I'm using CHDK on a SD850is which I'm sure is the same with respect to your questions.
You can use a 4 gig card and have CHDK autoboot without partitioning.
The reason you may see different
answers is because the card has to be formatted with a FAT file system and
a "standard" FAT file system cannot address more than 2 gig.
However, if you run with a larger than "standard" block size up to 4 gig can
be used.
Not sure which, if any desktop OS you will be using. Some can't format the
4gb cards with the non standard block size.
Off the top of my head I can't remember which but either Vista or XP
can't format the 4 gig card with a FAT filesystem. (I think it was XP)
Both Vista & XP can read them just fine once they are formatted.
I'm currently using an 8gig card. You have to partition to use that size
if you want it to auto boot. If you don't need autoboot, then you don't have
to partition.
While it works, it is a pain to deal with the dual partitioning on Vista and XP.
Microsloth for some reason won't allow the OS to see more than a single partition
at a time on SD cards. It can only see the "active" or boot partition which is
not where the images are stored.
It is because of how Microsoft treats "removable" media. There are some hack
drivers out there that make a USB SD reader look like a fixed USB drive which
makes the partition issue moot as you can then see both partitions at the same time.
If you have to deal with multiple partitions,
it's not that bad actually if you put CHDK on both partitions, there is a partition swap
option in CHDK that you can use to flip/swap the active partition.
You have to use this to swap partitions so you can see the image files on Vista & XP.
If you put CHDK on both partitions you can then boot the "alternate" CHDK and flip
the partitions back after the next reboot.
The big problem you may have is no access to the print button.
Without access to this button you may not be able to change any CHDK parameters.
Yes you can use CHDK by automatically booting it.
And you will be able to take raw images if you set it up prior to putting the
camera into the housing, but then you will not be able to alter any of the CHDK
parameters.
The way CHDK works, is it sits to the side of the normal firmware and can
override the normal firmware parameters by altering memory locations that the
normal firmware uses. This includes things like shutter speed, aperture,
focus, etc...
To alter these settings, you flip between "normal" mode and "CHDK" mode.
It is in CHDK mode where you can set all these parameters, and perform scripting
operations. Once you alter the parameters you flip back to "normal" mode
and the normal firmware is tricked into using these new settings.
Without access to the print button you may not be able to enter "CHDK" mode
so what you can do with CHDK will be limited underwater.
Perhaps there is an alternate button that can be assigned to enter CHDK.
My guess is that somebody has modified CHDK to re-assign the button to
something else - Check on the forums. If not, if you are into some programming,
it isn't that hard to modify the code for things like this.
As far as cards go, here is a link to the CHDK benchmarks if
you haven't see it yet:
CHDK memory benchmarks
I recently bought a few generic/bulk cards from Microcenter.
Microcenter SDHC cards
I've actually had pretty good luck with them. They are quite a bit cheaper than
the name brand cards. Currently $10.00 for 4gb and $15 for 8gb.
Speed is pretty good as they are class 6 SD cards.
I need to update the SD850is numbers on the CHDK benchmark page.
As an option, you could get an 8gb card and partition it into 2 4gb partitions
and not use but 1 of the 4gb partitions when using CHDK and then format
it as 1 8gb partition when not using CHDK.
Then if you decide to partition later or want the extra space when not using CHDK,
you have the larger card. - Just a thought.
--- bill
