Richard R. Meredith III |
depth of field focus issues said rmeredithiii 15 min. ago
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Alan N. Marcus |
Hi Richard, The smaller the working physical diameter of the lens aperture, depth-of-field is maximized. For these lenses the greatest depth-of-field is achieved when the aperture is set to f/32 for the 70 ~ 300mm and f/36 for the 18 ~ 200mm. The span of the depth-of-field zone increases with distance. Try backing up as far as you can and using a higher zoom setting. The span-of-depth-of-field is a range that extends towards the camera and away from the camera as measured from the point focused upon. This zone is not split down the middle equally. Rather it extends further away from the camera. The rule of thumb is: Depth-of-field extends 2/3 away from the camera and 1/3 back towards the camera as measured from the point focused upon. With this in mind, estimate the center of the desired span you want, then resist the urge to focus on this center location, rather, move the focus point a little back towards the camera. In summery: Depth-of-field is maximized when using the tiny apertures like f/22 ~ f/32. Depth-of-field is maximized when the lens is set to less magnification. Depth-of-field is expanded when the camera-to-subject distance is increased. Depth-of-field is maximized by focusing on a point nearer the camera than the center of the desired span. Alan Marcus (marginal technical gobbledygook)
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John P. Sandstedt |
Since I first began "noticing" digitial images [especially those by journalism photogs from Afghanistan,] I've notice that deptho of field is much more of an issue that with film. That is, in many instances there is no way to control it - the entire image is sharp. There may be several reasons. With point an shoot images, the chips are smaller and, accordingly, designers have less to work with. Thus, the variable aperture of these cameras [if there is one] offers lettle room for DOF. That's why the entire images is usually in sharp focus when P&S cameras are used. Moving to dSLRs, we have our choice of lenses. But, for most of these, the widest opening starts at 2.8. Zoom lenses start at 3.5 [3.6] or higher - and, that's too small an aperture to really allow for successful selective focus. Thus, we must find other ways to have the prime subject in sharp focus, while the background is blurred. There are a few lenses with 2.8 lenses; we can buy a Canon f/1.0 50 mm lens for a lot of money. Then there's Photoshop to the rescue.
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robert G. Fately |
Richard, while Alan and John's points are correct, there is the additional factor of DOF becoming very VERY thin at close-up distances. This has nothing to do with the lens itself (my dedicated macro lenses behave the same as my non-macro lenses when I use a bellows or close-up filters, etc.). When I shoot macro, I invariably have to stop down to f16, f22 or more (my 85MM PC Micro-Nikkor goes to f45) to get any kind of DOF. As John alludes, another factor accounting for the "depth" of the DOF is the size of the imaging area - everything else equal, smaller imaging areas force greater DOF. So the DOF I get on my D200 (APS sized sensor) at f22 is deeper than the same lens on the F100 (film), and the macro lens on my 4x5 view camera affords still less DOF. In theory, a tiny sensor would give tremendous DOF, but then there are other technical problems.
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
Isn't the deeper depth from digital because of the small lenses of point and shoots, which make an effective aperture/focal length combination for deep depth of field. Not the same lens on a different slr body?
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robert G. Fately |
Actually, DOF relates to three things: 1) lens focal length (shorter focal length = greater DOF all else being equal) 2) aperture (smaller aperture = greater DOF all else being equal) and 3) imager size (film or chip - smaller format = greater DOF all else being equal)
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Richard R. Meredith III |
Thanks all for your inputs, i'm going out to try some of the ideas.
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- Ken Smith Contact Ken Smith Ken Smith's Gallery |
You might consider the Helicon software, which allows you to combine images with a different focal point, into a single image. Kinda like Photomatix does for different exposures, Helicon does for the focus point: http://www.heliconsoft.com/heliconfocus.html After reading good reviews in Outdoor Photographer, I downloaded the "free" version (good for 30 days). You might check it out!
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
You forgot distance from subject. But depth of field isn't going to change if I take a 50mm from my A2 and put it on my D60. That's different than the small point and shoot cameras that have the smaller sensors, smaller lenses, and smaller effective apertures.
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