Peter H Posted March 15, 2010 Share #1 Posted March 15, 2010 Advertisement (gone after registration) Hi If you use a very wide lens such as an 18 or 21, and your main subject is very close to the edge of the frame, would you find yourself focussing and re-composing, or just using a small aperture and estimating the focus? I'm thinking of situations where you may not wish to alert your subject to the fact that he/she is about to be photographed by aiming the camera directly up their nose from a few inches away. Your thoughts would be appreciated. Perhaps I should add that despite many years as an M6 user, I strayed into the world of DSLRs a few years back and am only just about to return to the fold with an M9 which I don't yet have. Thanks Peter H Link to post Share on other sites More sharing options...
Advertisement Posted March 15, 2010 Posted March 15, 2010 Hi Peter H, Take a look here WA focussing: advice please. I'm sure you'll find what you were looking for!
Marty Posted March 15, 2010 Share #2 Posted March 15, 2010 Welcome. Never had a problem focusing and recomposing with the 18mm. Even wide open and close up the 3.8/18 ASPH already has a 1/3m depth of field. I know it is a somewhat vague concept but in practice with this lens it works. Besides when you are at the closest focusing distance you don't really have a choice, and when you are not then it only gets easier. Link to post Share on other sites More sharing options...
jaapv Posted March 15, 2010 Share #3 Posted March 15, 2010 An interesting question and a good subject for a thread. Of course it depends on how you are placing your image. If you are at medium or long distances, the apparent DOF caused by the low magnifcation of a WA lens will allow to get away with zone focussing. However, if you are using selective focus, have your main subject close up and/or are using a fast lens wide open, focus-recompose is the method of choice. For instance this shot (disclaimer-no artistic merit claimed- for illustration purposes only) could not have been taken without exact focussing on the stone in front, more specific, the grass growing on its base, even on a simple WA like the Summicron 35 asph. A wider and faster lens would have been even more illustrative. 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/115491-wa-focussing-advice-please/?do=findComment&comment=1260945'>More sharing options...
giordano Posted March 16, 2010 Share #4 Posted March 16, 2010 A good depth-of-field calculator (e.g. Barnack) will chart the focus-and-recompose situation for any combination of focal length, aperture, CoC and object distance. Sometimes it matters: the diagram below is from Barnack. It shows the field of view of a 21mm f/1.4 lens focused wide open at 1.5m on a full-frame camera. The black circle shows the area within which you can focus and recompose without going outside the depth of field (CoC 20µm). 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/115491-wa-focussing-advice-please/?do=findComment&comment=1261279'>More sharing options...
jaapv Posted March 16, 2010 Share #5 Posted March 16, 2010 But surely one compensates by leaning slightly forward when rotating the camera? Link to post Share on other sites More sharing options...
giordano Posted March 16, 2010 Share #6 Posted March 16, 2010 But surely one compensates by leaning slightly forward when rotating the camera? Only for some definitions of "slightly" and "forward". I think in terms of focusing and then leaning back, but maybe you think of it as compose - lean forward - focus - lean back and recompose. As for "slightly", with a 21mm lens, if you aim the camera at an object 1.5m away and focus on it, then recompose so the object is halfway to the edge of the frame, you need to lean back by a mere136mm to retain the precise focus (assuming zero curvature of field). With a 50mm lens focused at 1m and again recomposing so the original focus point is half way to the edge of the frame, you need to lean back by 14.7mm (depth of field at f/1 and a 20µm CoC is 15.2mm). My head isn't sufficiently well calibrated for this, so focus-and-recompose close up at wide apertures is a bit hit and miss. Link to post Share on other sites More sharing options...
jaapv Posted March 16, 2010 Share #7 Posted March 16, 2010 Advertisement (gone after registration) That is true aboiut accuracy, but do you know any other method? Yes, I was a bit elliptical. Focus, lean forward a bit and turn. Link to post Share on other sites More sharing options...
Peter H Posted March 16, 2010 Author Share #8 Posted March 16, 2010 As for "slightly", with a 21mm lens, if you aim the camera at an object 1.5m away and focus on it, then recompose so the object is halfway to the edge of the frame, you need to lean back by a mere136mm to retain the precise focus (assuming zero curvature of field). . Thanks for all the replies. Wouldn't the selected aperture affect this in quite a big way? How far would you have to stop down to make the focus-and-recompose method safe without adjustment assuming the subject is no more than 1m away but at the edge of the frame? Can it be calculated or is it trial and error? Perhaps the Barnack method is the answer, in which case, how do I get hold of it? Many thanks Peter H Peter H Link to post Share on other sites More sharing options...
Marty Posted March 16, 2010 Share #9 Posted March 16, 2010 Not really, because John is talking about precise focus not just the entire field of "adequate" focus. So the aperture affects it in a small way at most (some lenses more than others). You can calculate it exactly, but perhaps not while you are in the heat of shooting. So you use a rule of thumb which the others have already noted is either lean forward a tad or nudge the focus ring a bit. Depending on what kind of focus is adequate enough for you. But still at the end of the day we are talking about WA, which is where it all matters the least. You could of course try it yourself if you still have your DSLR or M6 Link to post Share on other sites More sharing options...
dpattinson Posted March 16, 2010 Share #10 Posted March 16, 2010 I'm pretty confident that any method involving consultation of DOF calculators will likely alert your subject if they haven't already wandered off in the meantime. If you mean that you want to shoot people face on, but place them on one side of the frame so that they don't realize they are 'in' the picture... well - i would suggest guess prefocus and stop down a bit if you care. When I shoot like that, it's almost always on the move, in the street, and I have the lens prefocused to the distance I expect to be shooting at... say for example 3-5 feet with a 28mm lens in a crowded street. I shoot when the subject hits the set distance, but often the subject is in the middle of the frame as I'm not really trying to be inconspicuous, just fast. I very often use a wide aperture - so i miss 'critical' focus quite often... but that's not usually the point of such a photograph imho. Link to post Share on other sites More sharing options...
Peter H Posted March 16, 2010 Author Share #11 Posted March 16, 2010 I'm pretty confident that any method involving consultation of DOF calculators will likely alert your subject if they haven't already wandered off in the meantime. I think you're right! In reality I do my best to get focus in whatever way occurs to me at the time, depending on circumstances, and sometimes it works and other times it doesn't, and I'm happy enough with that. I just wondered how others deal with it, and whether I could learn from people with more (or wider) RF experience than I have. By the way, I've taken a look at your Flikr sight and you have some really beautiful shots on there. Peter H Link to post Share on other sites More sharing options...
earleygallery Posted March 16, 2010 Share #12 Posted March 16, 2010 If you use a lens like that, at 5.6 or 8, and set to say 2/3M for typical street shooting, you will find that more often than not you will get a sharp image. This is how I use my 25mm Snapshot Skopar. Link to post Share on other sites More sharing options...
giordano Posted March 16, 2010 Share #13 Posted March 16, 2010 That is true aboiut accuracy, but do you know any other method? Yes, I was a bit elliptical. Focus, lean forward a bit and turn. One of us is confused and I don't think it's me. As I see it you need to focus, lean back and turn. Imagine you're standing square on to a brick wall with your 21mm lens at 1.5m range. The most important single thing in the picture is a detail of the brickwork half way to the left edge of the frame, and you want to focus on that. So you swing the camera to the left so as to point the rangefinder at the detail. The rangefinder shows just over 1.6m. If you now swing back so the camera is square to the wall, you have the camera focused at 1.6m while the wall is only 1.5m away. Leaning forward only makes it worse. Link to post Share on other sites More sharing options...
giordano Posted March 16, 2010 Share #14 Posted March 16, 2010 Wouldn't the selected aperture affect this in quite a big way? It doesn't affect the geometry of it at all, but the smaller the aperture the more likely it is that depth of field will cover any errors. There's a link to the "Barnack" website in my first post in this thread. Link to post Share on other sites More sharing options...
jaapv Posted March 16, 2010 Share #15 Posted March 16, 2010 If you lean forward to focus, you will automatically lean back to turn. You are saying exactly the same thing as I do. However, if you are focussing on a part that is 1.60 away, you'd better not lean at all. After you recompose, you still want to have focussed at 1.60 as long as the relative positions have not changed. Link to post Share on other sites More sharing options...
giordano Posted March 16, 2010 Share #16 Posted March 16, 2010 If you lean forward to focus, you will automatically lean back to turn. You are saying exactly the same thing as I do. What you actually said was Focus, lean forward a bit and turn. which is a different thing entirely and must have been a slip of the keyboard. Just so we all lean the same way in the end. Link to post Share on other sites More sharing options...
jaapv Posted March 16, 2010 Share #17 Posted March 16, 2010 Ok, the confusion was in the punctuation, not in the mind Link to post Share on other sites More sharing options...
250swb Posted March 16, 2010 Share #18 Posted March 16, 2010 Peter, you want to zone focus, which is pre-set the focus and aperture so you are likely to get everything in focus that you need. So if you are lurking with your 21mm lens and want to get somebody in who is say 4 feet away, you set the aperture to say f8, set the focus scale to say 3 feet at the f8 index mark on the lens and you will then know the picture will be more or less in focus from 3 feet to infiniity. Zone focusing is how you do it if you don't want to alert somebody or simply want to work quickly. Steve Link to post Share on other sites More sharing options...
Guest mc_k Posted March 18, 2010 Share #19 Posted March 18, 2010 ...As for "slightly", with a 21mm lens, if you aim the camera at an object 1.5m away and focus on it, then recompose so the object is halfway to the edge of the frame, you need to lean back by a mere136mm to retain the precise focus (assuming zero curvature of field). With a 50mm lens focused at 1m and again recomposing so the original focus point is half way to the edge of the frame, you need to lean back by 14.7mm... can you also provide the formula used and source? thanks Link to post Share on other sites More sharing options...
giordano Posted March 18, 2010 Share #20 Posted March 18, 2010 can you also provide the formula used and source? thanks The formula is Pythagoras's, so I worked out the details for myself. I haven't seen a really good explanation on the internet. The diagrams at Focus and Recompose Exposed - James Duncan Davidson - James Duncan Davidson are useful but the text doesn't really explain the geometry. Also it's useful to see the focus-and-recompose indicator in the Barnack depth of field calculator (link posted earlier in this thread). Link to post Share on other sites More sharing options...
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