a7x, a9 PDAF stripe noise technical analysis, part deux

Started 9 months ago | Discussions thread
ProfHankD Veteran Member • Posts: 6,238
450nm laser light preliminary results

JimKasson wrote:

Hank, here are some spectra from a Westcott LED panel at various white point settings:

You had a strong peak at 450nm... so, here are a couple of JPEGs (forgot to turn on raw... Doh!) lit by a 450nm 5.5w laser. Kids, don't try this at home.

First, with the laser light diffused and a flashlight as fill:

A6000 + Samyang 85mm f/1.4, lit by diffuse 450nm laser + flashlight for head fill

It looks really odd, but I don't really see stripe artifacts. Then again, I don't really see flare, and I couldn't get any with the diffuser on.

So, let's live dangerously and take the diffuser off. (Don't worry -- I wasn't living that dangerously because I and my student had laser safety goggles on for all these experiments and only the camera and the pink dragon saw the laser spot.) Just lit by diffuse reflection of the laser spot from the satin aluminum vacuum table, no flashlight. I got fairly heavy flare:

A6000 + Samyang 85mm f/1.4, lit by 450nm laser

There's texture, but not as expected. No doubt, it's from the laser light itself.

Incidentally, the laser really is a narrow-band emitter so you wouldn't expect to see colors, but the glowing spot is heated and thus is a wide-spectrum emitter. There are also a couple of other LEDs. Incidentally,the green LED you see on the top of the laser is not actually green -- the camera white balance just made it look that way, while the dragon really is day-glow yellow and pink. Point to Sony for AWB getting colors this close to reality out of lighting this wild. In other words, there were still light sources providing a spectrum so overall it wasn't a pure 450nm... but it sure has one heck of a 450nm peak.

In sum, the test is inconclusive because there is so much structure from the laser light itself and without raws I can't run my repair software, but it didn't seem like 450nm lighting alone is sufficient to cause the defect. The laser light isn't very diffuse, so the incident angles you can get are limited, and maybe that matters more?

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