I've finally got my battery and just need to find a gap in my time to be able to shoot my H4D-50 outdoors. Meanwhile I've continued my lab tests to see how it performs, and tonight I made the "wide angle color stability test", which I think is a good thing to do for anyone into tech wide angle photography when they get a new back. You do like this:
1) set up a color checker under a good stable CRI light
2) mount the widest lens you have (SK35 in my case) and shoot one reference shot with the color checker in center
3) shift all you can and re-adjust so you capture the color checker far out on the image circle, make a shot with horizontal and one with vertical orientation.
If your back has low color cast you can skip LCC shots and just use a color picker for white balance the color checker, it should cover a small area so color should be reasonably stable over that local area. If you have a really colorful cast, shoot and apply LCC.
If you have relevant levels of crosstalk you will notice that at least some of the colors get desaturated. You should see it with your naked eyes, if you don't probably noone else will see it either and then there is no crosstalk or very low levels so it's irrelevant.
Even with my large pixel 33 megapixel Leaf Aptus 75 I have visible desaturation on extreme shifts of the SK35XL, in vertical orientation (not in horizontal). In real shots it's very rarely a problem of course, but I have come across it on some extreme compositions, like the one attached. There you can see that the yellow leaves in the upper part of the image is a bit desaturated and greener than the ones closer to the center of the image. The trained eye also see that the greens of the pine trees are affected too. I've also seen this effect in real images with the SK60XL as it has a larger image circle and allows for more shifting.
Now I repeated the lab test with my H4D-50 and the SK35. This sensor has light shields between pixels in both directions, and it gives results. There's no visible desaturation in either horizontal or vertical orientation at the image circle edge. I was expecting this result as I've got real shots from other users showing excellent results from the SK28XL, but now I have really made sure with my own lab test. I'm not going to put together the color checker shots for show so you just have to take my word for it
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Although I can't say I've been limited by the Aptus 75 performance in this regard, I do see it as a plus that regardless what movements I do with the H4D-50, color will be stable. It should be said that the Aptus 75 has much much less issues than anything 6um Dalsa, I think few even knew that the Aptus 75 had any issues of this kind at all. And the H4D-50 is even more stable.
As Hassy hasn't been big on tech cams this excellent wide angle compatibility has been unknown to most. I think it's a bit unfortunate as it has also caused the popularity of the Schneider Digitar lenses drop as they haven't worked that well with the more recent Phase One's offerings.
This may be the last sensor of this kind we see for a while, so to anyone that thinks this level of performance suits them I recommend to keep this alternative in mind when evaluating alternatives. Having test files from a lot of backs I know backs based on this sensor (KAF-50100) is truly unique in combining relatively high resolution with the ability to take the whole Schneider Digitar range with its symmetrical wides with any shift amounts.