Optics people - entrance pupil, subject distance, and DOF?

[bclaff]

bclaff wrote: No just making the (important) distinction between depth of focus (what you show) and depth of field (which I was showing); there is a (subtle?) difference.

Not so subtle Bill, you are right. I am still wondering whether there is a better way to display the through-focus: choosing the central slice of the PSF, vs the central projection, vs...

What do you think would be a suitable cutoff for the CoC? Half of peak intensity? 10%? 1%? When we can't 'see' it any more (the image I showed had gamma applied for display)? This last one seems to yield results consistent with the literature (k = dz/N).

Linking DOFocus and DOField is not as immediately obvious as previously implied. Is there a better approach than taking depth of focus and multiplying it by 1/mn*1/mf (with mn and mf the near and far magnifications) - or approximately 1/m^2?

So for instance a 0.1mm depth of focus for a 50mm lens at 5m = about 1m depth of field?

But that 1m depth of field is not symmetrical about 5m (assuming that's perfect focus).
So depth of focus helps us intuit depth of field but the actual results are different.

Not so obvious. Of course with object distance, focal length, f-number and CoC in hand we could easily calculate the near and far field limits corresponding to a given depth of focus (read off the through-focus).

Jack

Regards

 

[Jack Hogan]

bclaff wrote: No just making the (important) distinction between depth of focus (what you show) and depth of field (which I was showing); there is a (subtle?) difference.

Not so subtle Bill, you are right. I am still wondering whether there is a better way to display the through-focus: choosing the central slice of the PSF, vs the central projection, vs...

What do you think would be a suitable cutoff for the CoC? Half of peak intensity? 10%? 1%? When we can't 'see' it any more (the image I showed had gamma applied for display)? This last one seems to yield results consistent with the literature (k = dz/N).

Linking DOFocus and DOField is not as immediately obvious as previously implied. Is there a better approach than taking depth of focus and multiplying it by 1/mn*1/mf (with mn and mf the near and far magnifications) - or approximately 1/m^2?

So for instance a 0.1mm depth of focus for a 50mm lens at 5m = about 1m depth of field?

But that 1m depth of field is not symmetrical about 5m (assuming that's perfect focus).
So depth of focus helps us intuit depth of field but the actual results are different.

Right, if we want the near and far distances we need all of the variables below. But then the through focus is (almost) useless :-(

Not so obvious. Of course with object distance, focal length, f-number and CoC in hand we could easily calculate the near and far field limits corresponding to a given depth of focus (read off the through-focus).