Continuos Shooting Mode rate limiting step?

Started Jan 6, 2009 | Discussions thread
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Canon55902
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Continuos Shooting Mode rate limiting step?
Jan 6, 2009

To get "spontaneous" photos of a very active 2 year old, I tend to use Continuous Shooting mode. I have a 450D body and a 70-200 f2.8 IS lens.

In an effort to optimize the number of shots in a given sequence, I purchased a presumably "fast" SD card (SanDisk Extreme III 30Mb/sec, 8 gig). However, I notice that sometimes I can only take 7 or 8 shots before the buffer is filled and I get the dreaded "Busy" screen right as my subject has the cutest smile ever (Is that Murphy's Law of Buffers?). Whereas at other times, I seem to be able to take 12 to 15 shots. This is even at the same image quality (High quality jpeg only. No simultaneous RAW image).

At first, i thought it was a function of images still being written to the card, but the variation in number of sequential shots can persist even after a few minutes, when presumably all pics would have been written to the card.

Or would they?

Does anyone know how big the actual buffer is? And is the writing speed of 30Megs/sec a "real world" speed or same unachievable lab benchmark? Is it possible that even after a few minutes, the camera could still be writing to the card from the buffer?

I thought that I had the fastest SD card SanDisk makes, so short of reducing image quality, are there any other ways of maximizing number of sequential shots in Continuous Shooting mode?

Also, is the difference partially a function of slightly different file sizes? File size ranges from 3,400 kb to 4,700 kb with my current image quality settings. Obviously, this is up to nearly a 40% variation in file size, which could account for some of the variation in writing time to the SD card, and time to clear the buffer. Is this a correct assumption?

Readers Digest Condensed version of questions:

Is the SanDisk Extreme III 30MB/sec the fastest SD card available, that is compatible with the 450D?

If any other faster SD cards are available or become available in the future, would the 450D's buffer size still be the rate limitng step?

Any ideas to get more sequential shots in a given Contuous Shooting mode sequence (other than manipulating image quality/file size)?

Thanks to all in advance for your help!

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