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Author Topic: Stereo 3D with two Autofocus DSLR's  (Read 6495 times)
Brian Hirschfeld
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« on: December 01, 2012, 12:44:50 PM »
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Hi, I know it can be done, I just can't figure out how. I want to have two DSLR's (Think two D800's, 5D's ,two H's, two 645DF's) on a bracket together, where their autofocus is sync-ed so that I can get the benefit of 3D and AF. So there are a couple of questions.

1) how do I sync the autofocus? is there some device that does this?
2) what is the best bracket for heavy cameras's like this, is there one with markings so I can figure out the distance between cameras?

I know there is an SI photographer who has done it, is it a custom job? If so where can I get it done?
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BartvanderWolf
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« Reply #1 on: December 01, 2012, 01:16:54 PM »
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Hi, I know it can be done, I just can't figure out how. I want to have two DSLR's (Think two D800's, 5D's ,two H's, two 645DF's) on a bracket together, where their autofocus is sync-ed so that I can get the benefit of 3D and AF. So there are a couple of questions.

1) how do I sync the autofocus? is there some device that does this?

Hi Brian,

I happen to have looked into this subject of Stereo photography just recently. My purpose was more of a photogrammetric nature, determining distance and a depth map, but the procedure would be similar for stereo photo's (from stereo pairs, and basically very similar for the production of lenticular stereo output).

Synchronizing the focus by external means is difficult, unless the lenses have a focus ring collar that only turns a fixed amount. Electronically focusing lenses will be hard to exactly synchronize. The best you can do is (auto-)focus on a subject at a fixed distance, or a focus target. Then proceed with Manual focus. Calibrating the AF between the lenses can help to keep things in sync.

If your subject needs to be followed with refocusing, then an adapted Follow-focus system could help to simultaneously change the manual focus of multiple lenses.

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2) what is the best bracket for heavy cameras's like this, is there one with markings so I can figure out the distance between cameras?

Really Right Stuff has some packages, or one could expand on perhaps existing RRS materials and just add what's needed for the stereo functionality. For stationary subjects one can of course also use one camera and slide it between shots. In that case the focus-distance will obviously be identical.

Cheers,
Bart
« Last Edit: December 01, 2012, 01:34:54 PM by BartvanderWolf » Logged
bill t.
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« Reply #2 on: December 01, 2012, 01:56:34 PM »
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I'm tempted to say, put one lens in autofocus, the other in manual.  Run something like a large o-ring or fine tooth timing between the two focusing rings, depending on friction and perhaps a few small dabs of tap or gummy stuff to avoid slippage.  Hope the lens in autofocus has enough spare torque to drive the lens in manual focus.  The elephant in the room is that on autofocus lenses the focusing rings are a slip-fit to the actual focus mechanism, so an out-of-sync situation is not only possible but likely.  Constant checking is advised.

Another possibility is to use a pair of selsyn motors to transfer the autofocus lens's position to the manual focus lens.  Not recommended.

Very difficult to get large camera bodies spaced at the normal eye space distance, especially with horizontal orientation.  Cameras with normal focal lengths spaced too far apart exaggerates the 3d effect in bizarre ways.  Having one of the cameras looking sideways at a 45 degree, front-surface mirror right next to the other camera's lens is one complicated possibility to close the distance.  It's easier with telephoto lenses, because in that special case you actually want rather large camera spacing (interoccular distance) to create a 3d effect with an apparent convergance point much closer to the subject than the camera location.

If you are shooting movies, you will need to have some way to control the convergance point, which is the point out in front of the cameras where the optical centers meet.  This is kinda-sorta roughly where the audience will perceive as the location of the black frame around the image.  If you get the convergance point wrong, bizarre effects show themselves, as in the case where the convergance point is farther away than the main attention-grabbing subjects in the scene.  That forces the image in front of the black frame, or "proscenium."   That's how you get the "jumping out of the screen" effect, just be careful the jumping out subject does not get clipped by the edge of the frame for very long.  Did a lot of 3d work in my movie days, the process imposes a lot of constraints and it was never easy.
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Petrus
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« Reply #3 on: December 01, 2012, 02:29:07 PM »
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I think some quite heavy re-engineering is needed to sync the focus of two cameras. At least you would have to reroute the the focus signal from one master camera to the slave. If you are prepared to sacrifice two fairly expensive cameras it could certainly be done. Also the triggering of the cameras has to be synchronized exactly. Making a rig to hold the cameras is quit simple compared to the electronic modifications.

Making any kind of mechanical connection between lenses is pointless, as most modern AF lenses have no mechanical connection between the focus ring and the focus system when in autofocus mode. You could of course rethink the need for autofocus, at least with fairly wide angle lenses it might not be necessary. Then you could just use two non-autofocus lenses and focus both by hand, of have a fairly simple mechanical connection.

You could also experiment with 2 DSLRs with individual autofocus to see if they pick the same focus often enough, making the trouble of expensive modifications unnecessary.
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Brian Hirschfeld
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« Reply #4 on: December 01, 2012, 04:31:05 PM »
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You could also experiment with 2 DSLRs with individual autofocus to see if they pick the same focus often enough, making the trouble of expensive modifications unnecessary.

This is a very good point, because I believe you can trigger AF / trigger the camera when using two pocket wizards with the proper cables correct?

and also as a general note, I was planning on using it for portraiture, so it certainly would be in the 85mm+ range to bill t's point. How can I determine the interoccular distance? and the convergence point?

I remember reading this a while ago "http://www.petapixel.com/2010/05/24/3d-portraits-with-two-nikon-d90-dslrs/" would this be a good design in terms of brackets? I understand they were able to simultaneously trigger the cameras but they do not discuss autofocus, which I belief is something controllable, again with pocket wizards, but I am not sure
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BartvanderWolf
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« Reply #5 on: December 01, 2012, 05:30:38 PM »
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and also as a general note, I was planning on using it for portraiture, so it certainly would be in the 85mm+ range to bill t's point. How can I determine the interoccular distance? and the convergence point?

The interoccular distance depends on a number of variables. There are programs like 'Stereometer' from triaxes.com to assist in finding the correct combination. Attached is an example of a setup based on 85mm focal length, assuming the optical axes can be positioned this close, and rotated.

Cheers,
Bart
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bill t.
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« Reply #6 on: December 01, 2012, 05:47:24 PM »
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For stills, the convergence point is not too critical if you have a relatively simple background.   The two optical paths can be fixed anywhere between parallel to converging at the average distance of your subject.  But if you have backgrounds that invite the viewer to look at them past the subject, convergence is more of an issue.  Just be sure the two optical paths do not diverge.  Uncontrolled convergence points cause extreme eye fatigue in movies, but not so in stills.  FWIW a lot of 3d motion picture cameras now have the optical paths locked down at parallel, with the convergence synthesized later with proprietary software.  Like stitching it results in a certain amount of image loss around the edges.  It may be possible to create the effects with the Free Transform functions in PS, or perhaps there is some third party software out there.
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BartvanderWolf
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« Reply #7 on: December 01, 2012, 07:11:15 PM »
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FWIW a lot of 3d motion picture cameras now have the optical paths locked down at parallel, with the convergence synthesized later with proprietary software.  Like stitching it results in a certain amount of image loss around the edges.

Hi Bill,

Indeed, it's more of a practical choice, even the parallel shots can allow to converge at any distance by shifting them horizontally relative to one another. However, for the given purpose, portraits, it will be beneficial (if only to maximize the amount of overlap) to use converging optical axes. When the scene does have some foreground/background detail, converging will be better than parallel.

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It may be possible to create the effects with the Free Transform functions in PS, or perhaps there is some third party software out there.

Yes, or the Photoshop displace filter with a custom depth map (which I used on the attached Red/Cyan Anaglyph image of the moon I took a month ago, a single image which didn't offer any stereo base), but it largely depends on the required output. For testing several output options (in particular Anaglyph), StereoPhoto Maker (for Windows, perhaps it runs on a Mac under Parallels, I don't know) is quite potent (and it's free).

Cheers,
Bart
« Last Edit: December 02, 2012, 07:28:10 AM by BartvanderWolf » Logged
Ellis Vener
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« Reply #8 on: December 01, 2012, 09:01:17 PM »
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I saw a video crew doing some 3D coverage of the Albuquerque Balloon Festival back in 2011 with multiple stereo =rigs . The rig I looked at most closely  consisted of two Canon 5D Mark II cameras with matching lenses, probably set manually to infinity. The cameras were mounted on  the longest Really Right Stuff Camera Bar (http://reallyrightstuff.com/ProductDesc.aspx?code=CB-28&type=0&eq=&desc=CB-28%3A-28-inch-Camera-Bar) with B2-Duo Double Clamp on the bars and PCL-1 panning heads in those clamps. The B2-Duo clamp allowed them to adjust the spacing between the two cameras and the PCL-1 clamps allowed for correcting parallax. The entire rig was mounted on a massive Arriflex tripod legset & head. The head was servo controlled for panning and fore/aft tilting so they could do tracking shots as the hot air balloons lifted off and went over the camera positions.
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Ellis Vener
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griffithimage
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« Reply #9 on: December 06, 2012, 03:34:38 PM »
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if your subject is still, you can shoot with one camera and use a slide bar (attached to a tripod).
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Fine_Art
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« Reply #10 on: December 06, 2012, 06:10:45 PM »
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They make dual mount tripods for telescopes.
http://telescopes.net/store/maz02-01-twilighta-ii-altaz-dual-mount-with-hd-tripod.html

They also have autoguiders and autofocus systems using small ccd cameras with motor control. You can select what to track from a laptop. Of course none of this is designed to drive your regular camera lenses. Can it be hooked up to a camera control input? Maybe if you are an electrical engineer.
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tintop
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« Reply #11 on: December 06, 2012, 09:53:58 PM »
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StereoData Maker (SDM) uses a software upload to your camera, CHDK (Canon hack development kit), that gives highly accurate synchronization of shutter/focus. Unfortunately, it can only work with Canon compact cameras. There's been effort to see if it will work with the larger sensor Canon mirrorless cameras, but so far, there has not been success.

http://stereo.jpn.org/eng/index.html

The LANC Shepard also does an excellent job of electronically linking two cameras. The cameras need an ACC port and I believe (at this time) it only supports small sensor cameras.
http://www.ledametrix.com/lspro/user.html

StereoPhoto Maker and StereoMovie Maker are easy to use, free, and essential software for proper alignment of your stereo images and movies.

David Klutho is the SI photographer who does their 3-D work. He's quite accomplished in 3-D and has published a couple 3-D sports books. He has used a variety of twinned DSLRs (and film cameras). I believe the DSLRs have all been electronically linked and I don't know who did that for him (or if he did all the micro soldering himself).

http://www.petapixel.com/2010/03/04/3d-dslr-setup-spotted-at-the-olympics/

There was a gentleman in Europe who twinned a variety of digital cameras (mostly small sensor cameras) for the stereo community. These electronically linked cameras functioned as master/slave, synchronizing the focus and shutter. He was the only person doing it, and had been working on the larger sensor Sony NEX 5n before he died earlier this year. Quite a loss.

http://world-of-3d.com/3d-igital-equipment/ekeren-3d-equipment/index.html
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Brian Hirschfeld
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« Reply #12 on: December 06, 2012, 11:54:08 PM »
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tintop, thank you for those links, so I need to find me someone Co van Ekeren
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tintop
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« Reply #13 on: December 07, 2012, 07:59:26 AM »
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Here is something you might like to look into (Shepherd for twin SLRs, digital or film). I came across a blog post of a photographer using a Canon 5DII twin rig who has had good results. Hope this helps.

http://www.ledametrix.com/slrshep/index.html
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tintop
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« Reply #14 on: December 07, 2012, 09:01:18 AM »
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Also, just to mention about StereoPhoto Maker (SPM). It's an excellent program for what it does. Unfortunately, it doesn't support RAW. Also, when you open an image file in SPM, it dumps whatever more advanced color space you were working in leaving you with sRGB. Therefore, a workflow workaround would be to align and crop your images in SPM first, save a tiff as a stereo pair or stereo L/R, and do your color adjustments in LR/Photoshop last.

tintop
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AFairley
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« Reply #15 on: December 07, 2012, 12:37:32 PM »
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Use live view, move the focus point on each camera to the same thing.  Buy a couple of the cheap eBay wireless remotes ($20 to 30 each depending on camera connector) and set them to the same radio channel.  You could do the same thing with OVF mode, but harder to get the focus points exactly the same.
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Brian Hirschfeld
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« Reply #16 on: December 08, 2012, 04:38:31 PM »
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@tintop that is very interesting and I am going to be reading about that trigger now.

@AFairley that is also a very good idea for precise autofocus.
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Brian Hirschfeld
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« Reply #17 on: December 11, 2012, 02:36:19 PM »
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I emailed the maker of the StereoShepard system to see if it would work with my requirements of it driving autofocus, trigger flashes (view pocketwizards in the cameras's hotshoe's) and if it could be used with an MFDB's.... we shall see, I will report back with the response.
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