I've been wondering what kind of voodoo magic Liveview has and i think i understand it now. After thinking about how an SLR camera works it kind of makes sense.
In an SLR camera, the aperture is an iris made up of aperture blades that close and open and is controlled by the aperture ring on a lens. Aperture has really nothing to do with the camera itself. In an SLR, light hits the lens and travels to the mirror which projects it up the pentaprism into the viewfinder which you then see looking into the eyepiece. So that explains why with a manual lens with no CPU contact, the camera has no idea what aperture you have selected, as it's inside the lens. When an SLR camera takes a shot, it pops up the mirror, opens the shutter curtain in front of the sensor and exposes the image onto the sensor, all happening very fast. Mirror pops down, shutter closes and you are back to the start.
A DSLR has to know the aperture setting of the lens prior to exposure, to be able to select the ISO and shutter for a correctly exposed image. On auto lenses with CPU contacts, the camera can tell the lens which aperture to close down to during that short period when you take a picture. This is of course not possible on manual non cpu lenses and therefor the camera is essentially driving blind.
Now, onto Liveview. When Liveview is turned on, the mirror pops up and the shutter curtain opens, essentially exposing the sensor to the light from the lens, so the camera doesnt really need to know what aperture is selected on the lens, because it only sees light and adjusts the electronic shutter and/or ISO to get the correct light. And since it can automatically correct exposure by controlling shutter and ISO, if you change the aperture physically on the lens to let less or more light in on the sensor, the camera instantly adjusts the light again. However if you lock the exposure, and then change the aperture on the lens, you should see the image get darker or brighter because you told the camera to stop compensating for light changes.
I'm not sure i have everything correct, but it makes sense to me.
In an SLR camera, the aperture is an iris made up of aperture blades that close and open and is controlled by the aperture ring on a lens. Aperture has really nothing to do with the camera itself. In an SLR, light hits the lens and travels to the mirror which projects it up the pentaprism into the viewfinder which you then see looking into the eyepiece. So that explains why with a manual lens with no CPU contact, the camera has no idea what aperture you have selected, as it's inside the lens. When an SLR camera takes a shot, it pops up the mirror, opens the shutter curtain in front of the sensor and exposes the image onto the sensor, all happening very fast. Mirror pops down, shutter closes and you are back to the start.
A DSLR has to know the aperture setting of the lens prior to exposure, to be able to select the ISO and shutter for a correctly exposed image. On auto lenses with CPU contacts, the camera can tell the lens which aperture to close down to during that short period when you take a picture. This is of course not possible on manual non cpu lenses and therefor the camera is essentially driving blind.
Now, onto Liveview. When Liveview is turned on, the mirror pops up and the shutter curtain opens, essentially exposing the sensor to the light from the lens, so the camera doesnt really need to know what aperture is selected on the lens, because it only sees light and adjusts the electronic shutter and/or ISO to get the correct light. And since it can automatically correct exposure by controlling shutter and ISO, if you change the aperture physically on the lens to let less or more light in on the sensor, the camera instantly adjusts the light again. However if you lock the exposure, and then change the aperture on the lens, you should see the image get darker or brighter because you told the camera to stop compensating for light changes.
I'm not sure i have everything correct, but it makes sense to me.