[northcoastgreg]

The thing that I have been responding to is the blanket-claim that Sigma lenses have a problem with colors, and specifically, that they render things in a yellow/green tone.

I wouldn't describe it as an issue of Sigma lenses having "problems with colors." Nor would I say that Sigma lenses render things in a yellow/green tone. White balance can somewhat compensate for whatever color casts may exist in a lens. The question is, once you've "fixed" the color cast, what sort of effect does it have on the overall color balance of the image? In the images over at photozone from the Sigma 30 look well enough (they've been cooled down a bit with the white balance); but I prefer the color rendering I've seen from properly white balanced images from higher end Pentax glass.

As for the FA 31 images at Photozone, many of them clearly have white balance issues. They need to be cooled down. If you want to see images representative of what the FA 31 can achieve, check out the better sort of images in the Pentax Photogallery.

Lenstip did spectrophotometer tests of a small selection of lenses some years back. Every lens tested (and they tested some pretty good lenses) showed evidence of color casts (or at least uneven distribution of light transmission across the color spectrum). Generally speaking, lenses perform better in the middle of the visible light spectrum than toward the edges. Visible violet, near the end of the spectrum, tends to do poorly relative to other colors. Greens and yellows usually do well. Reds tend to do a little better than greens and yellows.

How this all translates to visual experience is not easy to ascertain. In terms of visual experience, what is more important to keep in mind is that each company that makes lenses attempts to maintain a consistency of color rendering among their high end offerings. In short, each company has a sort of "house color." These differences can be subtle, and people suffering from even mild forms of color blindness (and many people are partially color blind without knowing it) may not be able to tell the difference. But they exist, and some people notice them and consider them important. Just the other day I was talking to a portrait photographer shooting Canon who wanted to switch to Nikon because she preferred the color rendition of Nikon glass.

Now it's a matter of taste which company's color rendition a person may prefer. They're all pretty good, including Sigma. However, if you did a blind test; if you made the exact same landscape image with a high end lens from each lens manufacturer, and then you asked people to judge which one they liked the best, in terms of color reproduction, my money would be on the image taken with Zeiss glass. Zeiss lenses feature a very distinctive, rich color rendition, with dark, brilliant greens and blues, and bright, vivid reds and yellows. I would say that, among Japanese lens manufacturers, Olympus and Pentax come the closest to the Zeiss standard when it comes to saturated, distinctive, aesthetically satisfying color rendering.

The takeaway from this is not that Sigma lenses have bad color cast or color problems, but that they render color different from other lenses, and that if color is really important to you, that's something you should take account of. And there's nothing wrong with preferring the color rendition of one brand to another. It doesn't make one a fanboy of the brand one prefers. Nor is it making mountains of molehills. The color rendition of a lens can have at least as much impact on a landscape print as the bokeh of a lens can have on a candid portrait. So why is it okay to fuss over bokeh but not over color rendition?

[Edgar_in_Indy]

So why is it okay to fuss over bokeh but not over color rendition?

We do fuss over bokeh, constantly. But the current discussion/argument wasn't about bokeh. It started about four pages back when you said that many Sigma lenses have a yellow/green cast. It's fine to say that if it's true, but if it's not true then you are essentially disparaging an entire line of lenses without just cause. And in my experience, I have not found it to be true, so that's where I'm coming from.

You also pointed to the 18-35mm as an example of a Sigma lens with a yellow cast. But in the pictures that Digitalis posted a week or so ago, where he took identical photos at the same time with the 18-35mm and the 31mm, it was the 31mm that had a distinctly yellow cast. And Digitalis does control for white balance. And further, he also confirmed the color cast of the 31mm.

So until some hard evidence comes forward, I will remain skeptical, and I'm not inclined to stand by silently when I think unhelpful misinformation is being spread. I don't have any hard feelings though, and I certainly respect everybody's right to their own opinion.

BTW, I appreciate your last post. Some of the information was very interesting, and I actually agree with most of what you said.

[Nicolas06]

I remember also having see a comparison (that was for bokeh at the begining) with a teddy bear in a house with many lenses. I clearly remember that some shoot had cold tones, some warner tones. Some had more sharpness(*), some less. There where many primes, some zooms... I didn't manage to find this one yet again. I found it very interrestive back in time.

For sure the difference in color rendering was clearly visible also as the hability to have a smooth bokeh as an ability to have great sharpness of the in focus subject. I will not say anything as who was best, I didn't remember the details I maybe saw it 1-2 months ago and many lenses where included! And as for color rendering and contrast, it is easy to hide part of it or get a false sense of a color cast just with a different while balence, exposure ...

(*) I mean visible sharpness that you can see looking at normal size like full screen size of a photo... Not what you can only see looking at 100% crop.