Sometimes when attempting to shoot continuously (at high speed) with my Nikon D90, something appears to block the smooth interval between shutter releases.
I have it set up to take RAW and JPEG images together and the specification suggests it can take 7 continuous shots (with the caveat that this "may vary depending on conditions"). I'd like to understand what these conditions are so I can attempt to minimise them.
I realise disk throughput is a big issue so I'm always careful to wait for disk access to finish before starting to shoot. Beyond that, I've observed the following phenomena when holding down the shutter release in continuous mode:
Sometimes it feels like the camera waits after each release until there is something either in focus or moving under the active focus area. I've tried setting focus (and everything else on the body and lens) to manual, but this still seems to occur.
Sometimes after the first shot is taken there is a long pause (20+ seconds) then the next 6 shots are taken in quick succession.
Sometimes it does exactly what I want and takes all 7 shots in quick succession at perfectly equal intervals (at roughly the 4.5fps quoted in the specification).
I can't tell what is causing these differences in performance. Can anyone explain?