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Notice all the bokeh and axial CA in the above photo. This was shot with my Rebel T1i and Canon 50mm f/1.4 USM. I was looking at Bryan
That does seem like quite a bit, however this particular situation may be a tough one (the sun is shining on the CA shoulder, right? There is no CA on the other shoulder). I don
It seems on shots where I was more backlit there was more CA. Which would make sense due to the high contrast border between the player and background, but I guess I was just shocked because I thought lenses never performed worse than on the ISO 12233 charts
<span style="color: #000000;"]<span style="background-color: #ffffff;"]The ISO 12233 chart light conditions and your scene light conditions are completely different. You can't even compere them.
And if in ISO 12233 chart test CA were only between F/1.4 - F/1.8, doesn't mean that in various conditions you won't see CA with narrower aperture. In certain conditions you can see CA even with F/4 or F/8.
If there would be special lens tests of CA characteristics and there will be written, that canon 50 mm F/1.4 shows CAs only between F/1.4 - F/1.8 and you would get visible CA for example with F/4, then we could consider, that there is maybe bad copy or something else.
ISO 12233 chats tests is mainly for sharpness [:)]
Quote:
Originally Posted by mmodica
All fast primes exhibit some degree of axial CA, and it's always worst at high-contrast transitions like the one on the subject's right shoulder, and at the contrast transitions in OOF specular highlights (which is why axial CA is also referred to as bokeh fringing). It does improve with stopping down, but only slowly.
<span>Quote:
Originally Posted by mmodica
It wouldn't help much, in this case. When I tested axial CA of the 85mm f/1.2L II, I found that it was evident at f/2.8, and even somewhat evident at f/4.
<span style="color: #000000;"]<span class="field-item-description"]
<span style="color: #000000;"]Quote:
Originally Posted by mmodica
<span style="color: #000000;"]Look at the tests in the photozone.de
<span style="color: #000000;"]Canon 50 mm F/1.2L
<span style="color: #000000;"]http://www.photozone.de/images/8Revi..._12/fringe.jpg
<span style="color: #000000;"]Canon 50 mm F/1.4
<span style="color: #000000;"]Comparing Chromatic Aberrations (CAs) section of both lenses, seems clearly evident, that 50 mm F/1.4 could show less CAs than <span style="color: #000000;"]"<span style="color: #ff0000;"]L" version.
<span style="color: #000000;"]The "<span style="color: #ff0000;"]L" doesn't mean, that lens always will have better CA characteristics.
<span style="color: #000000;"]
Interesting, thanks for the info guys.
I
Quote:
Originally Posted by mmodica
Yes :)
I don't know anything about lens design, but I'm pretty sure it isn't harder to make a prime than a zoom. I'd be very surprised if nice primes (like the 50 f/1.4) show more CA than zooms if you compared at similar f numbers.
Hmm. Interesting. I
The purple fringing is not always axial CA. One particular sensor designer, RKM, shoots Canon and is pretty confident that cases such as this are a reflection between the microlenses and the filter stack, and should be solved by multi-coating the microlenses (rather than single AR coated, as they are now), but that's probably expensive.
[Edit] Oh yeah, and another camera designer said that purple fringing can also be caused by overload, and that disabling electronic first curtain can help. (In Canon DSLRs, electronic first curtain is controlled is the "silent mode" liveview.)
Quote:
Originally Posted by Daniel Browning
Thanks Daniel. I didn't know. But... are these other causes more apparent with fast lenses?
Anyhow, in a controlled test, it should be easy to tell axial CA from these others just by adjusting focus a bit, right?
Quote:
Originally Posted by Jon Ruyle
As I understand it, yes. Reflections from the microlens are a function of the AOI (angle of incidence), and fast lenses tend to have wider AOI, so worse PF (purple fringing). If pixel overload was the cause, f-number wouldn't affect it, just absolute exposure.
Another reason I forgot to mention is infrared contamination. From what I remember of the explanation given to me by a brilliant lens designer (J. Brian Caldwell), the Bayer color filters tend to have different IR rejection, so any IR that gets through is going to increase brightness in varying amounts, typically resulting in purple fringe. I would imagine that since lenses also don't tend to correct IR to the same plane of focus as visible light, that would also contribute to the issue.
Quote:
Originally Posted by Jon Ruyle
Yes. Another test is to see if it improves by stopping down -- that's definitely axial CA and not PF. (There is a rumor going around that axial CA does not improve by stopping down, but it definitely does.)
As I understand it, axial CA improves from stopping down, but lateral CA doesn
Oh, more about the testing:
It was definitely axial CA because it gradually got better as I stopped down from f/1.4 to f/5.6. It also appeared all over the frame, not just in the corners. However, I was disappointed by the sharpness delivered by the fifty. I would have expected it to be better than my zoom, especially at (slow) overlapping apertures).
I can
Quote:
Originally Posted by Daniel Browning
But if PF from microlens reflections are a function of AOI, wouldn't they, too, improve when stopping down? (Probably not and I'm just being stupid)
Quote:
Originally Posted by Jon Ruyle
Good point. [Edit] The only way that stopping down would be a good test is if the f-number has no relationship to the AOI, but I don't think that is ever the case. There may be some lens designs (reverse tele, I think), where it's at least non-linear, between AOI And f-number, but even then it will at least change by some amount, partially invalidating the test.