Rollei 35 T lens infinity calibration

januaryabc · Aug 30, 2022

I recently acquired a Rollei 35 T. I first just want to add some grease to make the lens smoother when focusing. I also marked the relative position to ensure everything will be back to the original position. And by curiosity I use a binocular to try to test in the infinity focus is roughly correct by sticking a piece of paper on the film back and look through the lens with the binocular set at infinity. I observed that the infinity position seems off quite a bit and would just like to calibrate it by using a ground glass. But when I closely examine the film plate I discover that there is quite a bit of gap between the film rail and the pressure plate. This make me wonder if in actual usage the film will just being pull towards the film rail or just sit on the film plate. The gap is not small and is much thicker than the film thickness and so I guess it will definitely have an impact on the focus adjustment.

Does any one know whether the film position in actual usage of the camera?

Why the film pressure plate is designed to leave a gap and not just press all the way towards the film rail?

Huss · Aug 30, 2022

Is everything in the same position it was before you took it apart? If so take a few real test shots at infinity wide open and stopped down to check focus.
otherwise you are looking for a problem before actually knowing there is a problem.

Nicholas Lindan · Aug 30, 2022

The edges/sprocket holes of the film rides on the chrome rails. The back of the film is held flat by the pressure plate. The film's emulsion imaging area doesn't touch anything. Often cameras have another set of rails that hold the film side-to-side.

Try putting a ground glass on the chrome rails and examining it with a 10x or 20x magnifier with the lens focused at infininity. The results should be about the same with the camera's focus set to 1 meter and the distance from the subject to the film plane at 1 meter (an alternate method for when it is raining outside).

The real proof, though, is taking photographs...

Huss · Aug 30, 2022

Nicholas Lindan said:
The real proof, though, is taking photographs...

Exactly.

januaryabc · Aug 30, 2022

I know that taking real photo to test the sharpness at infinity is a way to test that. But I also guess that the exact infinity mark may not easy be tested out due to the DoF effect. What I want is to try to figure a method to test/ bring back the camera focus to infinity at its infinity position.

I searched the servicing manual and discovered that the film plate clearance is 0.22mm, which must thicker than film thickness. (i.e. The pressure plate is topped by the two outer rail, circled in red in the photo, to make the plate 0.22mm after the upper and lower film rail.)

Therefore I am doubting what focal plane (film rail or film pressure plate) should be used to test the focus.

Actually I already have an idea to put real film , with marks on them, in the camera and a tiny led inside the film chamber, and then use a binocular set at infinity to test the exact infinity position. That may be the only way to know how the film will position itself in real usage.

Huss · Aug 31, 2022

It has a 40mm 3.5 lens. Put film in it. Set it at 3.5. Set it at infinity. Aim at something very far away. Take a pic. Look at the pic.
Also do this stopped down.
That is the only way to see how it performs in real usage, and the first thing to do before you start adjusting stuff.
It just seems to me that you are fiddling with stuff w/o even having tried the camera first.

januaryabc · Aug 31, 2022

Huss said:
It has a 40mm 3.5 lens. Put film in it. Set it at 3.5. Set it at infinity. Aim at something very far away. Take a pic. Look at the pic.
Also do this stopped down.
That is the only way to see how it performs in real usage, and the first thing to do before you start adjusting stuff.
It just seems to me that you are fiddling with stuff w/o even having tried the camera first.

Thanks for your suggestion. Testing on film is the ultimate test, but I guess every camera out from production line will not be film tested. There must be a way to check the infinity without film. I am interested to know how to achieve that.

guangong · Aug 31, 2022

The Rollei 35s were purposely made with an f3.5 40 mm lens for the simple reason that focusing was intended to be by quesstimation, and not with a precise rangefinder. So unless the lens could be extremely off, I don’t see the concern. With great depth of field and sharp, I’ve enjoyed mine since first day they were offered for sale.
The Rollei 35s with Sonnar lenses were a decision from marketing, and not very practical in terms of actual use.

John Wiegerink · Sep 1, 2022

Huss said:
It has a 40mm 3.5 lens. Put film in it. Set it at 3.5. Set it at infinity. Aim at something very far away. Take a pic. Look at the pic.
Also do this stopped down.
That is the only way to see how it performs in real usage, and the first thing to do before you start adjusting stuff.
It just seems to me that you are fiddling with stuff w/o even having tried the camera first.

When I repair/cla an older camera, I check focus dead on and two to three places slightly before and slightly after (if possible) from the inf. setting mark. I'll use a small piece of masking tape on the moveable lens barrel and mark a dot at each focus spot. I check the film after exposure to see which dot aligns with correct inf. focus. So, with this Rollei I'd at least try a couple of tiny movements before inf. just to see which is better. Just an idea?

PS. Oh, always with the lens wide-open and again one stop down.

reddesert · Sep 2, 2022

januaryabc said:
Thanks for your suggestion. Testing on film is the ultimate test, but I guess every camera out from production line will not be film tested. There must be a way to check the infinity without film. I am interested to know how to achieve that.

The camera manufacturer had both full knowledge of where the focus was supposed to be relative to the film rails, and an optical testing rig to check the lens collimation (infinity focus). You don't have either of those things. You can try to make meticulous measurements to understand where the film is supposed to sit relative to the rails, and then attempt to calibrate it using a ground glass at the film plane, but then you'll have to test it on film anyway to be sure. I am not sure what your procedure was using the binocular and piece of paper in the first place, but unless it was very accurately placed, it was likely misleading. If you don't do this extremely carefully, you can make it worse and not better.

snusmumriken · Sep 2, 2022

Of course you had to open the lens to replace the grease and make the focus action smooth. I had the same issue with mine, so thought I might be able to help with the subsequent infinity issue. However, the interior design of the 35T is evidently quite a bit different from my early Singapore-made 35. At least your pressure plate doesn’t appear to be bent at the hinges, which is quite a common problem caused by previous owners.

Surely the film must lie flat from rail to rail with its backing flat against the pressure plate? The gap you indicate (if I understand you correctly) seems irrelevant. So your ground glass (I used plain glass with Scotch tape on the image side) should also lie across the rails, with the frosted side towards the lens. The moon makes a conveniently bright test image, in fact the only image I found I could work with. You also need to grow another hand to do this job.

snusmumriken · Sep 2, 2022

PS - when I get home tomorrow I’ll DM you the kind and very helpful advice that was given to me online when I had to do this.

januaryabc · Sep 2, 2022

reddesert said:
The camera manufacturer had both full knowledge of where the focus was supposed to be relative to the film rails, and an optical testing rig to check the lens collimation (infinity focus). You don't have either of those things. You can try to make meticulous measurements to understand where the film is supposed to sit relative to the rails, and then attempt to calibrate it using a ground glass at the film plane, but then you'll have to test it on film anyway to be sure. I am not sure what your procedure was using the binocular and piece of paper in the first place, but unless it was very accurately placed, it was likely misleading. If you don't do this extremely carefully, you can make it worse and not better.

The principle is to have both camera/ optical device set at infinity and seeing each other. If they are both calibrated at infinity we will get a sharp image.

What I plan to do is as follows:
1. Put some marks on film and put the film in Rollei 35. Also put the tiny led inside the film chamber.
2 get a SLR with split image, focus at far objects like moon and ensure the lines are match in split image.
3. Using the SLR to observe the marks on the film in the Rollei 35.
4. Adjust the focus of Rollei 35 until marks are lined up in split image. This should be the correct infinity position exactly for the film in real usage.

Please feel free to comment. Thanks.

Huss · Sep 2, 2022

januaryabc said:
2 get a SLR with split image, focus at far objects like moon and ensure the lines are match in split image.
3. Using the SLR to observe the marks on the film in the Rollei 35.
4. Adjust the focus of Rollei 35 until marks are lined up in split image. This should be the correct infinity position exactly for the film in real usage.

Please feel free to comment. Thanks.

How do you know that the SLR is correctly calibrated?

januaryabc · Sep 2, 2022

Huss said:
How do you know that the SLR is correctly calibrated?

When using the slr to focus on the moon and observe the split image to make the line match, we are already calibrating the focus to infinity, at the focusing screen. It does not have anything to do with the actual infinity point to the film plane of that SLR.

Huss · Sep 2, 2022

januaryabc said:
When using the slr to focus on the moon and observe the split image to make the line match, we are already calibrating the focus to infinity, at the focusing screen. It does not have anything to do with the actual infinity point to the film plane of that SLR.

Does that take into account that the mirror is correctly aligned and the lens is correctly collimated?

gone · Sep 2, 2022

I've never had to resort to taking test photos to confirm infinity.....at least not yet. The procedure is very simple, and it works every single time.

Put the camera on a tripod or something stable and have the shutter held open on B or T. Place a piece of GG or even Scotch Magic tape across the film rails (make sure you're placing it on the film rails and not on the edges protruding above and below, that's really easy to do).

Then focus on something at least 100' away. If you don't have a loupe, use a 35mm camera lens as a loupe, and get the image as sharp as you can get it. That's infinity. Put a mark on the lens, and make sure it stops there when you focus it to the infinity stop. If it's just a very little bit off, I wouldn't worry about it. It's doubtful you'll be shooting anything far away wide open at infinity.

januaryabc · Sep 2, 2022

Huss said:
Does that take into account that the mirror is correctly aligned and the lens is correctly collimated?

I guess the mirror alignment is usually taking about if it alignment so that distance from lens to upper and lower part of the focusing screen is always the same. As long as only one particular position is used throughout the whole procedure (i.e. the centre split image), then I dont thinks it will affect the result. The lens collimation is talking about the similar issue, about the optical centre, which affect the image sharpness or focal length across the image. So it is the same as the mirror alignment question, as long as will usually stick to the centre it will not affect the result.

It just like we got a clear bottle with inaccurate volume reading at all and then we pour exact 1 kg of water inside and put a mark on the bottle, then use this mark to calibrate for other container to have the 1L reading. How we know the infinity mark of the SLR is by our observation to the moon, not by the old infinity mark on the SLR lens. If the SLR lens even cannot reach infinity then there will be a problem.

januaryabc · Sep 2, 2022

momus said:
I've never had to resort to taking test photos to confirm infinity.....at least not yet. The procedure is very simple, and it works every single time.

Put the camera on a tripod or something stable and have the shutter held open on B or T. Place a piece of GG or even Scotch Magic tape across the film rails (make sure you're placing it on the film rails and not on the edges protruding above and below, that's really easy to do).

Then focus on something at least 100' away. If you don't have a loupe, use a 35mm camera lens as a loupe, and get the image as sharp as you can get it. That's infinity. Put a mark on the lens, and make sure it stops there when you focus it to the infinity stop. If it's just a very little bit off, I wouldn't worry about it. It's doubtful you'll be shooting anything far away wide open at infinity.

The issue is the for rollei 35 T there is around 0.22mm space between the film pressure plate and the film rail, as noted in the servicing manual.

Rollei 35 T lens infinity calibration

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Rollei 35 T lens infinity calibration

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