In a really good discussion of how technology has altered historical research David Turner writes
My only complaint, and I don't know if this is a complaint to be aimed at the camera manufacturers or the historians, is that I wish that there wasn't such a loud clicking sound when cameras take photos.
He's right that most digital camera users at the archives could eliminate that clicking sound. Digital compact cameras have the clicking sound merely to replicate the aural experience of a "real camera". Digital SLRs (and film SLRs, though how many people do archival photography with film?!) have to make that clicking sound. It's the sound of the shutter opening and closing to expose the sensor (or film) to light.
My most popular post on this blog has been Amateur Digitization for Historians, and I would now add one further variable to that discussion about digital compacts versus SLRs in the archives.
By way of background most archives don't allow flash (protecting the documents and protecting you from flash glare on glossy paper obscuring your images), and some archives don't allow copy stands, tripods and other stabilizing equipment. So a big concern in the archives is taking sharp photographs in low light holding your camera by hand.
Digital compacts typically use very high f-stop values which means your typical photo from a digital compact is sharper across the whole image with a wide depth of field. The foreground, center and background are all close to being in focus. But a high f-stop is not great in lower light (even room light), so many digital compact photos from archives without flash come out slightly blurry.
By contrast a digital SLR allows much lower f-stops than compacts. Now, with a lower f-stop your depth of field is reduced, but this doesn't matter as much in typical archival situations. Most parts of the paper are the same distance from the lens. SLRs also allow the user to set a very high ISO. This means you can compensate for the lack of light. Whereas a high ISO on film used to give you a very grainy image, digital SLRs give a much greater range of usable ISO values.
So, the short version of my advice is that if you can't use a stabilizing device, consider using an SLR for archival photography. You will lose many fewer photographs to being blurry than with a digital compact.
Another non-trivial advantage of the digital SLR is that it is much quicker. On a digital compact I find I can take about 400 photos an hour in the archives (mindlessly flipping from page to page). With a digital SLR I have taken over 1000 photos in an hour.
I think Turner's right that laptops, digital photography, and digitization of text are making fundamental changes to the practice of being an historian. My senior thesis advisor told me in the mid-1990s that how we do history hadn't changed much since Ranke or Beatrice and Sidney Webb (who wrote a great book about social and historical research). People looked at documents with their own eyes, and took notes. Then they analyzed and wrote about what they'd seen. Distance was a barrier to archival research. To be sure, the writing became quicker with the introduction of word processors in the 1980s, and computerized archival and library catalogs meant searching for sources was easier. But the process of primary historical research with old documents has been transformed in the last decade. Distance is less of a barrier to historical research, and the productivity of historians will increase tremendously as we take fuller advantage of the new technologies.