Quote Originally Posted by HDNitehawk View Post
Yes but if you are using MF and no IS and it is still slower then it tells quite a bit. The battery / power to run the lens wouldn't matter.
Ok, yep. That could tell you something. Aperture control, overall circuitry, etc could still be issues, but AF and IS are likely main power draws.

Quote Originally Posted by HDNitehawk View Post
Why would FPS and AF even be tied together? The camera apparently has enough power to focus. Do you have to achieve focus before the R5 takes a picture?
Mostly power supply as it does AF between frames. But my initial thoughts here were not directly AF vs fps, but rather overall power vs achievable fps with the R5 having the smaller battery than a 1D body. I am going off part of what I read, and part my own experience and thoughts on what I've seen. I have read that the reason the R5 drops FPS as the battery draws down is that certain capacitors cannot charge quickly enough at lower battery levels. Because electronic shutter is at 20 fps and that does not appear to be impacted by the 500 MK1, I am assuming the primary power demand other than the lens is the capacitor that drives the mechanical shutter.

The other piece of anecdotal evidence that the 500 MK 1 is a power hog, at least on the R5, is the video I linked earlier in this thread. For whatever it is worth, they burned through batteries and complained about battery life using the R5 and 500 Mk1. This does not fit my experience with the 500 MK II nor others I have seen use the R5 with MK II big whites. For reference, I was shooting all day, 4,500 to 6,500 images per day, at Laguna Seca and only once did I need a 3rd battery. The other two days were 2 batteries.