Quote Originally Posted by iND View Post
I have raised this issue on this forum on several occasions but I'm still not ready to give up on it.

More often than I care to admit I have an out of focus subject in a group because I missed my depth of field guess.

Yes I have tables and iPhone apps that I can use to calculate depth of field to great accuracy,

but in the heat of battle changing f stops and ISO and focal lengths (not to mention white balance) I get an out of focus subject in a group

only because I let the depth of field slip. Or I move three feet closer and the whole depth shrinks. Then in post processing I realize ooops.

Ok what I want is a depth of field display in my view finder to remind me, it could even blink if it wants to so I pay attention.

All the necessary data is in the camera. Look on photoshop bridge metadata. Its right there focal length 70, lens 24-70 aperture f2.8 camera 5d MARK III,

and subject distance 2.7 meters.

What is not there is the depth of field which in this case is 24cm, why could it not display or flash this data.

Or a nice SIRI voice that says "are you really sure you can fit all your subjects in to this 24 cm space".

Does anyone else have DOF issues?

Thank you.
I’m afraid an in-camera DOF calculator isn’t that easily implemented. There are a few important parameters unknown to the camera: The size of the final image/print, the viewing distance and the eyesight of the viewer. And if you don’t know these parameters you can’t calculate the DOF.

Of course you could guess for example that the long side of the final print will be 25 cm, and that the viewer is able to distinguish 5 line pairs per mm at a viewing distance of 25 cm. The resolution 5 lp/mm corresponds to a CoC (circle of confusion) of 1/5=0.2 mm on the final image. Since the sensor image must be enlarged by a factor 25/3.6 = 6.94 (for FF sensor) to get the final size, it corresponds to a CoC of 0.2/6.94 = 0.029 mm on the sensor. This value is commonly used by “DOF calculators”, but is based on the above guesses.

I guess the camera manufacturers are not willing to add a function that would attempt to calculate an exact number of something that’s actually quite ambiguous and subjective. I suppose they let us either calculate for ourselves or simply check if the result is sharp enough.