[G-CPTN]

Having just acquired a (secondhand) camera which has the ability to shoot RAW I need some advice.
At present I shoot only in JPEG and I have found that any sort of editing (even in Windows Photo Gallery to slightly adjust the exposure) reduces the size of the image (in KB if not in area). I presume this is due to the JPEG format?

Whilst the camera is 10Mp, the images saved on the SD card vary between 3600KB and 4400KB. Is this correct?

What size would a RAW image be?

I believe that the camera has the facility to save RAW and JPEG (there is also mention of compressed RAW format (PEF) and non-compressed RAW (DEG)).

At present I am 'short' of SD card capacity (256MB) so I don't want to fill this up un-necessarily.

What would others advise?

I'm not expecting exhibition quality, but I would like to use the capability of the camera when, perhaps, I want to enlarge a subject (I tried shooting high-flying airliners with vapour trails using a 300mm (450) lens but the image, whilst in-focus soon gets pixelated when I zoom-in).