stunsworth Posted February 14, 2010 Share #141 Posted February 14, 2010 Advertisement (gone after registration) 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. Olsen, I'm missing something here. Are you saying that it's impossible to focus any wide open fast lens accurately as they all front focus? Link to post Share on other sites More sharing options...
Advertisement Posted February 14, 2010 Posted February 14, 2010 Hi stunsworth, Take a look here Rangefinderproblems on new M9s. I'm sure you'll find what you were looking for!
Olsen Posted February 14, 2010 Share #142 Posted February 14, 2010 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. Wilson Exactly! This is how Leica (I am sure, Canon, Nikon etc. etc) will tune just any lens! And it will produce a slight front focus at full aperture on 'extreme' lenses like Noctilux etc. - with a widening DOF which centre travels backwards when stopped down. My Noctilux is tuned the same way. - Not that it makes this lens any easier to focus! But you know how it behaves. Link to post Share on other sites More sharing options...
Olsen Posted February 14, 2010 Share #143 Posted February 14, 2010 Olsen, I'm missing something here. Are you saying that it's impossible to focus any wide open fast lens accurately as they all front focus? Yess! - Or at least; very difficult. - Try for yourself with lenses producing a DOF of only 2 cm at 2 meters..... - With a DOF shift of 1,2 cm (or something like that). Link to post Share on other sites More sharing options...
jaapv Posted February 14, 2010 Share #144 Posted February 14, 2010 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.Yes, but if they had no sperical aberration they would not have focus shift. Link to post Share on other sites More sharing options...
lct Posted February 14, 2010 Share #145 Posted February 14, 2010 Yess! - Or at least; very difficult. - Try for yourself with lenses producing a DOF of only 2 cm at 2 meters... Most photogs have been doing this for decades, Olsen. One centimeter DoF here. No problem at all with a mere D70 (Nikkor 180/2.8, f/2.8 @ 2 meters). Link to post Share on other sites More sharing options...
wlaidlaw Posted February 14, 2010 Share #146 Posted February 14, 2010 Exactly! This is how Leica (I am sure, Canon, Nikon etc. etc) will tune just any lens! . Maybe that is how Leica should tune any fast lens with spherical aberration/significant aperture shift and it may be the case now that they have their computerised dual slit optical bench working pretty well. It certainly was not the case until recently. If a lens was not focusing correctly, it was nearly always a back focus error. I would put this down to the rather primitive projection technique they used to use for focus checking. I suspect but I would guess we will never know for certain, unless there is an internal whistleblower, that front focus errors were easier to spot with the old system. Complaints about new lenses being miles off seem to have dropped to near zero since the computerised optical bench was in operation. Of the 7 non-Visoflex Leica lenses I have, only the 35 Summilux front focuses and then only by a tiny amount, well within the DOF wide open. I am lucky that in the spectrum of aperture shifts of the 35 ASPH Luxes, mine seems to be about as good as they get and focusing correctly is never a problem with it, on M4, 8 or 9. I have posted photos of aperture shift test charts on this forum in the past to prove to sceptics, that really accurate focusing 35 Luxes do exist. I do agree with you that focusing a Nocti accurately wide open in its natural environment of low light, is very difficult and for older guys like me, next to impossible. If I was a right eyed shooter, it would be wholly impossible as my right eye is not nearly as good as my left. That is why for me personally, I would be very happy to see an optional electronic focus confirmation on the M10 (see 1,267 other threads). Wilson Link to post Share on other sites More sharing options...
ArtZ Posted February 14, 2010 Share #147 Posted February 14, 2010 Advertisement (gone after registration) My Noctilux returned from service/coding, back focusing by 2 meters at 10 meters Wilson, I think I'm very happy with my Nokton 50/1.1 :D (Picture taken this morning with the screen of my laptop at 45º and the camera at 1m) 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=1225735'>More sharing options...
wlaidlaw Posted February 14, 2010 Share #148 Posted February 14, 2010 Wilson, I think I'm very happy with my Nokton 50/1.1 :D (Picture taken this morning with the screen of my laptop at 45º and the camera at 1m) Manuel, I will buy it from you when you get bored with it ;-]] Wilson Link to post Share on other sites More sharing options...
Guest mc_k Posted February 15, 2010 Share #149 Posted February 15, 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 I find some of this confused. Note, a few people do use "front" and "back" in this context in the opposite sense, and maybe "near" and "far" are preferable. If the intended focus point was at 1m distance, and the plane of best focus turns out to be at 1.01m, we can say there is 1cm "back" focus. If we stop down without refocusing and the plane of best focus is now at 1.04m, the focus has shifted ("backwards") 3cm. The depth-of-field surrounds the actual plane of best focus, not the intended focus point--which I think you confused. The rule of thumb mentioned is 1/3 of the DOF in front of the plane of best focus, and 2/3 in the back, not the other way around. See for example Adams, The Camera, Ch. 5...and note I have used "front" in the same sense as he has. This rule of thumb is inadequate for focus testing. Link to post Share on other sites More sharing options...
jaapv Posted February 15, 2010 Share #150 Posted February 15, 2010 The 1/3rd-2/3rd rule applies at close focussing distances only. Once you are at say 3m on a 50 mm lens, it is more like 50/50. Link to post Share on other sites More sharing options...
elansprint72 Posted February 15, 2010 Share #151 Posted February 15, 2010 Nikon D700. nuff said. Link to post Share on other sites More sharing options...
Guest mc_k Posted February 15, 2010 Share #152 Posted February 15, 2010 ...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.... agree, but it is easier to talk about back and front focus in terms of, say, the image of a ruler that we photographed, and there is a one-to-one correspondence. Link to post Share on other sites More sharing options...
jaapv Posted February 15, 2010 Share #153 Posted February 15, 2010 Nikon D700. nuff said.You mean Nikon has found a way to make their cameras immune to the laws of optics ?? Link to post Share on other sites More sharing options...
jaapv Posted February 15, 2010 Share #154 Posted February 15, 2010 Thanks. I happily stand corrected. It only helps to show this "rule" is not valid. Link to post Share on other sites More sharing options...
Guest mc_k Posted February 15, 2010 Share #155 Posted February 15, 2010 Thanks. I happily stand corrected. It only helps to show this "rule" is not valid. sorry, I removed a previous post stating the 50mm at f/1.4, 0.7m will give about a 49 : 51 split of the DOF. ADDITION: stopping down to f/16 will still not give 1/3 : 2/3 Link to post Share on other sites More sharing options...
Guest mc_k Posted February 15, 2010 Share #156 Posted February 15, 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!.. can't comment on your findings from lack of experience, but I liked your report. Experiments and criticism are the lifeblood of the forum. Thanks for posting. Link to post Share on other sites More sharing options...
cliffp Posted February 19, 2010 Share #157 Posted February 19, 2010 Just a reminder of my previous situation plus an update: I have an M9 which had a focusing error of 2cm with a 90mm cron and 1cm error with a 50mm cron (in both cases technically backfocusing in that the point of sharp focus is IN FRONT of the target). I sent the camera and three lenses (50mm, 90mm and 28mm) off to Solms and got them back after 8 days. The 50mm is now perfect. A 35mm arit which I acquired a couple of days ago is fine but the 90mm is still out by 1cm (in the same direction as before). I haven't tested the 28mm yet. I think the guys at Solms adjusted the M9 and took a punt on everything else being ok. It looks like the 90mm will have to go back (its brand new by the way) Link to post Share on other sites More sharing options...
ArtZ Posted February 19, 2010 Share #158 Posted February 19, 2010 Just a reminder of my previous situation plus an update: I have an M9 which had a focusing error of 2cm with a 90mm cron and 1cm error with a 50mm cron (in both cases technically backfocusing in that the point of sharp focus is IN FRONT of the target). I sent the camera and three lenses (50mm, 90mm and 28mm) off to Solms and got them back after 8 days. The 50mm is now perfect. A 35mm arit which I acquired a couple of days ago is fine but the 90mm is still out by 1cm (in the same direction as before). I haven't tested the 28mm yet. I think the guys at Solms adjusted the M9 and took a punt on everything else being ok. It looks like the 90mm will have to go back (its brand new by the way) Cliff, I wouldn't sent it back. 1 cm is ok. Really. Try it in normal situation and you'll see it's fine. Regards, ArtZ Link to post Share on other sites More sharing options...
cliffp Posted February 19, 2010 Share #159 Posted February 19, 2010 By normal situation, presumably you don't mean at f2. I have taken a few shots at f2 of flowers etc and they have been out of focus. I know that at around 1m the dof is +/- 1cm but with the inevitable focusing error (human error, poor eyesight etc) it is easy to get the subject outside the zone where things are acceptably sharp. Maybe I shouldn't expect to use f2 at close range? Link to post Share on other sites More sharing options...
wattsy Posted February 19, 2010 Share #160 Posted February 19, 2010 A 35mm arit WTF is an "arit"? Link to post Share on other sites More sharing options...
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