Newb off camera/slave flash question
Now here's my question--with the flash off camera as a slave, does anything differ whether I want to use the flash as fill or as the primary lighting source? I know for flash compensation I have to dial it in on the camera rather than the flash (when the flash is off camera) but other than that is there a difference? In other words, with the flash off camera as a slave, do I still put it in A or S to use as fill and M to use it as the primary source?
You can still work the way you are working, you'll be fine. I do all manual myself in all the situations you listed, just easier for me.
One final question--is it possible using the set-up I explained (one sb-600 off camera and a d300s) to use the on camera flash as my primary light source and the off camera flash as fill?
Yes, if the sb600 is set so low that the built-in flash can overpower it. (or bouncing the sb600 off a wall/ceiling/etc, ND-ing the sb600... lots of options) A much better way would be to mount the sb600 to the camera (since you want the main light to be on axis... why do you want your main light to be on axis?) and use a reflector to harness the extra light back to the subject.
I cannot figure out how to do this in the custom settings for the life of me. The only thing I can think of is to set both flashes to TTL and set the camera to M and then dial back the exposure on the slave.
also another way. There are many, many ways, but using the sb600 as main from camera is your best bet for this particular scenario. Good luck.
Any thoughts? Thanks!