a7RII self-heating for long exposures

Started Aug 16, 2015 | Discussions
JimKasson
JimKasson Forum Pro • Posts: 25,469
a7RII self-heating for long exposures
23

There have been reports of strong self-heating effects at long exposures with the Sony alpha 7R Mark II (a7RII). I mentally discounted them, because I didn't know of a mechanism that would preferentially heat the sensor with the shutter open and the photodiodes sitting there back-biased and waiting to snag a passing photon.

But the posting of a7RII 30 second dark frame data that was at variance with what I was seeing in my own cameras made me want to do a long exposure self-heating test.

I set the camera's shutter speed to 30 seconds, which is as long as it will go. I set the shutter mode to EFCS, no silent shutter, single shot. I turned the IBIS off. I figured that's the setup you'd probably use for astrophotography. I set the ISO to 3200, which is higher than I'd use myself, but seems to be some kind of astrophotography standard. I hooked the camera to an intervalometer that was set to 1 second, so that would be the greatest time interval between exposures. I turned off lens corrections. I turned off long exposure noise reduction. I stopped the lens down to f/22 and firmly affixed the lens cap. I made 101 exposures.

I measured the standard deviation of a central 400x400 pixel sample. Here's what I saw:

There are a couple of glitches; a big one in the red channel and a little one in the blue channel. Ignoring those, we see a pronounced exponential heating effect with a time constant that looks to be about 70 shots, or 36 minutes. It looks to me like the asymptote is about 6.5 stops, which will be a stop and a half worse than where it started out. The dotted line is a linear regression line to the green channel data.

If you look at the entire sensor, you see something similar. Here's what you get at the beginning:

and at the end:

This is going to complicate long exposure testing. I wonder if it's common among other cameras.

Jim

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Promit Senior Member • Posts: 2,012
Re: a7RII self-heating for long exposures

People doing video work have found heat effects to be mitigated by pulling the rear screen away from the body. Did you leave the screen closed or pull it away?

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JimKasson
OP JimKasson Forum Pro • Posts: 25,469
Re: a7RII self-heating for long exposures
1

Promit wrote:

People doing video work have found heat effects to be mitigated by pulling the rear screen away from the body. Did you leave the screen closed or pull it away?

I left it closed. Another experiment to run...

Jim

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Unorthodox Junior Member • Posts: 36
Re: a7RII self-heating for long exposures
2

JimKasson wrote:

I left it closed. Another experiment to run...

Jim

Credit to you Jim for all these tests, you're a fantastic source of information :).

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GotoDengo Forum Member • Posts: 68
Re: a7RII self-heating for long exposures

Great work, Jim.  It feels like we're really in unexplored territory here!  I.e., as you ask, do other cameras do the same?  It's amazing that we really seem to have no idea.

Huge props for continuing to expand our knowledge in all these realms.

Horshack Veteran Member • Posts: 7,854
Dark current noise as function of temperature
1

Roger Clark has always included dark current noise measurements in his Canon reviews, including measurements over time/temperature. For example, see the "Dark Current and Thermal Noise" section of his 7D Mark II review. For the 7DM2 specifically he found the dark current noise doubles every 4.8C.

Btw many cameras have digital thermometers sensors inside and report the info in EXIF. I checked the EXIF of my A7s and found it has a battery temperature measurement. I checked an A7rII raw and didn't see any temperature field - it may actually be there but exiftool might not know where to look for it yet.

JimKasson
OP JimKasson Forum Pro • Posts: 25,469
Re: Dark current noise as function of temperature

Horshack wrote:

Roger Clark has always included dark current noise measurements in his Canon reviews, including measurements over time/temperature. For example, see the "Dark Current and Thermal Noise" section of his 7D Mark II review. For the 7DM2 specifically he found the dark current noise doubles every 4.8C.

Ya think my wife will object to the temperature chamber and the regular CO2 deliveries?

Btw many cameras have digital thermometers sensors inside and report the info in EXIF. I checked the EXIF of my A7s and found it has a battery temperature measurement. I checked an A7rII raw and didn't see any temperature field - it may actually be there but exiftool might not know where to look for it yet.

The latest version of RawDigger, 1.1.7, reports the battery temp on the a7RII:

This is at the end of a one-hour sequence of 1/125 second shots every 30 seconds

This is at the beginning

Jim

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Horshack Veteran Member • Posts: 7,854
Re: Dark current noise as function of temperature

JimKasson wrote:

Horshack wrote:

Roger Clark has always included dark current noise measurements in his Canon reviews, including measurements over time/temperature. For example, see the "Dark Current and Thermal Noise" section of his 7D Mark II review. For the 7DM2 specifically he found the dark current noise doubles every 4.8C.

Ya think my wife will object to the temperature chamber and the regular CO2 deliveries?

Btw many cameras have digital thermometers sensors inside and report the info in EXIF. I checked the EXIF of my A7s and found it has a battery temperature measurement. I checked an A7rII raw and didn't see any temperature field - it may actually be there but exiftool might not know where to look for it yet.

The latest version of RawDigger, 1.1.7, reports the battery temp on the a7RII:

This is at the beginning

Jim

I was one version old on exiftool. I just downloaded the latest (9.99) and it reports two temperature readings from the A7rII EXIF - battery and ambient. I think RawDigger has an embedded version of ExifTool so it may report the ambient as well. Here's what exiftool 9.99 reports:

Battery Temperature : 39.4 C

Ambient Temperature : 24 C

Trollmannx Senior Member • Posts: 5,460
Re: a7RII self-heating for long exposures
2

Very interesting findings and data - and now I am happy that I did skip the A7RII as my next astrophoto camera (standard setting is bulb, ISO 1600 and integrating exposures for an hour or so per run). Doubt the heat build up issue is much of a problem for ordinary photography.

Find the Sony cameras great for anything but astrophotography as I never expose for more than 30 seconds and never run long sequences in my ordinary photographic life.

Always interesting to see what you guys dig up when getting a new camera.

Had a hunch that the A7RII was a hot new camera, but did not expect it to be this hot... 

AksCT Regular Member • Posts: 227
Re: a7RII self-heating for long exposures

Nicely designed experiment, which shows thermal effect.

A quick question: how big is that noise (at the max level) compared to signal in typical scenes?

Perhaps, using a grey card (at various exposure settings) will show the change in SNR due to heat, for different signal levels.

JimKasson
OP JimKasson Forum Pro • Posts: 25,469
a7RII self-heating for short exposures
2

Is it just the live view doing the heating? I tried a sequence of 1/125 second exposures every 30 seconds.

The effect is diminished to the point where it is only of concern to testers, not people doing normal photography, and it's not strong enough to affect most tests.

Jim

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JimKasson
OP JimKasson Forum Pro • Posts: 25,469
Re: a7RII self-heating for long exposures
1

AksCT wrote:

A quick question: how big is that noise (at the max level) compared to signal in typical scenes?

At the max level, it's about 7 stops down from full scale. 18% gray is 2.5 stops down from 100%. Say an average ETTR photograph puts the highlights at half a stop down from full scale, which is pretty aggressive the way I look at it. That means that 18% card is, in the highest (usually, the green) raw channel, about 3 stops down from full scale, or 4 stops above the worst noise, instead of 5 stops above it when the sequence started.

The blue and red channels will usually be a little worse.

Jim

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Iliah Borg Forum Pro • Posts: 25,894
Re: Dark current noise as function of temperature
1

Horshack wrote:

JimKasson wrote:

Horshack wrote:

Roger Clark has always included dark current noise measurements in his Canon reviews, including measurements over time/temperature. For example, see the "Dark Current and Thermal Noise" section of his 7D Mark II review. For the 7DM2 specifically he found the dark current noise doubles every 4.8C.

Ya think my wife will object to the temperature chamber and the regular CO2 deliveries?

Btw many cameras have digital thermometers sensors inside and report the info in EXIF. I checked the EXIF of my A7s and found it has a battery temperature measurement. I checked an A7rII raw and didn't see any temperature field - it may actually be there but exiftool might not know where to look for it yet.

The latest version of RawDigger, 1.1.7, reports the battery temp on the a7RII:

This is at the beginning

I was one version old on exiftool. I just downloaded the latest (9.99) and it reports two temperature readings from the A7rII EXIF - battery and ambient. I think RawDigger has an embedded version of ExifTool so it may report the ambient as well. Here's what exiftool 9.99 reports:

Battery Temperature : 39.4 C

Ambient Temperature : 24 C

The readings are often taken before the shutter is opened. For other cameras I checked heating from the battery if present was quite visible in raw with black level subtraction off. I double-checked it removing the battery and installing a dummy, or using an external power supply.

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JimKasson
OP JimKasson Forum Pro • Posts: 25,469
Re: Dark current noise as function of temperature
1

Iliah Borg wrote:

The readings are often taken before the shutter is opened. For other cameras I checked heating from the battery if present was quite visible in raw with black level subtraction off. I double-checked it removing the battery and installing a dummy, or using an external power supply.

Good idea, Iliah. I'll run another test. Too bad I only have one decent intervalometer.

Jim

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Iliah Borg Forum Pro • Posts: 25,894
Re: Dark current noise as function of temperature
1

FLIR ONE is still a bit expensive ($250) and may be not accurate enough (limited low spacial resolution, too) to see what exactly heats up and to what temperature.

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Horshack Veteran Member • Posts: 7,854
Re: Dark current noise as function of temperature

Iliah Borg wrote:

FLIR ONE is still a bit expensive ($250) and may be not accurate enough (limited low spacial resolution, too) to see what exactly heats up and to what temperature.

I played with one of these at their CES booth in January. I pointed it at targets more interesting than electronics

JimKasson
OP JimKasson Forum Pro • Posts: 25,469
The effect is much less strong with the a7R
1

Self heating is not as much of a problem with the a7R for sequences of 30-secnod exposures. Vertical scale is the same as for the a7RII 30 second exposure graph.

Jim

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Iliah Borg Forum Pro • Posts: 25,894
Re: Dark current noise as function of temperature
1

Horshack wrote:

Iliah Borg wrote:

FLIR ONE is still a bit expensive ($250) and may be not accurate enough (limited low spacial resolution, too) to see what exactly heats up and to what temperature.

I played with one of these at their CES booth in January.

Compared to what I use, I was not impressed. A toy.

I pointed it at targets more interesting than electronics

It is meant for such.

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JimKasson
OP JimKasson Forum Pro • Posts: 25,469
External power doesn't help
1

In response to Iliah's helpful suggestion, thinking that the battery could be the source of much of the heat, I tried an external power supply.

No joy.

It's warmed up, so the camera started off worse than before, and got even worser (yeah, I know it's not really a word, but it seems to fit here). I had to change the vertical axis to get the curves to fit on the graph.

Jim

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Iliah Borg Forum Pro • Posts: 25,894
Re: External power doesn't help
1

So, not the battery, or you would just see it as an uneven "cloud" of veil in raw...

Different channels are affected differently, right?

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