CF memory speed

[EyeSpy]

As a relative newcomer to the use of the DSLR I would like to ask - if I want to buy a bigger compact flash card does the speed of the card have any relevance. Am I wasting money on a more expensive high speed card? I have a Canon 350d.

[pluto]

Slower card means it takes longer to save an image. This probably won't matter too much if your using it for astro stuff but it would make a big difference if you're trying to shoot stills continuously.
I'm sure if you got a really slow card the camera wouldn't be able to reach it's potential frames per second, but I also don't think the 350D is going to use a top of the line 90MB/sec extreme pro to it's full potential. So somewhere in between.
I've always been happy with my Sandisk Extreme 60MB/sec cards and if they're fast enough for my 5DmkII I'm sure they'll work for you too.

[mithrandir]

As Hugh says, for astro it should not matter what speed you get.

Assume you might want to be able to shoot long bursts. Take the fastest frames/sec the 350d can shoot (ie 3), multiply by the size of the images (RAW+JPG) in megabytes (about 8+1.5). That comes out at something like 30MB/sec. SanDisk Extreme would be fine. Ultra would be marginal. A 16GB card should hold about 1600 RAW+JPG images.

You're lucky. Extreme Pro get no-where near keeping up with the burst rate of my a77.

[RobF]

Solar eclipse work is one area where a faster card comes in handy mind you. I tried a larger faster card in my ageing 450D after coming back from Cairns and was surprised at the difference versus the original older "fast" cards.

Otherwise, when shooting minutes at a time its hardly an issue.