processing m45

[astrokat]

this is my first ago at m45 now the problem i got is that every time i try processing i get halo around the stars how do i get over this

thanks toby

[ATTACH]30143[/ATTACH]

[mint_mark]

Do you mean the cyan rings around the brighter stars?

That's the sort of effect I get if the curves have a dip in them.

If you start at a star in the image and move away from it, the light intensity goes down. On the curves graph this is like starting at the right hand side (high intensity) and moving to the left. If the curve has a dip in it, then after transformation the intensity will go down (into the dip) and then back up again, causing the brighter ring around the star.

Your rings are cyan, so is there a dip in your red curve?

[ollypenrice]

In M45 haloes are very hard to avoid. The stars are so bright. And they are also hard to control (though the points made by Mark are spot on) because they are embedded in nebulosity which will change as you try to change the halo.

But for another occasion, when dealing with haloes against a dark background, things are easier. Photoshop; make a circular selection around star and halo, larger than both, and feather it. Open curves and pin the curve at the level of the background sky. Don't let anything below that get a change. Then just above that point, drag down the curve and the halo will recede. If it is a blue halo then you can try doing this only in the blue channel. If the star itself becomes a little distorted then circular-select it closely, apply a small feather, and then give it a dose of radial blur at maximum to round it up.

That's a nice M45 anyway. It is very difficult to get a beauty. I'm still trying after four attempts!

Olly