SLR test / odd poor result

[Ranchu]

That's a good point, I thought it was interesting too. I'm somewhat suspicious of the whole ground glass on the film rails test though. I'm not convinced that's where the film lies. The cool thing about that thread is the guy tested the film plane off of the film while it was in the camera, with the excellent machine.

 

[Sarcophilus Harrisii]

That's a good point, I thought it was interesting too. I'm somewhat suspicious of the whole ground glass on the film rails test though. I'm not convinced that's where the film lies. The cool thing about that thread is the guy tested the film plane off of the film while it was in the camera, with the excellent machine.

Hans Kerensky is my role model for DIY camera repair, apart from his unrivalled ability to sniff out stashes of NOS factory parts, he got himself a Gokosha autocollimator a few months back, something I would love to do myself. But quite apart from the purchase price the delivery cost to Australia isn't cheap.

Re: the ground glass, I think it would be important to be very careful if a camera focus screen was being used. They often have mounting frames or edges that are not in the same plane as the part that records the focus image so depending on the screen there might be register issues when using some of them. But with a plain, flat piece of ground glass, providing it is firmly seated on the film rails (and not the pressure plate rails) I can't see why it would be a problem. Not for 35mm at least. With 120, perhaps? Using an actual piece of film supported by a glass placed over the pressure plate rails and a trusted SLR to collimate the camera being tested is probably as close as those of us without access to an autocollimator can get to setting focus precisely (discounting the obvious option of shooting some test film, which will inform you whether you have a problem, but won't quantify the adjustment needed on the camera, per se).
Cheers
Brett

 

[Sarcophilus Harrisii]

Oh you're so welcome, Dexter. Out of curiousity, has anyone found an slr to be out of register with the lens? How often would you say that that has been the case?

The thread I linked is very interesting but, thinking about it, is really discussing viewfinder accuracy, isn't it? Whereas the point you raised, the register of the actual lens to body, is related but not an identical issue. Thinking about it, the answer is yes, I have found several SLRs that have had their primary lens focus off. But not in the normal sense that the problem occurs with most SLRs, because I can recall a few Contaflexes I've worked on that needed to have their focus corrected. But these are a strange design by SLR standards, with the shutter integral to the lens and the focus helical mounted in the body rather than the actual lens itself, which is a "permanent" part of the camera body, unlike conventional SLRs where the entire lens array complete with its own helical is interchangeable with other lenses.

What happened with the Contaflexes is that the infinity height of the helical had either moved slightly as the fixing screws for the lens/shutter unit had backed off slightly or because of old, dried out grease no longer damping the helical. Or (and this is not unusual) someone tampering with the camera, not understanding how to put it back together correctly, and stuffing up the focus adjustment in the process.

It's not something I've really noticed with conventional SLRs, but although I work on the odd one I'm usually happier fixing a Contaflex, Rollei or some other German rangefinder and don't do many Eg. Japanese SLRs.
Cheers,
Brett

 

[Ranchu]

But with a plain, flat piece of ground glass, providing it is firmly seated on the film rails (and not the pressure plate rails) I can't see why it would be a problem. Not for 35mm at least. With 120, perhaps? Using an actual piece of film supported by a glass placed over the pressure plate rails and a trusted SLR to collimate the camera being tested is probably as close as those of us without access to an autocollimator can get to setting focus precisely

I'm willing to accept that you're right about that. But I'm still suspicious, or perhaps superstitious...

 

[colyn]

Oh you're so welcome, Dexter. Out of curiousity, has anyone found an slr to be out of register with the lens? How often would you say that that has been the case?

I have never found one to be out on its own but I have repaired and re-adjusted a couple that the owner tried to modify himself for whatever reason.. Too many wannabe repairmen...

 

[photomoof]

That's a good point, I thought it was interesting too. I'm somewhat suspicious of the whole ground glass on the film rails test though. I'm not convinced that's where the film lies.

The sprocket holes run on the polished inner rails. You do have to avoid the outer rails. That is why tape works so well, IMO better than glass, since many cut the glass too wide and it sits on the outer rails. Tape just "finds" the right place. Glass MUST fit between the outer rails, however microscope slides do.

Nikon F from: http://www.mir.com.my/rb/photography/hardwares/classics/michaeliu/cameras/nikonf/fbody/fcontrol3.htm

 

[Ranchu]

I meant those rails. Brett's method here is the better way to go though, because of the distance between the film rails and the pressure plate..

Using an actual piece of film supported by a glass placed over the pressure plate rails and a trusted SLR to collimate the camera being tested is probably as close as those of us without access to an autocollimator can get to setting focus precisely

 

[photomoof]

I meant those rails. Brett's method here is the better way to go though, because of the distance between the film rails and the pressure plate..

The nikon F has two sets of rails, there are cameras with only one set. The frosted side (toward the lens) sits where the emulsion would normally be. On the Nikon F the rails almost appear to be the same. The difference is minimal, but enough to cause collimator problems.

Here is a good page on placement for the ground glass.

http://monopix.z0g.eu/collimator.shtml

 

[Ranchu]

No, I understand. The pressure plate rails have to support the pressure plate above the film rails enough so the film slides freely (or less freely). The place the film sits on the pressure plate may not be the same place as the tape across the film rails. It's likely behind, imo..

 

[photomoof]

No, I understand. The pressure plate rails have to support the pressure plate above the film rails enough so the film slides freely (or less freely). The place the film sits may not be the same place as the tape across the film rails. It's likely behind, imo..

Perhaps, but not on a Nikon F, it is not that sloppy. But you may be right the film may off if the emulsion is thin.

The rails do keep the pressure plate slightly above the opening, but not by much. Amazingly the F does not often scratch film.

Edit: There is only so much play, emulsions cannot vary by much. But as you know the film is not absolutely flat, it is not a glass plate.

 

[Sarcophilus Harrisii]

I'm willing to accept that you're right about that. But I'm still suspicious, or perhaps superstitious...

Actually, I didn't discount your comment out of hand, quite the contrary. For example, Rollei made certain Rolleiflex models including the Wide, the Teles, and some of the Es and Fs with the option of fitting their plane glass in front of the film, so that the film running through the gate would be literally sandwiched between the pressure plate and the glass. And Modern Photography's period test of the Tele Rolleiflex with and without the glass fitted, did, indeed, demonstrate that there was a slight but noticeable improvement in film sharpness with the glass fitted (at the expense of dust etc. according to most owners who have actually tried to use it, I should add). The reason for the improvement is because, unlike a rigid piece of flat glass, a piece of film will not necessarily sit perfectly flat across the gate. Hence my comments about it being less of an issue for 35mm than, potentially, 120. I have copies of that test report about the Tele including their photos so let me know if you'd like to see it. A while ago I went to the trouble of tracking down the plane glass for my own Tele, they're reasonably uncommon and perhaps were sometimes broken, but I found one cheapish. It's a beautiful piece of optical glass...

By using a glass across the pressure plate rails, placed behind a clear film piece with some cross hairs scribed into it, one is simulating as close as it is reasonably practical to do so, the situation of a loaded film sitting in the gate on which to calibrate the lens to. Which one hopes would also extend to any deformation of the film in situ. In the absence of an autocollimator, it is the best I can do to set focus as precisely as possible.
Cheers
Brett

 

[photomoof]

The reason for the improvement is because, unlike a rigid piece of flat glass, a piece of film will not necessarily sit perfectly flat across the gate. Hence my comments about it being less of an issue for 35mm than, potentially, 120.

Indeed, there is always some compromise. Film is just not flat. 🙂

The early Nikon S uses a much more primitive film rail (a screwed on part) than the Leica M or the Nikon F, where the rail is part of the body casting.

By using a glass across the pressure plate rails, placed behind a clear film piece with some cross hairs scribed into it, one is simulating as close as it is reasonably practical to do so, the situation of a loaded film sitting in the gate on which to calibrate the lens to. Which one hopes would also extend to any deformation of the film in situ. In the absence of an autocollimator, it is the best I can do to set focus as precisely as possible.

Not sure I fully understand why place the film between the gate and the glass.

I am assuming that the emulsion is toward the lens, with the film base and some type of anti-halation backing against the pressure plate.

What am I missing here?

 

[Sarcophilus Harrisii]

Indeed, there is always some compromise. Film is just not flat. 🙂

The early Nikon S uses a much more primitive film rail (a screwed on part) than the Leica M or the Nikon F, where the rail is part of the body casting.



Not sure I fully understand why place the film between the gate and the glass.

I am assuming that the emulsion is toward the lens, with the film base and some type of anti-halation backing against the pressure plate.

What am I missing here?

Sorry, perhaps I should have been clearer in my previous post. On the topic of film flatness I mentioned the example of certain Rollei models which could have a plane glass fitted in front of the film (IE. between the film and the taking lens) in order to improve film flatness.

My subsequent comments about using a glass across the film gate were in relation to using another camera in order to examine lens focus at the film plane. The film is usually held in place by the pressure plate ensuring it is flat (flat being a relative term, as has been discussed). In order to see the film it has to be lit from the back with the lens open, meaning of course that the back has to be open or off the camera. Without a pressure plate present the film may not sit as it normally would. Hence a small piece of glass placed on the pressure plate rails will both hold the film in place as a substitute pressure plate and also enable a light source behind the camera to illuminate the film so that the target markings on the emulsion side are easily visible.
Cheers
Brett