At its fastest, with a speedy CFexpress Type B card, the Canon R5 eats RAW files at a rate of about 10 per second. This effectively gives shooters a 10 FPS camera without any cache limitations, even though the camera can shoot 20 FPS in bursts. But forum dwellers on the internet, in trying to figure out why they were getting different cache clearing speeds, discovered that the operation of the electronic viewfinder (EVF) radically slows down this ingestion rate.
Where the R5’s cache can be read out to the card in about five seconds, using the EVF while the cache is clearing causes it to take just under 20 seconds, a 400 percent slowdown. Whether from an additional power draw, or – perhaps more likely, additional processing needed – the delay is added on for only the time the EVF is activated. As many shooters set the camera to automatically turn on the EFV when their face is near the viewfinder, the cache clearing can be accelerated simply by moving one’s face away and watching the cache clear on the back LCD, which does not slow down the data transfer.
The effect is also negated by setting the EVF to the lower refresh rate. This accomplished by going to the red section in the menus, on the 8th tab, where “Display Performance” will be found.
The CFexpress card review published here, comparing the main cards available on the market, was unaffected by this phenomenon, as the data was collected with the camera on a tripod employing the LCD.