Simulating DSO's as seen through a telescope (photoshop tutorial)

[Moonhawk]

The flashy pictures in magazines etc often give begginers an unrealistic view of what astronomy will be like "out in the field".

There dont seem to be many resources out there that give a realistic view of what its like to look at various astronomical objects through a telescope.

I have been experimenting with photoshop and have come up with a technique that I thing can turn a long exposure pic into a fairly realistic representation of what you would see if you were looking at the object.

1. Open your picture in photoshop, avoid HST images - they are too good. Try and get hold of decent long exposure that an amateure has taken - I used this one for my experiments: (Note I havent posted any pics in this thread because I havent obtained permission from the author).

http://www.adventuresinastrophotography.com/images/nebula/M42-Orion-Nebula-20071003.JPG

2. Duplicate the layer

3. On the bottom layer - use the "Dust and Scratches" tool to remove the stars (I used a radius of 6 and a threshold of 25)

4. Go back to the top layer and make it a Difference layer - you should now have only stars.

5. Flatten the image using Layer-->Flatten Image. This is your "Stars" image.

6. Open the original "Nebula" image again - leaving the "Stars" image open.

7. On the "Nebula" image - add a new blank layer.

8. On the "Stars" image - use Select-->all, then copy and paste into the blank layer of the "Nebula" image.

9. Hide the "Stars" layer - then select the bottom "Nebula" layer. Shift the hue of the nebula until it looks greenish (I used +106), then decrease the saturation to about -60.

10. Make the Stars layer visible again - then make it a Linear Burn layer.

11. Reduce the opacity of the "Stars" layer to simulate different telescope apertures.

I reckon an opacity of ~90% gives the approximation of a view through a 4-5 inch scope - whereas an opacity of ~70% gives the view through a 10 inch scope.

Note - this method has removed the trapesium which would be visible in both scopes - but you get the general idea.