The HD DSLR revolution started relatively quietly in Cologne, Germany, when people saw the first SLRs that could record HD video. In 2008, at Photokina, both Nikon and Canon showed still cameras that used their Live View function to record video. In the past year, I’ve been invited to speak at a number of conferences, both technical and production-oriented, about using SLRs for production. (While it’s popular to call them DSLRs, I think we’re firmly in the digital world, and I’ve dropped the "D.")

There’s a lot of confusion about the technology, as was apparent in the discussions I had at the end of my presentations. I thought I would bring some of the questions I’ve received on the road back to the printed page.

An outfitted 5D Mark II on the set of Vincent Laforet’s The Story Beyond The Still.

Why So Popular?

There are a number of reasons why people are excited about this technology. Certainly, cost is part of the reason. But the size of the camera is also a big reason for the popularity. It’s the reason why the TV show House used SLRs for their last episode of 2010. The cameras allowed the crew to work in the tight spaces that the script demanded.

The small size also allows news shooters access to areas by being less obvious. Tim Mangini, director of broadcast for Frontline, comments, "HD SLR portability and ubiquitousness make them ideal for circumstances where a larger rig would be problematic. For instance, we were shooting a program in Washington D.C., and were able to shoot for two hours in the Hart Senate Office Building without a problem, but the minute we pulled out the XDCAM rig, security was on the crew immediately."

Why Is Depth Of Field A Consideration?

Form factor aside, the biggest reason for the popularity of SLRs has been the concept of depth of field. It also can be one of the more confusing aspects of SLR vs. traditional camcorder production. A dictionary-style definition of depth of field is something like "…the distance behind and in front of the focused subject that appears acceptably sharp."

The 5D Mark II’s full-frame (24x36mm) sensor.

It’s depth of field, or more specifically, control of depth of field that has made SLRs attractive to cinematographers. Being able to shoot with a very narrow depth of field can be extremely useful in cinematic storytelling. But why depth of field is different with SLRs is often explained incorrectly.

Recently, I read some promotional materials that talked about an image sensor that had great depth of field. In reality, image sensors don’t have a depth of field as we know it. Yes, depth of field is affected by image sensor size, but only because image sensor size changes your lens choice.

Lens choice is really about composition and angle—or field—of view. For a given setup, where your scene composition requires a certain field of view, you’ll pick a particular focal-length lens in order to capture that view. But that lens choice depends on image-sensor size.