Sony a7 noise floor in continuous mode

[ Note 21 Feb 2014] This post has been edited to reflect a series of re-measurements. The first series used Rawdigger’s default automatic black subtraction option, which gave anomalous results when combined with small shutter-speed related changes to the a7′s raw files. I have since gone back and redone all the measurements with no black subtraction in Rawdigger.

All of the histograms in the preceding post were made with the drive mode in single shot. When you put it in continuous, you get something different:

ISO 100:

iso 100 histo cont shutter

ISO 200:

iso 200 histo cont shutter

ISO 400:

iso 400 histo cont shutter

In each case, only every fourth bucket has data. The pattern is the same at other shutter speeds and ISOs. In single shot mode the a7 is a 13-bit camera. In continuous mode, it’s a 12-bit device. This characterization is only accurate at 13-bit raw values of 1000 or less; above that, the Sony raw tone curve reduces the resolution until near saturation, where it’s 11 bits.

A reader has asked if that’s true with auto-bracketing as well. I’m afraid it is. With auto bracketing set in continuous mode, you get 12 bits. With auto bracketing set in single shot mode, you get 13 bits.

Unless there’s interest, I don’t plan to do any more testing of the camera in continuous mode, since that’s not how I intend to use it. I’m sure the Sony engineers have some reason to do raw processing differently in the two drive modes, but it sure adds confusion to a user trying to figure out how to use the camera and aggravation to a reviewer not looking for extra work.

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