Mythmaker
Senior Member
fstop determines the depth of field... tstop determines the amount of light that goes through.
It's not that tstop @ 1.7 is bad, it's actually quite solid. It's just not as good as the Sigma 35 art @ 1.5. So if you are using both lenses side by side and using the same settings, the canon will be 1/3 stop darker. So to compensate for the 1/3 darker EV, you would have to increase the ISO or lower your shutter speed... hence tstop probably affects event photographers more.
