dark current noise

CrisPhoto wrote:

Astrotripper wrote:

alexisgreat wrote:

To any of you who have any of the larger Oly M43 bodies like the EM1,5, or 10, how does the EPL-6 handle dark noise at longer exposures at higher ISO compared to those cameras?

It's the same for all Olympus cameras with the 16mp Sony sensor. E-M1 is an exception, as it uses Panasonic sensor, and thus exhibits higher levels of dark current noise. See here , here and here for example. You can use google translate, but even looking at the table and histograms at the bottom of those should be enough. An E-PL5/6 might heat up a bit faster, but I kinda doubt that the difference would be significant enough to be noticeable.

Caution: You are mixing high ISO and long exposure here.

I'm not. I'm talking exclusively about dark current noise (the last section of the reviews I linked to)

And I doubt that the modern sonsors heat up significantly: My imporession is that during long exposures, the sensor does nothing. It sits there and waits for exposure.

That's not the case. Leave Live Composite mode for an hour (with 30 second exposures for example) and you'll see. Or set up a timelapse mode and take a few dozen long exposure dark frames and run stats on them. I did all that. The numbers are pretty straightforward. Besides, it's not necessarily the sensor itself that might be heating up. There's lots of electronics in the camera beside the sensor.

BTW, a couple years back, I read about a neat camera mod. Some guy figured out a way to cut down power to the sensor during exposure. The results were pretty amazing. Amp glow disappeared, dark current noise went down dramatically. It was a Canon compact camera, if I remember correctly. Since that time, I wondered why is this not how it works by design?

Where the sensor might heat up is video readout, EVF readout with frame rate high and during live composite/live bulb when fast 1 second reradout is going on.

That too, even more I imagine.

And does dark frame subtraction help remove a lot of it in camera?

Dark frame subtraction is for removing hot pixels, not dark current noise. It actually increases noise levels. That's why for astrophotography, dark frame subtraction is done with master dark frames that are a result of averaging many individual dark frames. This process makes sure all you are subtracting is hot pixels, and nothing else.

This is the theory, but for the average OMD user who compares sensors and who does not fiddle with averaged dark frames ...

First, hot pixel handling is roughly done by "pixel mapping" in the utility menu.

No, it's not. Pixel mapping takes care of dead or stuck pixels, as explained on Olympus website . It has nothing to do with hot pixels.

Second: At least the EM1 behaves more complicated: While it has no master and average frames, it actually reduces the noise by applying a single darkframe. Either it does some extra magic algorithm/noise cancelling thing (the rumored "RAW noise filter") or some low level dark current noise is still prominent even after hot pixel removal. It seems to be much better to remove the predictable noise pattern even for short exposure times.

I'm sure it does more than just a simple subtraction. BTW, does it affect RAW files, or is it only a JPEG thing? I never really tried it, it was the first function I disabled on my OM-D.