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02-07-2019, 10:24 PM   #1
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24mm differences

I am interested in a focal length prime around the 24mm range (for FF), and I was wondering how wide lenses vary in terms of distortion. I know that the edges can be more or less sharp, and there could be different aberrations, but is there a difference in the wide-angle distortion and/or the projection on the edges and corners? Considering the same focal length (like 24mm), is there any/much variation in this due to the optical formula?

02-07-2019, 10:45 PM   #2
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There will be some level of distortion, but i will depends upon the design. Opticallimits,com lists for rexample:
Pentax DA21mm - SMIA TV Distortion = -1.97%
Pentax FA*24mm - SMIA TV Distortion = -1.51%
Sigma 24mm - SMIA TV Distortion = -2.07%

Zoom lenses will have typically higher distortion. In my experience, a lens distortion below 1% is negligible.

Not that such lens distortion can be easily corrected in computer with appropriate softwares (e.g. PTLens).

Hope that the comment may hep.
02-07-2019, 10:58 PM   #3
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While I do appreciate less distortion of that type, what I am really asking about is the stretching of the image in the corners of the frame that occurs due to the rectilinear projection. Is there is really any variation with that, at all? (Or maybe there isn't, by definition of "rectilinear perspective".)
02-07-2019, 11:11 PM   #4
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Of the full frame lenses I have:

The DFA15-30 has the least barrel distortion. I'd say 24mm is just about its sweet spot - it barrels a bit at 15 and pincushions slightly at 30.
The DFA24-70 has the most.
The FA*24 is somewhere in between.

From f/2.8 they are pretty much equally (very) sharp. They are all pretty good at the edges. The FA*24 has nicer out of focus rendering, and gives a lovely soft-focus feel to its images wide open. The modern zooms have nine curved aperture blades and the old prime has eight straight blades if starbursts are your thing. I haven't tested the FA* for flare resistance, but the DFA15-30 is better than the DFA24-70 in this regard.

Then there's the filter issue. The DFA15-30 only takes 150mm Lees with an expensive adaptor. The DFA24-70 has an 82mm thread, and the FA*24 takes 67mm filters.

02-07-2019, 11:13 PM - 1 Like   #5
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QuoteOriginally posted by leekil Quote
While I do appreciate less distortion of that type, what I am really asking about is the stretching of the image in the corners of the frame that occurs due to the rectilinear projection. Is there is really any variation with that, at all? (Or maybe there isn't, by definition of "rectilinear perspective".)
The more more barrel distortion, the less the rectilinear distortion in the corners. Because they are less rectilinear
02-08-2019, 12:56 AM   #6
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A simple lens would project the image on a sphere, not a flat film/sensor, and the wider the FOV the more lens elements are required to do this, and as a practical matter the larger the acceptable distortion. That is to say the lens is no longer "flat field." This depends on the lens design, but the wider the lens the more difficult it is. This is why the barrel or pincushion distortion. Consider 50 mm macro lenses, they are typically flat field and thus may have more complex optics (especially if they are also relatively large aperture).

A related problem is not about distortion but lack of it--in the sense that the wider the FOV the more circular shapes at the edges become elliptical. It is correct, but its not the way we see things (especially other human bodies and faces) because we see a smaller FOV and turn our heads, so the wider angle lens seems wrong. This is often called distortion, but it really isn't. (Incidentally it is for this reason a fisheye lens, after correcting with Fisheye Hemi software, often looks more realistic than a very wide angle [rectilinear] lens.)
02-08-2019, 05:54 AM   #7
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Dan Eurritt has tested a bunch of wide angle lenses on sony fulll frame see here:

24mm SLR prime lens test, fourth round, shot on the Sony a7R
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