BetterPhoto Q&A
Category: Problems with Images

Richard R. Meredith III

depth of field focus issues

Ok, quick question, how do you handle depth of field focus issues. Taking pictures of an iris at F5.5 and 300mm, I have to select what part of the flower is to be the sharpest focus such as the edge of the peddles or the center of the flower. Even at other focal lengths I still have to pick what is the sharpest focus. And to be clear, I am only talking about a few centimeters at best. I am using Nikon better quality optics but not a macro lens (AF-S 70-300mm 1:4.5-5.6 G ED VR) and (AF-S 18-200mm 1:3.5-5.6 G ED VR). I am also running into this problem shooting dioramas about 15” deep. I seem to get the best focus issues in the F8 range when trying to focus on the whole diorama. Larger aperture setting gives great detail at the surface but lose focus very quickly with distance. How do pros take pictures with sharp detail from large areas and small detail flowers without losing depth of field? I relize some of the issues may do with optical quality of the lens. I thinking that there is something that I am missing, could it be post production editing?

said rmeredithiii 15 min. ago

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April 22, 2008

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.
To achieve you need to use a slow shutter speed thus the camera should be robustly mounted. To aid in the use of a tiny aperture you may need to elevate the ambient light (supplemental lighting). Setting the camera toa higher ISO facilitates the use of tiny apertures.

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)
ammarcus@earthlink.net

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April 22, 2008

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.