yossi
Well-known
Hello all,
I have acquired a Summar lens recently from the Bay. Clean optics, smooth operation BUT front focus quite a bit. Does anyone know if it is possible to adjust (DIY) the focusing of this lens? If so, how?
Thanks in advance for any info. or suggestion.
(BTW, I tried transferring all the optical modules from this lens to another Summar which is known to be focusing accurately, but it doesn't work. Focusing is out even more than the original one!)
yossi
I have acquired a Summar lens recently from the Bay. Clean optics, smooth operation BUT front focus quite a bit. Does anyone know if it is possible to adjust (DIY) the focusing of this lens? If so, how?
Thanks in advance for any info. or suggestion.
(BTW, I tried transferring all the optical modules from this lens to another Summar which is known to be focusing accurately, but it doesn't work. Focusing is out even more than the original one!)
yossi
Erik van Straten
Veteran
Maybe you can shim the optical unit, so moving the optics a little bit backward or forward.
If I was you I would not touch the focusing curve in the lens mount because it is in principle unchangeable, you cannot undo changes.
Erik.
If I was you I would not touch the focusing curve in the lens mount because it is in principle unchangeable, you cannot undo changes.
Erik.
What does the focus look like at infinity? If it's substantially off at close range, one would expect infinity to be less than acceptable also, and this should be your starting point. Also: does the RF patch merge correctly at the infinity stop?
How are you assessing lens focus?
How are you assessing lens focus?
yossi
Well-known
When lens is turned to infinity mark, the sharpest point appears to be about 50m rather than infinity (I use some very far buildings).
The RF patch does merge at the infinity stop.
I think somehow, the optical unit is a bit further away from where it should be. I am just wondering if there is any way to move it slightly nearer.
retinax
Well-known
50m or infinity is a tiny difference on a 50mm, I wonder how you could even make that out with certainty. Is focus also noticeably off at minimum focus distance? I'd start there, much more noticeable in normal use.
I agree, 50 metres for a 50mm lens is so close to infinity if not at it that splitting it seems almost impossible.
In terms of checking infinity focus the key is absolutely an 8 x or higher power loupe on one's ground glass so that there's sufficient magnification of the image to detect minor deviations from best focus (which will, of course, be much more evident at close range).
If focus is accurately keyed in at infinity, close range should also fall in correctly. It can take some practice and experience to really nail infinity adjustment well, because, of course, the depth of field is large and small alterations in focus point can be very hard to differentiate. If a lens that is calibrated at infinity is subsequently found to be at odds with its distance scale at close range (or, in this case, the rangefinder), the reason will usually be because the infinity calibration was close, but not optimal. I speak from experience! It's the best way of setting a lens but it does dictate patience and very particular inspection of one's ground glass.
retinax
Well-known
Because as you say it's hard to see variations at infinity, why not do the adjustment at close distance, as long as one doesn't want and need to work on the "slope" of focusing? That is of course assuming an accurate rangefinder. But at infinity one would assume an accurate rangefinder and/or infinity stop (which is more hit and miss in my experience), too.
It's harder to see minute variations at infinity, but not impossible. I definitely think that practice helps, because I've been doing it for years and I am definitely better at it now than I was at earlier times.
I should probably elaborate because your point about adjustments being easier to see at close range has some validity. In practice, to get a lens and viewfinder well calibrated I will actually check both infinity and close range, critically. But it has invariably been my experience that when the standard of adjustments really is good, the lens focus and finder will be tracking together well across the whole focus range.
For the sake of clarity I'm not saying, necessarily, that your alternative of matching lens and rangefinder at a close distance may not give satisfactory results. But camera manufacturers would typically key the tracking of lens and finder together via autocollimation, at infinity. I use infinity in the first instance because by carefully applying the same principles the maker would have I can be confident of the same result they achieved (if I don't get that it's indicative of other matters needing attention) and because I believe it results in a higher standard of calibration using the equipment I have access to.
I should add that I say "finder" in this post, as distinct from Eg "rangefinder" because whilst we may be discussing a rangefinder camera in this thread, it really doesn't matter if it's a TLR or SLR, the procedure is essentially the same, one ensures correct calibration of the lens to film plane focus and adjusts the viewing system image to match.
When the camera features interchangeable lenses, it's a little more complicated because (if you're starting from scratch) it's necessary to first inspect and if necessary, adjust the lens register (lens mounting flange to film rail distance) until it meets the makers specification, but for the purposes of this discussion, we're assuming the camera body is OK and that the finder (RF; TLR viewing lens; SLR mirror/focus screen) are already returning acceptable results with other, known good lenses (because the thread starters comments imply that this is the case).
So starting from this point I'll be setting the lens involved until the infinity focus is as perfect as I can get it. I may be looking into the ground glass for half an hour with a loupe making painstakingly small adjustments. Once I've got this as good as I think I can get it it's time to check the finder. At this point one hopes the finder infinity match is very good also. If it's not it will raise the issue of the Eg the rangefinder possibly being out of calibration (although one hopes that if it has been working well with other lenses this should not be the case, it might be, though).
Assuming the finder infinity is very good with the lens at the stop a check at close range will be done between the ground glass and the finder. I like to do what I refer to as a "blind test". By that, I mean that I'll get the lens focus on the ground glass as sharp as I possibly can on a target five or six feet away and then I'll note the position of the lens distance scale with exacting precision. But I won't even look into the finder, at this point. Instead (without moving the camera at all, this is critical), I'll simply slowly adjust the lens until the finder is as sharp as I can possibly make it.
At this point I'll look to the position of the lens focusing scale. If the finder and lens really do agree beautifully and you've been careful enough, the distance scale measurement will agree absolutely with its setting created by focusing the ground glass. That's a blind test. It's the best way of critically cross checking lens against finder, because, with the best will in the world, if one goes back and forth between ground glass and finder, looking for a match, it's been my experience that your (my) eye will see what it wants to see, and minute deviations are much less likely to be spotted.
If the two focus checks actually return the same result your adjustments are likely to be very good indeed. On the other hand if there is a variation between them, every time I have experienced this I've found that my initial infinity adjustments were good but not nearly ideal.
So in summary I am not really disagreeing with you. I think focus calibration should be checked at a close distance, and I actually do this. But I begin with infinity and subsequently check close range and then (if necessary) revisit infinity and so on, until they are both very good.
It's a workflow I'm happy with because it has consistently provided a very high standard of accuracy using some basic tools. The problem with checking only the close focus match (or, indeed, infinity, for that matter) between lens and finder, is it may look pretty good (and yes, perhaps for a lot of users they may be satisfied with this). But without testing both the infinity and close focus calibration against each other you are unlikely to achieve the same degree of precision that you can be satisfied you will have, if you've adjusted things so that there is excellent, verified tracking, across the whole focusing range. You could say that checking each distance helps assess the accuracy of the calibrations made to the other. If they are not in harmony it's the infinity I'll tweak until the close is also good, and whenever I have had to do this, I have been able to attain a small but perceptible improvement in the sharpness of the infinity image.
This probably sounds like a bit of effort and, perhaps it is. It's just how I approach it, and I know that it works, and I am very fussy, Ie goddamn PITA fussy, about getting best calibration I possibly can. I do hope it (a) makes some sense and (b) is of some benefit, sorry for such a long post.
Erik van Straten
Veteran
Great piece, Brett. I agree for 100%.
I may add some practical things for Leica - screw and M - lenses only.
To check the focus of a Leica lens and its coupling to the rangefinder the best thing you can do is using a Leica M3. Of course, you must be sure that the rangefinder of the particular camera is as perfectly adjusted as possible. The M3 has the most sophisticated rangefinder of all Leicas.
For this test, it is necessary to remove the back door of the M3. This is very easy to do, just pull the small pin of the hinge of the door to the right. When the door is removed, put the baseplate back on and put the camera on a very solid tripod. Next, mount a wire release to the release button and turn the speed knob to "B". Open the shutter and lock the wire release so the shutter remains open.
I have a Visoflex III-house that I only use for testing lenses. It is easy to get the frosted glass out of it. In the middle of the glass a small circle is engraved. Now place this frosted glass with the frosted side inward on the film guide rails of the M3 and fix it with adhesive tape, taking care that the small circle is in the middle of the film gate.
Now put the lens on the camera. (Screw mount lenses need an adapter, of course.) and look on the frosted glass, in particular to the small engraved circle, with a very strong loupe, or through a 35mm lens. Now focus the lens that is mounted on the camera on a particular object as accurate as possible and when that is done, look through the viewfinder and the rangefinder spot of the M3. It should be perfectly focused on the object you've chosen.
If this is not the case, a lot of things can be wrong. This simple test will give you insight in the accuracy of the adjustments of your gear.
Erik.
I may add some practical things for Leica - screw and M - lenses only.
To check the focus of a Leica lens and its coupling to the rangefinder the best thing you can do is using a Leica M3. Of course, you must be sure that the rangefinder of the particular camera is as perfectly adjusted as possible. The M3 has the most sophisticated rangefinder of all Leicas.
For this test, it is necessary to remove the back door of the M3. This is very easy to do, just pull the small pin of the hinge of the door to the right. When the door is removed, put the baseplate back on and put the camera on a very solid tripod. Next, mount a wire release to the release button and turn the speed knob to "B". Open the shutter and lock the wire release so the shutter remains open.
I have a Visoflex III-house that I only use for testing lenses. It is easy to get the frosted glass out of it. In the middle of the glass a small circle is engraved. Now place this frosted glass with the frosted side inward on the film guide rails of the M3 and fix it with adhesive tape, taking care that the small circle is in the middle of the film gate.
Now put the lens on the camera. (Screw mount lenses need an adapter, of course.) and look on the frosted glass, in particular to the small engraved circle, with a very strong loupe, or through a 35mm lens. Now focus the lens that is mounted on the camera on a particular object as accurate as possible and when that is done, look through the viewfinder and the rangefinder spot of the M3. It should be perfectly focused on the object you've chosen.
If this is not the case, a lot of things can be wrong. This simple test will give you insight in the accuracy of the adjustments of your gear.
Erik.
retinax
Well-known
I totally agree, Brett, if you are actually able to adjust infinity and close range, of course you should check both. I was under the impression that the OP could at best do some shimming of the entire lens, so I thought this degree of sophistication was out of the question, and most likely no slope adjustment would be possible or needed anyway because the lens can hardly go out of spec that way. It would also require confidence that the camera's rangefinder was absolutely accurate for it to be worthwhile unless one would never use the lens on anything else, or for more confidence in the scale on the lens than I have, if one were to calibrate it to that.
If the slope of the rangefinder on the camera is out of spec, that is not so easy to adjust for the layman, would at least require a proven precisely focusing, long, fast lens. My understanding is that slope adjustments, whether body or lens, should be rarely needed unless one wants to match a Leica and Soviet lenses or something like that.
If the slope of the rangefinder on the camera is out of spec, that is not so easy to adjust for the layman, would at least require a proven precisely focusing, long, fast lens. My understanding is that slope adjustments, whether body or lens, should be rarely needed unless one wants to match a Leica and Soviet lenses or something like that.
yossi
Well-known
There are two optical cells in the Summar lens tube. HOW to move these cells slightly backward (so that the whole lens assembly is nearer to the film plane/sensor) is THE question.
Btw, any idea what are the three small screws on the lens tube for?
Yes, those are all excellent points, too. In the particular case of a rangefinder (one that's sophisticated enough to offer the adjustment) if I was unable to finally reconcile coincident focusing across the focus range, fine tuning the gain or "slope" would be a possibility if the indications were that the system needed it. Obviously this impacts all lenses used with it, so should only be done when one is absolutely certain it's warranted.
Cheers
Brett
What's the camera involved? And how many other lenses have been found to focus accurately across their whole focusing ranges?
I'm asking this to try and narrow down the exact source of the focus issue you've asked about. If a variety of lenses are all known to work well with the camera at all distances, this would make it very unlikely the cameras rangefinder itself requires adjustment.
Yes I realise that would bring us back to where you started this discussion, Ie. how to bring the Summar into line—but using a logical process of eliminating problem causes is always the best way to accurately verify what it is that needs to be corrected.
Does the lens feature any internal shims? There are two ways you can get the lens go focus further out without adjusting the focusing helicals—move the entire optical assembly closer to the film—or reduce the distance between the groups. Best done by moving the front cell or group closer to the film.
I'm still inclined to suggest a critical examination of the infinity image. If the lens front focuses at close range and you're sure the rangefinder accuracy is ideal I would expect the lens is not reaching infinity even if it appears to be reasonably sharp.
Erik van Straten
Veteran
The three small screws on the lens tube fix the position of the whole lens group, but not that of the front lens. The front lens can be removed - like a filter - if the small setscrew in the name ring is removed. This small setscrew is easily damaged, be carefull. The front lens is often very tight. Use a piece of rubber (innertube) or a flexiclamp to remove it, just unscrew it like a filter. The front glass of a Summar is VERY soft, it is easily scratched.
Erik.
yossi
Well-known
I have tested this Summar over three different cameras, viz. Leica IIIf, MP (with a Leitz adapter), and lastly, Monochrom v1. Same result. At min. distance, the sharp focus point is about 1 inch in front of the target. At infinity setting, the sharpest point is NOT infinity, but somewhere nearer (a number plate on a building some 50m away is tack sharp, but the trees beyond 1-2 km appear to be soft.) Given this result, I got a feeling that this lens would not focus accurately at any distance and that is a shame. The optics are clean and clear with coating intact.
On those three cameras, I have tested a few other standard lens (50 lux E46, 50 lux ASPH, another two summar lens) all focus accurately, near or far.
I am pretty sure this summar focusing is off and I would like to rectify it, DIY if possible. Else, I would probably send it to DAG or Kento Camera for focus adjustment but that would be long long wait and $$$. Thanks for all the general theories about focusing, but what I really need is the experience/knowledge from someone who have a similar problem with this vintage lens and managed to solve it.
Cheers.
On those three cameras, I have tested a few other standard lens (50 lux E46, 50 lux ASPH, another two summar lens) all focus accurately, near or far.
I am pretty sure this summar focusing is off and I would like to rectify it, DIY if possible. Else, I would probably send it to DAG or Kento Camera for focus adjustment but that would be long long wait and $$$. Thanks for all the general theories about focusing, but what I really need is the experience/knowledge from someone who have a similar problem with this vintage lens and managed to solve it.
Cheers.
yossi
Well-known
Thanks Erik. I am aware about the front lens and the small setscrew.
When you said the 3 screws fix the position of the whole lens group, does that mean the position may be shifted by adjusting three 3 screws?
Erik van Straten
Veteran
I don't think this is a DIY-job. The elements must be repositioned.
Maybe the lens was in the past adapted to another camera. If the lens is coated, it was surely updated in the fifties as original Summars are not coated. A coated Summar in good condition is a wonderful lens. I would give it to a professional repairman to have it readjusted.
Erik.
Maybe the lens was in the past adapted to another camera. If the lens is coated, it was surely updated in the fifties as original Summars are not coated. A coated Summar in good condition is a wonderful lens. I would give it to a professional repairman to have it readjusted.
Erik.
Erik van Straten
Veteran
Most probably yes, but it is strange that the lens is not correct. Maybe it is tampered with. To reposition the lens elements is not a DIY-job.
The three small screws go into holes to hold the elements in position. But it is also possible that the front lens is not in the correct position. That can be the cause of your problem. It can also be that the front lens originally belongs to another lens.
Erik.
Erik,
the 5cm Summar is one of the very few Leitz lenses I have worked on, but it was years ago, so I have forgotten most of the details (although, I note for the benefit of certain others reading this that it was working correctly and focusing accurately, when I put it back together).
But according to the thread starter's comments in post 15, it sounds as though the lens is indeed front focusing across the entire range of focus. Do you think it is possible, with this lens, that someone who previously dismantled it has thrown the optics too far out by incorrectly re-assembling the helical starts? I don't know, (and the thread starter has not deigned to bless the rest of us idiots who have been trying our best to assist him with "general theories", with any images of this lens that he has apparently previously dismantled himself).
Cheers,
Brett
Erik van Straten
Veteran
I think so, but then it would be impossible to align the engraved infinity mark with the engraved index! And the three (sometimes five) big screws on the bottom of the helicoid could not be replaced either.
An interesting small book (and a great help) on cleaning the old lenses from Leitz is written by Kuramochi Noboyuki (Nobbysparrow) from Japan and is available on eBay in the English language: "How to clean old Leica lenses and accessories". Recommended!
Erik.