What is darks and flats actually mean and involve?

[bluesilver]

Hi,  I am just starting out in Astrophotography,  using a Modified full specrtum Canon EOS 600D,  Skywatcher evostar 150ED, AZ-EQ6 mount.

 

Have read many times that people are talking about  darks and flats,  No matter how i try to research this up i can't seam to find out what this actually means.

I have figured it out that it has something to do with the processing part,  at least that is what i think it is.

Or do i actually have to capture something else as well as the image i am working on?

So basically if i am say for instance photographing the Eagle Nebular,    Say i take 20 photos of it,  Do it hen need to take more of it at a different setting or something,  or is this term darks and flats only to do with the processing stage?

I am only just staring out with this so please keep it simple for me to start with if possible.

Thanks.

 

[Aramcheck]

In general you'll want to take a set of Bias + Darks & Flat frames in addition to the actual pictures of the nebula (usually called the 'Light' frames).

You can get away with re-using Bias + Darks, but Flats must be taken at the same time as the lights in order to accurately capture the vignetting, which will vary with camera position & focus.

Bias frames consist of a set of pictures taken with the shortest possible exposure & with the camera lens cap on. These are combined to produce a Master Bias image which will be subtracted from the Lights. The bias is a small pre-charge which is applied to each camera pixel and varies from pixel to pixel.

Dark frames consist of a set of exposures with the lens cap on, taken at the same ISO & exposure duration as your Light frames. These are combined to produce a Master dark, which gives an image of the thermal noise & hot + cold pixels, which again is subtracted from the Lights. (Some will say you don't need these but doing so halves my noise level on my 600D).

Flat frames consist of a set of exposures taken with the telescope & camera in situ & are taken with a flat light source. Some people use a diffuse white light source (eg white LED panel & white acrylic sheet, laptop screens & T shirts... or the clear sky & white T shirts). The Flats are combined to give you a Master Flat image. This is best described as a portrait of your optical system, which will generally be darker at the edges than the centre & will include any optical 'dust-bunny' effects caused by dust. When processing the Lights will be divided by the data in the Master Flat data to even out the pictures.

A good book to get started with Astro Photography is "Making Every Photon Count" by Steve Ricahrds.

Cheers
Ivor

[Denys]

Hi there,

I am also new to astrophotography, but I've come across this video on youtube and it was extremely helpful (at least to me), with very good explanations and showing each and every step of the whole process (he talks about the Bias/Darks/flats at around 1hour or so of the video). Maybe you will find in interesting:

 

[bluesilver]

Thanks for the replies and also that video link,  Might take me awhile to view that,  but so far looks spot on to what i need to start with.

Appreciated.