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Towards an explanation of the Italian Flag Phenomenon


Lindolfi

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These are a lot of partial explanations rolled into one and frankly I’m not buying all of it just yet.

 

I'm just relaying what I've been told, but I believe it for two reasons. First because it explains the phenomenon quite well and the second because the person that provided is an engineer that works with this stuff professionally and is a veritable encyclopedia when it comes to sensor design.

 

Just to prevent any possible misunderstanding: It is the lowest energy wavelengths (namely red) that penetrate deepest, not the other way round as one might presume. Just like the low energy red light from the sun penetrates deepest into the atmosphere whereas the high energy blue lights gets scattered, creating red sunsets and blue skies.

 

That's correct. It's because a longer wavelength means less interaction with the blocking material. It's the same reason why when your neighbor is playing loud music that you'll hear the bass much better than the treble and why long wave rather than short wave is used for long range radio transmissions.

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Interesting in the sense that the cure in design is obvious - mirror the cells. One wonders why that wasn't done anyway given the symmetrical nature of the sensor.

Sandy

 

Mirroring the structure would lead to a break in the middle of the picture!

Jan

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Mirroring the structure would lead to a break in the middle of the picture!

Jan

 

Not necessarily. But admittedly, it sure wouldn't be easy, and if the asymmetry is inherent in difference between the red, green and blue cells, then you'd have a problem - you wouldn't want to go from an GBGR cell to RGBG cell in the middle of the sensor, for example. That would require a raw converter that understood the structure.

 

Sandy

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Well this explanation fits very well with the observations.

 

As I originally said many months ago, the only possible cause is the assymetry of the bayer grid arrangement and consequent assymetric colour sensitivity.

 

The only thing I find slightly puzzling is why some cameras and lens combinations seem more prone than others ... unless this is due to very subtle variations in lens/sensor alignment..... or microlens misalignment. I can't see it being due to sensor variation, which must be minimal when you consider the method of manufacture.

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Isn't the cause the different angle with which the light hits bayer grid element?

Wide angle, tele, high f/stop, low f/stop.

 

See the off-axis experiments above.

Jan

 

The foveon sensor seems to have overcome its mirroring problems in the meantime.

Jan

Edited by jan_kappetijn
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Well this explanation fits very well with the observations.

 

As I originally said many months ago, the only possible cause is the assymetry of the bayer grid arrangement and consequent assymetric colour sensitivity.

 

The only thing I find slightly puzzling is why some cameras and lens combinations seem more prone than others ... unless this is due to very subtle variations in lens/sensor alignment..... or microlens misalignment. I can't see it being due to sensor variation, which must be minimal when you consider the method of manufacture.

 

Variation betwen different lenses probably has to do with the position of the exit pupil.

 

The old man with watery eyes

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One interesting experiment has been left out.

Namely a pin hole with the hole out of the center.

Or with a lens offering perspective control, the similar effect of course.

Jan

 

Here is a photo taken with a LeicaGoodies pinhole on the M9. I would estimate the EFOV of this pinhole is roughly equivalent to a 24mm lens. I think it does show Italian flag or at least a red left edge. It also shows that my sensor is overdue a good clean, although the very dark spec is actually an eagle or buzzard in the distance.

 

Wilson

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