More details on the small 3D beam splitter rig

The small beam splitter with a couple of hacked GH13s

It seems the beam splitter I designed generated more interest than I initially imagined, so here is some more info on how I built it, but before I´d like to mention a few things, such as why I decided to built this rig in the first place. I am a director and film maker by trade, I have shot commercials, music videos and documentaries with all sorts of sets ups and cameras from Sony´s F35, Red, 16mm film and 5D mk2, as well as a recent project in 3D: a commercial for a German bank´s charity, for Cinema release. The rig was from P&S technik if I remember well, we used a couple of Sony 900, the rig weighted well over MY OWN weight, it needed 3 guys to pass it from dolly to tripod. 

Versus the standard size 3D beamsplitter we used...

I wanted to have a 3D rig that could be hand-held, similar in some respect to the DSLR revolution, small, compact and enabling me to shoot easily wherever I wanted without the need of a crew to lug the gear around, pull focus, and so on. Imagine that at any time during that shoot, there was around the camera, at least the director (me), the DP, the stereographer, the camera assist, and fortunately no additional focus puller, but still 4 guys stuffed around that rig at all time (check the making of on www.bastienfrancois.com/3d/). 


When building the beamsplitter, what I wanted to achieve was a rig with the smallest footprint possible, with proper image quality. I am not yet totally happy with the results, but I am getting there. I am thinking of adding a 3D field monitor (bit heavy) or possibly pluging a pair of those LCD 3D glasses instead, so as to be able to check depth while shooting. The rig weight about 4kg, (that´s about the weight of a normal professional camcorder like the HVX 200) which is, as far as I know, the lightest rig with broadcast quality image output.

It took me a while before getting to build the rig, first trying to find technicians to help me, or build it for me, and after not finding anyone ready to help, wondering if I was up to the task myself. I am a pretty handy person, I have a few tools but then iron, drills and screws are not much part of my trade. I finally layed a basic blue print: the concept is in itself very simple really, but the devil is in the details. I bought the mirror online (it took me a while to find the right size as custom made mirrors are really expensive), I went to see a local company that builds aluminium window frames, and asked them to cut me a few pieces according to my specs.

The blue print was essential in getting the placement of the cameras correct, one of the most important things I´d say was to get the lenses as close to the mirror as possible so the least "amount of mirror" is needed for each camera, so as to maximise the useful interaxial distance of the rig. Let me remind you that the whole point for me was to build the smallest beam splitter possible, since after 10cm of parallax distance, it becomes much easier to shoot parallel (basically beamspiltters are a pain, side by side is MUCH easier, more about that in a moment). 
The whole point of a beam splitter is to be ablevto shoot 3D close-ups that you would´nt be able to shoot side by side due to the size of the camera. All I needed was a beamspiltter to accomodate the GH13 (in itself one of the most powerful camera around) for smaller interaxial distance.

The main problem with this rig is that it is VERY basic, so aligning the cameras can be a pain, I can change the placement of the upper camera for interaxial distance unscrewing and re-screwing at the right distance. I needed as well the possibility to accommodate two (very) different lenses, namely the stock 15/150mm and the 20mm, which are at oposites in terms of size. the 20mm is about 2cm thick, the 150 is a good 10 cm long, and weight 4 times as much, both are fantastic lenses. I have a pair of  zeiss FD 55 too, but I don´t bother much with them. I decided to stick to Panny lenses that offered me AF, since I´d be shooting quite a bit hand-held and moving around, and certainly without a focus puller to assist, what´s with the additional remote focus gear on the rig. Since the lenses are not synced, sometimes there are focus discrepancies (especially with the extremely slow focus of the 20mm lens) which obviously mess up the shot. I would usually shoot more takes of the same shot because of that. 

I am well aware that the guys at 3Dvision have spent quite some energy trying to sync both cameras perfectly, but there solution is too cumbersome for me, and I have found out that with a simple dual remote shutter, the sync problem was never more than 8/1000th of a second when shooting 50p, which is perfectly reasonable in most cases, except when there is loads of camera movements (not advisable in 3D in anyway).

The first results where horrendous, I have to admit, I spent quite many hours half sick in front of the 3D screen, and that is certainly not a feeling you wan tot inflict to your audience. It took me a while to nail down all the little details, such as the best depth of field and focus strategy, adding barn doors because flares on the mirror where a disaster.

The thing is  beam splitters are a transition tool, until small enough cameras at reasonable prices are available to get rid of beamsplitters altogether, they are a pain in the bum to calibrate, the mirror will eat your light (2 or 3 stops) and bring color shifts between cameras, it is one more surface/lens to keep really clean, bigger mirrors introduce yet more problems because the glass is never absolutely flat and bends slightly because of gravity, therefore squashing your view, which introduces more corrections in post, etc, etc. It is MUCH easier to shoot side by side, simple. Very efficient cameras are getting smaller all the times, and (shallow) depth of focus is not so much an issue in 3D, so bigger lenses/sensors are not so important. Most likely we wont hear of beamsplitters in five years except for macro really. My own two cents.

On this blog you´ll be able to see some demos and tests made with the rig, you can also have a look here at my own site for more stuff: www.bastienfrancois.com/3d/,(remove the /3d/ to see the 2d stuff) I hope you find this as interesting as I did building and experimenting with the rig, and please, leave some comments, let me know what you think of the results achieved.