Help judging performance of my FE55z, FE35f2.8z horizon/infinity

Started Jul 5, 2016 | Questions thread
l_d_allan
l_d_allan Veteran Member • Posts: 5,087
Bottom line: Are we in 'heated agreement' that Advanced DOF calculators With.Flexible.CoC's are OK?

JimKasson wrote:

Skipping to the "bottom line" of this post with

  • "Yes .. we both reject the pdf paper from the 1990's for view cameras (I don't recall the professors name ... started with "M"? ... advocated by Jerry F.)(?
    and
  • "No ... not a different approach" ...

Does that mean that we have been in "heated agreement" all along that advanced DOF calculators with flexible CoC's are fine?

Hmmmm ... I suspect I could do a Google search for "site:dpreview.com l_d_allan advanced DOF calculator", and probably find at least 5 times over the past 3 years where I'm suggested more or less that. (checked ... 56 hits, with Google removing some but nearly all duplicates, from less than a year ago)

However, I suspect that it might be a worthwhile exercise to understand DOF to "switch gears" from my standard, conventional DOF understanding to what you are advocating.

I recall when I was writing compilers and then assemblers, I could get them to work with an iterative approach, but "recursive descent" was much preferred once my brain adjusted.

If we have been in "heated/violent agreement", please ignore the remainder of this post.

If not ...

l_d_allan wrote:

If so, the "200" seems associated with the MTF-50 label with units of cy/ph.

You're thinking about the chart wrong. To get to 200, take the f.2,8 (yellow( curve, and track it back to where it starts bending down at 500m. Then convert 500m for a 55mm lens to 200m for a 35mm lens by multiplying by the square of the focal length ratio.

That puts the relevant MTF50 over 1600 cy/pn.

OK (and again thanks for your patience). It is added motivation to tackle the related TLW blog articles.

Does that indicate relatively poor (if not grossly unacceptable) 200 cy/ph IQ? Wrong link? Low or no comprehension on my part?

See above.

My experiences seem different, but the FL and aperture are very different:
With a fast zoom at 4x longer 200mm but two stops slower f/2.8, focus still mattered more than I expected. My rusty math is that for DOF purposes, I can't use the the chart for the Otus 55mm f/1.4 and the 200mm f/2.8.

with a 200mm lens, you'd multiply the 500m by (200/55)^2 = 3.6 and get almost 2 km. That would be incredibly conservative for a zoom, but maybe not for the Nikon or Canon 200/2 lenses.

At least by reputation, it's a darn good zoom. However, DxoMark res numbers do indicate the Canon 200mm f/2L is significantly sharper at f/2.8.

And ... even though I'm aware than non-linear relationships increase quickly, I probably don't fully appreciated how much.

Even ignoring that the Otus is sharper by at least 100 cy/ph at f/2.8 that the zoom, aperture is non-linear square, but FL may be linear?

As you have seen, hyperfocal distance varies as the square of the focal length.

No yet seen, but maybe after a careful reading (and a good night's sleep)

Or is it more complicated than that, and I need to carefully read 100's of pages of TLW blog articles ... after retaking some math classes and taking one or several courses in Optics?

Sounds fun to me...

I don't disagree, but I'll be missing some deadlines shortly.

** EDIT ** I'll hold off on continuing and assume we have been in "heated agreement".

Back to my fast zoom at 200mm f/2.8:
There were neighborhoods perhaps several miles away. Focus was still critical. With magnified LiveView, focus on the roof tiles of the Red house was obviously invalid for the Blue house just to the front of it or rear of it.

I've notices with my Nikon 500/4 that I can focus on something half a mile away and have hills 5 miles away be obviously OOF.

Focus at near infinity to Cheyenne Mountain signal towers at perhaps 20 miles away was obviously unacceptable for the Red house maybe 2 miles away. Also unacceptable for signal towers maybe 5 miles away?

I've never tried it, but my speculation is that at dusk and if I focused on a partial moon, that might not to appropriate for the Cheyenne Mountain towers.

A doubt that; see the above 200mm lens calculation.

Going back to the 200m issue with your Otus 55mm ... I will reluctantly concede that if I made a large'ish print with the focus distance recommended by the Object DOF approach, that DOF / CoC might be adequate ... if I used the full frame.

To me, that ignores the factor of cropping, which I don't think can and should be ignored.

Cropping linearly affects cy/ph.

If the lens + sensor is critically focused and is capable of A3+ 13x19" prints from 25% of the full frame, that's how I want to focus. And that includes for GCVBCT.

I think the argument that "as long as you can make large prints at 300 dpi, it doesn't matter" is maybe obsolete with Super-Exmor's with 42 mpx that encourage and allow significant cropping. I'll admit I need to think that through more carefully.

I'll look for the .DNG's. If necessary, I'll add to my "to do list" to re-take those images on another super clear day, and be that much more careful.

Is that consistent to the "extinction graphs" for a 200mm lens at f/2.8? It might be just an average 'L' prime, but it's a zoom with a reputation for stellar IQ, world class build quality / control.

I will attempt to read and comprehend what I think of as your Object DOF related extinction graphs. Maybe a light will go on?

Is there a graph on your web-site that would have 'extinction lines" that reflect a high quality 200mm lens?

Take the 55mm graphs and multiply the distances by 3.6.

Would I be better off testing my admittedly less capable FE55, and attempting to extrapolate to your Otus 55?

Those lenses aren't very far apart at all in the middle of the frame, at f/4 and narrower.

If I went back thru the previously ignored 20+ articles of the Object Mode + Protocol, would I find a "extinction graph" for the FE55?

No. I never modeled it. I haven't collected sufficient data.

I realize those graphs aren't answering the questions I'm asking. I'm being slow how they relate to GCVBCT, other than maybe how critical alignment is or isn't.

BTW, my impression is that you ended up your Object Model DOF in general or specific agreement with the paper that had the concluding summary like, "focus at infinity with the aperture being FL / 5". Or did you closely study that, more or less reject it,

Yes.

and came up with a different, but perhaps equally unconventional approach?

No.

I'll address my confusion on the issue of just how accurately it seems you'd have to have the horizon trees at the center, APS-C rule-of-thirds, and extreme corners in terms of distance in a separate post later.

And really, I want to be once again in error ... that TNIHT (tilted near-infinity horizon testing) is a relative "piece of cake" compared to brick-wall testing and still provides valid captures for whether to return a lens.

I learn less on the rare occasions when I'm correct than on the more typical posts when you point out my ignorance / misconceptions / carelessness.

I hope the above helps.

Jim

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