Monday, 25 May 2015

3D stereo images with two cameras

As new camera models are being introduced, the old ones can be bought at discount prices. There is a rumour currently that Panasonic is soon going to release the Lumix GX8, and I was able to get a pair of Lumix GX7 at a reasonable price. But why would anyone want to get two of the same camera?

Mounting them to a Desmond Mini Dual Camera Bracket, it is easy to set them up for 3D stereo photography. The stereo distance becomes about 140mm here, which is a bit wide, but quite usable:

Note the lenses used: I used an old and new version of the Lumix G 20mm f/1.7. You would want to use the same lens on both cameras, to make sure the images come out comparable. However, even if these two lenses do not look alike, they are optically identical, just having a different body design. See my comparison of the old/new lens here.

Also some accessories in the picture. Here is a complete list of the accessories needed, beyond the twin cameras and lenses:

In the rear is the Desmond Mini Dual Camera Bracket, used to mount the cameras on. The rectangular box in the centre is the receiver unit from the Pixel RW-221 radio remote control. There is a shutter trigger on the receiver unit, which supports half-pressing the shutter for autofocus. A full press will trigger the shutter. This remote control works with most Panasonic M4/3 cameras, except for the small ones in the GM and GF lines.

Finally, some cables for connection. All the jacks are 2.5mm, with three and four poles. The splitter is needed to connect two cameras, obviously. The extension cables have four poles on the angled end, and, oddly enough, three poles on the straight end. I bought all these cables off Ebay. Insert the angled ends into the camera:

An alternative setup is to mount them skewed on the bracket:

This is good in the sense that the stereo base becomes narrower, closer to that of the human head. On the other hand, the focus distance becomes slightly different. Unless you are taking closeup pictures, the different focus distance is hardly an issue, though.

With this configuration, the stereo base is about 95mm, slightly larger than that of the typical human head. A rule of thumb is that the stereo distance should be about 1/30th of the focus distance. Hence, this setup is good for distances of about 2.4m, i.e., typical people group photos with the wide angle lenses.

In use

Before starting to take photos, it is good to visualize about how far away your subject will be, and angle the cameras inwards, towards an object at that distance. That way, you make sure that the two camera overlap as much as possible, with less need for cropping later.

The timing is very important. You need to trigger both camera exactly at the same time. You may think that this is trivial, since they are both connected to the same remote trigger.

However, keep in mind that as long as you don't use manual focus or AF-C, the camera wants to confirm the focus before letting you take an image. And autofocus can take a different time with the two cameras, leading to the wrong timing if you just press the shutter all the way down at once.

To avoid this problem, be sure to always half press the shutter first, wait a short while so that both cameras have achieved focus, and then press it all the way down. This also goes when starting video recording.

It is important that you remember which camera is to the left, and which is to the right, so that you categorize the pictures and videos correctly later. I keep the camera with the lowest serial number on the left side, as a rule of thumb.

Viewing the pictures

Here is a pair of example images (click for larger):


Using the Gimp plugin "script-fu-make-anaglyph", I made the pair into a 3D anaglyph:

The image can look more pleasing if you take care to align the two images better, though. Here is the same image aligned to match better in the area of the main subject:

This picture must be viewed using red/cyan anaglyph glasses.

Example video

Setting the mode dial to the "movie camera" symbol, the remote will trigger the start and stop of video recording.

If you have autofocus enabled, it is important to half press the shutter first, to make sure both cameras have acquired focus, before fully pressing the shutter.

Here, I have combined the left and right videos into one 3D video. Again, depending on your Youtube viewing preferences, you probably need red/cyan glasses to see it:

If you see this a video like this in Youtube, you have the right settings for red/cyan glasses (anaglyph) view:

On the other hand, if you see this in Youtube, you either have the wrong settings in Youtube, or your device/operating system does not support 3D anaglyph view. This happens on some Apple devices, sadly:

Be sure to press play before concluding, as Youtube may change to anaglyph view only when starting the playback.

The way to upload 3D video to Youtube, is to mix both streams together. This is done by compressing both the left and right streams horizontally, and placing them left and right, respectively, in the video frame. So half of the horizontal resolution is lost in this process, with each stream becoming 960x1080 pixels.

Here is what one frame looks like:

For viewing, Youtube decompresses each frame, colours them appropriately, and merges them into one frame. It can also interact with a 3D display, if you have such a fancy piece of hardware.

The camera

You shouldn't worry about getting a one generation old camera, like the Lumix GX7 I used here. The image quality does not improve so much with each generation anymore. It was different when the Lumix GH2 was replaced with the Lumix GH3: I felt that was a big improvement to image quality.

Going to the Lumix GH4 did not improve the image quality a lot, but added a host of new features.

Its the same with the Olympus OM-D E-M5 II. The image quality is better than the predecessor E-M5. But not by much. On the other hand, the E-M5 II improves the ergonomics, and adds a number of fun features, like the multi exposure high resolution mode, tested here.


Having two identical cameras makes it easy to create 3D pictures and videos. However, triggering both cameras at the same time is not frustration free. The wired remote with half press to focus functionality is the best solution I have used so far, though, so this is not a big problem.

Also, there is a bit of post processing required, before you can actually view the 3D output.

Alternative 3D cameras

3D used to be a big fad, the new "thing" which would sell TV sets to consumers. Mostly, this flopped, and 3D is no longer important when people buy televisions. Nowadays, 4K is the new fad.

But some interesting 3D imaging products were released. Here is a list of some of them:

You could get the dedicated 3D lens for Micro Four Thirds cameras, the Lumix G 12.5mm f/12 3D lens (click for my review). It works on most Lumix cameras. However, I would strongly advice against buying it.

The lens has a fixed aperture of f/12, which is very, very small. The lens can only be used outdoors in daylight. Also, the stereo distance is 10mm, which is very short. This gives a quite weak 3D effect. The lens has no focus mechanism at all. The short stereo base distance could be used for macro images, but with the lens limited to be used at 0.6m or longer, this is not possible. Finally, you cannot record videos with it, except if you use this DIY trick.

There is also a dedicated Panasonic 3D compact camera, the Lumix 3D1 (click for my review). The camera has a shorter stereo base than the human head, but not by much. It works quite well, but doesn't have a stellar image quality. It records 3D videos in 1080p.

Fujifilm FinePix Real 3D W3 is probably the most serious dedicated 3D compact camera. It has a generously wide stereo base, and a good ergonomy with dedicated controls. It even has a rear screen which can display 3D images!

The Samsung 45mm f/1.8 2D/3D is an innovative lens which supports 3D recording. It achieves this by being able to mask off the left/right side of the aperture, to capture left and right images, however with a very short stereo base. Also, it cannot capture the left and right images exactly at the same time, leading to problems when photographing moving objects. It can also be used to capture videos. You also need a Samsung NX camera, obviously.

There is also a market for pro 3D camcorders. These are quite large and expensive. From JVC comes a full HD 3D camcorder, Panasonic has the AG-3DA1, and the Sony Td20v is a fairly compact 3D handycam.

Example images

Here are some more example images that you can view with red/cyan anaglyph glasses:

Lumix G 14-42mm II @ 14mm f/5.6:

Lumix G 45-150mm @ 150mm f/7.1:

Lumix G 45-150mm @ 45mm f/7.1:

Lumix G 14-42mm II @ 14mm f/5:

Lumix G 45-150mm @ 150mm f/6.3:

Lumix G 45-150mm @ 150mm f/5.6:

Example videos


  1. Very interesting.
    1.) How does your method compare to the Panasonic 3D lens?
    2.) Does our eyes also crop the image and rotate the camera according to distance?

  2. I would say the Lumix 12.5mm 3D lens is useless (see my review). It has a stereo base of 10mm, which is very short. And you only get a low resolution picture.

    Yes, your eyes will also shift inwards if you look at something close. Try to look at your nose as you lean towards a mirror!

    The brain is a very powerful processor, so it will not crop the pictures to fit, but extrapolates the 3D information based on previous experience.

  3. Do the cameras synch well enough to use flash?

    1. Good question! I will check that.

    2. I checked now, and the sync is not always good enough to work with flash. The flash can affect the other camera's TTL measurement, causing one of the units to underexpose. Some times, it works, but don't rely on it.

    3. I haven't used a pair of Lumix cams (have them & on the To-Do list...), but have done quite a bit of work & testing with a variety of Olympus pair -.E-P1 & E-P3, E-M5 & E-P5, E-M5mkII & E-P5, etc. Never 2 identical cameras for cost reasons (so far).

      I have gotten fairly good sync & decent flash results when I shut off as many features as possible. Anything the camera has to 'think about' might cause a delay, which is different in the L & R units, even if the ARE identical.

      So, shut off:
      autofocus (or pre-focus as mentioned),
      stabilization (or use continuously, and wait for both)
      focus assist light,
      real-time shutter/aperture effect,
      shadow/highlight blinkies,
      TTL flash (use manual),
      HDR or filter effect processing,
      In other words, don't use any of the modern conveniences you were attracted to and paid for!

      I can stop crashing waves at the beach around a body surfer's head, slightly fluttering leaves, a waterfall from 20 feet away, etc. I can get flash illumination in both cams about 70-80% of the time, especially if i use a short delay between trigger & flash (a feature of my radio triggers), or second curtain sync if I can reliably determine which is the first cam to fire (or 'force' one to be slower).

      Lumix pair testing coming up soon...


    4. Interesting conclusions!

      I have had success when using the flash from one of the cameras only. But using both doesn't work for me. I can see that TTL pre-flash and many of the other issues you mention may be the culprit, though.

  4. Yes, I never trigger flash on 2 cams, always one, and hope both shutters are open when it fires.

    Since I almost always use off-camera flash units with a radio trigger, I have recently thought of trying radio triggers on both cams, set to the same channel. Sort of a 'first come, first serve' approach, combined with a short delay between trigger and the strobe firing. If it works, then which ever camera is first to fire (trigger the radio slave), then it will be the trigger for any flashes, and the other trigger will most likely be ignored, since the flashes would be already going off or would be recycling.

    An appropriate short delay between trigger and actual firing of the strobe should make it more likely to fall within the time that both shutters are open, regardless of which came first (L or R). Think not first, not second, but 'mid-curtain' sync.

    Have not tried it yet, just had the idea last week. Based on my experience so far with one trigger, it *should* work better, especially for slow/moderate shutter speeds (below 1/100s), and reasonably low sync errors (10-20ms or less).

    I wish the M43 cams could be synced more reliably like the Canons are known for - or need to figure out how...


  5. I can't find the cables that you used for purchase. Do you have a link?

    1. I'm not sure this is exactly the same cable I used, but try this one, which looks right.

      Try to search for "2.5mm stereo jack splitter cable".

    2. That one only has two rings on the plug, whereas the one in your picture has three rings. I can't find any splitters with three rings. Will a two ring one work? Also, what about the other cables? They look just like the one that came with the Pixel unit, but I can't find anywhere to buy that cable separately. Thanks!

    3. Looking at my cables (and the pictures above), note that the splitter cable has four poles (three rings), while the extension cable has three poles (two rings). With this in mind, only three of the poles are transmitted, and the four poles are not needed.

      As for the extension cables, you could consider buying one more Pixel kit, to get another cable. They are not that expensive.

      I think I bought the cables off Ebay some years ago, but I cannot find the listing anymore.

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