Wednesday, July 9, 2008

handle with care - memory card best practice

I got a lot of great responses and feedback around yesterday's post on choosing a memory card. I wanted to take a few minutes to talk about the reliability portion of the post and expand the discussion a bit more. The big question of the hour is - why do memory card's lock up? Why do I get a card error (or CRD Err if you are on canon)? In order to understand the issue at hand - a little background information is needed...

When a modern DSLR captures a photo a series of processes is unleashed when the shutter release is depressed. The data goes on quite a journey before it reaches the memory card. First the sensor captures the raw data. Then the data is moved to the camera's processor where any noise reduction, sharpening, or color correction takes place. If you shoot RAW this still happens; however, the tumbnail image of the photo is the only thing that gets this processing (hence the fact that it is a RAW file). The image is then moved to the buffer where it waits in line until the memory card can accept the file. Ok, so in this journey the image is moved 3 times. Any time data is coppied there is a chance that this data can be corrupted (basically just means that a 1 gets recorded as a 0 or vicea versa). This generally doesn't happen in camera because the relationship between the sensor, processor, and buffer are all painstakingly calibrated at the factory by your manufacturer. The variable is the mempory card. Most corrupted data happens when the camera transferes the photo from it's internal system to the memory storage system. Since this is where most of the problems occure is there anything we can do? Unfortunatly, there is nothing you can do to 100% eliminate the problem; however, there are several things you can do to reduce the possibility of an error.
  1. ALLWAYS formatt your memory card in the camera. Formatting your memory card on the computer can give probimatic results. Cameras use a VERY SPECIFIC fileing system. Because their firmware is designed to do one specific task, the camera doesn't have the ability to flex or adapt if you move things around. Don't confuse your camera, this raises the risk of a card error
  2. ALLWAYS formatt. Never, Never, Never preform an "erase all" within the playback menu. This leaves scattered table data on the card that can interfere with the camera's numbering and fileing system. Formatting completely resets the card so it is clean. preforming an "efase all" is a shure way to find a card error
  3. NEVER open the memory card door while the camera is writeing a file. If the camera is unable to completely write a file to the flash memory the drive table takes a beating. Not a good idea
  4. Monitor the preformance of you card. Lexar makes a utility (Image Rescue)that ships free with their Pro cards that will tell you what the operating capacity of the drive is. I have an old 512 MB card that registeres 476MB. As soon as you see the size of the drive go down it is time to toss it. Or at least give it to someone you don't like ;-) When flash drive's loose their elasticity they stop holding data. I wouldn't want my memory card to stop holding data at a wedding YIKES! Once the drive starts to lose data it will continue to expanentially drop data - not only drastically increases the posability of a card error, it also means your photo may not actually save.
  5. Talk to your camera manufacturer to see what card they reccomend. More specifically, ask them if there is a card they don't recommend. For example, Canon has publicaly stated that LEXAR cards are problamatic in some situations. READ HERE
  6. Take care of your card physically. Don't leave the card in static prone areas (your pocket). Don't wash cards, don't allow them to get wet... feel like I am getting into an area of common sense here.
If you take care of your memory card and make sure you format as perscribed above you shouldn't ever have any problems. If you do, SanDisk and Lexar both ship recovery software that can recover images from a locked card as long as it has not been written over (works 99.99% of the time. I have never ran into a card that it didn't work on). A few extra dollars at the time of purchase goes a long way if you end up with a problem down the road.


Danny said...

Hey Rick,
Thanks for the info, quick question though. I've read that it's bad to completely fill up your card when shooting and I was wondering when you consider a card to be full and pop in a new one? I imagine it would vary depending on card size and image format, but I was curious what you do.

Rick Mead said...

I have heard that - but honestly I don't think that it is a valid problem to worry about. I consider a card full when the camera won't allow me to take any more frames. The argument for not filling the card to capacity comes from the fear that your camera will go to record a photo and there isn't available space. Best case you lose that photo. Worst case you lock up the memory card. Here is the hole in that argument - The camera knows approximately how large a file it will be creating at the current settings. It then looks at available storage and allows you to take a "safe" amount that engineers have spent months calculating. Try this: Take your camera and load an empty card in the slot (actually it doesn't have to be empty, just have some free space on it). Then set the ISO to say 200. Take a second and note how many frames your camera says you have. Now set the ISO to 800 or 1600. That number went down didn't it? As you make adjustments to your camera, anything that will impact the amount of available photos immediately posts.

The place that can get you in trouble is if you have deleted single photos from the memory card. When you hit the playback / review button see a bad photo and delete it the photo counter adjusts accordingly. So what happens if you delete a photo taken at ISO 200 and then go out and take a photo at ISO 800? Now the data is fragmented - meaning that part of the file containing the photo is in one part of the memory card and the other is somewhere else. As I talked about in this post - Camera file systems are very rudimentary. They use FAT 32 for cryin' out loud. Your goal should be to throw as few curve balls at your camera's data system as possible. This will reduce the possibility of a crash or other problem.