Repeatibility of a Skycrane Jib Position at DVinfo.net

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Old December 2nd, 2003, 09:54 PM   #1
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Repeatibility of a Skycrane Jib Position

Here is an interesting application where a jib with markings would come in handy. Say you want to photograph over a fence with a high resolution still camera. Set it up for delayed picture taking, and move the head into position, and wait for the picture to be recorded. Re-do this until you get the shot you want. But this is the hitch. Does the skycrane or any other jib have guides or reference points that will allow you to repeat a shot after you have moved off that mark? Better yet would be a stop you could set in azimuth and elevation.

Another approach- mount a mini-video camera on the shoe of the main still camera, and try to use the tiny guy to frame the picture. Probably a lousy idea, because the FOV's are different, huh? But this has to be better than pointing your camera in the blind. Here's why I want to use a still camera (digital). 11,000,000 pixels, baby. It beats the 380K you get with a video camera. You can do a lot of panning around after the fact with a multi-mega pixel tiff file.
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Old December 3rd, 2003, 01:17 AM   #2
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Marc, I'll ask SkyCrane inventor Bob Jones to come in and respond to your question tomorrow (er, later this morning, that is). Hope this helps,
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Old December 3rd, 2003, 05:58 PM   #3
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Re: Repeatibility of a Skycrane Jib Position

<<<-- Another approach- mount a mini-video camera on the shoe of the main still camera, and try to use the tiny guy to frame the picture. -->>>

Quite a few digital cameras have a video output for playing pictures back on TV. This can be used with a monitor to accurately point the camera. I have used this many times when trying to line up a shot in an wierd position. You can also get a pin hole camera from some place like supercircuits.com and place this near the viewfinder. I have done this with success on film based SLRs. You get an accurate view of what is being shown through the viewfinder. It is also handy for through the lense video, when needed for the effect (i.e. cut to the still as the picture is taken, etc.).
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Old December 3rd, 2003, 09:29 PM   #4
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You could also use masking tape and a sharpie to mark points on the jib.
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Old December 4th, 2003, 11:53 PM   #5
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Is accuracy a factor?

No matter how good you are or how many marks you make and how many measurements you take...it is pretty much impossible to duplicate your shot exactly, every time.

There are just to many factors involved in the distance traveled by the arm and the camera, even more if the camera is being operated and especially if zoom and focus come into play. If you are looking to pull off a "registration" shot then you might as well forget about it since ANY variation in ANY of the camera settings will throw your shot off.

If you need to be exact then you are looking at a motion control rig. This is computer operated and all your travel speeds, distances, zoom rates, focus settings, etc. are pre-programed into the computer and are duplicated exactly, every time.

Very effective but very expensive to hire.

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Old December 5th, 2003, 01:07 PM   #6
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Any mechanical device that is rigid will, when you set it at the same angles, will be able to repeat its position. As long as you can set it identically every time. This includes whatever you set it on. Certainly accurately enough to get you very close. Then it's time to use the camera to reset the position close enough that frame-to-frame change is not perceivable.

If you use a camera with a stored image /current image mixing function, the PD150 and DSR-300 are two that come to mind, you can then fine-tune camera position after the mechanical setup gets it into coarse position.

Of course that assumes that you have crane features that allow you to fine-tune position.

Bound to be hard to do.

I would suggest a different approach to the mechanics of placing a camera into a repeatable postion time-after-time.

A permanent footing would be the start to which one would mount a camera mast that would self-align. On top of the mast would be a locked-down camera mount. It would take some work but it would be relatively easy to construct something like this. As long as the footing didn't move, you could come back next century and re-establish exactly the same camera position.
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