Richard's Notes

If you use a high speed, high capacity Lexar compact flash card and use any Canon DSLR (Rebel, 20D, or their higher-end cameras) you need to carefully read the following links as there are problems that you will want to know about.

I noticed this a while ago on my Rebel: if I take some pictures and hit the Review button before the buffer is done writing (the red light is still flashing) the camera sometimes loses an image or two. I thought I was going crazy when I copied images from my CF cards to my computer as all the images I remembered taking were not there. I let it go thinking it was my leaky memory but this product advisory supports and explains my experience: it’s the compact flash card’s leaky memory when combined with these higher end Canon DSLRs.

I have two Lexar 1 gig, 80X cards within the serial number range affected by this and at some point soon Lexar will either recall them or offer a download of a flash upgrade for the firmware on the cards.

For more on this:

Problems with Canon SLRs and Lexar cards
Lexar Customer Advisory

I decided to order a backup card and did a bit of research and decided on a Sandisk 1 GB Extreme III Compact Flash Card. Unfortunately they are back ordered at B and H but I found them at Calumet for $10 more so I ordered one through them at Amazon.

Rob Galbraith has an excellent chart of CompactFlash Write Speed – Canon EOS 20D and you can use the pull-down to get a chart for other cameras. This should help you figure out what you might buy as a backup for the Lexar in case the recall involves sending card(s) back to them for re-flashing.

What’s interesting about this is that I’ve had a long time assumption that Lexar was the highest end flash memory and it may be; as these companies invent technologies to help unload pictures faster from cameras problems are bound to crop up.

Notes and Background
If you scan around on Amazon or other places where customers get to review these compact flash cards you’ll find mixed reports on the high-end, fast cards, but these reports generally show ignorance on the part of the reviewers about how cameras and cards work together. Here’s a very simple explanation.

Every digital camera shares one thing: a sensor that captures light. How many pixels (or megapixels) that sensor has on it determines its resolution.

Most current (as I write this) mid-range consumer digital cameras have sensors that have between 2 and 4 megapixels on them. Higher end cameras, like the above mentioned Canon Digital Single Lens Reflex (DSLR) models have 6, 8, or up to 11 megapixels on their sensors.

When you take a picture the camera records what is on the sensor by writing it to the flash media as a picture file. Once that write operation is done, the sensor is cleared and ready for another shot. How fast this process takes place determines how much lag there is between pictures. Lower end cameras have more lag than higher end cameras.

One mistake many novices make is to think that buying a faster media card, like the above mentioned Lexar 80X or Sandisk Extreme will help this write lag on all cameras. On lower end cameras buying fast cards may have no effect because the cameras don’t write and clear fast enough to get ahead of the cards.

As sensors have gotten bigger (more pixels) write times have gotten longer (more information to copy from sensor to media) and higher end cameras have an intermediate memory space called a buffer to handle this.

DSLRs are not only faster out of the box, but they have this buffer memory to allow the sensor to get ready for the next shot before the media card is fully written to: take a picture, write to buffer, take another picture while buffer writes first picture to media card, etc. Also, all DSLRs have single shot and continuous shooting mode (the digital equivalent of a motor drive for film) and this mode puts a huge strain on the buffer.

The size of the buffer determines how far ahead of the media writing process you can get when taking multiple pictures. Higher end cameras allow you to continuously shoot until the card is full, before the card is fully written to.

Because these higher end cameras can work so far ahead of the media card, media card companies like Lexar and Sandisk have embedded technologies on their cards to allow the cards to be written to faster. However, these higher speed cards are only meaningful on higher end cameras that have buffers and write fast. The intersection of buffer and embedded card technology is where the Lexar/Canon problem is taking place.

Back to the problem
One of the two problems the high speed Lexar compact flash cards are having is related to this: if you shoot ahead of the card and then quickly review while the card is still writing you are asking the buffer to do two things at once, which it should que and do in order but in fact it seems that sometimes some of the images that are in the buffer and not fully written to the card can get lost as you ask the camera to review or show the last images shot.

This problem will not happen on lower end cameras with no buffer, it’s just the higher end cameras that have buffer memory to speed up the process that seem to be getting confused and losing track of things.

One simple solution is to order a lower-end compact flash card that doesn’t have fancy firmware to increase speed and use it until this stuff gets sorted out.

Another even simpler solution is to continue using the high end Lexar cards but don’t review your pictures until the red light (card activity) has stopped blinking.