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Old January 12th, 2005, 04:45 PM   #1
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35mm adapter - double cameras.

I'm making a new 35mm adapter only the projected image will be split in two and filmed by two (identical) cameras.
My first tests (just a still frame) gave a very sharp picture after stitching them together on the PC.

I'll try to do it with one mirror to split the screen and the cameras on their sides.

Matt Champagne wrote:
The one thing I'd be worried about if you are compiling images like this is if your frame rates will properly synch up...if not your going to get something akin to very serious interlacing.


I thought about it, and came up with this:
Filming with two cameras will give you 4 audio channels (2x stereo)
If you have a portable audioplayer of some kind (even mono) and let it play a SMPTE synch signal, you could record that on the left channel of the first camera and the right channel of the second camera for example.

I know this code from music synch and it's a tic on every frame and is used in most audio and video software.


I'll post a test frame soon, I'm new here and have to figure out how.

Oscar
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Old January 12th, 2005, 05:01 PM   #2
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Ocar, forgive my ignorance but why would you want to do this? To create a 3D cinema type experience?
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Old January 12th, 2005, 05:47 PM   #3
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No, not for 3d. It's to double the resolution (you'll have the frames side by side, not mixed) The test I made, was with my consumer DV camcorder, and made a very sharp 1040x720 image.

Two cameras film one projected image (augus35 idea) and are stitched together again on the PC.

One problem would be if you need a slight overlap to get a seamless stitch. Maybe tilt the split-mirror a bit more than 45

Oscar
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Old January 12th, 2005, 05:51 PM   #4
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That's not so much what i'm talking about...yes that will solve your problems in post...but i'm talking about the synchronization of the cameras themselves...they have to start their frames at the exact same moment otherwise camera one may start recording its first frame..and camera two might start its first frame a few milliseconds later. It won't be that much of a problem unless you get into high shutter speeds or do alot of motion...but like I said if you did those things it would be like seriously strange half-screen "interlacing". Or more likely...peoples bodies being temporarily cut in two.

At first I thought you meant projecting the exact same image to both cameras...not one on one half, one on the other. If you did this...and say started two cameras that shot 30p 1/60th of a second apart from one another you could effectively create 60p. (This was what my dual camera idea was intending to do..I found machine vision cameras that shot hi-def with 1" ccd's...but only shot 15fps)

On that last note...man do I wish cameras had midi in/out/through...that would make external sound sync so easy....plus they could even use that as another control mechanism with some creativity. Can you imagine hitting a C# on your keyboard, and your camera zooms in? lol
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Old January 12th, 2005, 06:00 PM   #5
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Another thing occurred to me...theoretically would it be possible to take the raw image from a 35mm lens (not in a typical adaptor as we currently think of it)...and use mirrors in a simular way and project it directly onto multiple ccd's. It would be a simular idea...probably alot more engineering skill involved though...but you may be able to resolve the lens' image directly to the ccds to make a dof adaptor with no focusing screen/GG necessary. Just a wild idea...no idea if it would work.

But anyway...unless that extremely inspires anyone...its probably best to not worry about it.

Do you have any framegrabs to post of your results so far?
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Old January 12th, 2005, 06:03 PM   #6
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But if you deinterlace in post, it would be easy to synch with full frames, right?
The SMPTE code will match every frame, if they are full non-interlaced frames.

Maybe I'll get to that point in the next days and really understand the problems I'm facing.
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Old January 12th, 2005, 06:10 PM   #7
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You can get the timecode to match no problem. The problem arises from the fact that the information in each frame would have been acquired at a slightly different time between the two cameras. You really need to find a way to start and stop them together.
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Old January 12th, 2005, 06:24 PM   #8
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maybe interlace is a bad word....i just mean the effect would be simular. I should preface this by saying I may be totally wrong. You have the thing built...so give it a try I guess. But what I am saying is lets say you start both cameras at the what you think is the exact same time...but in fact they are not started at perfectly the same time. As long as the delay between cameras is a multiple of 1/30 second...your ok because you can correct that in post to some extent. But if its more like 1/50 of a second, then you what I am saying will probably occur. Lets just assume camera one shoots the top half of the image, and camera two shoots the bottom. If you panned quickly, or something ran across the screen quickly, you would notice the top half detach from the bottom half because it is delayed.

Now, I must admit now that I do the math....I think it won't be that much of a factor...maybe only a 7ms delay max between halves since greater delays could be offset by shifting the frames.
But deinterlacing definatly won't do anything.

All of that is also assuming your shooting progressive to begin with...I really don't even have an idea of what you have to consider interlaced.

Also, shooting 24p the delay would be a little worse.
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Old January 12th, 2005, 06:27 PM   #9
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I think if the cameras record the same SMPTE signal at the same time, and synched in editing software, the frames would be exacly in place.
But maybe it could be done with a clapboard.

Here is a frame (it was only one frame anyhow):

http://s01.picshome.com/52a/frame.jpg_t.jpg

or:

http://s01.picshome.com/view.php?image=/52a/frame.jpg
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Old January 12th, 2005, 06:38 PM   #10
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Sorry, the link was to a thumbnail. Again(it's compressed JPG, so don't zoom in):

<img src="http://s01.picshome.com/52a/frame.jpg" width="1040" height="773" border="0" alt="Picture hosted by PicsHome.com" />


I think I meant de-field. And I would film the left and right of the image, and maybe the artefact Matt is talking about, will be less if I can make a bigger overlap that fades the two images.

And I didn't build it already, I've started today. I've build the normal 35mm adapter but it doesn't have space for the second camera.
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Old January 12th, 2005, 06:39 PM   #11
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Looks very nice. I don't know if the SMTPE signal is even necessary if the frames line up. But what i'm saying is not so about the frames not being able to line up in post...but its the fact that they will likely always have a delay that is a fraction of a frame apart...so there is no movement of frames you can do to synchronize them perfectly. Unless, you go through the trouble of sycnhronizing the clocks of the camera.

Its like if you start two people adding 10 over and over again...but one starts at 0 and the one of them starts at 2. At the end of the day you are only allowed to add or subtract multiples of ten to their number, so there is no way you can ever make them say the say number.

But like I said...the delay may be negligible...probably 7ms or less. And I know audio delays of 30ms are hardly noticable...so can imagine the same thing is true of video. Before I did that calculation I thought it would be a serious problem...but now I feel like I'm just being nittpicky lol....Its probably really no big deal.
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Old January 12th, 2005, 07:25 PM   #12
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I think it would be like fields in video, TV's and monitors, you can't see it. (I hope)
Maybe some frame-blending will help too.
I'll start and stop the two cameras with the same remote, bur that won't be ms accurate, I'm sure.
Thanks for the replies, I'll post my progressing work and every suggestion is welcome.

Oscar
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Old January 12th, 2005, 07:49 PM   #13
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Oscar-
I thought about a similar idea but before you kill yourself trying to make one of these I might recomend that you try these two tests first:

1) I have a feeling that after you put your higher definition image on to a standard definition DVD your going to loose just about all that you gained. Try it with you still image test and find out. Make sure you also encode a example of the image from just one camera so you can compare it to two cameras side by side. DVD requires you to downrez to standard definition. Unlike in the film world, when dealing with video it doesnt really help to start with a HD master over a SD master if your going to SD DVD. Most people will tell you otherwise but thats because they are seeing the effects of the HD cameras better/less compressed image, wider latitude CCD, etc. But when all things are the same between two cameras except the resolution they will end up looking the same when put to DVD as long as both of them are shooting at least to the maximum resolution that SD can handle. People that have bought the new Sony HDV camera will unfortunately come to realise this in the months to come. Heres the proof:

http://www.dvxuser.com/cgi-bin/DVX2/YaBB.pl?board=sony;action=display;num=1103104690

2)Try shooting another test shot but this time at wide angle. You should notice that you can stitch the two together anymore due to minor distortion problems. You will have to bend the image completely flat again in post for them to come together seemlessly and doing so will result in some loss of resolution.

As to how to sync up to wild video camera perfectly - hit up these guys. Hopefully they will be willing to share.

http://www.camcorderinfo.com/content/3DVX-Announced-Finally-Portable-3-D-Made-Easy.htm
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Old January 13th, 2005, 01:54 AM   #14
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More than a few typos in my last post. Heres some clarification:

2)"....You should notice that you CANT stitch the two together anymore due to minor distortion problems..."

"...As to how to sync up TWO wild video cameras perfectly..."
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Old January 13th, 2005, 06:34 AM   #15
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Brett.

In the same way you get a seemingly better resolution if you blend or layer four or five frames of standard DV, would not two cams framed on the same actual image through a splitter prism achieve something similar, though probably not to same degree as a joined frame?

If splitting a single image, the optical splitter system on a single input - two output head-mounted night-vision would be an obvious place to start as a design base and possible source.

According to a DOP I spoke with, Disney's once made a special splitter lens for 35mm for making frame-accurate images and mattes. Two films were shot or something like that. I did not understand the tech at the time.

A interesting experiment is to print two consecutive frames from MiniDV on photopaper. Mount them side by side then make yourself crosseyed and look at both frames together.

You know, stick your finger up close to your eyes then focus on the center image of the three you see. The apparent resolution and contrast of that centre image is much improved.

Another variation on this experiment is to print two frames of the same subject, one sharp on the subject, the other sharp on the background, both shot through a long lens. An interesting 3D effect occurs.

Provided you de-interlace and apply motion blur by the method described on this very site and then layer the two timelines at 50% transparency, I suspect there should not be too much trouble even if they were up to four frames out in sync when there is little movement.
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