Julian Thompson Posted February 13, 2010 Share #121 Posted February 13, 2010 Advertisement (gone after registration) That makes sense - quite possibly - there is certainly a washer of some sort. About this *significant* focus shift when you stop down theory; even if you do believe that lenses do this (I don't personally) - surely you would be better with your camera set to be sharp when your DOF is at its shallowest, and then accept any focus shift on the smaller apertures when you have more margin for error? We just can't accept having to focus using the patch, then 'compensate' for something on top of this ! Link to post Share on other sites More sharing options...
Advertisement Posted February 13, 2010 Posted February 13, 2010 Hi Julian Thompson, Take a look here Rangefinderproblems on new M9s. I'm sure you'll find what you were looking for!
jaapv Posted February 13, 2010 Share #122 Posted February 13, 2010 It is not a belief - it is a fact caused by not fully corrected aberrations. Link to post Share on other sites More sharing options...
Olsen Posted February 13, 2010 Share #123 Posted February 13, 2010 That makes sense - quite possibly - there is certainly a washer of some sort. About this *significant* focus shift when you stop down theory; even if you do believe that lenses do this (I don't personally) - surely you would be better with your camera set to be sharp when your DOF is at its shallowest, and then accept any focus shift on the smaller apertures when you have more margin for error? We just can't accept having to focus using the patch, then 'compensate' for something on top of this ! It is not a theory. It's a physical law! I would warn just anyone here from fumbling with the rangefinder mechanism of their M9s without understanding this and having needed optical adjustment tools. Trust that Leica make their rangefinder mechanisms right 99,99% of the time. Rather, have your eyesight checked. Julian, If you have adjusted your M9 to the largest aperture set. See to that it visits Solms before you send it out on the 2.hand market... Link to post Share on other sites More sharing options...
Julian Thompson Posted February 13, 2010 Share #124 Posted February 13, 2010 Well I can adjust it any way I like - I don't need to send it away! I can set it to backfocus, frontfocus - howeverfocus you like! But I like it as it is If I sell it to you I'll be sure to make it front focus it's head off before I pass it over yes ? Link to post Share on other sites More sharing options...
Julian Thompson Posted February 13, 2010 Share #125 Posted February 13, 2010 Actually no - hang on I'll bite on that because it's clear you want to discredit my hard work here and make it sound like the fact I've loosened a screw and turned a cam a few degrees makes my camera some kind of leper! I I've just shot a couple of images - F2, F4, F8. There is no noticable focus shift at all that I can see that would require correction on my behalf. I've just got more tolerence on the smaller aperture - obviously. That means that regardless of the aperture set I still focus my M9 the same. I don't say 'ah well I'm stopped down so I best align the rangefinder' or 'ah I'm wide open, best backfocus on purpose' - and I'd be very surprised if anyone else is doing this either. Link to post Share on other sites More sharing options...
wlaidlaw Posted February 13, 2010 Share #126 Posted February 13, 2010 Sorry if this seems to be teaching grandmother to suck eggs but I still sometimes feel people are confusing back and front focus, with back and front DOF. The back and front focus refer to where the image is generated inside the camera. In other words, is the sharp image generated in front of the imaging medium = front focus or behind the imaging medium = back focus. If a lens is back focusing, the DOF will lie in front of the focus point and similarly, if a lens is front focusing, the DOF will lie behind the focus point. If a lens has a tendency to aperture shift then the back focus increases as you close the lens diaphragm down. Again this means that the point of sharpest focus moves forward. The well recognised "cure" for this is to set up the lens, so that with it wide open, you have some front focus. Commonly this will result in the focus fields being split 50% behind the focus point and 50% in front. 35% in front and 65% behind for a lens with severe aperture shift is acceptable. Then as you stop the lens down, the DOF will change towards the theoretically correct 2/3rds in front and 1/3 behind the focus point. If you focus correctly on the focus point, it should always be in focus, irrespective of the aperture. Apologies if I am stating the obvious but some of the posts on this thread seemed to indicate some confusion. The above comes from one of my lectures to students on lens optics. Wilson Link to post Share on other sites More sharing options...
Julian Thompson Posted February 13, 2010 Share #127 Posted February 13, 2010 Advertisement (gone after registration) If you focus correctly on the focus point, it should always be in focus, irrespective of the aperture. Right - thanks Wilson - well, in that case both Cliff's M9 and mine were not right ! In honesty though, I'm not suggesting everyone go out there and adjust their own camera. But I do think it's easy to get 'baffled with nonsense' sometimes and to create an 'aura' around things that intrinsically are very simple. At the end of the day you can adjust a rangefinder with whatever computerised optical monster that you like but it's YOUR hand/ eye that is going to focus it! I guess this is what drives me to want to learn more and I admit to gaining pleasure from learning to overcome such challenges myself. I don't know why I posted my findings up because I knew they would meet with scepticism and disapproval which I knew I would find hard to take after I'd become proficient at it and genuinely knew I had it licked! I guess this was why Carsten never took the time to post up his findings after he had successfully adjusted his M8. But I guess I was self congratulating myself somewhat which is always makes for a flawed viewpoint! (I do point out that during this process I have worn my heart on my sleeve and shown my learning curve in public so would ask for that to be taken into account before you criticise too much. Nothing is impossible to learn, you know.) I do, however, hope that my work here helps someone at some point. Best of wishes, Julian Link to post Share on other sites More sharing options...
ArtZ Posted February 13, 2010 Share #128 Posted February 13, 2010 Manuel, Thanks for showing that. It confirms to me that unless the mal-adjustment is as simple as the infinity roller having moved, it is much better to leave adjustment to be done with with the proper test rig and tools. Otherwise it is like trying to solve an equation with three variables, when you only have two formulas. I assume with the proper test rig, you adjust sequentially, rather than having to hunt backwards and forwards, as each adjustment alters the other two settings. Wilson Wilson, I fully agree. There's a fourth variable: whether the lens is properly adjusted or not. Two of my lenses (Summicron-M 28 ASPH and 90 APO ASPH) had to be re-adjusted by Leica for different reasons I explaind before. So, as I said to Cliff, you don't know always if the problem comes from the camera or the lens(es) or both. It's interesting to know how the system works (educational) but I still think having focus adjusted by a qualified technician is highly recommended Besides I partly disagree with Julian: The eliptical stop at C I have not touched but it determines the end stop for the pivot as the cam goes into the body. This is relevent only where the roller cam lever hits the stop as it goes INTO the camera body. The thin twisted bit of metal under the pink arrow (ie the stop in reverse) that bottoms onto the back of C is just there to hold the roller inside the body when no lens is present and does not perform any adjustment function. C is the least important setting and I can not forsee this ever needing adjustment as I stand right now. Of course, I'm not going to play with the screws in my cameras because both are spot on but... I made a test! Moving © it DOES change focus settings. When the tiny twisted lever moves counterclockwise (to the left), it cures front focus; when it moves clockwise (to the right), it cures back focus. Here's the test: I have come to this conclusion just putting a very small stripe of sellotape between the lever and ©, which it has the same effect than turning © counterclockwise because it has an elliptical shape that moves the lever to the left. Sellotape is not very thick but it produced a front focus of a few centimeters and infinite had also changed! As soon as I removed it, my cameras were again spot on. Once more, as © has an elliptical shape, the front focus (with sellotape) was different in each camera because © adjustment is also different for each camera. I know, it's not very easy to explain and, probably, not very easy to understand me. Sorry. In fact, I'm 100% sure now with the cam wheel ( you adjust infinity with and with © close focus and as you said, Julian, once you have adjusted close focus you have to adjust again infinity. This brings me back when I told you that (A) has not been adjusted by Leica in my cameras. You said: 'You don't have to leave traces of 'touching' screw A to adjust it' but I can see traces your picture while in my cameras (A) has not mark at all. As the screwdriver can not be aligned at 90º with (A) because to the lens mount, you may need a special tool if you don't want to leave traces. I can understand you can get good results adjusting (A) because when you say: 'So you need to shorten the arm by loosening (A) and twisting the cam slightly anti-clockwise. (If you have backfocus then it's obviously the inverse and you need to go clockwise to lengthen the arm and reduce your focus throw)' in fact you are changing the position of the twisted lever to the left (as if you had adjusted © counterclockwise), but I think you cannot cure back focus because you cannot change the position of the twisted lever to the right. Do you follow me? PS: Wilson, this was a way to keep myself busy in the countryside in a freezing cold and gray day of winter Link to post Share on other sites More sharing options...
Julian Thompson Posted February 13, 2010 Share #129 Posted February 13, 2010 This isn't correct Art - you are wrong. If you set your lens to infinity, look through the viewfinder and at the same time attach your lens... ... what happens? The roller cam is pushed BACKWARDS AWAY from that twisted front stop! It has ABSOLUTELY nothing to do with the infinity setting whatsoever!!!! And - I can understand you can get good results adjusting (A) because when you say: 'So you need to shorten the arm by loosening (A) and twisting the cam slightly anti-clockwise. (If you have backfocus then it's obviously the inverse and you need to go clockwise to lengthen the arm and reduce your focus throw)' in fact you are changing the position of the twisted lever to the left (as if you had adjusted © counterclockwise), but I think you cannot cure back focus because you cannot change the position of the twisted lever to the right. Do you follow me? No - the twisted lever does NOT move when the arm changes length. It stays static! Link to post Share on other sites More sharing options...
Julian Thompson Posted February 13, 2010 Share #130 Posted February 13, 2010 PS I do respect you trying to work this through Art but remember I've actually succeeded here and done the adjustment on a live camera - I don't have to make experiments or guess. I've seen it for real! You've not actually done it, so it's much, much harder for you to visualise what happens. Link to post Share on other sites More sharing options...
Julian Thompson Posted February 13, 2010 Share #131 Posted February 13, 2010 Maybe this will help visualise the action of changing the length of the arm. The dotted line is the real focus of the lens as it is rotated in terms of the actual image. The two solid lines are a rangefinder window which has an arm too short and then one which is too long. Both assume that the infinity point has been set, so that the graphs can 'start' from the same point. but you can see that the aim of the game is to get the arm just the right length so that the movement of the rangefinder window perfectly mimics the real world focus of the lens thread as it is twisted. Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/111791-rangefinderproblems-on-new-m9s/?do=findComment&comment=1224816'>More sharing options...
ArtZ Posted February 14, 2010 Share #132 Posted February 14, 2010 This isn't correct Art - you are wrong. If you set your lens to infinity, look through the viewfinder and at the same time attach your lens... ... what happens? The roller cam is pushed BACKWARDS AWAY from that twisted front stop! It has ABSOLUTELY nothing to do with the infinity setting whatsoever!!!! And - No - the twisted lever does NOT move when the arm changes length. It stays static! Julian, I don't understand what you mean when you say. '... what happens? The roller cam is pushed BACKWARDS AWAY from that twisted front stop! It has ABSOLUTELY nothing to do with the infinity setting whatsoever!!!!' Maybe I didn't explain it properly or you misunderstood me. English is not my first language I´ll try again in another way If you push it with a pencil or a screwdriver the twisted lever to the left, the roller cam goes backwards (inside) and when you push the roller cam, the twisted lever moves to the left getting away from © Now, we both agree ( sets infinity focus accuracy. I say © sets closest focusing distance accuracy. Of course, © has nothing to do with focus at infinty but when you adjust © counterclockwise, the roller cam goes backwards (inside) as when you push it with the pencil. So if you adjust ©, you need to re-adjust focus at infinity afterwards. The roller cam shouldn't move when you insert a lens set at the closest focusing distance (0.7m or 1m, depending on the lens) and the twisted lever shall touch ©. As soon as you increase the focus distance in the lens, the roller cam goes backward and the twisted lever goes to the left. Now, it doesn't touch © anymore. I invite you to put some scotch tape between the twisted lever (stick it to the lever) and ©. Check closest focus of the a lens and you will find front focus. This shows you that © defines/sets accurate focus at closest distance of the lens as ( defines/sets accurate focus at infinity. What I'm thinking now is that (A) probably defines/set focus at intermediate distances. I remember after the framelines and LCD upgrade, I discovered during holidays in Costa Rica, ALL my lenses suffered of front focus (about 6 cm) at 0.7 / 1 m and f/2 BUT most of them were OK at other distances except the Summicron-M 90 APO ASPH and MATE at 50mm. Before the upgrade, I didn't have this issue. I'm persuaded adjusting the ragefinder should be done for qualified personal only. Besides, using screedrivers for playing with (A), ( and © can cause serious damage to the camera (shutter, sensor and other damages) in case of user error... so better if the user is a Leica technician! Link to post Share on other sites More sharing options...
carstenw Posted February 14, 2010 Share #133 Posted February 14, 2010 I don't know why I posted my findings up because I knew they would meet with scepticism and disapproval which I knew I would find hard to take after I'd become proficient at it and genuinely knew I had it licked! I guess this was why Carsten never took the time to post up his findings after he had successfully adjusted his M8. First of all: congratulations on having done this. It is not a hard thing to do, but it is a very hard thing to get oneself to do it on such an expensive camera! And congratulations for reporting on it in such an in-depth fashion, much better than my hand-waving description. I did actually post my findings, and I would always recommend that everyone who does something neat and interesting like this should post their findings, and ignore the skeptics. If we always listened to the skeptics, there would be no USA or Canada. My original thread was here: http://www.l-camera-forum.com/leica-forum/leica-m8-forum/20134-leica-red-dot.html and the post where I reported success is here (for the vertical adjustment, which is now hard/impossible to move, since Leica has started applying a little black paint over the adjustment apparatus when adjusted): http://www.l-camera-forum.com/leica-forum/leica-m8-forum/20134-leica-red-dot-2.html#post213453 and for the near/far adjustment: http://www.l-camera-forum.com/leica-forum/leica-m8-forum/20134-leica-red-dot-5.html#post214167 Link to post Share on other sites More sharing options...
Julian Thompson Posted February 14, 2010 Share #134 Posted February 14, 2010 Hi Carsten :-) :-)) ArtZ - I invite you to put some scotch tape between the twisted lever (stick it to the lever) and ©. Check closest focus of the a lens and you will find front focus. Yes, you will I agree fully - but not for the reason you mistakenly think! It is because rather than allowing the piece of metal to come close to the end stop (which it does at front focussed position) you will hit the tape! In the scheme of rangefinder adjustment the thickness of tape is a lot. Try this to show what I mean: Set your lens to closest focus, look through the viewfinder and then attach the lens as you look. As you do so you will notice that the rangefinder window moves only very, very fractionally as the roller takes up the lens track and moves away from its stored position where the twisted metal sits on the back of that stop. When you try it with your piece of tape your roller is not actually touching the lens until you have started to focus, so as you do the experiment above when you attach the lens you won't see the rangefinder window move at all. So in summary - C does nothing once the lens is attached to set front focussing. Link to post Share on other sites More sharing options...
Julian Thompson Posted February 14, 2010 Share #135 Posted February 14, 2010 Artz I know how to nail this for you so you get it. You follow that the roller cam sets infinity. So think about the fact that the lens thread is a fixed pitch. That means that no matter how far you twist the lens, as long as infinity is right and the GEARING is right as per my graph you do not need a 'close' adjustment (moreover you can't have one as the lens thread is FIXED!) - but you do need the close 'stop' to stop the roller mechanically hitting something when the lens is removed. The distance between lens on, max close focus and lens off, metal on stop is less than the thickness of your tape - does that do it for you? Link to post Share on other sites More sharing options...
Julian Thompson Posted February 14, 2010 Share #136 Posted February 14, 2010 PS esides, using screedrivers for playing with (A), ( and © can cause serious damage to the camera (shutter, sensor and other damages) in case of user error... so better if the user is a Leica technician! Yes, but so can banging your camera against a wall, dropping it in a stream or knocking it on the floor - but you don't stop using it do you ? You've just got to have 'due dilligence' - you don't let yourself off that lightly!!:D:D Link to post Share on other sites More sharing options...
Olsen Posted February 14, 2010 Share #137 Posted February 14, 2010 Sorry if this seems to be teaching grandmother to suck eggs but I still sometimes feel people are confusing back and front focus, with back and front DOF. The back and front focus refer to where the image is generated inside the camera. In other words, is the sharp image generated in front of the imaging medium = front focus or behind the imaging medium = back focus. If a lens is back focusing, the DOF will lie in front of the focus point and similarly, if a lens is front focusing, the DOF will lie behind the focus point. If a lens has a tendency to aperture shift then the back focus increases as you close the lens diaphragm down. Again this means that the point of sharpest focus moves forward. The well recognised "cure" for this is to set up the lens, so that with it wide open, you have some front focus. Commonly this will result in the focus fields being split 50% behind the focus point and 50% in front. 35% in front and 65% behind for a lens with severe aperture shift is acceptable. Then as you stop the lens down, the DOF will change towards the theoretically correct 2/3rds in front and 1/3 behind the focus point. If you focus correctly on the focus point, it should always be in focus, irrespective of the aperture. Apologies if I am stating the obvious but some of the posts on this thread seemed to indicate some confusion. The above comes from one of my lectures to students on lens optics. Wilson Wilson, All lenses front focuses at full aperture! Those with a large aperture shifts more than those with a small aperture. It's not just a tendency. With extreme lenses, like the Noctilux 50 mm 0,95 -. or the old Canon 50 mm 1,0 - and the Cron 90 mm 2,0 (and a range other lenses...) this front shift is VERY noticeable. It is more than one cm - closer to two cm with my old Noctilux 50 mm 0,1. When you stop down just a click or two, the DOF widens and moves backwards, and covers over any mistakes the photographer might have done. This is quite normal and due to natural forces that Leica (Canon, Nikon etc etc) cannot fight. With these extreme lenses with aperture of 1,4 or larger, this front focus shift is 'about' 1,5 - 2 cm at 2 meters distance. It is smaller at longer distances, larger at shorter. When stopped down the shift movement stabilises at a center. At this center Leica would tune these lenses at. Thus, a slight front focus shift is 'normal' at full aperture. Look up this picture of Chalres Dickens.http://upload.wikimedia.org/wikipedia/commons/a/aa/Dickens_Gurney_head.jpg I was not present in the studio; it was taken some 120 years ago. But I think I know why the centre of DOF has landed farther back than what the photographer might have intended. The photographer has focused on the ground glass at full aperture. Then he has put in the 'film' glass plate in and stopped down a click or two, and exposed, - and the centre of DOF has moved backwards - and Charles Dicken's nose is outside the DOF. - Well, it is just my theory on why his nose is not sharp. But this could well be the result of a focus shift. The result will look like this. Are you all using a magnifier when focusing with these challanging lenses? I use a 1,4 magnifier with my Noctilux. Even then it is a challenge close to the impossible to focus. Link to post Share on other sites More sharing options...
carstenw Posted February 14, 2010 Share #138 Posted February 14, 2010 All lenses front focuses at full aperture! As far as I understand it, only if they have uncorrected spherical aberration. Link to post Share on other sites More sharing options...
wlaidlaw Posted February 14, 2010 Share #139 Posted February 14, 2010 Olsen, Sorry to contradict you but I am afraid you are incorrect in a number of ways. Few new Leica lenses front focus at full aperture as they come out of the factory. Leica's recent practice seems to be to set lenses (adjusted in two ways by the shim behind the mount, which alters both the position of the lens cell and the rangefinder cam and by adjusting the position of the lens cell relative to the rangefinder cam inside the the lens body) to either "natural focus" = DOF 1/3 behind focus point 2/3 in front or else in varying degrees of back focus. It reached the point about three years ago when we wondered if the lens focus department was being run by Mr. Magoo. Lenses were coming out with massive back focus. My Noctilux returned from service/coding, back focusing by 2 meters at 10 meters; my new 75 Summarit was so bad I asked for and was given a replacement. The degree of back/front/nil focus error is a choice made at the time the lens is built/adjusted and can be changed or adjusted subsequently. An appreciable number of forum members have had their 35 ASPH Summiluxes adjusted from natural or back focusing wide open, to slight front focus. That is how my 35 ASPH Lux is. Aperture shift on a modern lens shifts the external focus point forwards i.e. increases the BACK focus see article in LFI on the 35 Summilux - I can't tell you which edition, as all my back copies of LFI are in my French house but ? late 2007 early 2008. Thus if you have a lens set up with "static" front focus wide open, then the effect of aperture shift is to improve the focus. Wilson Link to post Share on other sites More sharing options...
Olsen Posted February 14, 2010 Share #140 Posted February 14, 2010 As far as I understand it, only if they have uncorrected spherical aberration. Sure, but then they have a relatively small max aperture. Then this focus shift is so small that it is not recognisable. It is the 'hefty' lenses with a very large max aperture that the focus shift is noticeable. Link to post Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.