Canon 6D Long Exposure Noise Reduction... worth it?

Started Mar 15, 2016 | Discussions thread
Jon Rista Contributing Member • Posts: 681
Re: Canon 6D Long Exposure Noise Reduction... worth it?

rnclark wrote:

Jon Rista wrote:

rnclark wrote:

Jon Rista wrote:

The 6D does not have that low of dark current. Even your own data indicates that, Roger.

At 1C (a very cold temperature for a sensor, difficult to get even in winter) you still have 0.217e-/s/px, which in a 5 minute sub gives you over 8e- dark current noise. That is in contrast to actually low dark current of 0.02e-/s/px or lower dark current of a regulated CCD.

However, the dark current of a DSLR is unregulated, and around 25C the 6D has a whopping 0.3e-/s/px dark current. That translates into 900e- worth of dark current, or 30e- dark current noise. More than read noise, probably more than skyfog noise for anyone outside of a deep red or white zone. That is a massive amount of noise, something which should not be ignored.

It is all too easy to have sensor temps over 20C during spring, summer, and fall as well. The 6D has slightly better dark current noise than the 5D III, but it is not what I would call particularly low in the grand scheme of things.

The 7D II is the only camera from Canon that I know of that actually includes newer dark current suppression technology and actually has lower dark current.

Jon,

I never said the the 6D has low dark current. You are confusing dark current suppression technology with low dark current. Dark current suppression technology blocks the DC signal from the dark current. That says nothing about the level of the dark current.

Dark current suppression technology reduces things like amp glow, the changing offset level with exposure time and the pixel to pixel variation in dark current between pixels. It does not block noise from the dark current. This is no different than subtracting a dark frame, only now it is done in the pixel before the signal ever leaves the pixel.

Roger

This is what I understand CDS, Correlated Double Sampling, to be. This exactly. CDS, however, is not new...it's been around in CMOS sensors since the late 1990's...and every DSLR that I know of has it. Not just Canon, but Nikon, Sony, Etc.

Canon has more recent patents (i.e. 2008 and 2011 filing timeframes) for literal dark current suppression, where it reduces the amount of leakage current flowing through each pixel. I believe that technology is used in the 7D II. It is probably also used in the 5Ds, and likely in the new 1D X II, however no one has done any testing or sensor teardowns, so I don't know for sure. Sony Exmor sensors employ similar dark current suppression technology do the 7D II which is why they also tend to have very low dark current/dark current noise (FAR lower than a 5D III or 6D at room temp.)

No, CDS is not dark current suppression.

I did not say it was. CDS is a means by which the offset from dark current is removed in the hardware...so I wouldn't call it suppression either, but it does remove the dark current itself. This is easy to test for, with any DSLR going back generations. Take successively longer dark exposures. While you will measure an increase in both hot pixel count and standard deviation of noise from the dark current that is flowing through the circuitry, you will generally NOT see an increase in offset.

CDS deals with all of the things you listed...amp glow, changing offset with exposure time, and either column or pixel variation in dark current response (depends on the exact implementation of CDS, most use column-level, some newer sensors are using per-pixel CDS units.)

From the Canon patents I read about their actual dark current suppression technology, they either disconnect the supply from part of the pixel circuitry during exposure, or they shunt the leakage elsewhere. That is what I would call actual dark current suppression technology, and as I stated before, the only Canon camera that I know of that uses that is the 7D II.

 Jon Rista's gear list:Jon Rista's gear list
Canon EOS 5D Mark III Sony a6000 Canon EF 50mm f/1.4 USM Canon EF 16-35mm F2.8L II USM Canon EF 100-400mm f/4.5-5.6L IS USM +4 more
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow