Sorry for the delay in getting back to this thread. I lost my internet service and can only get access on my trips to the library.
I know all metals will expand and contract with changes in temperature. (Dimensionally stable being relative, of course). I don’t think that I’m trying to reinvent the wheel here, because nothing mentioned will work for me. No stand and no tripod head that is already in production.
On Tuesday, February 5, 2013 7:30:34 PM UTC-5, anorton wrote:
"Searcher7" wrote in message
...
I haven't gottena all of the particulars worked out yet, but I am
working on designing a camera stand and trying to decide on the best
material to make most of it out of.
I'm not trying to reinvent the wheel, but a special project makes it
necessary to be able to take a series of as many as 180 equally spaced
photos across a 45� swing and be be able to do the same again without
any perceptable deviation.
In other words if I take a picture at 12-1/4� and then continue
turning the camera all the way to the end, when I return the camera to
the same spot I took the photo I will need to be able to stop and lock
the camera so that the photo next photo I take there is *exactly the
same as the previous one I took.
This is not plausible with conventional camera stands. So I'm trying
to decide on the best metal to make the moving parts out of. A metal
that will best retain it's dimensions under changing temperature
conditions.
To start. Would cast Iron be a plausible candidate?
Thanks.
Darren Harris
Staten Island, New York.
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Having experience building telescope mounts, I can say your main issue will
not be thermal expansion. Instead you will need to worry about stiffness of
the rigid structures, repeatability of the detents, stability of the
rotation axis, and quality of the bearings. You will probably need a shaft
of some length with bearings at either end.
Yes. All of that makes sense. And I intend to take all that into consideration. It was just that thermal expansion was the thing I wasn’t sure about..
If a metal structure is heated or cooled uniformly, that does not affect the
angular dimensions on the part.
Ok. Then I’ll not worry too much about that.
Aluminum is fine for telescope mounts and it should be fine for what you are
doing.
Thanks.
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On Tuesday, February 5, 2013 7:33:43 PM UTC-5, Tim Wescott wrote:
Well, if you really mean exact, then it can't be done.
Off by one pixel? Off by ten pixels? What's _really_ acceptable? And,
how much angle does a pixel subtend, on your system?
Yes. Perfection can never be achieved. The idea is to get as close as possible/plausible. I won’t know hoe close until I try.
If I were going to try this, if I were going to make just one, and if I
felt my time was worth anything at all, I'd base things on a rotary
table. You can get them with scary accuracies, if you're willing to
spend money on it.
Great idea. (Sometimes we miss the obvious).
It certainly would save a lot of design and work time.
But I have to mention that the camera will need to be at the end of a boom. The pivot radius will probably be in the neighborhood of 12 feet. (I don’t know the mathematically formula off hand, but isn’t that almost 14 feet between the far right and far left images taken?).
Then, depending on the accuracy I _really_ needed, I'd decide what I
needed to mount it on.
Well, nothing more than a hard surface would be plausible. The stand would of course have to be relatively heavy.
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On Thursday, February 7, 2013 8:39:31 AM UTC-5, Larry Jaques wrote:
On Wed, 6 Feb 2013 23:22:58 -0800 (PST), Stanley Schaefer
wrote:
On Feb 5, 4:20�pm, Searcher7 wrote:
I haven't gottena all of the particulars worked out yet, but I am
working on designing a camera stand and trying to decide on the best
material to make most of it out of.
I'm not trying to reinvent the wheel, but a special project makes it
necessary to be able to take a series of as many as 180 equally spaced
photos across a 45� swing and be be able to do the same again without
any perceptable deviation.
That's a 3 second shot with a fast movie camera, Darren.
Yes. That’s exactly what this is.
But I made an error. The camera will have to cover 90° of the horizon. (Not 45°).
Match up individual frames from the sequences using most any video
editing software. An electric motor should pan that for you pretty
easily. (What on Earth requires a quarter degree turn photo?)
Perhaps a motorized equatorial telescope movement would work for you.
Some are GPS guided, which would ensure your exact placement.
That wouldn’t work, because this would have to be manual (and simple). I think it is easier than having a motor stop the camera at each interval and then wait for any vibration to dissipate before taking the next picture. (Each frame must be the equivalent of a high definition image).
To elaborate further, I want to make what would amount to a 3 second video, but I need to have *complete control* over each individual frame. I can then manually pan *at various speeds*. Only 1/3 of the 90° of horizon will be viewable at any one time. This of course is going to take software not yet written. (And I haven’t even mentioned the other effects I’ll need to incorporate).
This would be a lot easier if there was a panoramic video camera that had a lens that would cover 90° and not have the customary distortion. Then I wouldn’t have to worry about panning.
Thanks.
Darren Harris
Staten Island, New York.