Does long exposure affect the sharpness of a picture, assuming no camera shake?

Assuming that the camera does not shake during long exposure photography, How does the sharpness of the image get affected? Would it be more sharp, less sharp, or remain the same?

Answer

In a perfect camera with a perfect sensor, sharpness would remain the same. No such thing exists so you have to consider two possibilities with whichever camera you have. The long exposure causes the sensor to heat and increases image noise:

1. 
   

   Your camera does not like that and therefore applies long shutter noise-reduction to clean things up and you get a less sharp image.

   
   


2. 
   

   Your camera is oblivious to the increase in noise and leaves it there. Speckles caused by noise destroy some fine details but make the image appear sharper sometimes.