Color fringing problem with the D70 + 18-35mm

[robert_ades1]

Please see the attached link, and notice the purple/yellow color

fringing in various parts of the image. This was taken with a D70, EI

200, f/8.0, 18mm, using an 18-35mm Nikkor. This problem goes away at

35mm.

Is this something that can be solved with a better lens (remember,

this was shot at f/8.0), or is this an inherent problem with digital

sensors when used in conjunction with wide angle lenses?

 

http://www.pbase.com/robertades/test_shots

[eric friedemann]

It is likely the lens; as I have no fringing problem with wider lenses I own, like the 14mm f/2.8 or the 12-24mm f/4.0. The problem is certainly not a blanket issue with using SLR lenses on DSLR cameras:

 

http://www.kenrockwell.com/tech/wideslr.htm

[grepmat]

I can see chromatic abberation along the black/white edge of the window, along with quite strong jpg compression artifacts, but presumably you were looking at the original images.

 

An SLR super-wide zoom lens is necessarily a retrofocus design (e.g., the diaphragm is much farther from the focal plane than the focal length at 18mm), and one that would not seriously change the angle of incidence of light upon the sensor as the apparent focal length changes. Therefore, the "sensor with wide angle lens" theory doesn't work well at all. I don't know much about the quality of this lens, but my presumption is that it is to blame.

 

Cheers.

[robert_ades1]

Grepmat and Eric, I certainly hope you're both right. I have a replacement 18-35mm on order to see if that's the cause. If not, then I'll be bummed because I really need a lens that gets down to 28mm equivalent. Meanwhile, I'm going to do some test shots on film with the lens today.

[ky2]

Try the 17-35/2.8 instead.

[ilkka_nissila]

I recommend the 20 mm f/2.8D AF Nikkor.

[robert_ades1]

Thanks for the suggestions, but the 17-35 weighs too much. And the 20mm isn't wide enough.

[john_carter_rhodes]

Colour fringeing and other chromatic aberations on DLRS are down to diffraction around the sensor, not the lens in use. Very slight differences in lenses of the same design...I guess way below that currently possible for the QA at the machine manufacturers...will have effects on the sensors. I don't believe that any of these defects are down to lens design, rather down to the intollerance inherent in the digital sensors.

 

John.

[robert_ades1]

John, are you suggesting that diffraction in the sensor would be the same regardless of lens focal length, too?

[john_carter_rhodes]

Hmmm....I'm not sure. Let me have a think. I would have thought that focal length would, indeed, have an influence. Although the incidence of light onto the sensor through the F mount should be pretty much the same regardless of the lens in use, so maybe not. I'll get back to you. :)

 

John.

[john_carter_rhodes]

Well I've had a think....not sure it did any good at all. ;)

 

I think that, theoretically, light should fall from the lens onto the sensor regardless of the focal length. However, small variations in lenses will affect this. I believe, though I'll leave it up to any experts out there to correct me, that these small discrepancies will lead to various abnormalities with digital sensors.

 

John.

[grepmat]

John, your opinion that this effect is due to "diffraction around the sensor" is one of several popular misconceptions about digital cameras. As you agreed, this really shouldn't change much with the focal length in a typical SLR zoom lens, and "small variations" really doesn't get one very far at all. Also, this sort of theory does not explain why it is most commonly purple, and so on. Let's us and Occam's Razor agree on the obvious: it's chromatic abberation in the lens. Cheers.

[john_carter_rhodes]

Well I totally disagree. Why does this lens not cause problems of film SLRs if it's a lens problem?

 

John.

[john_carter_rhodes]

...and I'm not exactly making up hypotheses...just stating the plain truth that digital sensors introduce multicoloured artifacts into an image. Processing may reduce the impact of these, but the sensors themselves just can't help it. It's inherent in the design. The individual pixels acting like tiny lenses (some in fact include microlenses) that create interference.

 

John.

[grepmat]

John: First, who said it doesn't cause color fringing on film? You? Why do other lenses not cause the problem? Second, if you believe this theory is "plain truth," and you aren't just quoting something you read in some other misinformed post, then please explain the mechanism involved in more detail, or at least point to a site where it is actually explained fully (and not just a self-proclaimed expert stating his opinion). Why is it "inherent in the design," etc. And, the one I've never heard addressed yet: why is purple so frequently the dominant color (purple being the classic dominant color in chromatic abberations of lenses)?

 

I really don't understand how this idea became such a universally believed "truth". I've seen it in post after post, but never with a proper explanation or pointer to one. It's the "face on mars" of the digital camera world. I can only guess that it arose when people started examining their digital pictures at 100% and finding significant amounts of CA in their digicams with their tiny sensors and super-zoom lenses (the exact conditions that would exacerbate the issue). They had never before looked so closely so easily at tiny portions of film and never had used 10x zooms before, so they never really noticed it much before. Hence-forth, all CA suddenly became the fault of the sensor, and with one misinformed post after another relying on someone elses misinformed post, it became the party doctrine.

 

I'm not stating for an absolute fact that the sensor is not somehow involved. I just cannot see how it would be, and if it is, I would like a proper explanation that would shed light on the situation instead of just hearing it stated as "plain truth" over and over.

[scott_blair1]

Optical chromatic aberration is red and green, is most apparent at the edges of the frame, is worse at wide angle and can disappear at longer focal lengths, and is not limited to dark/light interfaces. It is particularly noticeable along slightly out-of-focus edges.<P> The single purple or blue around strong highlights is "blooming", and is a digital phenomenon. It can occur anywhere in the frame at any focal length. It is not necessarily related to a sharply <I>focused</I> edge, since extreme contrast can create its own "edge" in the image. <P>Chromatic aberration is quite apparent, when it exists, when viewing a slide on a lightbox, with even a high quality (color corrected) 4x loupe. So it's not something that has fallen through the cracks, so to speak, up until the so-called digital age.

[grepmat]

Scott, chromatic abberation is not "red and green", it can be any color at all. Most lenses are not well corrected towards the ultraviolet, however, and this is why I state that purple tends to dominate.

 

Blooming is not responsible for "purple fringing." First of all, blooming only occurs when pixels are completely saturated. Therefore, blooming is not an issue, for example, when viewing dark branches against a blue sky. Second, when blooming occurs, it will be (on average) white, not blue or any other color. If it's purple, in general it's not blooming.

 

Finally, I didn't say that chromatic abberation has never been noticed in film. Of course it has. I was just musing on whatever has led to the notion that "purple fringing" is a new phenomena in the sensor and not what it plainly appears to be: simple chromatic abberation.

 

Cheers.

[john_carter_rhodes]

Well I've got nothing more to say, if you won't even listen to another point of view.

 

Try, please, to open your mind, then secondly read some more on the subject before you post.

 

Thanks,

 

John.

[john_carter_rhodes]

I contribute here to try to be helpful...and occasionally ask questions myself. I'm no 'expert' on anything. I don't post here in order to be abused.

 

John.

[grepmat]

John, Perhaps you thought my comment about "self-proclaimed experts" refered to you? It did not, and I did not abuse you in any way.

 

Second, I am quite open minded, though I do ask for rational explanations of the process involved.

 

Lastly, though I hesitate to mention this, I have a Ph.D. and actively work and publish in the field of solid state sensors. So I may say that I have read extensively on the subject.

 

Cheers.

[john_carter_rhodes]

Try here:

 

http://www.dpreview.com/learn/?/Glossary/Optical/Chromatic_Aberrations_01.htm

 

and here:

 

http://ray.cg.tuwien.ac.at/rft/Photography/TipsAndTricks/Aberration/

 

and here:

 

http://www.outdooreyes.com/photo26.php3

 

Is that enough? Well I won't be looking for more. Maybe you'd like to?

 

John.

[john_carter_rhodes]

Posted that last one before I read your last post. Honestly, do any of them help? I truly don't believe I'm wrong on this, but I'm always open to be corrected. :)

 

John.

[grepmat]

Hi John,

 

I'm sorry if you felt I was making a personal attack.

 

In your first link, they make the statement: "In digital cameras, microlenses can also be a source of chromatic aberration and the visibility of chromatic aberrations is sometimes amplified by blooming." This is basically wrong. While it is true that microlenses would be subject to chromatic abberations, they are each aimed at one pixel only. Any CA here is irrelevant. Blooming is utterly unrelated to CA and does not "amplify" it in any way.

 

The second link makes the claim that blooming results in colored fringes. I admit that the image presented appears to be a convincing example, especialy since the other highlights have much less pronounced purple. I'd like to know what sort of camera was used here. As an aside, these days most CMOS sensors have anti-blooming circuitry, and should be much less prone to the phenomena. In any event, there is no explaination for why this should happen. I'm interested in why and how "blooming causes purple fringing." Again, why purple? Why not white, as it really should be? And, of course, "purple fringing" occurs when blooming is not happening at all. The simple explanation is that the particular specular reflection in this photo is so bright that the normal lens CA is similarly bright and hence very pronounced. Blooming and CA would be visible together, even though they are unrelated.

 

The third link simply repeats the notion that it's in the sensor without providing any support or explanation at all, and hence doesn't add anything to the discussion.

 

Cheers.

[john_carter_rhodes]

Hi Grepmat (is that your name?)

 

Okay. I agree that this is not a scientific sample, but why do all these people, who seem to have no axe to grind, talk about it?

 

Each pixel in a sensor will itself act like a lens and the interraction between those lenses will cause diffraction.....am I wrong?

 

Processing can reduce, or possibly, completely counteract this effect, but it can't eliminate it altogether.

 

Can you tell me how the combination of thousands of receptors won't introduce interference?

 

Sorry myself for misunderstanding you. :)

 

John.

[scott_blair1]

Grepmat, it's fun to nitpick and debate, but it's tedious and unproductive. Maybe when you finally get a digital camera and use it extensively, you will understand what I am talking about. That is my reference; not some website. You should try photography yourself--it's fun.