dark current noise

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.

It's still been mostly cloudy around here so I haven't been able to test it- but basically what I'm looking for is if the noise is fairly low up to ISO 3200 and 1 minute exposures for pictures of constellations like Orion?

ISO 3200 might be too much for 60 second exposures. You might end up with the core of the nebula blown, at least when using a fast lens. For exposures that long, you can use lower ISO. Here's a shorter, 40s exposure at a very small aperture:

See it on flickr

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.

Oh, and obviously, temperature of the sensor makes a difference. Just leaving the camera on for a few minutes will make for increased noise levels at long exposures. Cooking a sensor for an hour in Live Composite mode will make high ISO completely useless for long exposures (talking from experience here). So a cold winter night is actually a pretty good time for long exposure photography

Very nice image! I think you can see stars down to about 14th mag in it, no?  Thanks about dark frame subtraction, I did not know that.  It sounds like what we have to do for CCD cameras, you need to take a "library" of darks at different temperatures.  I haven't used Live Composite mode yet- is that only for star trails?  This is the peak time for astrophotography here, arctic air is finally here!  It would be nice if the wind lowered a bit though lol.