Sigma Cine vs Cooke Sp3 - Differing Depth of Field at the Same Stop?
I'd like someone with a better understanding of lenses to chime in here. I've been shooting on the Sigma Art lenses sine they came out as my all purpose lens, picked up a set of the Sigma Cine for commercial work, and have been looking into getting a set of SP3's for my Ronin 4D. I grabbed the 25mm and compared it to the Sigma 24mm. Not apples to apples, but close enough.
Without moving the camera, and matches the stop on the lens, the Sigmas were much shallower. I opened the Cooke all the way 2.4 and matched the aperture on the Sigmas. As you do in these scenarios, I'm using my wife who's sitting at the table as a test subject. Both lenses focus on her eye pointing into my living room. The beams on the ceiling are substantially more out of focus on the Sigmas.
Before you ask if I accidentally set the Sigma to t/1.5 by accident, no. I had it matching 2.4 both on the lens marker and in the electronic readout of the adapter in camera. The Cooke was also quite a bit darker all around. It looked as if 75% of the frame was under a heavy vignette and the center was the only part that matched the Sigmas in exposure.
Why is that?