Folder focus adjustment, more complicated?

[fidget]

Hi,
I have another folder on the bench. A nice 6x4.5 Ensign 1620 with Ensar triplet. In common with most folders I buy, it needed the glass cleaning and the simple shutter flush out with lighter fluid & lube (no dis-assembly of shutter).
After careful re-assembly, I use a ground glass screen in the film gate and focus on an object at infinity then fit the scale ring at infinity. Ta-Da! All focussed up! This has served me fairly well for several folders, but the last couple has left me thinking that my approach may be too basic. I may even have misunderstood how these things focus.

The "new" problem is that after careful focus setting at infinity, a check of the focus at say an object at 5ft shows that the focus scale is at nearly 7ft. This is a difference of between 20 and 30 degrees rotation of the scale dial....an enormous discrepancy.

I am always careful to rebuild using all the parts which came off the assembly. In this last case a set of 5 shims from behind the lens, each of different thickness has given me some doubts that my simple focus setting (I mean thinking that after set at infinity, all closer distance settings will be right) is good enough. Why would the lens be shimmed? I think that these parts are more than spacers.

Anyone got the knowledge?

Dave....

 

[VictorM.]

I set infinity using the "Ed Romney" backsighting method. Rick Oleson has instructions here: http://rick_oleson.tripod.com/index-123.html This is much more accurate than trying to focus something at "infinity" on the groundglass. However, after setting infinity, I then check the close focusing, usually at 6 feet. If the focus is off, and it rarely is, I then readjust so that the closer distances are favoured. My theory is that shooting at infinity is usually done outdoors with the lens stopped down. Depth of field will then cover the very small difference.

 

[wupdigoj]

I have exactly the same problem with a color skopar, only reversed: at (say) 6 feet, correct focus is at 5 feet in the scale. I am not sure where is the problem, but when you collimate this kind of lenses (frontal lens focusing), there are two variables: the lens-film distance and the position of the frontal lens. If you screw in the frontal lens, the focal length of the lens is increased, so you have to put the lens away of the film plane (adding shims). I am not sure how these settings affect the accuracy of the distance scale. I have tried several settings without a definitive conclusion.

Another (different) problem is the effect of the distance between the frontal and rear groups. Although compur shutters have usually the same distance some I have found some (small) differences between them. Perhaps putting shims between the elements and the shutter would alter also the focal of the lens and the lens' scale?. I don't know.

Some insight in these problems would be very appreciated.

Regards.

Javier

 

[fidget]

Thanks for your points. I had not thought of trying the infinity focus method, although I am aware of it. I will give it a go. I did notice that focussing on a distant object at say 300m is not quite the same as one at 2km. The difference is only a very small part of the rotation of the dial.
I could be being tricked here, I had not yet set infinity and checked for a close distance without collapsing/erecting the lens assy and refitting the screen, so any variation in these would mislead me.

 

[fidget]

I remember that after spending a couple of hours setting the focus of my last folder, the test pics I took showed around 6 inches of back focus at 5ft.
Rather than go through another focus setting session, I moved the scale ring to suit, so what was 5ft became 5ft 6inches.
I'm still taking pics with this cam and have no problems (in fact it's very good), although I don't take too many pics where the aperture is wide open on a scene which would show up focus issues well.

So, I've popped a film in this latest Ensign and it is now toasting under light with the lens retracted. Next unexposed frame will be the same with the lens erected (checking for light ingress through the back/front). Then a series of shots to give some basic confidence in it.

 

[Windscale]

This is probably because the lens to film plane distance is not correctly set. If this is done properly your infinity and all the distances will match. That's why you need all the spacers. This is what I wrote about one week ago in another thread:

"Very likely your lens is not properly calibrated. It is not just as simple as adjusting the infinity. As you only adjusted the front element to get this. But you will have to adjust the distance between the whole lens unit (including the shutter) and the film plane. You may very often find paper spacers between the lens unit (just behind the shutter) so as to adjust the distance between it and the film plane. Once you have got infinity, 3m, 6m and 10m (or corresponding distances from the scale of your RF) correct by actual measurements then your lens will probably match with your RF. You will also find that only when you have got these distances right that your Novar will perform well, or else you will get very blurred edge definition even stopped down."

I have done it this way for over 20 years.

 

[fidget]

How do you go about setting the correct distance with shims?
Perhaps more to the point, how do you know what the correct distance is and where it lives?

Dave....

 

[Windscale]

I am afraid it is a matter of trial and error. But from experience, the right place may be where you turned the front lens furthest in and then turn back about the distance of 3 minutes (according to your watch), then stabilize your lens by the use of spacers, then measure infinity and 3m 5m etc as described. Try again with 4 minutes, 5 minutes and so on until you get it right. If you are lucky it will take no time. If you are not, it will take a day! Therefore, it is important when one takes a folder apart one doesn't discard the spacers because they were used by the factory to fix the lens to film plane distance.

 

[sevo]

The professional way would be to collimate each lens part as you build up the lens - but for that you have to know the focus length of each subgroup. And you would need a collimator test bench, if (or rather as) you have to collimate at distances beside infinity or with negative focus length.

Sevo

 

[fidget]

Hey, this is heavy duty stuff!
My first thoughts when I saw just how many shims were on it was that these are there to get the screwed-in position (infinity) at a sensible point on the thread. It wouldn't look neat if infinity were 6 turns out of the scale ring.....but this sounds uncomfortable.
I'm not entirely sold on this idea.

 

[wupdigoj]

I am afraid it is a matter of trial and error. But from experience, the right place may be where you turned the front lens furthest in and then turn back about the distance of 3 minutes (according to your watch), then stabilize your lens by the use of spacers, then measure infinity and 3m 5m etc as described. Try again with 4 minutes, 5 minutes and so on until you get it right.

This is what I did with a color skopar, without success. At all the settings, the scale was off. I suspect this is due to the fact that the lens is mounted in another shutter not the original, so I suppose that the space between the lens groups plays a role also. I finally made another scale for it.

Nevertheless I agree this is the route to follow. If you have a 35mm SLR with thread mount (pentax thread), and some extensions tubes, you can mount the lens in the SLR (with some cardboard, glue and a little ingenuity) and it is a lot faster to check the optimal position. Regards

Javier

 

[chippy]

Dave 5 shims sounds an awfull lot, i seems to me this camera may of had some trouble before.

assuming you have set infinity perfectly, and used all the original spacers, then it sounds like it still needs another shim

 

[Windscale]

This is what I did with a color skopar, without success. At all the settings, the scale was off. I suspect this is due to the fact that the lens is mounted in another shutter not the original, so I suppose that the space between the lens groups plays a role also. I finally made another scale for it.

Nevertheless I agree this is the route to follow. If you have a 35mm SLR with thread mount (pentax thread), and some extensions tubes, you can mount the lens in the SLR (with some cardboard, glue and a little ingenuity) and it is a lot faster to check the optimal position. Regards

Javier

If the "other" shutter was for another Color Skopar of the same largest f number then it should work. If it is for some other lenses, then it will definitely NOT work. Once this is sorted out, there is only one optimum lens to film plane distance which must be found. Otherwise, even if infinity is set, the lens won't perform to its best, and one would only get a small centre patch being sharp even at f11. Whereas, if all is set properly, all corners should be sharp at f8.

I have read the original post again. I read it that your 5 shims mean 5 spacers. Honestly, I have been messing about with folders and their conversions for over 20 years and I have never seen 5 spacers in any one camera. I have converted a few Ensigns during that time. 3 was my maximum. So I think your lens was not the original lens on the body. Maybe someone took the more expensive Ross Xpress and replaced it with a cheaper Ensar. But the principle is the same. You may have to try without spacers and add on more as you go along to get the proper distance. You will eventually get there.

 

[fidget]

Hmm, thanks for the input and ideas.
This camera is in really good condition. It brings to mind that "maxim" used for our FSU cameras....."if it's mint it probably never worked properly".

It will have to wait for a couple of weeks before I do more on it. I'm preparing for a holiday and am packing the camera(s). The folder to take will be my Isolette II as this one is too far from being trustworthy.

 

[FallisPhoto]

Hi,
I have another folder on the bench. A nice 6x4.5 Ensign 1620 with Ensar triplet. In common with most folders I buy, it needed the glass cleaning and the simple shutter flush out with lighter fluid & lube (no dis-assembly of shutter).
After careful re-assembly, I use a ground glass screen in the film gate and focus on an object at infinity then fit the scale ring at infinity. Ta-Da! All focussed up! This has served me fairly well for several folders, but the last couple has left me thinking that my approach may be too basic. I may even have misunderstood how these things focus.

The "new" problem is that after careful focus setting at infinity, a check of the focus at say an object at 5ft shows that the focus scale is at nearly 7ft. This is a difference of between 20 and 30 degrees rotation of the scale dial....an enormous discrepancy.

I am always careful to rebuild using all the parts which came off the assembly. In this last case a set of 5 shims from behind the lens, each of different thickness has given me some doubts that my simple focus setting (I mean thinking that after set at infinity, all closer distance settings will be right) is good enough. Why would the lens be shimmed? I think that these parts are more than spacers.

Anyone got the knowledge?

Dave....

1. If you are going to use the ground glass method, then after setting it at infinity, you fine tune it at closer ranges.

2. The back-sighting method is more trouble, but is also more precise.

3. The shims are usually there because: (a) paper shims were sometimes used to compensate for differences in the way low grade lenses were ground. (b) sometimes they were needed for certain types of lenses, when more than one type was offered as an option and some of those options were less than an ideal fit. (c) maybe the lens on your camera is not original to it and a repairman installed the shims to compensate for the difference in the lens to film plane distance between the lens on your camera and the lens on the donor camera. The last is by far the most likely.

 

[FallisPhoto]

Dave 5 shims sounds an awfull lot, i seems to me this camera may of had some trouble before.

assuming you have set infinity perfectly, and used all the original spacers, then it sounds like it still needs another shim

What do you want to bet that the lens on his camera didn't come from a different folder? The presence of five shims would make a great deal of sense then.

 

[wupdigoj]

If the "other" shutter was for another Color Skopar of the same largest f number then it should work. If it is for some other lenses, then it will definitely NOT work. Once this is sorted out, there is only one optimum lens to film plane distance which must be found. Otherwise, even if infinity is set, the lens won't perform to its best, and one would only get a small centre patch being sharp even at f11. Whereas, if all is set properly, all corners should be sharp at f8.

Thank you for your answer. It is not. I am pretty sure the shutter is from a 75 mm 3.5 Tessar, and the lens is a 80 mm f3.5 skopar. The camera is a ikonta 521 4.5x6. I purchased the camera (in an impulse, I must say) because I wanted a good body to mount an heliar in it, but I was not possible (the heliar seems to be something like a 71 mm, not 75 mm).

Apart from the missfocus issue at closest distances, the skopar lens is very sharp. At infinity it approaches my iskra with much more contrast. The reduced negative size also helps.

Regards

 

[fidget]

It was just as well that I thought that perhaps I shouldn't take this cam whilst on holiday. I ran a test film through a P&S (very keen to see if it works) and thought that I would dev my test film from the Ensign at the same time. They're all drying at the moment, but failure is easily seen already.
A surprise! not much in focus on any shots. Most amusingly my standard test shot of a few beer cans arranged at 3 inch intervals from 6 inch in front to 6 inch behind the target can at 12 ft showed...none in focus. Hmm...(but don't worry, no beer was spilled during this test).
Even the infinity shot is not sharp. All these were around f5.6 to wide open (4.5).
Back to the ground glass....later.

 

[Windscale]

Please do make sure that you have used the right side of the ground glass, or else, even your infinity will not be sharp.