Depth of Field and Sensor Size...

[DUCeditor]

With some regularity we see comments about the effect that sensor size has on available depth of field (DOF). For some reason these comments always highlight the negative: That with a smaller than 35mmm frame size sensor one will have trouble getting the shallow DOF necessary for good portraiture.

While I do not (cannot) argue with the basic observation that smaller sensor cameras will, indeed, have greater DOF for a given aperture and field of view I do wonder about the one-sided criticism.

Is not extended depth of field for a given field of view equally useful?

If larger film gate/sensor size is so important than why didn't the complainers reject 35mm and go up to or remain with larger format sizes back in the 'good old days' of film?

I ask because I equally had available 6x7cm, 5x7 inches, and 35mm film cameras. Never once do I remember the availability of shallow depth of field being the determining factor in my making a choice as to which format to use for a given shoot. More important was 1) image quality, 2) availability of a lens with an appropriate field of view, 3) availability of that lens with adequate light gathering ability, 5) hand-hold-ability if necessary for the shoot and 6) the lens/formats ability to get adequate DOF.

Why more rather than less? Personal shooting style no doubt played a part. A fashion photographer, for instance, would have different needs than my own. I tend toward making images that offer a new way to see a common object. And for me that has often meant using lenses with a large field of view and great DOF. (Fortunately those two go hand in hand.)

Sports and scenic photographers' would likely find the list of priorities above quite similar to their own.

My point, again, is not to argue either with the effect of smaller sensors on available DOF or against that quality's usefulness shooting some types of subjects, but to point out that maximizing shallow DOF is only one of many criteria and for most shooting situations not even the most critical one.

-don

[SS904]

My simple take on it is that with a larger sensor, such as that on any current SLR (35mm format or the more common crop cameras), is you can have both a shallow depth of field for subject isolation, without getting uncomortibly close to your subject, and a deep enough feild of focus the pull off nice landscapes. Small sensor P&S cameras have a harder time pulling off the shallow stuff. Not one being better than the other, but a larger sensor does offer the versitilitly if you have the lenses too. You can get a shallow DOF on a small sensor, but the camera has to be capable based on design. My current P&S has a 2/3 sensor and an f2.0 to f2.8 zoom. It has better than average ability to create a shallow DOF for a P&S, but it does not in any way compare to my 1.3 crop and 135 f2.0. On the other hand, I can get a good shutter speed in low light, WITH a deep enough DOF to not have to worry the eyes will be in focus, but the nose will not! Choose your weapon. It is nice to have the creative option a larger sensor provides.

Edit to my original reply! (Lame excuse to follow) I was waiting for my company car to have its oil changed while reading and replying on my (not so) smart phone...

A Re-read of what you posted at home on the big screen has me thinking you may have been comparing the "full frame" purists to us crop sensor users. I don’t really buy too deeply into the idea you need to have the 35MM sensor to get the really shallow DOF. It does of course have the ability to generate a shallower DOF at a given aperture, FL and distance from the subject, but I could easily get a shallow enough DOF on my old 1.6 crop 40D to be almost silly and honestly kind of unusable. Not sure more is that much better here. IMHO any DSLR with the right lens can really do great things with subject isolation if that is what you want to do. I base my discussion of this subject on the difference between a DSLR and almost any of compact digitals which fall short in creating that effect due the small (read really tiny) sensors.