Close focus Canon 50/1.2?

[randomm]

Dear Brian,

I thought I could do your simple modification for my Jupiter-3 lens to make it focus down to 0.7m, but it turns out that I cannot take the two halves apart. I have taken apart the J-8 and J-9 which just unscrew from each other, but I'm beginning to think my J-3 has been glued together! It focuses well on a film body so that's fine, I would just love to have one 50mm lens that would go focus down to .7m

... thus to the question: do you think it would be possible to modify the Canon LTM 50/1.2 to focus closer than 1m/3.5ft??

with many thanks!

Jani

 

[randomm]

Well well well... after writing the first message here I thought I'd give the J-3 one last try, and I did manage to unscrew the halves from each other with the help of a piece of bicycle inner tyre to add grip. It took quite a lot of force to get them unstuck, but after the initial effort they unscrewed fine.

I managed to do the modification and am now going out to shoot to test it. The RF was accurate at 1m, so lets see what happens at 0.81m (which is where the focus stops when the limit screw is removed). Thank you Brian for your info on the J-3...

Still curious about the Canon though 🙂

 

[Sonnar Brian]

I had to let a J-3 sit in solvent for weeks to get a module out. I took the glass out. Either cement, or the lube fried into cement.

The Canon- will give a look. I suspect there is an internal groove that has to be cut. Take the optics module out, undo the retaining ring. You will see how the mechanism works.

 

[randomm]

I'll answer to myself as I took mine apart to lubricate the helicoid:

Close focus modification is possible, but very difficult to accomplish. Good news is that there is plenty of helicoid to allow outwards travel for the optical bloc, i.e. theoretically speaking this would be possible, but the bad news is that one would have to remove metal that also acts as a structural component in the outer half of the helicoid. There is a strut connecting the inner half of the helicoid and the optical block, allowing the optical block not to rotate when focusing. This, and the fact that the lens has a long throw, are the problems: there is not enough metal to be taken away from the outer half of the helicoid to allow closer focus, while retaining the lens' originally intended functionality.

This, just in case, anyone else is wondering if this might be possible.

Instead, I reattached the infinity stop screw into my J3, as I didn't like the fact that it went slightly "past infinity", sculpted some metal off the innards of the outer helicoid in the J3 and now I have a 0.77m focusing J3 with proper infinity stop! Thank you again, Brian.

 

[Daan]

I took mine apart to lubricate the helicoid:

May i ask how you did that? I've got one that could use some lubrication.
I know how how to take de lens elements out, but wondering what i should do next.

And what would be a good lubricant?

Well thanks in advance.

 

[randomm]

May i ask how you did that? I've got one that could use some lubrication.
I know how how to take de lens elements out, but wondering what i should do next.

And what would be a good lubricant?

Well thanks in advance.

I should have taken pictures so it would be possible to explain properly, but basically you remove all screws that you can see, except, the very very small screws holding the distance scale in place (from outside barrel).

Take one step at a time and its pretty obvious what does what.

I've used lithium bearing vaseline / grease, which is probably not the stuff one should use. It makes focusing rather stiff when shooting below -5 degrees Celsius, so I'm going to clean it out at some point and use something better. You only need very very little. If someone knows what really should be used, I would love to know! I would guess that any roughness with your lens is due to deposits and dirt in the helicoid, so take good care to clean it thoroughly (I use Q tips for this). Also, when unscrewing the helicoid halves from each other it helps to make a small mark on both halves with a marker pen where the two halves disconnect from each other - so you don't have to spend ages trying to figure out if you are joining them at the correct starting point. I once did not make a mark when cleaning a Rokkor 40/2 and spent two hours trying to find the right starting point!

I'll see if I get a chance to take some photos later so I can perhaps give a better explanation...

 

[Daan]

Thanks Randomm! I'll give it a try

 

[Phil_F_NM]

With the Canon 50mm f/1.2 you can squeeze out another couple centimeters of close focusing by cutting the stop tab just enough so it doesn't contact the end of the groove at close focus but DOES contact the other side at infinity.

Phil Forrest

 

[ankaka]

You should take some pictures to show it.

 

[randomm]

With the Canon 50mm f/1.2 you can squeeze out another couple centimeters of close focusing by cutting the stop tab just enough so it doesn't contact the end of the groove at close focus but DOES contact the other side at infinity.

Phil Forrest

That's true, but its really literally going to be couple of centimeters.

 

[Phil_F_NM]

If that hoop that keeps up the center helical were a hardened tool-grade steel, the lens could get significantly closer. That, or if someone were to find a bad optical sample to use as a donor and then put new helical sleeves in with a different rate, close focus could get down to .5m. Of course, then we're talking mere conjecture since that's some intense machining and fitting.
Fun to think about though.
One interesting thought is to use a Canon 50mm f/1.4 helicoid for a donor since it has a quicker focus throw and can be modified more easily for close focus. The rear element of the f/1.2 would probably fit into the back of the helicoid. All that would have to be done is to ensure infinity focus and the lens would have to be shrouded to prevent light leaks within the aperture mechanism.
Well, maybe that would work.
With enough Dremel-ing and gaff tape, anything is possible!

Phil Forrest

 

[randomm]

If that hoop that keeps up the center helical were a hardened tool-grade steel, the lens could get significantly closer. That, or if someone were to find a bad optical sample to use as a donor and then put new helical sleeves in with a different rate, close focus could get down to .5m. Of course, then we're talking mere conjecture since that's some intense machining and fitting.
Fun to think about though.
One interesting thought is to use a Canon 50mm f/1.4 helicoid for a donor since it has a quicker focus throw and can be modified more easily for close focus. The rear element of the f/1.2 would probably fit into the back of the helicoid. All that would have to be done is to ensure infinity focus and the lens would have to be shrouded to prevent light leaks within the aperture mechanism.
Well, maybe that would work.
With enough Dremel-ing and gaff tape, anything is possible!

Phil Forrest

That's right! Shorter throw would indeed do it. I wonder what the diameter of the rear opening on the 1.4 is...

 

[Phil_F_NM]

but basically you remove all screws that you can see, except, the very very small screws holding the distance scale in place (from outside barrel).

Unless I missed something, this lens comes apart without removing very many outside screws at all.

To get at the helicoid for lubing:
-Remove the retaining ring at the rear of the lens, taking care not to scratch the substantial rear element.
-The optical block will slide out. It may take a bit of coaxing. Set it aside. Don't lose the brass washer that may be stuck around the base of the rear element shroud or inside the helicoid.
-Remove the black knurled lens barrel ring by unscrewing 4 screws in it. No need to unscrew the chrome infinity stop tab.
-Remove three small screws that hold down a brass stop tab. This will allow the helicoid to come completely apart for cleaning and re-lubing.
**Make sure you index your entry point for the helical threads correctly with a scratch awl

To get into the optics for cleaning:
-The rear element simply unscrews. There are variations on this lens, so make sure it doesn't have a grub screw.
-The front optical group doesn't need to be removed if you are careful to clean the rear surface of the group adjacent to the aperture.
-If you are servicing the aperture due to excessive oil on the blades, there are three grub screws that hold the front optical block in place. Loosen these then you can unscrew the optical block from the aperture housing. I like to use sections of latex bicycle inner tube to grip these surfaces.
**don't bend the aperture spring tab that holds down the bearing for your aperture index marks. There is almost no clearance within the whole assembly and bending it a tiny bit will cause drag and then it will catch on the chrome infinity stop which is attached to the black focusing ring you removed earlier.
-Only 1 group can be separated from the front optical block for cleaning, simply by unscrewing. Make sure if any of the black paint flakes off the side of the glass, you replace it or you could get errant reflections inside an already flare prone lens.

I've found that using very light watch seal silicone gel is just about perfect for damping the helicoid of the 50/1.2. Don't forget to clean out old lube from the rotating cradle that the optical block sits inside. It's got a tight tolerance and I used a liquid silicone lube so the tiny brass tab that takes the brunt of the torque to keep the optics from rotating doesn't have to work too hard.

Sorry for the novel. I got carried away.

Phil Forrest

 

[Phil_F_NM]

That's right! Shorter throw would indeed do it. I wonder what the diameter of the rear opening on the 1.4 is...

It's very close to that of the 50/1.2 if I recall correctly. The rear elements are quite similar but the helicoid may rest within the LTM couple. In the 50/1.2 the helicoid is built around the optics which gives the lens it's "tuna can" appearance. If it's the case that the f/1.4 rear element sits within a shroud that acts as the rear of the helicoid, then the f/1.2 rear element will be a few millimeters too wide.

EDIT: Looking at views of both these rear elements online, the brass shroud that acts as the focusing cam for the f/1.4 lens has a thicker wall but as it is meant to fit within the inner diameter of the M39 couple, it COULD WORK. Extreme care would need to be taken so the focusing cam isn't damaged but the wall thickness would need to be reduced to fit the rear element of the f/1.2 lens. It's possible that a stronger steel shroud with thinner wall could be substituted and given a shoulder to properly locate and lock in the optical and aperture block of the f/1.2 lens.
Then it's just a matter of modifying the f/1.4 for closer focus.

I think it would be easier and cheaper to find an FD 50mm f/1.2 SSC and couple it with a fixed tab or partial cylindrical section of a pipe to act as a focus cam. Then it's just a matter of getting a good adapter to mate the FD lens to an M body.

Phil Forrest

 

[randomm]

Okay, I finally had the courage (or stupidity!) to try this out, although, previously I stated that it can't be done!

You have to machine in two places and without taking too much brass off one can get the lens to focus down to 0.84m (or at least in my case). 0.80m might also be a possibility, but this'll do me fine. I'll post some photos once I have them on the computer.

 

[randomm]

Photos:

You don't actually have to take the black focusing ring off the outer half if you're doing a clean and re-lube job. I just wanted to be able to clean everywhere so I took it off.

This is the arm connecting the inner half and the cylinder in which the optical block sits when mounted, making it possible for the optical block not to rotate when focusing. It also bumps into the infinity stop, and close focus stop, so you only really need to take the arm off to clean and re-lube the helicoid, as after removing this you can just unscrew the two halves of the helicoid from each other.

This is the point where the helicoid halves on mine disengage from each other.

The LTM mount needs to be machined a bit as otherwise the RF cam won't be able to follow the lens closer than 1m. Notice the machined bit, a 3mm deep "dent" in the mount.

Here you can see the machined bit on the left side of the outer helicoid (outer as in further from the camera body). I lengthened the rotation by perhaps 20mm so that you can focus closer. Should have taken a "before" photo as well to see the difference, sorry.

I completely forgot to take photographs of the cylinder where the optical block sits in that also requires lubrication, if one is doing a clean and re-lube job. It comes off simply by using a lens spanner and pulling the tight fitting cylinder out from the outer helicoid. Clean the surfaces and re-lube.

The outer half of the helicoid (the half with the LTM thread) also has a shoulder that acts as a close focus stop. To enable closer focus you have to machine that too. Easily done, but, again, forgot to photograph it. Have to take the lens apart again after a test roll to do so.

 

[randomm]

Just thought to report back, in case some other DIY minded individual is interested, that I managed to modify a Canon 35/2 to focus down to 0.77m. This is a rather complex modification though, requiring one to shorten one of the helicoids in the process, but it can be done. I may have some pictures if someone is interested in modifying theirs.

A portrait from the Canon 35/2, focused at 0.77m (wide open):


Konrad by randomm, on Flickr

A portrait from the Canon 50/1.2, focused at 0.84m (I think either f1.2 or f1.4):


Tommi by randomm, on Flickr

 

[menos]

Very interesting stuff !
Thanks for sharing this!

I am very interested in your Canon 35/2 LTM mod, as I have two of these sitting on the shelf, both scheduled for CLA, but I might as well modify one of them for close focussing ;-)

 

[randomm]

Very interesting stuff !
Thanks for sharing this!

I am very interested in your Canon 35/2 LTM mod, as I have two of these sitting on the shelf, both scheduled for CLA, but I might as well modify one of them for close focussing ;-)

The 35/2 modification is rather more complex than with the 50/1.2, I'm afraid. It requires shortening one of the helicoids as well as other machining. The helicoid requires hand filing the entry/exit points as otherwise focusing jams around 1.5-2m when focusing towards infinity. This can be done, and my lens has a smooth focus throw from 0.8m-inf, but I'm not sure if I would attempt another one.

 

[Phil_F_NM]

yeah, modifying a helical is a one-time shot. It would be awesome to have access to an end-mill to do this with a precision grind then to hand file each thread and finally lap them to mate them up for smooth focusing.
Ahh, if a benevolent someone wouldn't just win that lottery already and buy me a full metal workshop... One can dream. maybe I'll marry rich.

Phil Forrest