Article

Taking 3D Images with 2 Cameras

This article is part of a collection of articles on 3D photography, here we are looking at live action 3D using two cameras. This is by far the most difficult end of 3D and one of the most complex areas of any photography. The results can be well worth it.

Before tackling this article it would be wise to take a look at:-

3D Photography - An Introduction  - this covers a general overview of 3D.

3D Photography Types - explains the type or methods of producing 3D images and although you can use the some photos to produce any type of 3D image its probably that you would want to know what you were hoping to achieve.

Taking 3D Images with One Camera  - covers the ways that photos can be taken with a single camera and as most people would read this before reading this page I have not repeated the information that is contained in this article.

3D Photography Stereo Base - covers working out the distance the cameras will need to be apart. The factors that affect this are the focal length of the lens used, the distance to the nearest item and how far away the furthest item will be.

So we start this article by assuming that you have read at last the last two of the list above, and understand how you would take photographs with a single camera and how much you would have to slide a camera to take the images.  Using two cameras requires you to be able to not only operate the two cameras, and allow for the stereo base shift,  but to understand and control every aspect of what you do. The cameras for example must go off at exactly the same time for true live action 3D, and if you use flash then the flash has to go off when both cameras have their shutters open.  Every change you make to one camera you are likely to have to make a change to the second, but not necessarily exactly the same.

On top of this we have more chance of equipment giving us problems like a camera head dipping on one camera, so that the two are not parallel, or lens creep occurring so one camera is at a different focal length or focus than the other.

With so many things to think of and stay on top of, using two cameras is a lot more than twice as difficult as using one.

So why, you may ask, are we going to all the cost and problems, and carrying so much kit, using two cameras where one could be used.

The answer to this is that in some situations we want to capture live action in 3D and to capture this we need both photos in the pair to be taken at exactly the same time, for example a horse going over a jump, a steam train approaching us at speed, or a butterfly in flight. We can't take one photo move the camera and take a second in these situations.

It might be for some situations we could construct a simpler arrangement of a frame into which two point and shoot cameras could be fitted with a fixed focus lens of a known focal length and for them to be fired together in some way, the cameras are at a fixed stereo base and items near not photographed, this is possible and some who take 3D photos of steam railways are happy with this. However this does not allow us the creative freedom and quality that we are used to when using our DSLR cameras, so here we are concentrating on achieving just that, everything that you can take normally you should be able, by one means or another, to take in 3D.

To use two cameras you need:-

• A means to hold both cameras parallel, and if you can, still move the whole lot about.

• Two lenses that are similar enough to appear the same.

• Two cameras similar enough that they will produce the same image at exactly the same time, so one not having a longer shutter delay than the other. They need to be a model that allows remote firing of one from another.

• A cable to connect them together.

• A substantial tripod that can carry this setup.

• Probably someone to help you carry and move all of this kit.

I use two Nikon D300 cameras, with matching lenses, on a Multi camera bracket,   since the images shown in this article were taken, I have replaced the two smaller cheaper tripod heads the Nikons sit on, with two Manfrotto heads, this is far more stable and easier to set up. Connecting these two cameras I have a cable, see Cable to Parallel 2 Cameras. 

To set this up I need to point both cameras at exactly the same distant item, so zoom to maximum and use the grid or grid on liveview to get this right. Once this has been done, and the tripod heads adjusted, they are locked and you need to take care not to move the positions again. I can move the whole arrangement as there is another larger tripod head under the multi camera bracket. The tripod in use is a large one made for professional video recording. I can take off the head from the tripod and fit the multi camera bracket directly to the tripod, and in the studio I sometimes do this as this tripod runs on a dolly (set of wheels).

Where I can't point at a far off item, for example when inside, I use a flat piece of material and using a short builders spirit level, I position the lens hood of both cameras against, and the spirit level to check the top edge of both hoods are level. This is not as accurate as the other method but close enough to produce good results.

It is important that both cameras go off together, so you can't have anything set that will stop this, so for example set at least the second camera to manual focus, or so that it has shutter rather than focusing priority when taking. If you are using flash then you need to think about the shutter speed and flash setting so the flash goes off while both shutters are open, this is easily achieved by using rear flash and setting the shutter to be open longer on camera two than the first camera, the first camera being the one you are firing by pressing the shutter release. If firing a number of Nikon flashes with creative lighting you need to control this by using a controller on the first camera. Using rear flash and thinking about the shutter speeds is the secret to making this work.

You will see that there is lot to think about and a lot to go wrong, and to make this a practical proposition when there are others about, time is limited and other problems have to be overcome, we need a fixed list of steps that we are going to use and to have worked this out in advance as far as we can.

A rough guide of these steps are:-

1. The start point is to decide how far we are going to be away from the subject, the focal length we are going to use and what the maximum distance will be in the shot. From this we can determine the Stereo Base,  as long as nothing is very close, if we end up a little out on this its not going to be noticeable.

2. On arrival we need to select our position and set up the tripod checking its level, add the multi camera bracket.
3. Add the two cameras with matching lenses and if using filters matching filter sets as well.
4. Set up the two cameras so they are parallel (see above) at 90 degrees to the multi camera bracket and the desired stereo base apart, and lock the camera positions.
5. Set the focal lengths to match on both lenses.
6. Adjust the shutter control or focussing selection so that both cameras will fire at the same time, when connected. You don't want one camera still doing something with auto focus when the other goes off.
7. Determine the exposure settings, taking into account the speed to stop the item and aperture to give us the depth of field required.
8. Determine the white balance settings.
9. Now connect both cameras together with the special connector.
10. Turn on liveview, check all looks right and take a test shot. Both shutters should fire exactly together. Compare results, being careful not to knock the cameras out of alignment.
11. Take a photo of a marker, possibly sky, or someone stood in front so you know where the matched pairs start later when you get back.
12. You can leave liveview on for an extended period, as the cameras have a safety feature to stop overheating and they time out. You can leave the camera set up and turned off so when you want it operating you can turn it on and activate both and liveview.
13. Use liveview to point the cameras in the right direction, using the larger head under the multi bracket to select the view.
14. Where you can, take a number of shots and be aware at all times that both images should be very similar and that you hear both cameras fire together.
15. Add extra marker shots occasionally so that you can sort out any situation where a camera did not fire or other problem existed.
16. Occasionally check all settings, even if you haven't changed anything, you may just spot something you overlooked before.

Like all photography, practice is essential, and things will get overlooked and go wrong, with so many possibilities of something going wrong in this case, you need a routine, and to have practiced this on your own where you are not under pressure or distracted.

This all seems a bit much but at the end of the day the results can be magical, and worth all the effort.

Items like trains that are moving can only be photographed using either a special camera
 with two lenses or two cameras wired together as explained above.

See Also our 3D Section for more articles and projects on this topic.