The specifications of your camera should tell you the exact bit rate for the format you are shooting in. From this figure, it is quite easy to calculate how much storage you’ll need.
Start with this formula to find the maximum card size:
|Coverage / day = (in minutes)||Total Footage Time (in minutes) / Days in Production|
E.g., if a 2 hour movie is shot at a shooting ratio of 5:1 on a Canon C300, then the storage required in total will be = 6.25 x 2 x 3,600 x 5 / 1024 = 220 GB.
This does not mean you need 220 GB of CF Cards!
If you have a 32 GB CF Card, then you can record about 87 minutes of 1080p footage on a C300 at broadcast quality. That’s about 1.5 hours, and in our example the total hours of footage is only 10.
Once I’ve calculated the total storage required I look at my production schedule and see how many days of shooting I have in total.
E.g., say my low budget indie has to be wrapped up in 15 days and I have to shoot 10 hours of footage. That means I have to shoot 10 x 60 / 15 = 40 minutes of footage per day.
At the end of the day I’ll be offloading all this data to external backup storage (I’ll cover that soon).
If I keep up my average coverage per day, I could get by with only one 32 GB CF card. If I double my speed and shoot 80 minutes per day, I’ll still only need one 32 GB CF Card.
Does that mean one 32 GB card will suffice for the entire production? No, of course not.
In this case I’ll choose three or four 16 GB cards instead, or even three or four 8 GB cards. Why? Because that allows the data wrangler the chance to offload data after each setup. If a full 32 GB card fails at the end of the day, I’ll lose the entire day’s work. It’s important to strike a balance.
In our example, I’m shooting 40 minutes of footage per day, which is 14.7 GB. Let’s assume I’m covering 5 scenes per day (or 5 setups, it doesn’t matter. Just divide into chunks that work for your production).
Use this method to find the lowest card size per day:
|Card Size (GB) =||Total Footage per day (in GB) / Average setups or scenes per day|
Continuing with our example, the lowest card size works out to be about 3 GB.
Cool. Now we know our sweet spot is somewhere between 4 GB and 32 GB.
What I end up choosing will depend on the budget. I will consider the possibility that if all my media is lost or stolen, and I’m only left with the one in my camera, then it should get me through to the end of the day.
This is why for this particular example I chose 16 GB. It’s smaller and more manageable than 32 GB. It’s cheap enough and I’ll still have enough storage to get me through to the end of the day in case every other card is lost.
This 16 GB card is then multiplied by whatever figure that’ll give me piece of mind. As a rule I always carry three cards – two for rotational work and the third as backup. The third card is not kept with the other two.
As cards get cheaper, one can avoid the fuzzy mess of having to choose the right card length and just get multiple copies of the maximum size required per day. In our example, it would mean at least 3×32 GB cards.
Why do I do it this way? Simple. Once I’ve covered a scene or setup, there’s almost never any time (or money) to go back and redo it. Can you imagine a production grinding to a halt for lack of a memory card?
Rule of thumb: You can’t afford to lose footage, so the smart thing to do is backup at every opportunity; or at least after each scene is done and before you’re moving on to another location or setup.
Finally, after you’ve determined the right size of memory card and how many of them you’ll need, you can look at options.
- Write speed of card should be at least one thirds faster than the maximum data rate
- Read speed must be as fast as your backup system, if possible
- Recommended manufacturers only
- Tried and tested over new untested technology
- Easily available and replaceable
For the rest: Sony makes them all!
Cases or Pouches
Memory cards, like coins, need wallets.
My personal preferences:
- Hard plastic for physical protection
- Non-metallic to avoid ‘shorting’
- Transparent so I can read what’s on it
- For cloth, only micro-fiber
- Silica gel/Desiccant for moisture control
- Album-style, so I can see every card at a glance
When I’m looking for cases, I always look first at what the card manufacturer offers, like this one from Sandisk. If Sandisk can make and ship millions of cards, one hopes they know how to store them, too.
If there is something that a manufacturer stresses, do it. If for nothing else, do it for warranty’s sake. They might not always offer the perfect solution. At worst, their advice is conservative, and that’s not a bad thing.
To search for memory cards on Amazon, click here.