Lens__ Circle of confusion

[xkaes]

Yes indeed...when a previously finely focussed point becomes visibly softer and visibly "enlarged," we see this as "confusion," and this in increasing increments as this "circle" gets larger.

I guess where this terminology fails for me is in the use of the word "circle."

True a circle can be used to define the outer visible "diameter" of an AREA of "visible confusion," but there is no actual visible circle, excepting perhaps for certain optics like mirror-based lenses, or in certain instances where certain types of light sources (in concert with optics) can begin to acquire a circular affect as they become less focussed in an image.

But I cannot right now think of another term which so handily refers to this optical principle. ("area of confusion,?" "zone of unsharpness,?"). Hmmm...maybe when the morning coffee kicks in I'll have an epiphany!

The term "circle" does conjure up the idea of a halo for many people, and perhaps a better term would have been "ball", "globe", or "sphere" of confusion, but those are 3-D concepts. "Area" or "Zone"? Perhaps. I think I'd prefer "BLOB of confusion".

[xkaes]

Range of focus.

Range of in-focus focus.

[Alan Klein]

Exactly. Whether the DOF scale is on a Nikon, Minolta, or Yashica/Tomioka lens, it's just the manufacturer's personal decision. If you want less "blur", just use the next-smaller-f-number scale. For example, after focusing, instead of using the scale for f8, use the scale for f5.6 -- but keep the aperture at f8.

I used to do that all the time. Calculate the DOF using charts or the lens scale and then stop down one additional stop.

[rawitz]

I used to do that all the time. Calculate the DOF using charts or the lens scale and then stop down one additional stop.

Better stop down 2 steps, this was the consensus in the 70th among professional photographers when the high resolution films like Kodachrome film came and the new generation of HR optics from Nikon, Canon, Leitz ao. The "official" 35film COC of 0,03mm is a conventional value (not physical calculation like f-stop) out of the phototechnic of nearly 100 years ago. But we still find it today in the standard DOF calculation.
For HR digitalcameras, the COC should be even smaller. Fuji defines for the DCameras GFX a COC of 0,01mm.

Second odd is that the DOF calculation is not relating to film-, sensor- or lensresolution, but to a reference print of f.e. 10x FFfilm to 240x360mm. As this reference printsize 240x360mm is fixed, for the larger filmsizes like 120film the COC grows up to 0,05mm and so on.
But this will equalize the PQ advantage of the larger filmsizes, so who needs it?

regards Rainer

[xkaes]

That's a convenient way of doing it.

[Alan Klein]

This app allows you to calculate DOF based on film or sensor size. You can also select the COC size.
https://www.dofmaster.com/dofjs.html

[Alan Klein]

This app allows you to print out a chart for DOF based on film or sensor. (auto setting .1 for 4x5 and .2 for 8x10 - is that good?) You can also select the COC size manually.

https://www.dofmaster.com/doftable.html

[xkaes]

This app allows you to print out a chart for DOF based on film or sensor. (auto setting .1 for 4x5 and .2 for 8x10 - is that good?) You can also select the COC size manually.

https://www.dofmaster.com/doftable.html

That's the link I provided in Post #13.

[Alan Klein]

That's the link I provided in Post #13.

Oh I didn;t realize it. I have one of these charts printed out for each of my lenses. Here's one I marked off to quickly show hyperfocal criteria.

[Joseph Kashi]

For a full generalized explanation, check out “Airy Disk” on Wikipedia.