Dithering vs Darks?

[Larry 1969]

Hello all!

Since I've started guiding I've been dithering on every exposure. It's pretty quick (under 30 sec) and seems to work well.
My question is this: I've read that dithering accomplishes the same task as dark frames so are darks really needed with dithering?

Thanks!

Larry

[yobbo89]

no. they don't do the same thing .. darks subtract dark current, one of the major problems from dark current is from large heat build up which is called amp glow, where the edges of the chip or sides get interference from circuitry heat during long exposures,only dark frames will fix this ..

from what i've read, a bit of dithering can help with one shot cameras, the noise pattern from osc is typical red/green blue, a bit of molt pattern/colour can be reduced from dithering follow through with dark frames.

[Larry 1969]

Thanks!
I was afraid the answer would be something like that... I hate taking darks...

Larry

[bobharmony]

Larry - I have asked this question in the past and received the same (unsatisfactory ) response. If I were curious enough I would take a set of dithered images that I have already processed with darks, flats and bias frames and restack them without the darks, then reprocess them to see what the result looks like. Experience can be as good a teacher as receiving the answer to a question sometimes.

Now you are going to make me try it - see what you've done?

Bob

[Larry 1969]

Now you are going to make me try it - see what you've done?

Bob

I actually thought of doing just that but got lazy and asked...
I really have nothing but time at this point so I'm sure boredom will win...

Larry

[JayTee]

My understanding is that dithering causes the "data" pixels to move and the dead (cold) pixels to move and bright white (hot) pixels to move so DSS or your other stacking program can identify all those items within the image and keep the good and erase the bad. What dithering doesn't address is the dark current noise and this is why you need darks. Dark current is a current that flows even when no photons are incident on the camera. It is a thermal phenomenon resulting from electrons spontaneously generated within the silicon chip (valence electrons are thermally excited into the conduction band). The variation in the number of dark electrons collected during the exposure is the dark shot noise. It is independent of the signal level but is dependent on the temperature of the sensor. So, dark current noise will be there and constant (for a given temperature) whether you dither or not.

Cheers,
JT

[Stuart]

There is a difference between dark current signal and dark current noise. Dark masters subtract the dark current signal, but do not subtract the noise. You can never subtract noise. You minimize the noise in your dark master by taking a lot of individual dark frames so as to maximize the S/N. The big problem with DSLRs is that the dark current signal will vary from shot to shot as the temperature varies on the sensor chip, so one dark frame will have a different dark signal from another dark frame that is at a different temperature. If dark signal were linear based upon sensor temp it wouldn't be a big deal as it can be scaled, but it's not.

Dithering should ALWAYS be done, no matter what your camera is.