Stereoscopic with two 7D's

[Pavel Houda]

Hello Heinz. Thank you for your explanation. I understand how you start the cameras at sync with one another, by manipulating the power control, so that the communications bursts, which are alligned with the sycs end up alligned with one another as well. I am not sure how is the long term drift controlled, but I can see how the initial allignment is achieved. I saw a paper some time back, that showed a long term control, but I was not sure about the applicability to all camcorders. You are no doubt familiar with this: http://dsc.ijs.si/3DLANCMaster/Files...ster_paper.pdf . The simple thing that I hacked cannot achieve those results. Thank you for your great clarification. Your method is certainly very clever.

[Bruce Schultz]

I really don't understand what results all of this LANC discussion for 3D is supposed to yield. If the two cameras are not genlocked together so that one camera or an external sync generator drives the clocks in both cameras simultaneously throughout the shot duration, then starting the cameras at exactly the same time is a moot point. LANC is not genlock. Besides, there is a much easier and cheaper way to derive a common head sync point which is almost 80 years old - use a clapper slate, or a still camera flash, or clap your hands at the beginning of a roll and use your NLE to move both shots to that exact frame. Now at least the first few frames will be in dead sync, but the inevitability of drift will appear shortly thereafter. That drift may or may not be noticeable at first but will be over time - how much drift is dependent on the cameras used but is not a mathematically predictable event that can be adjusted later. The drift will be asynchronous and variable from camera to camera. I have been shooting video (now digital) cameras since the 1970's and we have ALWAYS had to genlock two or more cameras together to achieve dead sync. Nothing has changed, not the basic principles nor the techniques - the internal clocks of all of the cameras must be driven by a common sync reference whether it be black burst for standard def or TriLevel for HD.

One can will and wish it were otherwise so as to enable more inexpensive solutions like DLSR's to work, but it's not going to happen any time soon that I can see. The reason is simple and obvious - all of these camera manufacturers make higher cost cameras that have the genlock function and don't want to see a lower-end sibling siphon off profits. Cynical maybe, but it's a business model that I have watched all of the camera manufacturers employ for as long as I've been in the biz.

Listen, I use two Canon 7D cameras to do non-pro 3D work, mostly of natural landscapes and if you are careful with your settings, it can turn out OK - not perfect but viewable. But for sync sound or any professional work, you must use two cameras that are in guaranteed dead sync, and the only way to do that is with genlock. Interestingly or ironically, that is why genlock was invented.

[Pavel Houda]

Clapper will not synchronize the capture within a vertical sync period. Half the frame time (16.666 ms) can result in the frame capture to be too far apart, in some instances. Since the vertical syncs are free running, if one manages to power up the two cameras in a scattered fashion so that the syncs start at nearly the same time, the sync skew will remain within and acceptable tolerance for several minutes based on the tolerance specs of the crystals and the fact that the cameras are running at a pretty close temperatures. Since the comm bursts back from the cameras are slaved on the vertical syncs, one can measure and compare their return channel timing and synchronize the cameras quite accurately by controlling their power up command precisely. For limited time duration, as well as genlock can. The paper I refered to can actually shows how in some cases this can be done for a very long time, if the phase lock loop scaller can be controlled in small enough steps. The skew can be monitored and signaled back to the controllers, so based on the desired treshold, the operator can re-sync and start again, if the skew gets unacceptable. If you wish to be mathematical about it, even genlock will have minute delays and skews between the cameras, but usually tolerable for most standard video work. The sub-frame accuracy is very important in the case of fast motion of either the subject or the camera, and miss-alignent is very obvious to see. If you don't capture fast moving objects, cars, sports, and have the cameras on tripod or some other fixed support, clappers are fine. Some of us want to get the most of the technologies, even though we don't want to deal with the cost or bulkiness of genlocked gear, so interestingly someone came up with rather clever solution, that is good enough for what some of us do. There is enough interest that there are several products solving this issue on the market. In general case, consumer cameras have no need for multi-camera sync, so adding genlock there is just a waste of profit for the manufacturers. Since some of us are interested in sub-frame sync of consumer grade cameras, we discuss it in this forum.

[Bruce Schultz]

The name of this thread refers to using two Canon 7D cameras for 3D and that was what I was referring to. You are discussing in very good detail how to do this with a couple of camcorders, and I appreciate the depth and breadth of the discussion, but I haven't seen any method to use that process with two DLSR cameras which are not equiped with that protocol.

It's an interesting theoretical discussion, I'd be interested to hear and see real world results of it's application.

[Arnie Schlissel]

Originally Posted by Steve Shovlar

What are the smallest and cheapest cameras out there with Genlock?

Probably the Cannon XH-G1s, about $7k. Also the JVC GY-HD250U, also about $7k, no lens. Both shoot HDV to miniDV cassettes. Both have SDI out if you want to use a better recording system.

you might be able to find some sort of HD box camera for around the same price with genlock in and SDI out. A box camera would not have any built in recording, though.

[Tim Dashwood]

Originally Posted by Steve Shovlar

What are the smallest and cheapest cameras out there with Genlock?

Small & cheap don't exist in the same product! The smallest genlockable HD cameras available are the Iconix, Cunima and SI-2K mini, but none of these have built-in recording. They are just the heads.

[Steve Shovlar]

HI Tim, I thought that was the case!

I am playing around with a couple of consumer Sony HC 5's and must admit the results are quite encouraging. I don't like the 1080i the cameras use but I am relatively pleased with the results. For test purposes only of course.

Might see if I can pick up a pair of Canon HV 30's as they shoot progressive.

[Alister Chapman]

The PMW-10MD has genlock, this is a very samll "C" mount 3 chip remote head (1/2" 1920x1080 sensors) that connects via an umbilical to a control box/recorder that records on to SxS cards. Not cheap though, around 12,000 Euro !!

If you get a pair of Canon's or Sony's with Lanc, getting them in reasonable sync is pretty easy.

[Steve Shovlar]

Alistair, what do you tink of the Colorcode 3d lanc control?
http://www.colorcode3d.com/LANC.html


Worth the money?


I have a couple of HC5's and a HC3. I might either buy another HC3 or flog all three and get a couple of HV30's.

It would be nice to have higher end cameras for 3D ( and I will be buying another EX3 to go with the one I already have) when I need it.

The results I have got with a couple mof HC5's are excellent considering its interlaced single chip HDV. Not good enough for any commercial work but good enough to learn how to make good 3D, and they are very light.

[Bicky Singh]

Hey guys,

I just wanted to double-check something about using the 7D's for 3D. I understand they can't be used correctly for 3D, unless the image is static.

But I remember reading in a couple of places that if you shoot in 720p @ 60fps that you can possibly shoot quite effectively with the 7D for 3D which includes motion.

I was hoping you guys could confirm if this is possible or still not acceptable.

The 3D content I plan to create will only be displayed on 3D monitors and/or 3DTV's. Not for the big screens. I was wondering if 3D content is more comfortable to view on smaller screens even if the 7D's aren't perfectly synced that may cause retinal rivalry, considering they are shot in 720p @ 60fps.

This is my last hope to use the 7D for some 3D projects before purchasing an SI-3D system.

Looking forward to hearing from you guys.

Best,

[Bicky Singh]

I did some quick research on the possibility of recording on the Nano3D recorder with the 7D. That would be nice. But it seems like we're all waiting on 'Magic Lantern' and "Syndicate" to come out with the hacks to record through the HDMI output.

I hope they crack it soon, perhaps thats the key to make the 7D's come alive for 3D shooting.

[Patrick Williams]

With the advent of 3D TV now, I would expect a lot of manufacturers to start building two cameras in one, where they would share the same power supply and sync. These current work around methods might get results today, but I'm hoping that later this year or early next that even Nikon and Cannon will offer stereoscopic cameras. Perhaps the cost of a single unit might even be cheaper than two 7Ds, and you won't have to jump through hoops to get it to work.

[Alister Chapman]

The Colorcode Lanc controller is great value for the money. It works well and will start the cameras in sync almost every time. It does look a little home made, but it does the job and is a lot cheaper than most of the others.