Download pdf, for printing (359 kB)

 

Introduction

Here's a small astrophotography tutorial for astrophotography. I found it difficult for myself to start editing astrophotographs with photoshop, as I understood very little of photoshop.
So here you can find the step by step instructions. Someone who doesn't know photoshop will understand this (I hope so :)

 

The tuturial is about removing light pollution and uneven field illumination. Here's the example we will work with:

Orion - straight scan	Orion - photoshop enhanced

Here's what we need to do:

1. Create a new layer, called 'LPR'
2. Apply Gaussion blur to new layer
3. Invert new layer, change opacity
4. Contrast change

1. Create new layer

Easy: menu: Layer > New > Layer...

Call the new layer 'LPR' (actually the name doesn't matter).

Now select back the background layer: click on Background in the layers tab

Press Ctrl-A (to select the whole background layer image), then Ctrl-C (to copy the whole image)
Now select the LPR layer (as you selected the background layer) and press Ctrl-V (paste the whole image in the LPR layer).

Now we've got two layers, with in each layer the same, original photograph.

2. Gaussian blur

This is to remove all the stars from the LPR layer image, so you don't see any detail in it anymore.
Menu: Filter > Blur > Gaussian Blur...

Experiment with the new dialog so you just don't see the stars anymore, I set the radius to 95 pixels.
You set get something like this (depening on your original image)

3. Inverting the layer, set opacity

Now you should invert the LPR layer: Menu: Image > Adjustments > Invert
You should now see the LPR layer in negative colors:

Now set the opacity for the LPR layer:

Experiment with the value, but it should be around 50%. Look at your photograph, you should get an even grey thing, like this:

If you see the image background is very even grey, you should join the 2 layers: Menu: Layer > Flatten Image

3. Adjusting contrast, brightness, color, ...

Now the final touch, which should be done carefully. You should get realistic colors for the stars, a black sky and no CCD/scanner artifacts.
Experiment with all things mentioned here, until you're happy with the final result.

• Play around with levels: Menu: Image > Adjustments > Levels:
  
  See what resuts you can get by experimenting with the slides (the 3 arrows)
  The strange thing is that I get blue stars :p
• Adjusting Curves: Menu: Image > Adjustments > Curves
  
  Be careful here, so you don't remove the faintest stars!
• Adjusting the color
  As you see, I get blue stars. You should change the color balance (if necessary!): Menu: Image > Adjustments > Color Balance
  
  To remove the blue from the stars, I had to select 'Highlights', and remove blue by sliding the arrow to yellow (away from blue).
  Experiment with the color balance to see the best results!
• Sharpening: Menu: Filter > Sharpen > Unsharp Mask
  Experminent with this, don't go too far, you may destroy your photograph.

By doing this whole proces again, I got a better final result for my photograph :-)

1'15" piggyback shot, manually guided. 85mm f/1.8 Nikor lens @ f/2.4; Nikon F-50
Film: Agfa RSX II 135 pro (200 asa).

Good luck and clear skies!!!

Pieter Tieghem

Back to my homepage.