Re: How Useful is Merklinger's "Object Field" Focusing ?
WilbaW wrote:
Detail Man wrote:
Do you find that focusing directly on the most important subject-matter (even if that exists at "infinity") provides better results as compared to using so-called "Hyperfocal Focusing" techniques ?
Absolutely, without a doubt.
Something that puzzles and troubles me a bit about Merklinger's "Object Field" focusing approach is that it does not appear to take into account the effects of individual human visual acuity when viewing an image (of some particular viewing-size, and from some particular viewing-distance).
Well, you could argue that it doesn't need to because it maximises the possible sharpness where it matters.
Thank you for expressing your thoughts (with which I do agree) ! The rub (where applicable) is in the required foreground resolution (which may be variable in certain situations when a shot is set-up). Allowing for a borrowing (from near-field) - in order to be able to effectuate maximal focus upon a given element at (whatever) distance of the resultant plane-of-focus of - seems best, indeed.
Attention to (and the intentional omitting of when framing a shot) existing near-field subject-matter saves the disadvantages of having (later) to ("heavily") crop-out otherwise desired portions.
What I am wondering is this:
The "price paid" for focusing at "infinity" (as opposed to focusing at some Hyperfocal Distance derived from some given Circle of Confusion diameter) seems to be that the Near Focus Distance (of a "depth of field of acceptable focus") from the camera is doubled in value as a result. Depending upon the intended nature of the composition as it relates to the subject-matter desired to be in "acceptable" focus, this may (or may not) represent a significant sacrifice.
AFAIK, Merklinger only advocates focussing at infinity in very specific circumstances, it's not his method as such, so you may be wondering about something different. (It's a good exercise for the reader to find out when he said to focus at infinity and why.)
Yes. I "focused" (in the rhetorical sense) upon the extreme (being focus at "infinity") to state the (as much as) doubling of the lens-system F-Number necessary to achieve the same Near Focus Distance (from the DOF identities). This consequence can be a factor (depending on distance to any foreground of subject-matter of interest, and the spatial frequency resolution thereof).
It seems that the "sensitivity" of the Near Focus Distance - when comparing focusing at "infinity" and focusing at (many) finite camera-to-subject distancess - is not going to be high ?
The Near Focus Distance increases from the Hyperfocal Distance divided by 2 to being equal to the Hyperfocal Distance itself. Seldom would I be inclined to double the F-Number in order to "buy back" that. The (squared) decrease in sensor-level exposure would seem (to me) to in many cases not be a worthwhile trade in return for a somewhat closer Near Focus Distance.
Using lower valued Focal Lengths (may in some cases) help considerably - but only in cases where the Angle of (and thus Field of) View works out desirably when recorded (without post-cropping).
If the viewer of a printed/displayed image may (as a result of individual visual acuity, viewing-size, and viewing distance) be unable to perceive (some or all of) the increased resolution of the image's far-field subject-matter, then would Merklinger's "Object Field" focusing technique represent a net improvement - or are (some or all of) the alleged advantages of the technique (relating to the resolution of far-field subject-matter) diminished or negated as a result ?
Depends on what you mean by his "technique" - focus at infinity, or focus on the furthest thing that you want to be truely sharp in the image?
I meant Merklinger's "Object Field" focusing technique(s), ranging from "infinity" to closer focusing. Yes, the question was proposed too generally (as answers may correspondingly differ).
My guess is, if the viewer can't see well enough to differentiate levels of sharpness/focus/resolution in the image, it doesn't matter whether you went hyperfocal or beyond. IOW, if the alleged advantages of focussing on the furthest thing you want to be sharp are negated, then so are the alleged (and far more dubious) advantages of focussing at the hyperfocal distance.
It seems that a "developer" (of processed images) is wise to take note, and to factor-in, the intended viewing-size, viewing distance, and (the possibility of) 20/20 visual acuity in viewing.
In intentional, analytic, and predictive cases - where parameters such as operational focal-length, sensor resolution, image-processing characteristics, print/display characteristics, viewing-size, viewing-distance, and 20/20 visual acuity are reflected upon and understood in an operational sense - knowing the lower limits of spatial optical resolution expected (for 20/20 visual acuity) could be valuable knowledge where it comes to any focusing decisions involving focusing in front of the subject-matter of primary interest to the eye (that might alternatively take place).
Where it comes to image enlargement-factor in relation to photosite dimensions, some finite lower limit of a viable "COC diameter" would seem to reasonably apply in the processes of specifying print/display size at presumed viewing-distances. That (minimum) dimension would seem to be some measure of the effective "size" of the photosite-data (as affected in the composite system sense, with lens-system diffraction, any optical filter(s), and (as well) after de-mosaicing.
Below such image dimensions exist known hardware/software/print/display limitations - as opposed to specific limitations in ocular angular resolution at some viewing-size and viewing-distance.
Such things are better determined by measurements than by analysis, as the product of wavelength and F-Ratio is an independent variable in identities describing the effects of de-focusing (due to some COC dimension) combined with diffraction (quite complex), in addition to any optical filtering and photodetector sampling effects, as well as lens-system optical aberrations - where (as I understand it) ray-tracing analysis must be used - in modelling a composite system spatial frequency response (at a RAW-level, and prior to the additional effects of whatever de-mosaicing algorithm may be utilized).
Best Regards,
DM ...