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Lens infinity positioning & rangefinder infinity focus
Old 11-22-2019   #1
Cortexturizer
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Question Lens infinity positioning & rangefinder infinity focus

So, I took my Olympus 35 RD for a shutter blade cleaning procedure (thought mine won't be affected by oil from the helicoid but of course it did) and I watched as the repair guy and his helper used HUGE force to be able to unscrew the lens using a small hammer and many attempts (I read and saw on other places that 35rd lens is unnaturally tight on there) and after that all went fine and the camera is as it was, with some exceptions:

- rangefinder infinity focus was off (apparently because of the hitting the camera with the hammer)
- the focus ring itself now has a point in it's travel where there is some friction, not a lot but enough to make me frustrated

Is it possible that the focusing helicoid was physically altered during this procedure, curved in some way, or smt? The repair service assures me that it isn't, but then, there is that friction during focusing that was not there before.

And also, is it possible that the lens has been positioned differently now and never reaching infinity focus in juxtaposition to the roll of film distance from it? I lack the terms to explain it well but I think you get what I mean. And if that is even a possibility (another thing the repair service assures me hasn't happened), how to be sure? What procedure to do in order to check it etc.

I tried attaching an OM system focusing screen on the inner film rails, and looking at it using a magnifying glass but I couldn't determine jack sh... pardon my language here, but it was a frustrating ordeal that left me with a headache from all the squinting.

What do you think guys?

I did a roll of film since, and it looked mostly fine, but it's kinda hard to tell if infinity is razor sharp when looking at distant buildings trees etc

Cheers
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Old 11-22-2019   #2
retinax
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Regarding the focusing feel, try untightening the screws that hold the focusing ring a little. They severely affect the focusing stiffness on the RD. But of course real damage seems a possibility.
I agree that checking infinity focus with a ground glass is very hard. I'd check close focus that's much easier, and if that's accurate I'd wager shooting a roll to verify infinity is, too; it very likely is.
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Old 11-22-2019   #3
Cortexturizer
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The thing is, I tried using a focusing screen and the magnifying glass, tried focusing on an object that was for example 2 meters away, and I focused it on the screen but when I looked through the rangefinder the rangefinder patch was very much off, the double image was very much visible.
On the roll of film I deliberately shot some close objects and it seemed fine, although not quite as sharp as I remember it being before. I really have no idea how to fine-tune this?

Will it have to be a trial and (film develop and) error kinda thing? Kinda hate that this stuff is not more easy to crack but what can one do right
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Old 11-22-2019   #4
retinax
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You had the rough side of the ground glass sit on the film rails, yes? And you saw a horizontal double image? Well then the RF needs adjusting. I don't know how it's done but it's usually not very hard. But in your case, I'd have the repair person do it, adjusting to make the whole camera work should be part of any repair.
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Old 11-22-2019   #5
Sarcophilus Harrisii
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Quote:
Originally Posted by retinax View Post
You had the rough side of the ground glass sit on the film rails, yes? And you saw a horizontal double image? Well then the RF needs adjusting. I don't know how it's done but it's usually not very hard. But in your case, I'd have the repair person do it, adjusting to make the whole camera work should be part of any repair.
Good idea—perhaps he can re-set the rangefinder with his hammer?
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Old 11-22-2019   #6
retinax
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Quote:
Originally Posted by Sarcophilus Harrisii View Post
Good idea—perhaps he can re-set the rangefinder with his hammer?
I'm positive that if he can't get it done with the hammer, he has an angle grinder at hand.
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Old 11-22-2019   #7
Cortexturizer
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Hah, well I am always for inspiring some fun in people... glad you guys are laughing behind screens

The guy is not the first to loosen up a particularly tight lens with a hammer that's for sure.

I've done the OM focusing screen on the film rails method another try now, and repositioned the rangfinder patch to match when I see the split picture aligning to a very close tolerance.
I'll run a roll of film and see where it takes me.
The infinity focus (on the patch) is now off, so let's say I am making an emphasis on having good close focus now.
I am curious to see what results this will bring. I'll deliberately shoot at bigger apertures to make the dof small and see if the focus falls where I wanted.

Will report after done in a few days.
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Old 11-22-2019   #8
David Hughes
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With old cameras you have to laugh as the only alternatives are to cry or bang your head on a wall a few times; it's the second* thing you have to learn...


Anyway, I'll wish you luck with the camera.


Regards, David


* The first is RTFM.
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Old 11-25-2019   #9
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Reporting after having developed a roll of film and after adjusting focus as per method described in my last post.

The pictures have never been sharper. I deliberately shot most of them at 1.7 and the focus is dead on. I am so so satisfied.

The infinity focus is now, at least according to the rangefinder patch, off by a noticeable margin, but it seems that I shouldn't even care, if I want infinity I'll just focus the lens at infinity and not worry about what the rangefinder says.
My close focus pics were never so sharp with this camera.

Very happy with this now.

Cheers and I hope this helps someone.
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Old 11-25-2019   #10
retinax
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Congrats! But are you taking for granted that infinity focus according to the scale one the lens/the hard stop is more accurate than by the rangefinder? It's possible but I think less likely than that the rangefinder is more trustworthy. Does the scale on the lens agree with the RF focus at close range? If it's off here by a few mm on the focus scale, that will be a few cm at minimum focus distance but it will be off at infinity by dozens of metres. Iirc the focus ring can be adjusted so that it lines up with the RF fairly easily.
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Old 11-25-2019   #11
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You are probably right, hm. But at this point I am experiencing severe fatigue around this stuff and just wanna make photos in all honesty. I'll reaproach the matter at another time when more fresh I guess.

Also, if I am now honoring the rangfinder patch, and focusing on where it lands, won't the DOF and it's 2/3ds further after the focus point handle the rest? At smaller apertures especially. My next test will be to emphasize those kinds of shots more and see where it leads me. So far, for what I shoot, where I came with the focusing on this camera left me satisfied.
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Old 11-25-2019   #12
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Yes I think it's likely that your rangefinder focusing will be fine now for all distances, I just wanted to caution against relying on the scale and infinity hard stop under these circumstances.
Pictures at infinity are mostly taken with smaller apertures anyway, so you might not notice an issue even if things aren't technically spot on.
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Old 11-25-2019   #13
Sarcophilus Harrisii
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I would not recommend using a split wedge screen to inspect the lens focus at the film plane. A plain ground glass, providing it is resting on the film rails may be harder to read but it will never lie to you, something that, in certain situations, can occur with a focus screen split wedge. In order to make accurate assessments of the state of focus, a loupe is essential for a better view of the image formed on the glass.

Using a single lens reflex focus screen across the film rails can work OK, but it is always important to note that focus screens are not designed to rest on film rails, they are always made to fit the screen housing beneath the finder. If there are any irregularities around the screen edge that prevent the ground surface from resting exactly on the film rails you will not obtain accurate results. As a general rule one should always be checked for fit to ensure that it will rest on the proper plane of focus, if it is being applied to this use.
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Old 11-25-2019   #14
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Yes, I checked that it was resting perfectly on the film rails, and focused an object with a huge vertical line perfectly on the split screen, using a loupe with 30x magnification. I made minute adjustments to the focus until I was satisfied, then did the same with the rangefinder patch focus.

I'll definitely try the plain glass method in the future, but having it cut to measure is a bit of a pain, a focusing screen I already have and it's of perfect dimensions so I went with that.

What do you guys think about this colimator method? http://rick_oleson.tripod.com/index-123.html

I don't understand it very well.
I do have an OM-1 on hand, so how would I use it to check infinity focus on my 35 RD?

put both lenses facing each other? the glass shouldn't touch, or should it? I should focus both on infinity and what should I see through the OM1 viewfinder?

am I right in thinking that if I tape the OM focusing screen on the film rails of 35 RD I should see the split screen circle sharply if I look at it through the OM1 into 35 RD lens both set at infinity?!

excuse the confusion.... cheers
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Old 11-25-2019   #15
Sarcophilus Harrisii
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Quote:
Originally Posted by Cortexturizer View Post
Yes, I checked that it was resting perfectly on the film rails, and focused an object with a huge vertical line perfectly on the split screen, using a loupe with 30x magnification. I made minute adjustments to the focus until I was satisfied, then did the same with the rangefinder patch focus.

I'll definitely try the plain glass method in the future, but having it cut to measure is a bit of a pain, a focusing screen I already have and it's of perfect dimensions so I went with that.

What do you guys think about this colimator method? http://rick_oleson.tripod.com/index-123.html

I don't understand it very well.
I do have an OM-1 on hand, so how would I use it to check infinity focus on my 35 RD?

put both lenses facing each other? the glass shouldn't touch, or should it? I should focus both on infinity and what should I see through the OM1 viewfinder?

am I right in thinking that if I tape the OM focusing screen on the film rails of 35 RD I should see the split screen circle sharply if I look at it through the OM1 into 35 RD lens both set at infinity?!

excuse the confusion.... cheers
A correctly adjusted lens will project collimated light when focused to infinity. So when two properly calibrated cameras are aligned lens to lens the effect will be a sharp image of the film target when observed through the reflex viewfinder. Yes it can work well although, again, I have personally had accuracy issues when relying on a split wedge to judge accuracy. So I'd suggest referring to the remainder of the OM-1 screen if it's fitted with a split, as opposed to the split itself.

If you are going to use auto-collimation to inspect focus of your camera you will need a suitable target. I prefer to use an actual piece of film it is after all what you are trying to set the lens to. So a piece of developed but unexposed black and white is good for this purpose as it's clear, enabling you to place a source of illumination behind the film gate. I will place a piece of glass across the pressure plate rails (in place of the pressure plate) to keep the target film in the same plane a live film would sit. You'll want to rule some sharp pen lines across the emulsion side of your clear film so you have something opaque to inspect the focus of. Being particularly fussy about getting best results I rule a grid covering the whole film gate so I can compare sharpness at various points. Wide open no lens is equally sharp from centre to corners but I doubt you'd detect this visually using another camera lens to inspect. That said—if there's a noticeable variation in sharpness at different parts of the gate Eg side to side or top to bottom, it would inform that a check of the register distance and alignment should be carried out. (I use a granite surface plate and digital depth gauge for this task).

The idea behind using a second camera is to magnify the target image at its infinity setting. For best results, then, suitable magnification will be needed. It's no coincidence that professional auto-collimators tailored for optical calibration applications tend to be fitted with lenses of quite long focal length (there's some variation depending on format they're optimised for, Eg various Gokosha models for 35mm or medium format will have objectives of different focal length). But if employing an SLR as an auto-collimator you should try to fit it with a lens that is at minimum twice the focal length of that attached to the camera being checked.
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