A simple test: Tripod the camera, set in M(anual) mode. Aim at a fixed target. With the kit lens at 28mm and f/8, take an exposure reading (hit the Green button). Shoot. Now replace the kit lens with your A28/2.8 (which is worth what, around US$50?) set to f/8. Shoot. Now you have two exposures of the same target with two lenses with the same shutter and aperture. Are they of equal brightness? Now, without moving the camera/tripod, and with the A28 still at f/8, hit the Green button again. Does it give the same exposure reading? Try the exposure readings comparison again at f/11, f/16, and f/22. Do they differ between lenses?
Originally posted by paperbag846 Ah ha! And by extension, a prime less would have the advantage of less elements (not all the time of course), leading to primes having in advantage in light transmittance! Thanks so much... I was rather baffled.
I'm not sure if this is a factor, but consider that the A28 is an FF lens projecting an image circle that fully covers an FF frame (43mm diagonal), while the kit lens is designed to fully cover an HF/APS-C frame (29mm diagonal) -- and it definitely vignettes on FF below 25mm. IOW, that A28 (or any FF lens) may just pump more light to the viewfinder than an HF/APS-C lens of the same focal length would. Alas, I have no HF primes with which to test this. Any volunteers?