Working in Libanon on a documentary project we had to interview several people in different living conditions, light setups etc. Although all the shots should look "familiar" and have a strong "recognition" from scene to scene, we also had to preserve the natural feel and look and make it look very much like a documentary rather then a high gloss head shot.
Most of the interviews were supposed to be longer then the traditional broadcast "soundbite", so we decided to bring in 2 cameras to have a dynamic wide-close-up option during editing.
Although we weren't sure if we rather would stick with one or the other shot, we felt more comfortable having both options.
Unfortunately, we didn't have the luxury of having two same camera bodies. That is actually a real problem and in general should be avoided. But for the fact that it wasn't essential to have both shots and if something would have gone wrong, we would have been ok with just sticking with one of the cameras in the post production.
The only other cam that came close to the looks of the A-Camera ( 5D Mark III ) was my old Canon 7D.
This camera, although it was very good and for its time far ahead in some elements, it shows nowadays its age. Having a natural crop factor, we decided to make it the close-up camera.
For sync we just let the internal microphone record while the 'good' sound was recorded directly on the 5D, which is much better suited for sound recording.
Thanks to modern waveform analysis, it is barely necessary anymore to have a sync signal (clap) or similar old-school tools, when working with a multi camera setup.
The first thing that strikes you is, that it is general not easy to match the look of the images from both cameras. Sharpness, color etc. can be quite different. You have to invest some time to play around with the white balance and ISO settings to come as close as possible. Especially the noise can be a pain for the 7D producing quite a substantial amount of it. When seeing it on screen, you might not notice right away, but in the editing room you see pretty fast that those 2 cams have years of development between them.
For light we brought one Kino Flo setup that normally delivers pretty balanced, even and color neutral lighting. Despite that, we spent a good amount of 30 mins of trying to sync the general look and feel of the cameras at the beginning ( it sped up in later shoots but it was surely not perfect ).
Shooting on AVCHD and H264 you also don't get so much out of it in the post production. The codec falls apart pretty fast and especially the 7D files where a headache occasionally. But we had to touch pretty much each video in the post to match them...if you have the time, no big deal, if you are in a tight spot, maybe rather stick to one cam then going all "fancy".
Conclusion: Well, apart from the fact that it is always preferable to shoot on the same camera with similar performing glass when shooting on a multiple cam shoot, there are times you find yourself in the spot having to make do with what you've got. When shooting with DSLR's, the fast development of new chips, sensors and algorithms can have a significant impact on the looks of your video. Cameras too far apart on the R&D timeline I would rather not mix up.
For seasoned camera operators that is pretty much a no brainer, but all your broadcast folk that just switch from stills to moving pictures etc. it is worth a thought.