I'm trying to photograph a painting without using any lighting equipment, just the natural light in the room on a cloudy day (i.e, little or no direct sunlight). I am shooting straight on with a tripod and DSLR using Av mode with ISO set to 100. (By the way, I am also shooting RAW).
The goal is to reduce glare as much as possible and so it is important to have the painting as evenly lit as I can without using lighting equipment.
My question is this: what's the difference between shooting a long exposure in a dark room versus shooting in a well lit room, when the only difference in the two photographs is the shutter speed and all other settings remain the same? In theory, I would hazard to guess that it should produce the same image, but in practice I don't think this is true. In my tests, the long exposure is definitely not as sharp when viewed at 100% while the normal exposure appears to have more pronounced highlights and shadows (due to the fact that there is a stronger light source?). Hopefully someone can shed some light (no pun intended) on the difference here.
Just to clarify: in the "dark room" scenario, the shades are closed over the window but there is still some light entering the room. In the "well lit room" scenerio, the shades are open but there is no direct light entering the room.
Kind of an odd question I suppose, but thanks in advance.
Edit: I just realized I had forgotten to turn off image stabilization on my lens, which may account for the lack of sharpness in the long exposure.