Dept of Field Data

[iND]

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.

[neuroanatomist]

Naive question - have you tried using the DoF Preview button?

[iND]

Yes I have used the DOF preview button but it is not the same. If I had the data I would have a better handle on how to fix the problem.
The data would be much more valuable.

[HDNitehawk]

I always found the DOF preview not that good.

I am sure the data could be in camera, it probably hasn't been in the past because of the pixel and processor power race. Dedicating processing to IQ and FPS is more important. Maybe we will see a DOF calculator in the future, but why stop there? Display subject distance, FOV and other info as well.

[andnowimbroke]

That sounds nice to have. I often forget to check half the crap it throws at me though.
I'd rather have zebra or focus peaking in the viewfinder. Could be what they are trying in the next M model.

[cls]

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.

[andnowimbroke]

calculate an exact number of something that’s actually quite ambiguous and subjective.

That's something that they are quite good at

[HDNitehawk]

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.

Print size wouldn’t matter as far as the calculator goes. The camera does know focus distance, it displays this in the exif files with some programs. My near sightedness doesn't affect the DOF of my pictures. I think it is easily implemented, and should be as accurate as the ones that are on-line. On-line calculators only need to know a few things; lens, aperture, distance and sensor size. All of the pieces of information are available in camera.

[cls]

That's something that they are quite good at

Very true, white balance and exposure are two of the things that the cameras sometimes calculate differently from what I think. I should have been more carful with that conclusion .

[cls]

Print size wouldn’t matter as far as the calculator goes. The camera does know focus distance, it displays this in the exif files with some programs. My near sightedness doesn't affect the DOF of my pictures. I think it is easily implemented, and should be as accurate as the ones that are on-line. On-line calculators only need to know a few things; lens, aperture, distance and sensor size. All of the pieces of information are available in camera.

Yes, but when they need to know sensor size it's because it is put in to the "magnification factor" calculation (from sensor size to the assumed print size of 25 cm / 10 inch long side). The assumption of the viewer's ability to distinguish 5 lp/mm at a viewing distance of 25 cm is also built in (typically these parameters are not inputs to DOF calculators). But sure, the same simple algorithm as can be found in various DOF calculators could be implemented also in cameras. But the result would still be based on assumptions.