In days of yore, yer grampfer used to use these to touch up his photos:
Paasche type F single-action airbrush
Paasche type VJR double-action airbrush
Type VJR stripped for cleaning
I don't use them for photo-retouching. The airbrush is a valuable tool for creating realistic images:
Jaguar E-Type series I rendered using both the above airbrushes and Rotring acrylic ink on Bristol Board.
I'll have another go when I can afford to buy a good compressor. The old one doesn't have a storage tank on it so it delivers a pulsed air supply which is not good for fine detail work as you end up with a line of dots. There's one in Millers for £200. I'd hope for something a little cheaper.