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The Image Bank allows shots to be done to a CF, AND the IB as back-up .... not bad for those once in a lifetime shots ... and it works with all CF and HD cameras ... so you can shoot with multiple cameras.
Plus, IF you own an H2D or H3D camera, you can't use the back on a technical camera remotely without the Image Bank because there is no way to power the back.
I use the 16GB card and noticed that if you use the older firmware version 233 you can actually get 663 images per card. As soon as i upgraded to the newest firmware version the card capacity dropped to 493. Therefore, I switched back to version 233.
Have heard - not sure - that they algorithm to calculate the ammount of remaining pictures was changed to a more conservative way. Finally the
ammount of remaining pics is the same ! (to be verified...)