Thanks, not a crop though that is the full frame shot at close to MFD. I was originally shooting a blue ball but lighting change so switched to the gold color all. Turned out to be a better choice.
Picture 7: Canon EF300mm f/2.8L IS USM & EF 2.0x II @ f/5.6 (even it's said that extenders, specially 2x make the bokeh worse it doesn't look that bad)
Thanks for the LCA test, Samuli! On becoming familiar with CA, it's all I can see. Really takes the fun out of selective focus - unless the lens has caliber approaching the 280/4 APO-Telyt-R!
rico wrote:
Thanks for the LCA test, Samuli! On becoming familiar with CA, it's all I can see. Really takes the fun out of selective focus - unless the lens has caliber approaching the 280/4 APO-Telyt-R!
FWIW, though it has the same source, it's not strictly longitudinal CA unless it's present at the focal plane. A lens can be a apochromatic and still have defocus colour, though being an apo is a good indication that the degree will be moderate. As with longitudinal CA, stopping down usually reduces the effect as well.
olyacme wrote:
FWIW, though it has the same source, it's not strictly longitudinal CA unless it's present at the focal plane.
Agreed, although I don't know the scientific term. In more words, one could say we want the exit pupil to have the same angular diameter at the image plane throughout the spectrum.
olyacme wrote:
FWIW, though it has the same source, it's not strictly longitudinal CA unless it's present at the focal plane. A lens can be a apochromatic and still have defocus colour, though being an apo is a good indication that the degree will be moderate. As with longitudinal CA, stopping down usually reduces the effect as well.
Thanks for the information, I assumed based on people talking here that "LoCA = bokeh CA". Do we have name for this green/magenta(red in some cases with 85L) thing in bokeh?
Based on new definition of LoCA neither Makro-Planar or 85L don't have LoCA since it doesn't happen in focal plane.
By stopping down this goes away around f/4 in both lenses tested. Now I realize when I had the coins and lightning set up I should have tested Elmarit-R 90, 135L,180L and 200L as well in order to see which are my alternatives if I have to shoot something which is prone to cause this effect.
Samuli Vahonen wrote:
(...)
Picture 7: Canon EF300mm f/2.8L IS USM & EF 2.0x II @ f/5.6 (even it's said that extenders, specially 2x make the bokeh worse it doesn't look that bad)
Thank you Samuli.
A 2x extender can sometimes actually improve the bokeh (adding aberrations I guess, making the bright rings in OOF highlights lessen or even disappear). I have seen images taken with Pentax A50/1.2 (by itself showing harsh rendering with the bright rings mentioned in background OOF highlights) and a Pentax 2x extender. The bokeh was totally seen much improved. CA was still there of course. regards, /Jonas
It's a quite nice lens on a cropped camera unless you need images sharp from corner to corner, or even border to border... Big, heavy and expensive though.
Lol - I see I forgot an s there. Darn.
cogitech wrote:
I disagree on the direction some are going on the LoCA definition.
I would prefer it just to be LoCA, it's annoying to write "the green/magenta stuff in bokeh".
I checked wikipedia, dpreview, etc. definitions for LoCA and any of the ones I did find didn't say that definition is only limited to plane of focus. However all definitions mention that lens is not able to focus all colors to same plane (or something like that).
Also it seems that Lloyd Chambers is also not calling it LoCA, example at his Coastal Optics 60mm f/4 UV-VIS-IR APO macro article, he calls it or actually lack of it to "magenta/green color fringing" and discusses it in separate chapter from chromatic aberrations.
Really hard to read these scientific texts on 2nd language at midnight, I'll continue testing CTO gels compatibility with my living room lights...
Too much talk, no images, Leica Elmarit-R 90mm f/2.8 @ f/5.6, pretty smooth bokeh considering subject, and no LoCA/bokeh color fringing
I guess my point is that LoCA does not show up on the focal plane, but in front and behind the focal plane.
CA on the focal plane is what I (and most authorities on the matter) refer to as "lateral CA" or just plain old "CA". You know, the type that shows up in the extreme corners (usually) on contrasty subjects in the focal plane (like tree branches against bright sky).
I guess my point is that LoCA does not show up on the focal plane, but in front and behind the focal plane.
CA on the focal plane is what I (and most authorities on the matter) refer to as "lateral CA" or just plain old "CA". You know, the type that shows up in the extreme corners (usually) on contrasty subjects in the focal plane (like tree branches against bright sky).
Paul, I don't think us fighting over this adds any value. Like I said I would prefer LoCA to mean this magenta/green fringing in bokeh as well, and that is the way how I have understood it all the time before I was told few posts above that it's not LoCA since it's not in focal plane.
However I disagree LoCA does not show up on the focal plane - if you look at the definition picture at dpreview (or any other location, they all have similar picture): http://www.dpreview.com/learn/articles/Glossary/Optical/images/chromatic_lens01.gif
In theory if LoCA is severe enough at focal plane I don't see no reason why this would not show up in focal plane also. In practice of course I have never seen this, and I would assume that applies for majority of people working with camera optics, due to which reason "most authorities" call focal plane CA as "CA" or "lateral CA" and this bokeh thing "longitudinal CA".
So for me it's fine (and preferred) that LoCA definition is how you understand it. End of discussion from my part, unless somebody proof otherwise I keep calling bokeh magenta/green fringing LoCA as I have done before.
Samuli Vahonen wrote:
In theory if LoCA is severe enough at focal plane I don't see no reason why this would not show up in focal plane also. In practice of course I have never seen this, and I would assume that applies for majority of people working with camera optics, due to which reason "most authorities" call focal plane CA as "CA" or "lateral CA" and this bokeh thing "longitudinal CA".
Longitudinal CA shows up in the focal plane all the time. It's the classic cause of the "Purple Fringing" effect so often erroneously blamed on sensor bloom. As a general rule, if the colour fringe is the same radially, and diminishes when a lens is stopped down, it's longitudinal CA - a failure to bring enough of the spectrum to common focal depth. Lateral CA, on the other hand, is a failure to bring enough of the spectrum to common magnification. It results in colour fringing that differs radially and generally does not diminish as a lens is stopped down.
A lens with low Longitudinal CA can still show significant "Defocus CA" because although the different parts of the spectrum did eventually arrive at common focus, it's very common for them to take significantly divergent paths through the lens before arriving at that focus. This allows some colours to become concentrated or diluted radially within the light cones, ahead of or behind the focal point. This becomes obvious when high contrast areas are imaged out of focus.
To my knowledge, "Defocus CA" doesn't have an official term because the people who named the various aberrations were all either microscopists or astronomers. As a rule, these two fields only care about the qualities of the focal plane.
A series of spot plots from someone with access to Zemax and a reference design would probably make that much clearer at a glance than I can put it in words..
I wouldn't mind trying the Zuiko 28mm out myself...
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