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Old Jul 12, 2008, 4:47 PM   #1
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Okay, this is kind of an elementary question on the face of it, I'll admit. But, really, just how much impact does the spec-speed of a given memory card (CF or SD) have on the performance of a camera in the field? I'm not talking about how long it takes to download images to one's computer.

To be more specific, I'm talking about DSLRs here. For example, since most sub-$1000 DSLRs don't have blazing burst speeds - limited generally to 3 or 3.5 fps - can a really fast card improve that performance? Or is the camera manufacturer's published burst speed for a given camera the "best possible" figure - meaning anything slower than the fastest SanDisk Extreme IV card (or equivalent) will give you a slower burst speed? Or does it really make a noticeable difference at all?

I wonder if a camera like Pentax's K200D - with a notoriously slow 2.8 fps - or any other DSLR can be made to perform a bit better with the best card available? Could one possibly squeeze out an extra shot - or close to it? Would faster, more expensive DSLRs respond more readily to the capabilities of a faster card?

For my film SLRs this was never an issue, of course. And my smaller digital point-and-shoots came with too much delay for the card to make a real difference in terms of speed.

Just asking. Perhaps I'm being naiive or forgetting something obvious.
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Old Jul 12, 2008, 9:35 PM   #2
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Digitral cameras have internal buffers they use to store and process images before they write the final version to the card. The speed of the memory in that buffer is one factor that determines the burst speed spec. You can get 3 frames per second or 5 frames per second, or whatever the spec is for your particular camera, up until the buffer is full. Once the buffer is full, then the speed of the flash memory card determines the burst speed.

For instance, you might be able to shoot 5 consecutive frames at 3 frames per second, but if you've got a slow flash memory card, your camera can only take 1 shot per second because transferring photos to the card is slow.

As an example, I can shoot 5photos in RAW formatat3 fps on my Konica Minolta Maxxum 5D. Once I take the fifth shot, things slow down. If I'm using a SanDisk Ultra II, I only get 6 frames every 10 seconds, but if I'm using a SanDIsk Extreme III I can get 11 frames every 10 seconds.

The speed of the internal buffer determines the initial frame rate, but the speed of the flash memory card determines the subsequentframe rate.

If you have different flash memory cards, you can try it yourself. Set your camera to manual focus andmanual exposure, leave the lens cap on, and hold down the shutter button. You will hear the initial 5 or 10 shots go by quickly, but then, suddenly, it slows down quite a bit. Count the shots that occur within a 10 second time span. Then, switch to another card and try the same thing. Which ever card gets the highest number of frames with 10 seconds is the faster card.

And, you can't make a slow camera faster by putting a faster card in it, because the speed of the buffer doesn't change.
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Old Jul 12, 2008, 11:08 PM   #3
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That makes perfect sense and kind of reinforces what I suspected might ultimately be the case. I appreciate the response.
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