Modifying RF Lenses for Closer Focus?

[das]

This may be kind of an odd question. Is anyone aware of whether it is possible to modify a RF lens that has a native minimum focusing of 1.00m to go down and RF-couple down to 0.7m? Like taking a Canon 50mm f/1.4 and shortening its minimum focusing? If so, are there any known shops that can do this? I am aware that such products exist for digital systems with liveview, but this would be for film. Thanks!

 

[mpaniagua]

I don't think it would be easy/cheap doable, since it would involve recalculate/remade the focus helicoid and probably the rangefinder focus coupling mechanism.

 

[Godfrey]

It's not a practical thing to do with a rangefinder camera. To change a lens' minimum focus, you'd need to (at least) reposition or modify the near-limit stop in the focusing helicoid (presuming there are enough threads in the helicoid to do that) and modify the rangefinder coupling cam to suit the different close focus limits, presuming that the rangefinder CAN focus accurately to your new lower limit. AND presuming that you want RF focus coupling.

Close focusing is what SLRs and EVF/LCD cameras are really good at, and is not what RF cameras do easily. Best to use the right camera for the task.

G

 

[Phil_F_NM]

You can squeeze a little more focus out of the existing helicoid by modifying the close focus stop. You'd grind it down to allow the extra travel. I don't know if you'd be able to get the extra .3 meters out of it, but there certainly is a way it can be done. No new helicoid necessary. No cam grinding either due to the Canon's lens travel matching the RF focusing rate.

Phil Forrest

 

[mpaniagua]

You can squeeze a little more focus out of the existing helicoid by modifying the close focus stop. You'd grind it down to allow the extra travel. I don't know if you'd be able to get the extra .3 meters out of it, but there certainly is a way it can be done. No new helicoid necessary. No cam grinding either due to the Canon's lens travel matching the RF focusing rate.

Phil Forrest

Valid for the lens on the example, but not necesarily for other lens, since focus helicoid may not have enought thread. But yeah doable that way.

 

[mpaniagua]

Also, if used on a Leica M or other camera (like Bessa) with framing corrections, frame lines will become unusable.

 

[das]

I totally agree about the SLR thing. And the hard stop removal thing is also very interesting. So, fabricating a new helicoid or adapting maybe an existing 0.7m 50mm Leica focusing helicoid would be the way to do it?

I noticed that these folks have done something to M39 Sonnars to bring the minimum focusing down from 1.00m to 0.85mm -- maybe they are fiddling with the hard stop? https://skyllaney.com/2020/04/02/sonnar-resurrection/

 

[narsuitus]

I usually use an SLR when I need close focusing. However, I carry a +3 diopter supplemental close-up lens to mount on my rangefinder lens should the need for closer focusing arise.

 

[Phil_F_NM]

The hard stop is just a tab. If I recall correctly, the Canon 50/1.4 has a ~180 degree focus throw.
What you want to do is to remove the stop which physically causes the focus barrel to stop rotating at the close-focus point. The problem is that you will need to ADD a new one at a new point in the lens' travel; if not, you'll unscrew the whole assembly and it will be rattling at your feet, and getting wet from your tears.

I sold my 50/1.4 long ago but I did have the whole thing apart when cleaning the obligatory haze off the inner element surfaces. It's a really easy lens to work on as far as rangefinder optics go. If it has a 180 degree focus throw, you should be able to extend the focusing distance by grinding away part or all of the stop tab. Since I don't have it in front of me right now, I can't say where to grind or how much.
Now I need to go listen to Darling Nikki by Prince.

Phil Forrest

 

[mpaniagua]

Just curious. Why do lens makers limit the minimal focus distance? Not really sure why thye limit to 1m instead of 50cm for example. Any idea?

 

[das]

Just curious. Why do lens makers limit the minimal focus distance? Not really sure why thye limit to 1m instead of 50cm for example. Any idea?

I believe it had to do with the reliability of the focusing accuracy of early rangefinder bodies. Leica's M39 cameras could only focus to 1.00m, so for lenses of that era, it did not make sense to make a lens that could focus more closely than that because you would not know if the subject was in actual focus. However, there were at least some lenses that could focus more closely than 1.00m with the expectation that you would have to physically measure the remaining distance or get some fancy external device -- like the M39 50mm f/1.4 Nikkor. The Leica M3 could only natively focus down to 1.00m, so Leica made a bunch of special gear to allow it to focus more closely, like the DR Summicron and the goggled lenses. With later Leica Ms and the Canon 7, etc., rangefinders were calibrated down to 0.7m so lenses could also follow suit. Like was stated above, I also trust SLRs far more at these closer distances because you can actually see what you are going to get.

There are a bunch of Zeiss ZM lenses that can focus more closely than 0.7m, at which point the RF of a Leica M will uncouple.

 

[Phil_F_NM]

Just curious. Why do lens makers limit the minimal focus distance? Not really sure why thye limit to 1m instead of 50cm for example. Any idea?

Physical limitations and accuracy of the rangefinder itself.

Phil Forrest

 

[das]

Thanks for the explanation. So the potential increase in minimum focus is going to be dependent on how much helicoid is left to add a new stop tab? Interesting.

The hard stop is just a tab. If I recall correctly, the Canon 50/1.4 has a ~180 degree focus throw.
What you want to do is to remove the stop which physically causes the focus barrel to stop rotating at the close-focus point. The problem is that you will need to ADD a new one at a new point in the lens' travel; if not, you'll unscrew the whole assembly and it will be rattling at your feet, and getting wet from your tears.

I sold my 50/1.4 long ago but I did have the whole thing apart when cleaning the obligatory haze off the inner element surfaces. It's a really easy lens to work on as far as rangefinder optics go. If it has a 180 degree focus throw, you should be able to extend the focusing distance by grinding away part or all of the stop tab. Since I don't have it in front of me right now, I can't say where to grind or how much.
Now I need to go listen to Darling Nikki by Prince.

Phil Forrest

 

[mpaniagua]

Thanks for ur info davidde1000 and Phil.

 

[Sonnar Brian]

It depends on the mechanics of the lens. It's always possible, but the complexity of the focus mechanism will drive how much work needs to be done.

For the single-helical Jupiter-8, just rethread the helical incorrectly to reverse the action of the start and stop screw. Re-index the scales, and file down the threads of the mount to allow the RF Cam follower to move deeper into the lens.



1975 Jupiter-8, wide-open, 0.65m.

 

[bluesun267]

I have done this successfully on both the Canon 50/1.8 and 50/1.4 LTM lenses. It may be possible on others but I cannot confirm any but those two. I wouldn't even try it on anything other than a 50mm for the already stated reasons.
Cameras such as the Canon P and 7 are natively able to focus down to about .7m, including the frame line parallax correction.
There is plenty of helicoid (and outer barrel) on both these lenses to allow focus down to .7m. Of course you will not have distance markings below 1m unless you wanted to print up a sticker or something but I have never bothered. One drawback is your focus tab will end up in front of the rangefinder window at times.
You also need to cut a notch in the mounting threads to allow the rangefinder cam sufficient movement.
It's important this notch be in exactly the right position and of right width otherwise you'll run into trouble when trying to use it with an M-adapter.

But I would think twice before doing this to a nice lens. It's just that these two lenses are sufficiently plentiful/inexpensive (and often have damaged glass) that I've been able to practice on them.

 

[das]

Wow, that looks great Brian. And Bluesun, very cool that you were able to do that. The lens I was actually looking at is not a Canon at all but rather an uncommon m39 50mm f/1.9 Hexanon. Is this modification something that an experienced RF repairperson could tackle? Or is it more of an esoteric surgery best reserved for the skilled experimenters?

 

[bluesun267]

Also, here is a trick I use on any 50mm screw mount lens, provided the camera has sufficient close focus coverage (such at the P or 7): simply focus lens to 1m, then unscrew the lens from the body a couple turns. Just short of removing the lens from the body is about .7m. Hold the lens firmly w/ left hand while viewing your rangefinder patch and move the entire camera back and forth to lock in focus. Your rangefinder will be accurate. It takes a little practice but works.

 

[bluesun267]

Wow, that looks great Brian. And Bluesun, very cool that you were able to do that. The lens I was actually looking at is not a Canon at all but rather an uncommon m39 50mm f/1.9 Hexanon. Is this modification something that an experienced RF repairperson could tackle? Or is it more of a esoteric surgery best reserved for the skilled experimenters?

I think it just depends on the repair person. I suspect many would reject the idea out right, but you never know. You can PM me if you decide to go that route.

But, please don't do this on the Hexanon! It's far too rare (and wonderful) to alter this way!



I've been shooting closer than 1m with the Topcor-S 50/2 "unscrew" method and it has worked wonderfully.

 

[das]

Oh for sure, I would never cause harm to any gem of a lens. Just was wondering more broadly about the possibilities in general. I find that the close focus abilities of more modern RF 35s and 50s really make these lenses shine but the better of the older 1950s lenses are unfortunately stuck at 1m.