UWA magenta cast on the NEX7? Even from Sony's own lens?

[twiki]

Hi All,

We've all read the reports of UWA's showing the magenta cast on the NEX7. Luminous Landscape, for one, has explained that this is primarily caused by the design of the lens, and not just the focal length. The article is Legacy Wide Angle Lenses A NEX-7 / NEX-5n Comparison. Simplistically, lenses of symmetrical design create more problems that lenses of retrofocus design.

Michael Riechmann goes on to test the Tri-Elmar 21/18/16 lens. He quite clearly shows that, even at 16mm, there is no resulting magenta cast.

Fine.

But check out blog.kasson.com and FlickrHiveMind (nex7, 16mm), and you'll see definite evidence of Sony's own 16mm ƒ2.8 lens on the NEX7 causing a very noticeable mage cast. This one, in particular, is bad.

What's going on here? Sony's own lens shows this problem?
Or am I not reading this right?

 

[JMKasson]

The 16/18/21 Tri-Elmar has about the same 5-Delta-E (in chromaticity) cast as the 16mm Sony when tested at f/8. See blog.kasson.com, post 1241 The Sony lens is probably worse wide open, because it's a faster lens and the purple corner effect gets worse as the lens opens up, but I haven't tested it.

Jim

 

[JMKasson]

WC chrominance error @ f/8 -- CIELab Delta-E
Sony 16mm f/2.8 E mount 5.0
Leica Tri-Elmar 16/18/21mm f/4 @ 16mm 6.0
Leica Tri-Elmar 16/18/21mm f/4 @ 18mm 6.0
Leica Tri-Elmar 16/18/21mm f/4 @ 21mm 5.0
Leica Super-Elmar 18mm f/3.8 ASPH 7.8
Leica Elmar 24mm f/3.8 ASPH 9.4
Leica Elmarit 24mm f/2.8 ASPH 5.1
Zeiss Biogon 35mm f/2 3.6
Leica Summilux ASPH 50mm f/1.4 2.2

 

[TME]

Yes, it is very obvious.... I wonder why... does the 16-80mm CZ and the 16-105mm SAL also exhibit this purple colouration at 16mm?

 

[Atarandas]

I am not sure if thats just vignetting and Chromatic Abbreviation displayed by the wide angle lens ? Those pics in Flickr looks pretty ok to me , maybe I too unpro to see any problems

 

[sdchew]

Keep in mind that the Leica lens mentioned also have some issues when used with Leica's M9. That's the reason why they need the dot coding or manual input of the lens model in order for the camera to compensate and correct.

 

[twiki]

Hi JM Kasson, thanks for the input. You seem (to me) to be saying that the lenses listed all impart some sort of color to the image.
It's kinda technical, so could you simplify it for us a little?

The more I read into this, the more I think I see magenta everywhere...

 

[twiki]

Jim (Kasson),

I've just read your blog post NEX-7 — purple corner testing summary, and now understand it a little more.
It's quite a bit more complex that most of us think and pretty much all lenses will impart some sort of coloration - even fine ones like the Summilux ASPH 50mm f/1.4.

One problem with photographic measurements is that you can identify problems that you were happy ignoring. Some people, after they’ve see the numbers for the Sony 16mm, will look critically at pictures taken with it and want to fix the corners.

Another thing to consider is, although I’ve been calling it the purple corner effect, the errors aren’t always the same hue. Look at the results in the previous post; you can see hues from red to blue, and you can have different hues at different parts of the image.

Numbers are one thing.
How we perceive the image is another.

And it made me think of Eric Kim's articles Buy Books, Not Gear, and Why You Should Always Use and Abuse Your Gear. :embrass:

 

[JMKasson]

You seem (to me) to be saying that the lenses listed all impart some sort of color to the image.
It's kinda technical, so could you simplify it for us a little?

If the errors are small enough, you can probably ignore the corner color shift. CIELab Delta-E's of 2, or maybe 3, are pretty small to me. One CIELab Delta-E is supposed to be about a just-noticeable difference, although CIELab is not strictly perceptually uniform. If you want to fix images that have excessive corner color shift, you can use programs like Cornerfix. One of the big problems is that the corner color error varies with aperture at apertures wider that about f/5.6, so there's a lot of calibration to do.

In my blog I describe how to test your lenses for corner color error.

If you don't like numbers as well as pictures, and if you subscribe to Lloyd Chambers DAP service, you can see photographs that give a gut feel for the errors of many lenses at many apertures.

I'm working on a "what to do about this" post, and I should have it up in a day or so.

Jim

 

[twiki]

But chromaticity aside, I'm presuming that the sensors (say comparing the 5n and 7) are different enough that a particular lens may show extreme coloration on the 7, but not on the 5n.
Make sense?

 

[JMKasson]

I'm presuming that the sensors (say comparing the 5n and 7) are different enough that a particular lens may show extreme coloration on the 7, but not on the 5n.
Make sense?

Right you are. I've tested the NEX-5, and it doesn't have nearly the problems that its big brother does. Look at the Jan 23 post on my blog. I've read that the NEX-5n is pretty good, too.

Jim

 

[twiki]

Hi Jim,

I'm particularly interested in all this, as I'm on the cusp of jumping from FX Nikon to something smaller and lighter.
One of my favorite lenses on FX is my 17-35mm so I just know that I'll be looking at UWA on the NEX7 before long.
Would the 5n be a better choice than the 7 for this reason alone? I'm primarily a JPEG shooter, and am unlikely to devote time to a lot of raw post-processing to remove color casts.

Still, it seems likely that I would begin with a lens like the 24mm ZA, despite the misgivings I've had over the physical size of this lens. No coloration to speak of, and good with focus (automatic and manual).
And then I read your experience with manual focus on the ZA. Oops...

But I was also pleased to read your conclusion on this:

But there is a magical feature of the NEX-7 when combined with the Sony and Sony/Zeiss lenses that make all of these problems moot. You can set the camera up in autofocus mode, let it do its thing, and then, with the shutter release still partly depressed, twist the focusing ring. The image in the viewfinder is instantly magnified. You can complete focusing, finished depressing the shutter release, and you’ll have a sharp picture. This feature gives you the best of auto-focus and the best of manual focus simultaneously. When you don’t have time to focus, you can let the camera do the job for you, and hope for the best. If you got a extra second or two, you can twist the focusing ring, tweak the focus, and get the shot.

Unless you want to focus the lens once and then take several shots with the same focus setting, or focus once and then wait for something to happen, I can’t see any reason to use the manual focus menu selection with the Sony lenses. When I use autofocus, I always use the mode that allows me to set where in the frame the camera should focus; when you twist the focusing ring to shift into manual mode, the place you set is the place that’s magnified. You don’t get a chance to go back and look at the whole frame before you take the picture, but you get used to that, and it works well and most circumstances.

Are you an arms-out photographer, or do you have the clip-on EVF for the 5n?

Right you are. I've tested the NEX-5, and it doesn't have nearly the problems that its big brother does. Look at the Jan 23 post on my blog. I've read that the NEX-5n is pretty good, too.

Jim

On a(n) (un)related note, why do we not see similar coloration issues for the micro-fourthirds system cameras?
That's another system I'm currently considering.


Thanks.

 

[JMKasson]

...Would the 5n be a better choice than the 7 for this reason alone? I'm primarily a JPEG shooter, and am unlikely to devote time to a lot of raw post-processing to remove color casts...

...Still, it seems likely that I would begin with a lens like the 24mm ZA, despite the misgivings I've had over the physical size of this lens...

..On a(n) (un)related note, why do we not see similar coloration issues for the micro-fourthirds system cameras?...

Thanks.

The 5n would be a better choice if you don't need the 7's features. I never used a 5n. I am not an arms-length photographer, and only bought the 5 to use with the 16mm and the clip-on optical finder.

The 24mm ZA is a fine lens once you correct the chromatic aberration. If you don't like post processing, you'll have to live with it.

As to similar coloration errors in micro 4/3 cameras, you'd need similar pixel pitches and similar angles of incidence. Micro 4/3 cameras do have similar pixel pitches, but they'd need short flange distances or lenses that stick back into the camera beyond the flange (a la the 50mm f/2 S-series Nikkor) to get sufficiently acute angles with the smaller sensor. I'm just guessing, though. This is uncharted territory.

Jim