Hi everyone I wonder if you could help me? I am going on a trip where I will be out in the field for about a week and although I have a lot of CF cards for my Canon 7D its quite expensive to buy card after card. Can you get battery operated portable Hard Drives with a CF reader built into that you can copy RAW files onto? If so what do people recommend? Thanks in advance.
While the OTG method was already mention and sounds very attractive. I never managed to get it to work with any of the phone I tried. It just never mounted two storage devices at once.
Back when my cameras were using Compact Flash cards, I had the perfect solution which will work for you. It is a portable DVD burner with built-in memory card readers for multiple formats. It can be both battery or A/C powered and the battery lasts for 10 burns in a single charge which gives you 47 GB of backups between recharges. This is ideal since DVDs are incredibly cheap and durable. They have no value to anyone else (so unlikely to be stolen) and you can get backups by duplicating each card into 2 disks. I used to do this, keep one copy with me and mail myself the other. Replication and distribution which is what you want for backups.
Saldy for me, they never updated it to support SDXC cards. So what is left is to backup to an external drive but those are costly. You must buy a $200-300 portable case with card reader, plus the storage inside it. One can use a standard HDD but that is very risky, so you must really go to SSDs which as you may know are costly.
The bottom line is that buying more CF cards will probably be the most cost-effective solution. CF cards are also incredibly sturdy and much less likely to fail than other methods.
If you have an Android phone or tablet with an SD card (say 128GB), then you can use a card reader and an OTG cable to backup up your cards to the phone or tablet. This assumes that your device can act as a USB host. (I don't know if this is possible with an Apple device or not)
I have used this option myself for a trip to Cuba last year. The cost depends on what you already have on hand.
In my own case, I copied them to the tablet and to USB sticks (cheap) so I had 2 backups of everything. I did an end of day backup from the card I used to the tablet.
If you don't have compatible devices already, then it might be cheaper to simply buy more cards, but the tablet is a nice solution that also allows you to view and/or edit if you want, as well as use for any other non photography related activities.
The closest thing to what you seem to be asking for is one of the Sanho HyperDrive ColorSpace UDMA 3 Wireless Storage Device models. Having never used them I can't exactly recommend them, but these check the "battery powered storage" and "CF compatible" boxes.
That said, I wouldn't buy one of these in order to be able to re-use CF cards in the field. I'd buy one to back up my CF cards during the trip, and buy more CF cards in order to shoot more. At $1/GB, cards are much cheaper than film ever was, and if you already own "a lot" of them you shouldn't need that many more to cover a week of shooting.