50mm Summicron and infinity

[lightwriter]

I recently aquired a R-D1 on which I use my 50mm Cron. I adjusted the vertical patch and tweeked the rangefinder foucus a bit. Rangefinder is spot on to lens focusing from 2 ft to about 10-12 ft. After that it starts to front focus quite severely. When I set my lens to infinity, from what I understand, it should focus on infinity regardless of what my rangefinder shows. Well, at infinity the lens focuses at about 35 ft. In other words, while the lens infinity mark lines up, infinity is way out of focus. And an area that is approximately 35 ft in front of me is tack sharp. I would need to be able to turn the barrel just a little bit more in order to get infinity to come into focus. I have not had the lens very long either. How can I determine if there is indeed a problem with the lens?

I'd appreciate any help you can give me. My M7 is off being repaired so I got the R-D1 to have something for the holidays and now it seems like I may be without a camera altogether.

 

[lightwriter]

Brian, thanks for the response. I figured it was the spacing to the sensor. Did not know about the shims though. The way I see it-the lens is too far away from the sensor. if it were too close, then infinity would come into focus at some point before the barrel infinity mark and backing off on the barrel would bring it into focus. Does this ake sense, or am I thinkning backwards?
I have not really taken any pics at infinty with M7. I'd only shot a couple of rolls through it and had noticed that while the close up pics were sharp, I was unimpressed with the pics at any considerable distance. I had noticed the same with the pics I had taken with the R-D1 as well but had simply attributed it to my lack of experince with the system. I just figured this infinity thing out while adjusting the finder on the R-D1-I set my lens to infinity, turned the center screw until the images at infinity lined up. I also verified it with the two marks on a piece of paper that are spaced a distance equal to the base length. Regardless, the lens should focus at the distance printed on the barrel despite what the rangefinder shows-atleast that is how I understand it.

I briefly tried my 90mm after I came to this conclusion and it seemed to front focs just slightly at infinity but have not been systematic enough to really get anything out of it. I will see what I get with the 90mm tonight. I also have a 35mm nokton on order.
Thanks
-Carlos

 

[Stu W]

I have been having my own Summicron disappointments of late. I own 2 summicron 50's, and all have an "apparant" front focus problem, more pronounced at close distances and wide open. Stopped down in good lighting and all seems well. The problem doesn't exist on my Summitar, Elmar, or Elmarit. I looked at the dof specs on the 50 and the depth of field at large apertures and short distances is mostly in front of the point of focus. Increasing the distance and stopping down dramatically shifts the depth of field to the rear of the point of focus. This to me makes working with the lens difficult in available light as a portrait lens. The table I referred to was for later Summicrons, but it seems to apply to mine. Any suggestions are welcome. Stu

 

[Stu W]

Brian, the only adjustment I found was a shim under the front element. I took a test roll with and without the shim and found that the point of focus was moved back about 8" at 4' without the shim, so it seems I can adjust the point of focus by changing the thickness of the shim, but I don't know what it will do to the optical formula of the lens. Stu

 

[lightwriter]

ok, just did a quick test with the 90mm and I am now more certain that it IS the Cron that has a problem. The 90 looks sharp at infinity. Now I have to to fix the 'Cron. Is this something I can do myself provided I get some instructions. Is there a book. I've seen one called rangefinder camera and lens repair....maybe I'll try to find it. I am pretty handy (machinist turned enginerd) but am a little worried about opening a $1k+ lens. .1mm is about 4 mils (thousandths of an inch). Is that a typical shim thickness? For now I think that I will adjust the rangefinder to the 35mm Nokton. This is my favorite (effective) focal length plus at f1.2 it needs to be spot on. The Cron must be fixed though. I'm glad that I'll atleast have a camera for the holidays.

 

[Stu W]

Carlos, I would think that the focusing problem should be consistant at all distances, as I think that the cam on the Summicron 50 is linear in travel. Someone else on the forum was having the same problems, but his was a film path problem on an MP. Stu

 

[Ed Schwartzreic]

Can you tell us what version of the 50 Summicron you are using? I had this problems years ago with a SM Summicron collapsible, and had to lightly grind down the focusing helical on the lens (under supervision from an expert) near the infinity position.

If you have an older summicron that comes apart for the Viso and other focusing accessories, be sure that the head is well tightened. I've had this problem also., but this is easily corrected.

Ed

 

[Stu W]

Well Brian, I spent the whole day trying to make a shim but I think that it is beyond doing with hand tools. We're dealing in thousandths here. I lapped down the original shim until the focus was almost right on but the last lapping round killed it. I'm sure Leica had them in numerous thicknesses but where to find them? Too bad, cause the lens is close to mint. Stu

 

[Stu W]

Brian, it's approx 32mm od and 29mm id. As far as how thick, maybe as thick as paper or a little thicker. I put my Summarit on but most of my accesories are 39mm, so I'd like to use the Summicrons. Stu

 

[lightwriter]

Can you tell us what version of the 50 Summicron you are using? I had this problems years ago with a SM Summicron collapsible, and had to lightly grind down the focusing helical on the lens (under supervision from an expert) near the infinity position.

If you have an older summicron that comes apart for the Viso and other focusing accessories, be sure that the head is well tightened. I've had this problem also., but this is easily corrected.

Ed

I have the latest version Summicron. Shims I think I can handle but the helical...well, that may be a little out of my league. 🙂

 

[lightwriter]

Well Brian, I spent the whole day trying to make a shim but I think that it is beyond doing with hand tools. We're dealing in thousandths here. I lapped down the original shim until the focus was almost right on but the last lapping round killed it. I'm sure Leica had them in numerous thicknesses but where to find them? Too bad, cause the lens is close to mint. Stu

Stu, do you have a micrometer or calipers? I would not think it wise to do this sort of thing without one or the othere simply b/c you have no way of keeping a reference. You should be able to use your old shim as a template to cut new ones. If you do not have the tools to do it, then a local machine shop can-though it probably won't be cheap. If you are able to get a thickness measurement off of the one you ruined, you could then get another stock one and lapp it down to just before that thickness. Something else you can do is go to your local Sears and buy a set a feeler gauges for a few bucks. Take them apart and cut them in half to use as temporary shims to find the right thickness. Once you do, you have a number to shoot for when your lapping in the new ones-provided you have a means of measuring them. A good Starret 0-1" micrometer goes for a about $35. Dial calipers are more but far more useful. I may look into what it costs to make shims. The first one is the most expensive...it usually cost a few dollars more to make 20 than it does to make just one.

 

[lightwriter]

Does anyone have any instructions or input as to how to take a latest version Cron apart. I am a little hesitant, just need a nudge...

 

[John Shriver]

Be sure your Summicron isn't a "mutt". The focusing mounts were made in about 8 different varieities, for lens bodies of different focal lengths. They measured the focal length of the final lens, and put it in the correct focusing mount. They may also have adjusted the length of the outer barrel for length (with a file), since there's no spacing shim in there.

For instance, my LTM Summicron is scratched 51.9 on the outside of the inner lens barrel, and is mounted in a focusing mount stamped 8 on the back of the focusing tab. That's a correct mount, so it's not likely to be a "mutt".

According to Puts' book, the group numbers for LTM Summicrons are 2 (50.1mm), 3 (50.4mm), 4 (50.7mm), 5 (51.0mm), 6 (51.3mm), 7 (51.6mm), and 8 (51.9mm). As you can see, very small differences in focal length demand different mounts!

There's a different set of focal lengths for M mount Summicrons, I think. Also, if you have a Summicron with a detachable head for macro use (like a "rigid"), the serial number is engraved on the lens and focusing mount, and must match.

There are a LOT of things that have to be right for accurate focusing. The flange to film distance must be 27.80mm for an M mount (28.80 for LTM). The lens must focus at infinity (mechanically). The focusing cam must protrude 6.5mm from the flange at infinity (7.5mm for LTM). The focusing cam must move out at the right "rate" for the actual focal length of the lens. The camera's rangefinder must focus at infinity when pushed in 6.5mm from the lens flange (7.5mm on LTM). The rate (slope) of the rangefinder's function must be correct.

It's a hell of a lot simpler on an SLR. All that's required is that the focusing screen be the same distance from the lens flange as the film is.

 

[lightwriter]

Thanks John. I'll look into it!