Originally posted by stevebrot Out of curiosity, does this thread have anything to do with your other thread regarding possible purchase of the DA 55-300/4.5-6.3 over your existing FA 100-300/4.7-5.8? My take is that if you are not happy with the FA 100-300, it is probably that lens for your subjects rather than that lens on APS-C.
Yes, right, the FA100-300 made me thinking of this long time ago, but today I was thinking of FA 35/2 vs. DA 35/2.4. I am no optics engineer, but I think a good approximation for the resolution of the optical system would be the sum of inverses (analogous to the total resistance of resistors in parallel; this is why we cannot directly compare resolution of lenses tested on different sensors - now we have two variables in one equation:
Lens Pixels and
Sensor Pixels). If we use a smaller fraction of the circle projected by the lens, then
Lens Pixels gets smaller. Hence,
Total (Mega)Pixels get smaller as well.
Footnote 1: I am aware that light flux is not made of pixels... but I think you would agree that we could define a
pair of pixels as an inverse of the spatial frequency where contrast drops to 50% of its low frequency value (I did not invent this; this is how Line Pairs per Picture Height is determined).
Footnote 2: Did you notice you also lose light flux as well when using an FF-lens on a cropped sensor? Full-frame FA 35/2.0 performs as a 53/
3.0 lens on the APS-C sensor. Yeah, a full stop of light is literally wasted illuminating the throat of the camera. Those "pixels" are wasted bouncing off the walls of the camera and pentaprism
I wonder where they go (perhaps, this is how hot pixels are born!).