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Sony a7s purple noise


Sebastien Ross
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Hi guys,

 

I've been testing a lot the a7s in low light and I've ran into some purple noise issue coming from the sensor. Sony canada is pretty useless about that...

https://www.youtube.com/watch?v=zpvACzU1Nj0&feature=youtu.be

 

I've tested it with 5 different A7s, they all do the same...In video mode, going under 1/50th with iso higher than 12 800, always give me that purple fringing (not as bad as the youtube video...witch is at the worst setting, but still, it's a bit frustrating) Technically, i know it doesn't respect the 180degree rule going under 1/50th for 24p/25p...but it could be useful is certain situation.

 

At first, they blame the metabones ...just like everyone (ex:

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Alright purple half vignette hahah 

 

Been running for 2min before. Like I've said I tested it in store too, with brand new one, demo, etc...

Lens or Body cap on.

 

It as something to do with the shutter speed for the a7s specifically... 

 

The purple noise is minimal or absent at 1/50 and 1/60...but keep increasing when you go under those shutter speed (at very high iso)

 

I know It is hot iso, not asking it to be clean...i'm curious why it is left top and bottom corner mostly. Might have something to do with the sensor readout or fuzzynormal could be right.

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With the purple colour put aside, vignetting would suggest it has something to do with the lens and/or the lens adapter used, wouldn't it. Especially if/when the vignette disappears in crop mode. I wonder if the vignette appeared with any lens and any lens + adapter combo, or just with one particular lens? 

 

Or, if the vignetting happens on one side only, that would suggest it has something to do with a de-centered lens array inside the lens in use. So does that lopsided vignette happen with any lens or just one lens? A dumb question, perhaps, but just to make sure, as the story didn't reveal that little tidbit. 

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I'll be able to test more once I have I get my other adapter, but it sounds like it is happening to all cameras in the same way. Not sure though...

 

 

All cameras with any lens? Or all cameras with that one particular lens/adapter?

If the lens or the adapter is dodgy, it will happen the same way with each individual camera. 

 

As for the purple vignette, suppose that would not be too surprising with a "suitable" legacy or another non-native lens, a wider angle lens in particular, under "suitable" conditions. One would think the vignetting is likely to disappear or at least happen less frequantly with a native lens. Unless one wishes to shoot under some extreme conditions.  

 

But after testing it with sony native FE lens....

 

...the vignetting is still the same? Or does it appear only with one FE lens, or any FE lens? Or only during some unusual conditions, regardless of the lens?

 

Just curious, too, as I don't own an A7s, and wondering if it's about a given lens, or could it have something to do with uneven internal heat buildup or something... or whatever. Hoping it was about a given lens, rather than an internal issue.

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I just read in the comments of the vimeo video posted above:

 

"I've also observed the "purple fringing" on three different A7S. It's no light leak. There is one or the other sensor out there with similar problems. "Black shading" calibration is the keyword."

 

I have a different adapter than the metabones and I am using FD glass. I don't have any native lenses to test unfortunately. This only happens at really high isos. But it is still unfortunate as it looks like the rest of the image is pretty clean except for this part.

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Perhaps it is better to test with no lense and a cap on the mount. In this way you are eliminating one variable. It does happen that depending on the electronic arrangement in cameras, some component might cause interference. I did happens on Dslr (forgot Nikon or Canon) that lens or VR or non motor or motor lense caused some noise etc, long time ago.

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