If I have two different lenses, and I take a shot at the same aperture, shutter, iso and focal length, should brightness levels be equal?
Right now I have a Pentax 18-35mm and a Tamron 28-75mm. Shooting conditions was Raw with no image processing. 28mm, two 60w incandescent overhead lights on ceiling, wall is approx 7ft from lens.
As you will see below, the pentax is brighter all the way through until f4.5, to which both lenses are about even. Is this difference due to a faulty lens, or the fact that the Tamron is an IF lens, blocking some of the light? Or, is this just normal variance for different lens manufacturers?
Tamron on left, Pentax on right (sorry, the pentax was a bit misfocused). All shots at 28mm, ISO 800, 1/10 sec, and respective aperture:
Last edited by rmtschanz; 07-03-2009 at 12:23 AM.