I suppose it depends on whether your digital camera will let you, for a start.
Even with film cameras some do and some don't. The biggest
disappointment about my N90s is that it doesn't. Amazing.
As for using PS to do it, that's where layers come into the picture.
--
Emily L. Ferguson
mailto:elf@xxxxxxxx
508-563-6822
New England landscapes, wooden boats and races, press photography
http://www.vsu.cape.com/~elf/
