The Beastgrip is probably familiar to most of you, it's been around for a while now and has been used in many a film. The Depth of Field Adapter has also been around for some time but this newer version has only recently been delivered after a successful Kickstarter campaign. Once a lens in fitted, the set up can pull heavily on the threaded mount, hence the rig that basically supports that weight.
How does it work? Very simply, the lens projects its image onto a fresnel screen in the adapter which, in turn, is the image the iPhone camera focuses on.
Does it work? Hmm, yes and no. Due to the variation of smartphone lenses, the DoF adapter may show some vignetting when used straight out of the box. It took a few emails to Beastgrip to find out this was normal and that in some cases, (we were using an iPhone 7 Plus), you'll need to zoom in slightly to remove the vignette. Not ideal but we understand the limitations of this system are actually the vagaries of smartphone lenses.
Once we took it out to test the set up (with a Canon 50mm f1.8) it took a couple of shots to remember to zoom in. Duh!
What we found was that the lens you use has to be fast. This 50mm was used wide open in order to get enough light (on a cloudy day) down the tube to the fresnel. Using it wide open also gave a better result with the depth of field. Obviously. However, there are issues with shooting with the lens wide open on an iPhone. The depth of field is so narrow it's easy to screw up the focusing, as you can see in a couple of the shots in the video below.
The set up also creates issues when doing anything from a low position. There's no way to get a live image feed from the iPhone to a monitor that could be better positioned to view the scene. And that iPhone screen is REFLECTIVE!! So it definitely takes time to create the shot from any position where you can't easily see the screen, or with a bright sky behind you.
Having given you a few negatives/limitations, here's the positive. The depth of field effect created by the adapter is REALLY COOL! It'll take time to familiarise ourselves with all the quirks, but having such an effect from such an easy to use tool will undoubtedly make some elements of filmmaking better. We're definitely looking forward to using it for a couple of commercial pieces we have coming up.