DoF may not exist...

Started 3 months ago | Discussions thread
Erik Kaffehr
OP Erik Kaffehr Veteran Member • Posts: 6,186
Re: It is Science and Perception
1

JimKasson wrote:

DMillier wrote:

I suspect expectation plays a part.

You have pixel peeped so many ultra sharp GFX shots now, that maybe your brain can't accept even the most conservative CoC values.

I gave Greg a test to perform to see if using a conservative CoC worked. That was a year ago. He has not performed it. So we don’t know if a conservative CoC fits with his perception. It would be a useful experiment, and would probably go a long way towards getting to the bottom of this.

I also posted examples of low-CoC images, and asked Greg to look at them. He refused to do so.

Maybe it's a bit like aliasing. Lots of people seem to be completely unbothered by the most obvious luminance aliasing because they don't know what they are looking at. But once seen it can't be unseen.

Perhaps in your case, your brain is now so finally tuned to absolute sharpness that you can no longer tolerate a CoC that most people are fine with. When diffraction is doing the softening, perhaps it does so in a way that affects all the pixels everywhere by the same amount, so the tell-tale gradual fall-off of insufficient (for you) depth of field your brain latches on to is not present.

Just thinking about the "other things" that provide an explanation beyond the normal science.

You are a pixel peeper but it would be interesting to find out whether you see the same effect in prints.

I don't know about Greg, but it is important that DoF is about 'acceptable blur'. Also, that blur is a combination of lens aberrations, defocus and diffraction.

Going back to Jim's data on the GF 110/2:

Optimum sharpness is achieved at 2.07 m at f/2.8. Every other combination yields lower sharpness.

It is quite interesting that some photographers are quite happy using f/2 on the GF 110/2, that is because they want short DoF. A good example is Manzur Fahim who seems to forgotten the existence of an aperture ring when shooting his portraits of young ladies that are both beautiful and respectful:

https://www.manzurfahim.com/People/
Even in landscape photography, it may be that a slightly out of focus image may show some separation of depth, that would be lost with all in focus:

This image has the islet in focus. It could be that a blur enhances perception of separation of the islet from the background.The background is obviously much more blurred on the f/5.6 image. The f/11 image shows some loss of sharpness, much indicated by the absence of color aliasing, that is clearly present in the f/5.6 image. These images were shot on 24x36 mm, but I may reshoot on P45+ as I plan to revisit that place in a few days.

Stopping down also means either a longer shutter time, higher ISO or underexposure, with first increasing risk of subject motion and the other decrease in signal/noise.

So, in essence, I would say that DoF is not a fixed notion. It is a notion of acceptable blur, translated into distances in the object field.

Normal DoF tables are only discussing geometrical blur, ignoring diffraction and lens aberration. In essence, I would say DoF tables are a first order description of acceptable blur. At some point, diffraction needs to be taken into account.

Just to say, the Oskar Barnack era definition of DoF still has some merits. It doesn't held up for close scrutiny. But show two 16"x23" images, one sharp and one with 1/1500 diagonal CoC, side by side and the difference may be lost on casual viewers.

The reason is that most viewers will not look very close and if you have a few viewers, there will be some social distancing between them.

Also, very few viewers may be obsessed by sharpness and more interested in content.

Just to say, folks commenting on my images appreciate the technical quality but I think they are more impressed by content, point of view, perspective and visual impact.

Technical quality is more about workmanship...

Best regards

Erik

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Erik Kaffehr
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Magic uses to disappear in controlled experiments…
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