Depth of Field

[cratermaker 0]

I read a question about the accuracy of the Depth of Field(DoF) scale on a camera's lens. The writer wondered if there was a difference in DoF between SLRs and DSLRs using the same lens. Well, yes. Here's my answer.
A camera len's DoF scale is base on a full frame camera body. A manufacture's lens made specifically for its' camera's sensor size MAY have the DoF scale correct for that body/lens combination. We'll proceed based on the fact all other lens don't.
There are several types of camera bodies. 1.5/1.6/full frame conversion bodies are the main ones we use. This represents Nikon/Canon/full frame conversions. I'll use a 24 mm focal length lens for an example. On a Nikon this would be a equal to a 36 mm lens, 38.4 mm lens on a Canon, 24 mm lens on a full frame. We all understand this when we purchase a lens. Here is the tricky part.
In determining the DoF of a lens, one of the constants in the formula is the Circle of Confusion(CoC). Just like the conversion of the lens length, it is used on the CoC. This is the CoC for the bodies list above. Nikon-0.020, Canon-0.019, and the Full frame-0.030. Divide the full frame CoC(0.30) by your body conversion factor and you'll see the CoC for your camera body. In this world, each body/24 mm lens combo will have a different DoF scale. A fact of life for videographers with still cameras.
If you were to purchase a Sigma 24 mm F1.8 EX DG, the next question would be for which camera body? Whether it is Nikon, Canon, or full frame, you are only changing the mount fitting on the lens to match the body. The DoF scale remains the same. What we need to know is the DoF on each body for each F-stop. From there you can remark the DoF scale if you wish. Sound like too much work? It is.
Here is your cheat. Go to http://www.dofmaster.com/doftable.html and check out this DoF table. Look the site over carefully. There's lots of info there. First, follow our discussion and try the 24 mm lens on the three different bodies. At the bottom of each table you will see the CoC for that body. Notice the different near/far distances for each F-stop of each body/lens combo. Not too hard to do.
What does all this mean to you? Don't know. I just have more awareness and info on my camera system's use in photography and videography. Any discussion?

[DSE 3]

APSC vs full frame sensors have been discussed at length in the forum, you might want to do a search.
it's a common discussion, and doesn't hurt to revisit it, but fortunately, there is a lot of information (and much less complex than how you're presenting it here) on the subject both here in this forum and on the web in general.

[pilotdave 0]

Interesting... I never realized that some lenses have a DoF scale on them. Only one of my lenses even has a focus distance scale.

Dave

[PhreeZone 15]

Primes tend to have it on the lens.

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