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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses
Thread started 26 May 2014 (Monday) 16:09
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EF85 f1.8 CA and DXO

 
corndog ­ cabernet
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May 26, 2014 16:09 |  #1

A lot of people remark about pronounced color fringing from the EF85 f1.8 and yet DXO shows this lens measuring very low CA. Can anyone help to square this for me?




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KirkS518
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May 26, 2014 16:22 |  #2

In high contrast situations, it produces a (IMO) horrendous amount of CA. I had to toss more than a few shots because the CA wasn't even correctable in post. Mind you, that in 'normal' shooting situations it's a fantastic lens, but occasionally (and too frequently for my personal liking), there will be CA that other lenses wouldn't have issue with.

I also think their results may have to do with what/how they test the lens.


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corndog ­ cabernet
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May 26, 2014 16:37 as a reply to KirkS518's post |  #3

Thanks for your reply. It is somewhat typical of other's comments.
You mention the mystery might lie in DXO's methodology. I have two things to say about that...

DXO, if anyone knows, seems to know what they're doing.
http://www.dxomark.com ...urements/Measuremen​ts/LCAexternal link

And, if they use the same method for every lens, and you consider relative values, then almost every other lens should have higher levels of CA.




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KirkS518
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May 26, 2014 16:44 |  #4

From my understanding, as light is passing through glass elements, a prism like effect occurs, splitting the colors, and then rejoining them. My guess is that some lenses have a better ability to rejoin those colors better then others. Why? I have no idea. Why wouldn't/hasn't Canon improved this on the 85mm? Again, no idea, but I would imagine it's part of the reason it's an affordable quality lens. Additional R&D and different optical formulas would result in higher costs, and they maybe wanted to keep the lens at a certain price point. For the price, it's still a great lens, even with the CA.

As for the testing, it could be that the testing distance or other component of the test falls into the 85's better area of performance.


If steroids are illegal for athletes, should PS be illegal for models?
Digital - 50D, 20D IR Conv, 9 Lenses from 8mm to 300mm
Analog - Mamiya RB67 Pro-SD, Canon A-1, Nikon F4S, YashicaMat 124G, Rollei 35S, QL17 GIII, Zeiss Ikon Ikoflex 1st Version, and and entire room full of lenses and other stuff

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corndog ­ cabernet
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May 26, 2014 16:57 |  #5

KirkS518 wrote in post #16931851external link
As for the testing, it could be that the testing distance or other component of the test falls into the 85's better area of performance.

If that were the case, wouldn't that call into question ALL of DXO's results?
Any testing would be flawed if it didn't apply equally to all lenses. At this point I'm finding myself skeptical of "results".




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Varago
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May 26, 2014 17:18 as a reply to corndog cabernet's post |  #6

Instead of calling into question the value of a tester that has in all probability tested more lenses then all the others sites combined why dont you ask them :) Seems to me like the smart thing to do.


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GregDunn
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May 26, 2014 17:55 |  #7

KirkS518 wrote in post #16931851external link
From my understanding, as light is passing through glass elements, a prism like effect occurs, splitting the colors, and then rejoining them. My guess is that some lenses have a better ability to rejoin those colors better then others.

Lenses are constructed not from single elements but rather, mostly multiple elements cemented together, and multiple groups thereof. By using glass of two different shapes and refractive indices, the prism effect (aberration) of spreading out the different wavelengths is countered by the other element(s), giving magnification or focusing of the image while minimizing the aberrations.

The aberrations are harder to control at large apertures regardless, and depending on what qualities are being optimized in the lens, they may have to sacrifice aberration performance for less distortion, better focus tracking, less complex figuring of the elements, fewer groups, etc. etc.

I don't know what choices were made for the EF85 f/1.8 but apparently the designers felt it was more important to make these optimizations than to reduce CA.


Canon 1Dx | 5D3 | 7D2 | 6D | 70-200L f/2.8IS | 70-200L f/4 | 24-70L f/2.8 | 24-105L f/4IS | 100-400L f/4.5-5.6IS | 17-55 f/2.8IS | 50 f/1.8 | 28-105 f/3.5-4.5 | 4x Godox AD360

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corndog ­ cabernet
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May 26, 2014 17:57 |  #8

Varago wrote in post #16931917external link
Instead of calling into question the value of a tester that has in all probability tested more lenses then all the others sites combined why dont you ask them :) Seems to me like the smart thing to do.

Absolutely. That is my next action. And BTW I am not calling into question DXO's testing methods. I am thinking there may be a typographical problem however and there may be others, if that's the case. I'll let you know in this thread what I find out from DXO.

In the meantime, try not to shoot the messenger ;)




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corndog ­ cabernet
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May 26, 2014 18:03 |  #9

GregDunn wrote in post #16931996external link
....I don't know what choices were made for the EF85 f/1.8 but apparently the designers felt it was more important to make these optimizations than to reduce CA.

The point is the discrepancy between what people's experience is and what DXO writes.




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raptor3x
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May 26, 2014 18:06 |  #10

corndog cabernet wrote in post #16931785external link
A lot of people remark about pronounced color fringing from the EF85 f1.8 and yet DXO shows this lens measuring very low CA. Can anyone help to square this for me?

It's because DXO is only reporting lateral chromatic aberration and the 85's problem is with longitudinal chromatic aberration.


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KirkS518
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May 26, 2014 18:36 |  #11

I just was reading DXO's test methods, and they say:

The DxOMark Score is measured for defined exposure conditions corresponding to low-light scene with 150 lux illumination and an exposure time of 1/60s. These conditions were chosen as we believe low-light performances are very important for today’s photography and it is also important for photographers to know how well lenses perform at the widest aperture.

So (and this is what I was getting at earlier), the 85mm has CA issues in high contrast situations. I have a feeling that a 'scene' with an illumination of 150 lux isn't going to produce high contrast areas. Keep in mind, I'm ONLY GUESSING, but it seems somewhat logical to me. :)


If steroids are illegal for athletes, should PS be illegal for models?
Digital - 50D, 20D IR Conv, 9 Lenses from 8mm to 300mm
Analog - Mamiya RB67 Pro-SD, Canon A-1, Nikon F4S, YashicaMat 124G, Rollei 35S, QL17 GIII, Zeiss Ikon Ikoflex 1st Version, and and entire room full of lenses and other stuff

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2ndviolinman
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May 26, 2014 19:04 |  #12

The chromatic aberration that I read the most complaints about and see most often with my EF85 f/1.8 is strong purple fringing at very high contrast edges and around specular highlights, which is a different type of aberration. Lateral CA shows as color offsets in the image as you leave the center.


David
5Dc, 5Dii, Canon 16-35 f/4L IS, 40/2.8 Pancake, 85/1.8, 100/2.8 Macro, 135/2.0L, 200/2.8L, converted 35mm TS, Sigma 50/2.8 Macro, 70/2.8 Macro, Zeiss ZE 21/2.8, Zeiss Contax 28/2.8, 50/1.7 & 85/2.8, Jena 135/3.5, Voigtlander 90mm f/3.5 APO, Canon 28-135.

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corndog ­ cabernet
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May 26, 2014 19:34 as a reply to 2ndviolinman's post |  #13

I've gone to DXO's site and registered so I could post a thread on this. It won't allow me to post. In their instructions DXO says to not email them with such matters but to post in the forums instead. So, I'm a bit stymied.

But, lets review a bit from this thread....

DXO tests for Lateral CA and not longitudinal CA.
They test under specific low light conditions.

Is it any wonder a discrepancy between people's experiences and DXO's numbers exists?

How are we to take away from the information they provide and apply it in an attempt to make an informed decision?

And lets not forget about the relativity thing. Since most lenses score worse than the EF85 f1.8 for LCA, does that mean they are more prone to perform worse under brighter, higher contrast situations as well?
That doesn't seem to jibe with the common experience, unless all we are seeing is longitudinal CA. And since this is such a pronounced issue with some lenses, why is longitudinal CA being ignored? And why such narrow testing parameters?




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KirkS518
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May 26, 2014 19:48 |  #14

It's a conspiracy. ;)


If steroids are illegal for athletes, should PS be illegal for models?
Digital - 50D, 20D IR Conv, 9 Lenses from 8mm to 300mm
Analog - Mamiya RB67 Pro-SD, Canon A-1, Nikon F4S, YashicaMat 124G, Rollei 35S, QL17 GIII, Zeiss Ikon Ikoflex 1st Version, and and entire room full of lenses and other stuff

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bacchanal
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May 26, 2014 20:19 |  #15

corndog cabernet wrote in post #16932209external link
I've gone to DXO's site and registered so I could post a thread on this. It won't allow me to post. In their instructions DXO says to not email them with such matters but to post in the forums instead. So, I'm a bit stymied.

But, lets review a bit from this thread....

DXO tests for Lateral CA and not longitudinal CA.
They test under specific low light conditions.

Is it any wonder a discrepancy between people's experiences and DXO's numbers exists?

How are we to take away from the information they provide and apply it in an attempt to make an informed decision?

And lets not forget about the relativity thing. Since most lenses score worse than the EF85 f1.8 for LCA, does that mean they are more prone to perform worse under brighter, higher contrast situations as well?
That doesn't seem to jibe with the common experience, unless all we are seeing is longitudinal CA. And since this is such a pronounced issue with some lenses, why is longitudinal CA being ignored? And why such narrow testing parameters?

The take away here is that DXO and test charts in general are not solely adequate for determining how a lens performs. Some real world feedback is helpful also...and for that there are plenty of user/professional review sites with subjective analysis.

I don't think you can assume that LoCA necessarily correlates to purple fringing/hight contrast type CA.


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EF85 f1.8 CA and DXO
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