Today I was reminded of a simple but effective way to more easily isolate dust spots on your photograph while working in Photoshop. (which I had neglected to do!)
I was printing a 12"x18" enlargement of this vermillion flycatcher for an upcoming show (photographed at Lindo Lake, Lakeside, California). Although the image looked fine on my monitor, after I printed it I noticed two faint but distinct, large dust spots to the right of the bird.
I went back to Photoshop, and made a curves adjustment layer which markedly increased the contrast of the sky.
It became evident that there were even more dust spots!
The spot healing brush quickly eliminated them.
Move the curves adjustment layer to the trash, and you're left with a dust-free sky!