I know how to do such tasks as focus stacking and that many people will shoot two exposures for landscapes (one to expose the sky and other for the foreground) then merge them in CS, but is there an easy/possible way of doing it for portraits besides the quick selection tool?
What I want to do is to shoot a composite type portrait in low light and do one exposure for the actual scenery and then one exposure for the model. For example: you're shooting a model at night sitting on a bench on a moderately lit street. To keep the image as clean as possible, you could shoot the surroundings at ISO 100 with a long exposure then shoot the model on the bench, focusing primarily on exposing the model correctly and under-exposing the background then merge them later in CS6.
Would the blend layers work for this or what steps would you need to do to achieve this? I have seen quite a few photographers that take such clean portraits at low ISO in very low light, their exit data seems like it would be merged so I'm wondering if this is possible? Unlike a typical composite portrait, I'd like to shoot the model in the exact same place and layer them in instead of shooting them in a studio and doing the scenery separate.
for what you want to do, you really need to create a mask. The focus stacking is just for images that contain the same content. Using a blen mode like lighten will help blend in the edges of your model a bit easier, but depending upon your background and subject lighting, you still will have to mask.