practical problem .... do nothing ;)

Edited by thighslapper
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Thanks Thighslapper, the answer to your basic question is NO. If I use the rangefinder the image is NOT sharp.

 

If I use the infinity mark on the lens the images are super sharp at F2.

 

Because the rangefinder is accurate with my other lenses I conclude the problem is not the rangefinder but the lens cam.

 

Bill

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The 75mm Summicron has a nightmarishly complex mount. There are three things happening as you turn the focussing ring - the lens barrel moves out at one rate, the surface pressing against the roller moves out at a second rate and the close focus group moves at a third rate - can't remember if it's in or out. I agree from what you say that it's the focussing cam which needs adjustment but it's a job best left to a repairer with the required equipment and experience.

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Further thought. At first sight, it might seem all that's required to solve your problem is to adjust the focussing cam helicoid relative to the barrel helicoid so that at the infinity stop, the barrel is in the right position, the focussing ring is in the right position and the focussing cam is in the right position. The problem is that this will add a fixed offset to the focussing cam position which will apply throughout the focus range. So, a crucial question - is the lens focussing correctly, close up? If so, it's not just a simple rotation of one helicoid relative to another which is needed.

 

Looking closely at my copy of the lens, I can see the focussing cam is itself profiled and is not just a flat surface that the roller bears against. This has the effect of adding some extra "push" to the rangefinder roller as the lens is focussed towards infinity.

 

If your lens is focussing correctly close up but not at infinity, it may be that changes to the cam profile are required. My copy is an early example of the lens (3994xxx) and it has been back to Solms for focus adjustment. There's some evidence of handwork on the focussing cam - metal ground away - to change the cam profile. If the misadjustment of the rangefinder patch at infinity can be fixed by turning the focussing ring back slightly from infinity, this could be fixed by grinding away more metal but if it's the other way, I think it will need a new reprofiled cam.

 

Bottom line is that the lens should go back to Leica.

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Re Mark´s observations: My 75/2 copy (somewhat later than Mark´s) is fortunately dead-on at all distances ever since I first got it. The cam surface doesn´t show any signs of profiling, so, since Mark´s has been back to Solms, I guess that´s how they do the adjustment. Hardly a DIY project, or something to be trusted to a non-authorized service facility...

 

Besides, and as a general observation, if Mark, of all people, feels the job has to be done at the factory, no sane person should try any shortcuts...:)

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I would send the lens in for professional repair. It sounds like Leica changes the index of the main cam- that requires custom machining to get the index correct. The lens is front-focusing. The cam needs to be ground down. The alternative is to change the focal length of the lens, make it longer. Trying to get it right without instructions and a lot of experience and/or training: expensive lens to start with!

 

If it were a Jupiter-9 85/2: why not. Good, cheap lens to play with. A Leica 75/1.4, I would send to Leica.

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Thank you all for your input - most appreciated!

 

The sad thing is that this lens already went to Leica for adjustment and it seemed fine when it came back. It has since deteriorated which led me to wonder if the cam was adjustable by something as simple as a set screw.

 

Anyway, I will NOT be trying to fix it myself!

 

Bill

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There are three things happening as you turn the focussing ring - the lens barrel moves out at one rate, the surface pressing against the roller moves out at a second rate and the close focus group moves at a third rate - can't remember if it's in or out.

 

The rear group moves out in net movement - but it moves out less than the front group.

 

Sadly, I have soured on the 75 'cron. It was a lens I really, really wanted (Heck, I nearly "invented" it: Care to join me in a little fantasy? - Photo.net Leica and Rangefinders Forum ). When it works, it is amazing. But the floating element design was, IMHO, simply a "bridge too far" for a lens of this speed and focal length in a rangefinder configuration. My 75 Summilux is not as crisp at .75 meters - but at least it focuses consistently.

 

Just too many threads like these:

 

http://www.l-camera-forum.com/leica-forum/leica-m9-forum/199874-focusing-error-summicron-75mm-leica-m9.html

http://www.l-camera-forum.com/leica-forum/leica-m9-forum/178181-summicron-75mm-apo-asph-back-focus.html

http://www.l-camera-forum.com/leica-forum/customer-forum/168975-summicron-75-jerky-focussing-low-temperatures.html

http://www.l-camera-forum.com/leica-forum/leica-m9-forum/112605-apo-summicron-m-75mm-asph-focus.html

http://www.l-camera-forum.com/leica-forum/leica-m8-forum/100318-75-summicron-asph-focus-out-infinity.html

http://www.l-camera-forum.com/leica-forum/leica-m8-forum/89365-m8-summicron-75-focus.html

 

I hope Leica has learned a lesson, and does NOT add FLE to the 90 Summicron-M APO-ASPH or a hypothetical 75 APO-Summilux. It will just be another "Hangar Queen," spending all its time in Solms for tweaking.

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