CF Card Questions

[thomasm516]

Hello All,

Recently, while in the process of trying to order a Canon EOS 40D (an order which I subsequently cancelled because I think the merchant was jacking me around) I was told that a standard CompactFlash card will take 4-5 seconds to record a digital image. I recently purchased a 16 GB Kingston CompactFlash Elite Pro 133X. According to the Kingston site, the card has a 25MB/sec. read speed and a 20MB/sec. write speed, has a minimum sustained write speed of 133X, and is specifically designed to get the best performance from high-end imaging devices.

Given the read and write speeds quoted above for my 16 GB Kingston CF card, can someone tell me if this card will deliver acceptable performance with the Canon EOS 40D? Are there faster CF cards out there, designed specifically for digital photography? If so, what are the technical specs that I should look for on such cards?

Thanks for any help that you can offer!

--Tom

[Anbesol]

The card write time is irrelevant even if the technical write speed of the card was that low (which it isn't). Before the data is written to the card its written to a buffer built in to the camera, the buffer doesn't fill up till several photo's are already taken. So CF Data write speeds are only relevant when you shoot a burst of some 20+ photo's in 4 seconds (overflowing the data buffer). 16 gb is HUGE too, it will take you a long long time before you fill that up. The only time you'll really notice the data write speeds will be when you transfer the shots to your computer. That 16gb is fine, the $5 1gb CF Card at wal-mart is fine.

[Franglais]

UDMA CF cards are faster than 133x CF cards - theoretically they go up to about 40MB/sec (266x or 300x marked on the card). However a UDMA card can only be used in UDMA mode with a camera than is able to do UDMA, otherwise it emulates the normal mode - which may be slower than a 133x card

The 40D can't do UDMA mode. There is no point in getting anything above 133x. As Anebesol says you don't need more unless doing long bursts of shots in RAW.

[thomasm516]

Before the data is written to the card its written to a buffer built in to the camera, the buffer doesn't fill up till several photo's are already taken. So CF Data write speeds are only relevant when you shoot a burst of some 20+ photo's in 4 seconds (overflowing the data buffer)...

That 16gb is fine, the $5 1gb CF Card at wal-mart is fine.

Thanks for the information. I'm new to digital photography, but I do work in IT and the more I thought about it the more I realized there *had* to be an internal buffer. I just came to the realization that a removable storage media might be fine for single shots where there is time between pictures to write the image to the card, but it wouldn't be able to handle burst mode without an internal cache. However, being new to digital photography I figured that I should verify that point just to make sure that I understand how it works. Thanks for the information!

BTW, that 16GB card cost me $40. Need4Digital.com wanted to charge me $219 for a 4GB card!!! That's when I hung up the phone.

--Tom

[Franglais]

The camera doesn't just write the image to card - it has to process the image as well. This means:

- all the colour correction, sharpness, saturation etc. treatment that you have defined
- convert to JPG and/or convert to RAW with the parameters you have defined (12 bits/14 bits)
- write the JPG and/or the RAW file to card

My D300 can do up to 8 images/second. A RAW file is about 15 MB and a JPG about 2MB. That's quite a lot of data to process. I think that the internal buffer is used to hold data that is waiting to be treated by the image processor as well as data that is waiting to be written out

[Frog]

Check our camera dealer feedback forum. Need4digital has been getting recent posts as one of the dealers to avoid.
About the only time you'll notice a difference in card speeds is when downloading the pics.

[thomasm516]

The camera doesn't just write the image to card - it has to process the image as well. This means:

- all the colour correction, sharpness, saturation etc. treatment that you have defined
- convert to JPG and/or convert to RAW with the parameters you have defined (12 bits/14 bits)
- write the JPG and/or the RAW file to card

My D300 can do up to 8 images/second. A RAW file is about 15 MB and a JPG about 2MB. That's quite a lot of data to process. I think that the internal buffer is used to hold data that is waiting to be treated by the image processor as well as data that is waiting to be written out

Again, thanks for the information. I've been thinking about this whole issue a bit more since posting the original message in this thread, and I have another question. I'm trying to understand what happens immediately after snapping a photo. As you point out, the camera needs to do processing on the image, so I imagine that right after the picture is taken that all the data gets shipped off to the image processor. You might be right that the buffer queues data waiting to be processed by the image processor. Once the image processor is done doing its thing with an image, does the picture get written to the storage card at that time?

Also, I assume that the image gets written to the card automatically and does not need to be transferred by the user. Is that assumption correct?

My cell phone writes to internal storage and I have to go in a move each picture to card one-by-one, so I thought that I should be clear on that point just to make sure. Granted, a digital SLR is much more sophisticated than a cell phone, which is why I assume that the transfer is done automatically. Still, thought I should just verify that.

The camera has been shipped and should be here in time for the Thunderbirds performance later this month. SA-weet!

Thanks for any help that you can offer.

--Tom

[Franglais]

A camera is more powerful than a cell phone because it has much more data to treat, but they work just the same.

When we're talking about the internal buffer of a camera or cell phone, we're talking about RAM i.e. high-speed memory that does not keep its contents when the power is turned off. It's linked directly to the image processor.

The CompactFlash card is NAND Flash memory that keeps its data when the power is turned off, like a disk. It's much slower to write than RAM. It's seen by the system as being a disk and is formatted in FAT32 usually. Plug your telephone or camera into a computer via the USB port and you will see it as a hard drive.

In your cell phone you have the internal memory buffer plus TWO Flash memory devices - the removable card and a non-removable built-in memory. When your cell phone takes a picture it stays in RAM while being treated then it gets written out to the fixed Flash drive automatically. If you want to get it out on the removable Flash drive you have to move it.

In a camera you have just the internal memory plus the Flash card. The camera treats the image in RAM then writes the result out to the Flash drive.