M101

Started Apr 6, 2013 | Photos thread
mike clemens
Regular MemberPosts: 118
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Re: M101
In reply to NancyP, Apr 9, 2013

NancyP wrote:

Beautiful.

What is the difference between a dark bias (taken on site at ambient temperature) and a dark flat? Do you even need a flat file if you run everything through the auto lens correction module on Lightroom on the way to generating tiffs for stacking?

Hi thanks Nancy

Calibration and processing is not my strong spot, but here is my understanding of the four types of calibration images I shot for this pic of M101:

Bias - takes away the noise of the camera that is in every exposure, no matter how long. Even a zero second exposure from your camera woudld introduce this noise. Taken at 0 seconds and the same ISO as your shots of the galaxy/subject.

(I made 40 of 0 seconds each at ISO1600)

Darks -takes away the noise that is built up during an exposure of the length you are exposing for. Taken at same length and ISO of the shots of your galaxy/subject.

( I made 40 of 5 minutes each at ISO1600)

Flats - makes every pixel of your camera equally sensitive.  (Gets rid of vignetting, sensor dust, etc.) Taken at any ISO you can get a clean halfway-there histogram at. I look for a lump right in the middle or slightly less.

( I made 40 of these at 8 seconds each ISO200 )

Flat Darks - takes away the camera bias and dark noise built up during the duration of your flat exposures. Removes noise from your flats.  Make them identically to how the flats were made.

( I made 40 of these at 8 seconds each ISO200 )

Sorry, I don't know how Lightroom could be incorporated into an astro-workflow except as the very last step making something look pretty.

My workflow for this image was -

1) collect lights until bedtime : )

2) collect bias and darks while I sleep

3) make flats next day with white posterboard on wall

4) make flat-darks immediately after flats with black cloth to cover camera

5) Set Maxim DL up to use the calibration images from steps 2-4

6) Calibrate all the light images while still in Maxim DL

7) Color convert all images from RAW to RGB while still in Maxim DL, save as 16 bit TIFs

8) Align images in Maxim DL or Registar

9) Stack images in Maxim DL, save single TIF 16 bit

10) Expand the dynamic range in Photoshop, basically - curves, curves, saturation, levels over and over again until the image is fully baked or starts to comb out the histogram with noise.

11) Lightroom, try to make it pretty.

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