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-   -   A GG, two magnets and a spring? (http://www.dvinfo.net/forum/alternative-imaging-methods/44685-gg-two-magnets-spring.html)

Oscar Spierenburg May 16th, 2005 06:08 PM

A GG, two magnets and a spring?
I came up with an idea..then searched the board and found a similar theory by Aaron Shaw. His idea was to vibrate a ground glass between two magnets to loose the grain, Dan Diaconu said it would give a beginning and end point which would show the grain (because it only vibrates from side to side)

My idea is to attach the GG to a spring (that pulls the GG to one position) and two small electro magnets that form a triangle with the spring around the GG.
The actions is: if the GG is pulled back by the spring, one magnet will be activated (receive electricity) so the GG will be pulled to that magnet, than just before it hits the magnet, it is turned off (mechanically) and the other magnet is activated. When the GG comes near the second magnet, it is turned off, so the GG will be pulled back by the spring and everything repeats over and over again (unless I get the spring in my eye and the GG against my forehead)

If I'm not clear at all, I'll make a drawing.

Note that I've messed around with a lot of old pinball machines.
I don't know if a triangle motion is good enough to loose the grain, I don't know if the magnets would run too hot after a while and it will be difficult to make it silent.

Daves Spi May 17th, 2005 02:23 AM

I thing main problem is movement just in X an Y axis, not Z. Im not sure this will work. You will also need very tight movement, and Im not sure springs will do it. Just my opinion...

About loosing grain - you can move it so fast, faster then shutter, so grain will be blured and become invisible. But you need very fast vibrations, 60/s and more. OR you can move it so slow, that you just make grain to move and you will not see it in final movie.

Another idea what I have is rotating GG by its center. On sides you will get very big speed, in the middle it will be less. I would like to put center of rotation 0.2mm out of center of GG. Its pretty easy, so Im working on it...

Next idea on which Im working is GG attached on slider from diskette drive. In X axis I have two sliders from 3.5 drive, on Y axis two sliders from 5.25 drive. Motor with shaft is doing the job.

Little thing with spring is GG attached on three rolling wheels, which are inside in ring. The rign is ecentric, roling on next three wheels positioned outside. So the GG is doing ecentric movement. Little bit complicated :)

Brett Erskine May 17th, 2005 02:27 AM

Your talking about a x and y axis motion here. Dont forget about the ultra critical z axis. When in motion if the GG moves even a fraction of a mm towards, away or off angle to the lens you will have a image that is soft and/or shifting focus. Also dont forget about what happens to the GG when you point the camera up, down, quick movements, etc. "Gravity is a bitch". Using grooves to keep in place creates friction, wear and perhaps noise.

For this reason traditional hard mounts might be the only way to go.

Oscar Spierenburg May 17th, 2005 05:43 AM

The spring was intended to move the GG not only in one direction, but in a triangle. If a spring isn't fast enough, it could be a magnet too.
I made a drawing to explain. I didn't put the electrical part in the drawing, but they should be electro magnets of course.


I know the GG cannot move in and out of focus on the Z axis,but that's more of a mechanical problem. Everything should be attached to something stable of course.

I like Daves ideas too, but don't really understand the last part.

Daves Spi May 17th, 2005 07:37 AM


Originally Posted by Oscar Spier
I like Daves ideas too, but don't really understand the last part.

Take a look here : http://test.datriware.com/v.jpg

Rollers are brown. they are similar to rolers you can find in tape drives to roll the tape (walkmans, cassette players...). Arrows means springs. Blue and green circle is little bit bad painted, but imagine ring with blue hole and green outer edge. Outher edge is eccentric. So the GG inside is going in eccentric circle. This is my friends idea and his painting. We agreed its to much complicated and based on this we created yet better system, which I mentioned as first.

Second idea with diskette drive sliders has totaly zero Z axis movement, its very shock proof, camera movements proof, but little bit complicated to build everything together.

None of this systems were tested yet, next week I bring some photos and maybe some footage.

Oscar: do not stop, try it and let as know... In fact if you put GG on sliders, you get to my second idea. Just the movement made by motor with shaft you replace with magnets. I thought about the same thing few months ago, but cant imagine any holding mechanics.


But... maybe too much care about nothing...


If I look at my shots with static GG, I do not see any extra grain and after compression on DVD, it disappears anyway >:-)

Hope to get better image, who does not...

Oscar Spierenburg May 17th, 2005 06:53 PM

That's funny...I have a very similar drawing like your friend made right in front of me. I made it just before reading your post. It is different, but based on the same eccentric movement with a GG within a circle.
It should work, but we (I think) are searching for something that is easy to built, so people who are able to make the rotating GG, can also make this.

The best way is to find some existing mechanism that can be used for this.

Looking at your friend drawing...I can imagine a fast rotating ring that holds one or two normal magnets that attracts a different side of the GG (with metal strip) when it passes. Just a thought. But anyway, with all options, the difficulty is to get the GG stable on the focal plane.

EDIT: I won't stop...I have a working adapter with a rotating GG, but I want to use my 6x6cm Rolleicord in front of a GG. Rotating a medium-format GG would mean something like the size of a vinyl record as GG, so I need to make something oscillating in stead.

Daves Spi May 26th, 2005 07:17 AM


Originally Posted by Oscar Spier
Rotating a medium-format GG would mean something like the size of a vinyl record as GG, so I need to make something oscillating in stead.

Do not forget you can rotate it by its center but from outside, and not just rotate, but oscilate together. All you need is just three rollers and ring inside of them. Not tested yet, but should work great...

About the linear movement from point to point look here :
I posted some videos there.

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