Is DoF an optical, perceptual or a hybrid property ?

Started 4 months ago | Discussions thread
guy_incognito1 Junior Member • Posts: 41
Re: Is DoF an optical, perceptual or a hybrid property ?
1

Le Artiste wrote:

Spin off from https://www.dpreview.com/forums/post/65136361

There appears to be a popular notion that the circle of confusion used to calculate the DoF of a given photo should be calculated for a given print size viewed from a given distance, usually the distance equal to the focal length.

I think this is problematic, since it would follow that:

Changing the print size or viewing distance is equivalent to changing the aperture stop during capture.

Cropping the image whether in camera, in post-production or on paper alters the DoF of the remaining image.

I always thought of the DoF as an intrinsic property of the optical capture system that cannot be altered by crops, reproduction size or viewing distance - the fact that this property can sometimes be masked by output magnification and viewing distance does not make them equivalent similarly to how digital exposure correction or ISO change is not equivalent to actually changing the exposure.

It appears that at least Fujifilm is aware of the discrepancy as its cameras offer the choice of 'film format' vs 'pixel' as the basis for the DoF scale in manual focus mode, the film format option presumably uses traditional APSC film CoC radius whereas the pixels one is based on the pixel pitch - the later is more sensible to me even though it results in much narrower DoF bands and a longer hyperfocal distance for a given aperture but it guarantees that things that are 'in focus' are in focus regardless of the output size, method and viewing distance used.

Why don't you try it yourself?

https://en.wikipedia.org/wiki/Depth_of_field#Effect_of_lens_aperture

Look at the last of the 3 pictures on your browser embedded in the page how it is displayed compared to the first 2. What do you think is acceptably sharp in the 3rd image? what is it's "depth of field"? for me, on my monitor it looks like the column with 4 is pretty sharp and 5 is getting maybe just a touch soft. So for me, the depth of field is probably around 4-5.

Now click on the image and blow it up to 100% on your screen. At full resolution, 3 is pretty clearly out of focus, and 4 looks just gross.

That is the effect of cropping/viewing changes/etc. It's all dependent on the human eye.

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