>>3681796Thanks, now I got it. Here's the reasoning:
Speed boosters lower the focal length by keeping the aperture diameter constant, thus concentrating light, thus decreasing the t-number based on the new focal length, constant based on the old focal length. This could result in equal SNR due to increased luminance on less sensor area. In mathematical terms, integration of higher signal over less area. Literally, the total amount of light can be constant here.
So for conventional equivalent focal length (not speed boosted) the aperture diameter is dependent on the new focal length, not the old focal length, the t-stop is constant. This lower the SNR due to equal luminance on less sensor area. In mathematical terms, integration of constant signal over less area. The total amount of light is less here, yet the resulting image is supposed to look the same.
There was my confusion. The graph shows exactly the latter, the amplification and the noise floor are higher, thus the dynamic range decreases.
