biglouis Posted December 4, 2007 Share #1 Posted December 4, 2007 Advertisement (gone after registration) OK, what is backfocus? How would I know a lens exhibits it? Can you still have it if you hyperfocally set depth of field? I only ask because it keeps on coming up in the forum and I feel either I'm the only person in the world who does not suffer from it, or alternatively I don't recognise it in my pictures. LouisB Link to post Share on other sites More sharing options...
Advertisement Posted December 4, 2007 Posted December 4, 2007 Hi biglouis, Take a look here Backfocus. I'm sure you'll find what you were looking for!
mgcd Posted December 4, 2007 Share #2 Posted December 4, 2007 OK, what is backfocus? How would I know a lens exhibits it? Can you still have it if you hyperfocally set depth of field? I only ask because it keeps on coming up in the forum and I feel either I'm the only person in the world who does not suffer from it, or alternatively I don't recognise it in my pictures. LouisB I have NO idea what it refers to either, I guess I've never been hit by it, whatever it is. Cheers, Link to post Share on other sites More sharing options...
xjr Posted December 4, 2007 Share #3 Posted December 4, 2007 I think this a .....digital disease and has to do with the sensor of the camera or so they tell me. Link to post Share on other sites More sharing options...
rob_x2004 Posted December 5, 2007 Share #4 Posted December 5, 2007 It comes from using a smelly old raincoats and hipshots, Louis. Link to post Share on other sites More sharing options...
imported_peter_m Posted December 5, 2007 Share #5 Posted December 5, 2007 Smelly Raincoats can't be it..... got one... using it..... I don't think I have a backfocus problem. But then I am about as wise as all of you in this regard. One theory I have is..... must be something you get if you shoot to many test charts Peter Link to post Share on other sites More sharing options...
farnz Posted December 5, 2007 Share #6 Posted December 5, 2007 Isn't it what you have when you get chronic back pain? Pete. Link to post Share on other sites More sharing options...
zapp Posted December 5, 2007 Share #7 Posted December 5, 2007 Advertisement (gone after registration) OK, what is backfocus? How would I know a lens exhibits it? Can you still have it if you hyperfocally set depth of field? I only ask because it keeps on coming up in the forum and I feel either I'm the only person in the world who does not suffer from it, or alternatively I don't recognise it in my pictures. LouisB Plane of optimum image sharpness and sensor plane may not fall in the same place for all apertures of a lens. In such case the plane of optimum sharpness may be in front or behind the sensor. 1/10 mm makes a huge difference here and using hyeprfocal distance may not always solve the problem. Check image sharpness after you took the shot in your digital camera. While some people say the effect is more visible in digital images, backfocus has the same influence on digital as on film. Since digital images are more demanding for image sharpness (half a pixel can be seen = 0.005 mm while for analog we assume a circle of confusion of 0.030 mm). Well, now you should ask what plane of optimum sharpness means and why it moves, ... In practise, make sure what the effect means, how you can check on it (double check digital image ), and understand that old lenses were not designed to minimize backfocus enough for the digital era. Link to post Share on other sites More sharing options...
jaapv Posted December 5, 2007 Share #8 Posted December 5, 2007 Plane of optimum image sharpness and sensor plane may not fall in the same place for all apertures of a lens. In such case the plane of optimum sharpness may be in front or behind the sensor. 1/10 mm makes a huge difference here and using hyeprfocal distance may not always solve the problem. Check image sharpness after you took the shot in your digital camera. While some people say the effect is more visible in digital images, backfocus has the same influence on digital as on film. Since digital images are more demanding for image sharpness (half a pixel can be seen = 0.005 mm while for analog we assume a circle of confusion of 0.030 mm).Well, now you should ask what plane of optimum sharpness means and why it moves, ... In practise, make sure what the effect means, how you can check on it (double check digital image ), and understand that old lenses were not designed to minimize backfocus enough for the digital era. Hehe, that ain't backfocus, that's focus shift. Backfocus is the plane of focus of the lens falling behind the film/sensor surface at all or most apertures. Link to post Share on other sites More sharing options...
zapp Posted December 5, 2007 Share #9 Posted December 5, 2007 Hehe, that ain't backfocus, that's focus shift.Backfocus is the plane of focus of the lens falling behind the film/sensor surface at all or most apertures. I admit that the answer is basically discussing focus shift, but actually it is much closer than the nonsense said before and HEHE I am only talking focus shift that results in backfocus, so nothing wrong. We should just add that backfocus is typically based on a misalignment of the lens sensor distance. Again 1/10mm or 1/100mm make a difference here. Nice camera manufacturers will provide you with a shim kit others require you to adjust focus or send in the camera for adjustment of MF or AF focusing system. Link to post Share on other sites More sharing options...
jaapv Posted December 5, 2007 Share #10 Posted December 5, 2007 Well, on rangefinders it is rangefinder adjustment that is out, on SLR''s it usually is the matte screen and on DSLR's indeed as you say, the lens/sensor distance. Link to post Share on other sites More sharing options...
wizard Posted December 5, 2007 Share #11 Posted December 5, 2007 Well, on rangefinders it is rangefinder adjustment that is out, on SLR''s it usually is the matte screen and on DSLR's indeed as you say, the lens/sensor distance. No, backfocus has NOTHING to do with rangefinder adjustment. Instead, backfocus relates to an incorrect lens/sensor or lens/film distance. Of course, rangefinders may be incorrectly adjusted, too, and the result will be unsharp pictures, but the cause is a different one. Cheers, Andy Link to post Share on other sites More sharing options...
bobtodrick Posted December 5, 2007 Share #12 Posted December 5, 2007 Backfocus seems such a common problem now, and is especially troublesome for those who experience it and yet their camera checks out okay. Here's a plausible reason relayed by our local Nikon rep. Film emulsion had 'depth'...enough so that the light rays could be slightly 'off' yet you still got sharpness. Not so with sensors...the recording medium is all on the very surface of the sensor...no depth. Here's what they (Nikon) found when people complain about backfocus. Often it is with portraits...or something where the subject is off centre. Many people typically focus, hold the shutter halfway to hold the focus and then recompose. In the film days this usually meant a great shot...now it seems the ears or the back of the head or some part of the background is in focus, but not the prime subject. Because the minute shift caused by recomposing is enough to throw you focus point off of the surface of the sensor. There findings were that people that shift the focus points instead of recomposing seldom experience backfocus issues. Makes sense to me. Link to post Share on other sites More sharing options...
biglouis Posted December 5, 2007 Author Share #13 Posted December 5, 2007 OK, well thanks for the many, varied answers, including the amusing ones. I very rarely, if ever, take portraits. Mostly I am shooting buildings or urban landscapes and often at high f-stops and long distances, perhaps that's why I have not yet been troubled by the phenomena. Or maybe the R-D1 is just more forgiving? LouisB Link to post Share on other sites More sharing options...
Iron Flatline Posted December 5, 2007 Share #14 Posted December 5, 2007 Nah, the R-D1 has other issues. Got an R-D1 and an M8, love 'em both. Yes, if you're shooting at f/8 or so the back-focus thing is not really an issue. But if you're shooting close-up portraits with a nice 35mm lens at f/1.4 though, and suddenly you realize things are always a little out of whack. Link to post Share on other sites More sharing options...
lct Posted December 6, 2007 Share #15 Posted December 6, 2007 Mainly a DRF issue IMHO. Never got focussing problems with 4 M bodies in 30+ years, only with my R-D1 and R-D1s bodies and the M8 i've tested in the meantime. Both the Epson's had a slight vertical RF misalignment and the M8 was out for some reason. (my old M3 is still great thank you) As soon as i had the bodies adjusted, the focussing issues disappeared so my 20+ Leica lenses were not the culprit fortunately. Also its true that digital is less forgiving than film as far as DoF and some digital users spend more time testing their stuff with rulers and other gadgets than taking photos and decide by themselves if they are good or not. As long as they don't use laser technology, Leica cameras will never be as accurate as a Leica Disto anyway. Link to post Share on other sites More sharing options...
rob_x2004 Posted December 6, 2007 Share #16 Posted December 6, 2007 I know its a bitch but cant you just learn the lens? Link to post Share on other sites More sharing options...
Craftsman Posted December 6, 2007 Share #17 Posted December 6, 2007 I'm not sure I'm following. I've read quite a few posts saying my new lens is back focusing and they were sending it back for repair. If the lens is calibrated to the correct distance for say the M8 sensor is it going to focus correctly for your film body? How is the correction actually made? Isn't this a quality control issue at Leica? Link to post Share on other sites More sharing options...
gyoung Posted December 6, 2007 Share #18 Posted December 6, 2007 I'm not sure I'm following. I've read quite a few posts saying my new lens is back focusing and they were sending it back for repair. If the lens is calibrated to the correct distance for say the M8 sensor is it going to focus correctly for your film body? How is the correction actually made? Isn't this a quality control issue at Leica? I think we are getting confused here, surely inaccuracy in the nodal point to film plane distance is REGISTER ?? and is certainly an adjustment/ quality control issue. Most wide angle lenses for movie cameras had to be adjusted to a particular body, such as 5.5mm for Bolex 8mm, almost anything for the Arriflex I once used, and even the fairly nasty 55mm for the equally unsatisfying Mamiya C330 which my employer once foisted on me. I have always thought of 'backfocus' as a non technical term, i.e retro focus lenses (i.e.wide angles for reflex cameras) have a longer back focus than 'normal' designs, (i.e. for rangefinder cameras), and is a design issue. Gerry Link to post Share on other sites More sharing options...
biglouis Posted December 6, 2007 Author Share #19 Posted December 6, 2007 Nah, the R-D1 has other issues. Got an R-D1 and an M8, love 'em both. Yes, if you're shooting at f/8 or so the back-focus thing is not really an issue. But if you're shooting close-up portraits with a nice 35mm lens at f/1.4 though, and suddenly you realize things are always a little out of whack. OK, then I definitely do not suffer from backfocus (so far) on the R-D1. The results from taking low light shots at f1.4 with my 35lux close in have always been in focus, albeit selective focus. LouisB Link to post Share on other sites More sharing options...
biglouis Posted December 6, 2007 Author Share #20 Posted December 6, 2007 Now that's what I like to see.... distances in something I can understand: feet and inches (if I have now alienated all my friends in Europe and the rest of world, I apologise). LouisB Link to post Share on other sites More sharing options...
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