I have this lens cap with integrated gray card for my Sony Alpha gained 57, to carry out a quick manual white balance on the spot, if I want to make JPEG recordings. For RAW images I use usually a gray card that comes with the first shot; for later post-processing on the PC. Functionality: perform keep lid's lens, the light source, manual white balance. Possibly AF off beforehand. Works for me but not indoors under artificial home lighting (floor lamp, etc.), as the light source then too weak. Since such conditions rarely play a role in me, I am generally satisfied with the product.
