>I have been having a similar issue. Doing star trails set for >30 second exposure with 20 second gap in between exposures and >set for 450 exposures. tried this twice and the camera stopped >at 179 exposures the first time and 129 the second. I can't >believe it's a write speed issue given the 20 second gap >between exposures - set at JPEG medium. It is a Class 10 16GB >card also. Given previous experience in burst mode, this pace >of writing to the card should be no problem. Could it have >something to do with the sensor given the continuous long >exposures?
I think you're falling into a trap that many have visited before you. The 'interval' is not the time between the end of one exposure and the start of the next, but the time between the camera triggering one exposure and attempting to trigger the next. Since you have 30s exposures and 20s interval, the camera tries to trigger the 2nd exposure before the first completes. You'll only get, at best, half of your intended exposures. I suspect you may have Long Exposure NR on, which takes the time for each exposure out to a bit more than 60s, so you get just 25% of the programmed shots.