I got some extension tubes made for the Sony Alpha. How do I control the lens’ aperture when using the tubes?
There are inexpensive extension tubes that do not have the electronic contact pins to connect the lens with the camera. And then there are more expensive ones (such as those made by Kenko) that have the contacts. There is no way to control the lens aperture except through the camera. And if the camera can’t talk to the lens (because there are no electronic contacts on the tubes) then the aperture will have to stay wide open. There is no other way to control it. So if you have the inexpensive tubes with no contacts, you will have to use the lens wide open, and you can control the image only with the shutter speed. If there is too much light to get a good shot, the other alternative would be to use a neutral density filter to darken the lens.