Im not sure, i guess its like with humans, if you take them out of their dark hide and flash a bright light in their eyes is can be very uncomfortable (however this is to do with the dilating of the pupils, you pupils are larger so take in too much light). So, do snakes pupils dilate?
Mine hardly ever notice when i take pics but i always make sure the room is light enough and that the snake has been out or in the light for a while before i take them