Rangefinder lens disassembled: how to calibrate focus?

mariozelaschi

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Hi everyone, I was fixing my rangefinder Olympus 35 RC and ended up disassembling the lens because the focus ring was moving with difficulties. I put a little bit of new grease in the lens thread and now is smooth as butter, but I realized that stupidly enough (it's my first lens I disassemble) I didn't mark the lens position in any way.. now.. The rangefinder seems to be in order, I measured roughly the distance between the camera and an object and it checks out with the distance reported in the ring, but I am not so sure that the lens is following the same focus..
How to align the focus properly without developing a film?
What I did to mount it back was to "screw" the lens all in, align the focus ring of the camera to the end and put the screws back.. do you think it is good enough?
 
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John Koehrer

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Is it continuous thread like a nut & bolt? most RF's are. Since there's only one start point everything should be good.
If you want use a ground glass or frosted tape at the film plane to check fpcus.
 

OAPOli

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It seems you unscrewed the lens helicoid? Those have a coarse, multi-start thread.

Place frosted glass or plastic on the film rails, open the lens on bulb, point at a distant subject and check the image with a loupe. Should be sharp on the infinity setting. If not, unscrew the helicoid and re-insert at another entry point on the multi-start thread. Repeat.
 
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mariozelaschi

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Hi everyone, and first of all, thank you for the responses and the warm welcome!
No, I haven’t unscrewed the helicoid, and the lens assembly is fixed to the camera body in a unique manner. To reassemble it, I screwed it all the way into the helicoid and then set the focus ring to the infinity stop.

My question arises because the bracket that needs to be screwed onto the lens body—which causes it to rotate—doesn't have predefined holes for the lenses. This means I could potentially attach it without fully tightening it, leaving it, for example, unscrewed by a few millimeters.

So, the question is: since the lens body is fully screwed in and never removed from the helicoid, is it factory-set with infinity focus, and therefore sufficient to fix it to the selection ring at the infinity stop? Or should I adjust it by a few millimeters to achieve proper focus? As an experiment, when I look at a distant object at infinity, the rangefinder indicates it’s in focus.
 

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baachitraka

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:-| I don't under estimate your fine mechanic skill but anything for the time does not go as planned esp., with camera rebuilding.

Nevertheless you can still tape the frosted glass at the film gate and check and calibrate the focus.
 
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mariozelaschi

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I am trying to do so, but I find it extremely difficult. I am using a 50mm lens at 1.8 and infinity focus as magnifying glass, but if I attach the back of the lens to the frosted tape I cannot focus it, and to have it in focus with the rangefinder image I have to go further with my lens.
I was reading that it is possible to do this operation easily using another digital camera (that I have), but I struggle to find more precise information
 
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mariozelaschi

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I may have found a way, just correct me if I am wrong
Since the rangefinder was accurate before disassembly, and since when the lens rotates also pushes the rangefinder pin, if the rangefinder is in focus (3ft minimum distance and infinity) then the lens is in focus as well.. Is it correct?
 

baachitraka

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go slow...you will figure it out. Do you have any assembly manual with you?
 
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mariozelaschi

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Unfortunately not looked for it but no luck. Would be amazing to have replies from someone that already did this kind of disassemble on this model
 

baachitraka

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http://rick_oleson.tripod.com/index-134.html
 

OAPOli

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Is this correct? The RF pin follows the gray bracket (first pic), which itself is attached to the lens + male helicoid assembly, as well as to the focus ring. The female helicoid (fourth pic) is screwed onto the camera.

Your concern is that the gray bracket is only clamped to the lens, and you can move the lens in or out and it still grabs?

There is some lacquer on the bracket so you can use that as a reference. Also I think that your are correct, if the RF was aligned properly before and it still is, the position should be correct.

You can confirm infinity using the pseudo collimator described above. You should add a piece of scotch tape (0.05mm) on the film rails because actual film sits a tiny bit behind the rails. You can tell the difference when using the collimator.
 
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mariozelaschi

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Unfortunately I removed the lacquer while cleaning the metal because it had lots of dried up grease that I replaced. Again, worst outcome possible, but at least, lesson learned.
But yes, your description is accurate, this is how it works this focus system. I tried to adjust the focus at the minimum focusing distance by specs and marking on the ring, 3 feet, and I needed to adjust a few mm the helicoidal, so it was not completely screwed. I used a book with details on the cover to adjust the focus while having a 3ft quite precise distance between the tip of the glass of the lens and the book itself.
But then while trying to focus on distance it seems to me it is a bit off and thinks objects are nearer than they are. Also, compared to the pic I toke, the screws are mounted slightly differently, and if I try to mount the screws as similar as possible than in the picture the focus is quite off when measuring at the 3ft distance.
Am I missing something?
Btw, I never did the collimator before and since focus needs to be so accurate I feel it will be off anyways.
I am really pissed of by myself, and devastated that a good camera could be unusable because of my clumsiness
 

baachitraka

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slow down, you will figure it out.
 

koraks

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Not sure what trouble you're running into here, but the frosted tape/makeshift ground glass trick that @baachitraka mentioned really is the most accessible way of determining correct focus. It helps to put the camera on a tripod, aimed at something far away (looking out of a window). This way you should be able to set the rangefinder to infinity and then check the actual film-plane focus through the lens using your makeshift ground glass. You can go back and forth between the rangefinder/viewfinder image and the ground glass as long as you keep the shutter open (use Bulb if it has that setting).

I've done the same many times, also with rangefinder cameras that required calibration. It requires no complex hardware, no additional camera, no collimator etc. Just a simple tripod and something that can act as a ground glass. Frosted tape will work, I've used actual ground glass, or just a piece of clear & clean transparent plastic that I roughened up with some sand paper. You can even get away without the sandpaper and put some scratches on a piece of clear plastic, then tape that to the film gate. Just keep in mind that the rough side of your makeshift ground glass goes towards the lens, not towards the back of the camera!
 

Tel

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mariozelaschi said:
I used a book with details on the cover to adjust the focus while having a 3ft quite precise distance between the tip of the glass of the lens and the book itself.
Click to expand...
This may have caused your focus to be off; you want to measure the distance from the target object (book) to the film plane, where the image would be formed, not the lens itself. Many cameras have a mark on the top cover indicating the precise location of the film plane, but it appears from a google search of images of the 35RC that it does not have this mark. So your best option is to collimate the lens at infinity, as described above.
 
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mariozelaschi

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Ahhhhh ok!! Thanks for the hint, I will try to do that, and to use the infinity focus test to double check then!
 

Tel

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baachitraka said:
go slow...you will figure it out.
Click to expand...
True! I used to be frustrated by collimating until I found a dead tree visible from my front porch and a good distance away that I can use for “infinity”. I can do the collimation slowly and carefully using a tripod, with a suitable beverage handy and it’s actually enjoyable. (Tree branches and antennas are good for this—it’s very clear when they are in or out of focus.)
 
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mariozelaschi

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How many meters do you suggest to have the subject for it to work best? Is 20 meters enough?
 

Tel

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I just went outside to guesstimate how far away my dead tree is. In Dark Ages units, it looks like at least 200 feet, so maybe 70m? I have to confess to owning an old Arnold & Richter collimator that I sometimes pull off the shelf and put to use (on days like today when it’s 10 degrees F outside, for example) to fine-tune the focus. It rarely make a huge difference, though. For most purposes a dead tree (or equivalent) should do.
 
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