Hacking the 75mm f/1.8 Heliar

[Phil_F_NM]

Several days ago I realized that at the closest focus stop of the 75mm f/1.8 Heliar there is about .7mm of focusing cam depth available to travel for the RF cam follower to further interface with. Sorry, I'm meaning to say that the lens was possibly built with closer focusing in mind since there is ample space for extra travel of the cam.

So today I took apart the lens. Had it down to the two parts of the helicoid and saw where I need to cut an extra 6mm in order to allow the helicoid to turn a bit more and bring the lens to .7 or even .65m for close focus.

The thing that stopped me is my lack of a very narrow spanner wrench. Sitting about 20mm deep, between the outer helical threads and an inner sleeve which translates the motion of the helicoid to a stationary cam, is a brass lockring that holds the sleeve in. If the sleeve can be removed, the camera-side of the outer helical can be machined out by perhaps 6mm to allow the three stops to travel a bit farther and decrease the focusing distance.

Once the outer barrel was machined, the close-limit hard stop on the mount itself would have to be relieved in order for all that hard machining work to be worth anything (or the limit screw can just be removed.)

There are a few issues with this approach though.
*The cam is a floating unit that is moved inside the aforementioned sleeve with three nylon rollers. If the outer helical is machined to allow extra movement of the rollers, the roller channels would overlap and the cam would have to be held in place with a thin wavy washer to act as a spring in order for the nylon rollers to not "jump" when they travel past the manufacturer's original limits. I don't see this as a problem so much as a possible issue.

*The machining would have to be done rather precisely as the 3 rollers' movement doesn't so much control the rate of the movement of the cam but definitely affects the smoothness with which the cam moves. It looks as if just one roller would be enough to impart motion to the sleeve for cam movement so this would save a lot of work.

Sorry I didn't take photos to demonstrate it all. The lens is pretty simple to operate on in case someone wants to tackle it. If one were to have a focusing issue with the lens it is extremely easy to correct by adding or subtracting shims which reside just under the focusing cam which is held in by a lockring and easily removed with a normal spanner.

If I actually go ahead with this operation, I'll make sure to have a macro-capable camera nearby so I can document the process in photos.

Phil Forrest

 

[raid]

Take it easy, and advance cautiously, Phil.
Good luck.

 

[menos]

Pictures, pictures, pictures ;-)

Always interested in seeing innards of lenses!

As has been mentioned - take it easy though and proceed with caution.

 

[Chriscrawfordphoto]

Do you know how to put it back together and have focus still be accurate? THAT is the VERY HARD part of all this. Most lenses are easy to take apart and put back together, but with rangefinder lenses, you must have that cam set right for focus to be accurate! I have a lens I made that mistake with that is unusable now because I can't get it to focus right. Repairmen have special equipment for calibrating these things. You and I don't 🙁

 

[johannielscom]

Still highly interested in the CV 75/1.8 since it is an almost exact copy of the 73/1.9 Leitz Hektor. Would love to have an uncoated one with closer focus as added bonus!

Good luck, post some shots from the process if you can Phil!

 

[rxmd]

Still highly interested in the CV 75/1.8 since it is an almost exact copy of the 73/1.9 Leitz Hektor.

It has a vaguely similar lens diagram, but I'm not sure whether that similarity buys you much.

From there to being an "almost exact copy" it's still quite a bit of way, with 70 years' worth of evolution in glass and coatings - look at the old and new 50 Heliar.

The old Hektor was in fact quite a mediocre lens even for contemporary standards (i.e. Zeiss 85/f2). If one wants the Hektor look for some reason, one shoudl probably get a Hektor.

 

[johannielscom]

hm,

maybe you're right rxmd, and the Heliar would be too good a lens for my mediocre work 😛

Thing is, I like mediocre lenses for their ability to introduce surreal characteristics in the image. But those darn Hektors keep being expensive!

I hoped to pick up a used 75/1.8 for a decent price some time from now, but recently ran into a 1951 Jupiter-9 with a Zeiss optical block in it, so my quest may be over once I manage to effectively shoot that lens wide open...

 

[haempe]

From there to being an "almost exact copy" it's still quite a bit of way, with 70 years' worth of evolution in glass and coatings - look at the old and new 50 Heliar.

Which old one?

 

[Sonnar Brian]

It's not too hard to shim a lens. Digital calipers help, they are cheap these days. I use a Canon III with bad curtains for the RF and a through the lens viewer bought for $15. Having a Digital RF makes it easier, and I use the M8 or M9 for a test after setting the shim. Having a spanner is almost mandatory, mine ran $25.

Custom machining can be expensive, but we've had several RFF members that do their own.

 

[rxmd]

From there to being an "almost exact copy" it's still quite a bit of way, with 70 years' worth of evolution in glass and coatings - look at the old and new 50 Heliar.

Which old one?

Sorry, that was misleadingly phrased. What I meant is the classic Heliar design for a normal lens, as opposed to things like 12mm Ultra-Wide-Heliars that share nothing but the name. Of course not every normal lens is a 50.

Voigtländer did sell a 50 Heliar in the 1930s for movie work. However, I doubt whether it would have covered 35mm - according to their own sales brochures, it didn't entirely:

$30 in 1930 translates to about $350 today according to the Consumer Price Index, so it actually seems like a bargain. 😀

 

[haempe]

Ok, thanks for clarification.
I had in mind, the CV Heliar was the first Heliar-design-lens for 24x36mm format. That's why I was confused...

 

[Phil_F_NM]

An M8 or M9 is special equipment enough for lens calibration. The hardest thing to do if one is completely taking a lens down to individual helical barrels is to make sure that there is an index point for where the threads line up when they separate. Once you make a few mistakes, you learn to not make them anymore.

The design of the 75mm f/1.8 is very simple though. The lens moves X amount (I don't have my calipers handy to actually measure the total movement of the optical unit) and that movement must be translated to the same movement of a 51.6mm lens throughout its focal range from roughly 1m to infinity. The way that the Heliar moves the cam in the lens is via three rollers and each of the sleeves or unit parts are keyed in such a way that improper assembly is easily averted if one pays a bit of attention.

Most Leica lenses longer than 50mm use dual helicoids which move inside one another or the rotational movement is transferred from the main helicoid to the intermediate one that drives the focusing cam. These are much more complex than the Heliar but still very workable with good spanners and sharp screwdrivers. (Try disassembling an 85mm f/1.8 AIS Nikkor and know the true meaning of painful insanity if the helical barrels aren't properly indexed.)

As far as this project goes, the hurdles are unlocking a lockring which is quite deep then maching an extra 6mm to the end of the channel where the rollers translate movement to the cam. If it turns out that I have to do all three in order to get smooth, even motion of the cam then I'll hang up the project. That would entail machining three channels inside a barrel, each 120 degrees from another, all at the exact same rate. I got an A in CAD class but never moved on to practicals, not to mention that I would need to find access to a machine that could do it. And a machinist that was willing to do it for hire.
(of course, there is always the machine shop at school if I can wait for the semester to begin...)

BUT...
The limitations of this lens only stop with the machining of the roller channels in the driver sleeve for the cam.
Now, seeing as buying TWO 75 /1.8 Heliars brand new in box would still be less than half the price of a used 75 'cron or 'lux, you could artificially set one lens to new limits by spacing it farther from the mount. Shimming under M flange would be easy or shimming under the main mount would be a little more proper looking. Regardless, you'd gain say, an extra millimeter of travel on the close end of the focusing range but lose out on infinity. With some shims and copper foil and enough maniacal patience, you could have a very sweet lens that focused to the absolute closest possible point that the M rangefinder could allow. If you had a Zeiss Ikon, that would be .5 meters, even closer than the rest of the M bodies. Probably perfect for inside a studio or candids inside a room.

Thanks for the encouragement too.
By the way Buzzardkid, the 75 /1.8 Heliar is waaaay to sharp to be even mentioned in the same sentence as the old 73 Hektor. It's comparing the space shuttle with a rubber band powered airplane.

Have fun y'all
Phil Forrest

 

[Doug]

...With some shims and copper foil and enough maniacal patience, you could have a very sweet lens that focused to the absolute closest possible point that the M rangefinder could allow. If you had a Zeiss Ikon, that would be .5 meters, even closer than the rest of the M bodies. Probably perfect for inside a studio or candids inside a room.

Phil, while some ZM lenses will focus to .5m, the ZI RF will not track that close, pretty much like an M body, decoupling at about .7m. I know our hopes were otherwise at introduction, but... And good luck with your hacking if you embark upon it!