Mini35 Oscillating Ground Glass Idea

Jim Lafferty · September 27th, 2004, 07:17 AM

Curious...

Why all the talk of oscillating the glass and no ideas of spinning it anymore?

If you step back and think about it, there's a perfectly stable way to rotate ground glass from its edge -- instead of its center -- and thereby maintain the compact size, and relatively low cost of the current adapters. What you need to do is sandwich your ground glass between two ball-bearing rings, with machined teeth at the edge of the GG. Then, mounting a motor externally, rotate the GG from its edge.

I've already worked out light sealing issues in theory but have yet to execute my plans -- just figured it might simplify things for those of you who are finding moving GG necessary (understandable at higher resolutions.)

- jim

Juan M. M. Fiebelkorn · September 27th, 2004, 09:24 AM

That way you will need a really high RPM motor I guess...or a big gear....

Giroud Francois · September 27th, 2004, 10:12 AM

for your info it was made on first model of the real miniDV.
They stop because the "vortex effect".
Obviously rotating something has always a common point.
The center moves slowly than the outer edge, even the center point does not move at all. this is the problem.

Les Dit · September 27th, 2004, 01:02 PM

The key is there is a difference between rotating the GG and oscillating it. With the later, there is no common spot that will have no motion and be visible.
-Les

Jim Lafferty · September 27th, 2004, 10:47 PM

Quote:

The center moves slowly than the outer edge, even the center point does not move at all. this is the problem.

Good point. Thanks for that. Though this is a problem only if it's assumed that the projection is cast on the glass's center...

Quote:

With the later, there is no common spot that will have no motion and be visible.

I don't understand, Les -- what do you mean?

- jim

Les Dit · September 27th, 2004, 11:03 PM

Jim, in the design I used, the glass is moving in an 'orbital' motion of about 1.5mm radius only . The middle is moving the same amount as the center. The glass is not spinning, it makes little circles.

<<<-- Originally posted by Jim Lafferty : I don't understand, Les -- what do you mean?

- jim -->>>

Jim Lafferty · September 27th, 2004, 11:46 PM

Yeah, I get your design -- my question pertains to the above suggested spinning glass as a GG spun from its edge -- if the image is projected off-center, and the glass spun sufficiently fast, what visual anomalies would arise (if any)?

As a related note -- why hasn't anyone taken up the wax process? Are the claims of it showing no grain false, or is the process too costly -- in time, money or energy?

- jim

Les Dit · September 28th, 2004, 12:34 AM

Oh, OK Jim.
I think the spinning glass can work just fine. The adapter will be a bit bigger than an orbital system, obviously.
I don't see why spinning it from the edges would be of any help. You can't use the center anyway, so there may as well be a tiny axle there to spin it.
-Les

Jim Lafferty · September 28th, 2004, 03:55 PM

Well, if you spin from the edge, you can use space up to the center, and the rig will likely be a smaller design than one with the motor placed at the center -- especially given that where a center axle rests, you'd have to also place your motor just behind (or further complicate things with belts or gears to move it off-center).

I'm getting somewhat handy at 3dsMax -- when I get the time, I'll put up a model to more directly explain what I mean.

- jim

Brett Erskine · September 29th, 2004, 12:44 PM

Jim-
I undestand what your trying to say and IF you put the motor in the middle with a axis right there then yes it could be too large and cause a line of sight problem.

IF you want to rotate the GG from the outside like you mentioned I might recomend the smoother, quieter option of using large ring bearings. If you havent heard of them before image a sealed ball bearing thats as large as say a CD but has a inner hole just a few mm smaller than the outer diameter. In other words the bearing is the size of a CD but only a few mm wide and deep leaving a huge opening in the middle for you to see your image.
By mounting your GG to something like this you dont have to work about it shaking at the edges and ruining focus.

Its definately easier to build than a oscillating GG mechanism BUT your setup will be at least twice as big as it would have been if you had oscillated it. Also there could be a small chance that the "vortex" grain problem will still be there if you rotate it.

Personally I would oscillate it but if you dont have access to precision tools to make a oscillating adapter then the ring bearing is going to be your second best choice.

-Brett Erskine

Anders Floe · October 1st, 2004, 03:11 AM

To Les Dit

I just read about the 4 shaft 12 ball bearing offered kit, with motor,belt, misc parts to make a complete GG orbiter for $350,

Is that offer still there? If it is - could you then please send me some further info to my e-mail??

Thanks

Les Dit · October 1st, 2004, 03:56 AM

Email sent.
I'm trying to see if at least 4 people need these kits. Then it's a go.
-Les

Jim Lafferty · October 2nd, 2004, 08:29 PM

Thanks Brett -- I'd only rotate the glass anymore if I could do it at a smaller scale than you're speaking of.

Otherwise, I'm editing footage done with my static adapter at the moment and I'm finding the grain all but disappears on an NTSC viewing source, and for web delivery it's gone when the file's compressed to even a 1mb/sec, 360x240 Quicktime file. Since the grain really makes itself evident in the highs, a little Glow filter does a bit to suppress it as well.

The real problem I'm having is the damn dust -- there's four glass elements to keep clean with this thing :(

edit: Just now reading this thread closer from the beginning, and Giroud's stills look fantastic! I'd love to see some footage, though...

- jim

Daniel Moloko · October 3rd, 2004, 12:10 PM

Les,

i really need this Kit.

this one works with the JVC HD10U ?

send me the email too

danielmoloko@hotmail

ciao

Anders Floe · October 5th, 2004, 09:09 AM

To Rai Orz

Have you made a working relaylens for the XL-1????

<<<-- Originally posted by Rai Orz : Justin, in principle yes......Arround the 35mm solutions, i think this products are possible:

Prism-Set, suitably for the backside for UP-Side-Down correction

Relay-Lens-Set for XL1 or other

The products are here on my table, but yet i dont know details about prices or delivery. -->>>

September 27th, 2004, 07:17 AM	#166
Jim Lafferty Major Player Join Date: Dec 2003 Location: Brooklyn, NY Posts: 636	Curious... Why all the talk of oscillating the glass and no ideas of spinning it anymore? If you step back and think about it, there's a perfectly stable way to rotate ground glass from its edge -- instead of its center -- and thereby maintain the compact size, and relatively low cost of the current adapters. What you need to do is sandwich your ground glass between two ball-bearing rings, with machined teeth at the edge of the GG. Then, mounting a motor externally, rotate the GG from its edge. I've already worked out light sealing issues in theory but have yet to execute my plans -- just figured it might simplify things for those of you who are finding moving GG necessary (understandable at higher resolutions.) - jim __________________ Realism, anyway, is never exactly the same as reality, and in the cinema it is of necessity faked. -- J-L G

September 27th, 2004, 11:46 PM	#172
Jim Lafferty Major Player Join Date: Dec 2003 Location: Brooklyn, NY Posts: 636	Yeah, I get your design -- my question pertains to the above suggested spinning glass as a GG spun from its edge -- if the image is projected off-center, and the glass spun sufficiently fast, what visual anomalies would arise (if any)? As a related note -- why hasn't anyone taken up the wax process? Are the claims of it showing no grain false, or is the process too costly -- in time, money or energy? - jim __________________ Realism, anyway, is never exactly the same as reality, and in the cinema it is of necessity faked. -- J-L G

September 28th, 2004, 03:55 PM	#174
Jim Lafferty Major Player Join Date: Dec 2003 Location: Brooklyn, NY Posts: 636	Well, if you spin from the edge, you can use space up to the center, and the rig will likely be a smaller design than one with the motor placed at the center -- especially given that where a center axle rests, you'd have to also place your motor just behind (or further complicate things with belts or gears to move it off-center). I'm getting somewhat handy at 3dsMax -- when I get the time, I'll put up a model to more directly explain what I mean. - jim __________________ Realism, anyway, is never exactly the same as reality, and in the cinema it is of necessity faked. -- J-L G

October 2nd, 2004, 08:29 PM	#178
Jim Lafferty Major Player Join Date: Dec 2003 Location: Brooklyn, NY Posts: 636	Thanks Brett -- I'd only rotate the glass anymore if I could do it at a smaller scale than you're speaking of. Otherwise, I'm editing footage done with my static adapter at the moment and I'm finding the grain all but disappears on an NTSC viewing source, and for web delivery it's gone when the file's compressed to even a 1mb/sec, 360x240 Quicktime file. Since the grain really makes itself evident in the highs, a little Glow filter does a bit to suppress it as well. The real problem I'm having is the damn dust -- there's four glass elements to keep clean with this thing :( edit: Just now reading this thread closer from the beginning, and Giroud's stills look fantastic! I'd love to see some footage, though... - jim __________________ Realism, anyway, is never exactly the same as reality, and in the cinema it is of necessity faked. -- J-L G

October 3rd, 2004, 12:10 PM	#179
Daniel Moloko Regular Crew Join Date: Sep 2003 Location: Brazil Posts: 124	Les Les, i really need this Kit. this one works with the JVC HD10U ? send me the email too danielmoloko@hotmail ciao

September 27th, 2004, 09:24 AM	#167
Juan M. M. Fiebelkorn Major Player Join Date: Jun 2004 Location: Buenos Aires , Argentina Posts: 444	That way you will need a really high RPM motor I guess...or a big gear....

September 27th, 2004, 10:12 AM	#168
Giroud Francois Inner Circle Join Date: Feb 2004 Location: switzerland Posts: 2,133	for your info it was made on first model of the real miniDV. They stop because the "vortex effect". Obviously rotating something has always a common point. The center moves slowly than the outer edge, even the center point does not move at all. this is the problem.

September 27th, 2004, 01:02 PM	#169
Les Dit Major Player Join Date: Oct 2003 Location: Southern Cal-ee-for-Ni-ya Posts: 608	The key is there is a difference between rotating the GG and oscillating it. With the later, there is no common spot that will have no motion and be visible. -Les

September 27th, 2004, 11:03 PM	#171
Les Dit Major Player Join Date: Oct 2003 Location: Southern Cal-ee-for-Ni-ya Posts: 608	Jim, in the design I used, the glass is moving in an 'orbital' motion of about 1.5mm radius only . The middle is moving the same amount as the center. The glass is not spinning, it makes little circles. <<<-- Originally posted by Jim Lafferty : I don't understand, Les -- what do you mean? - jim -->>>

September 28th, 2004, 12:34 AM	#173
Les Dit Major Player Join Date: Oct 2003 Location: Southern Cal-ee-for-Ni-ya Posts: 608	Oh, OK Jim. I think the spinning glass can work just fine. The adapter will be a bit bigger than an orbital system, obviously. I don't see why spinning it from the edges would be of any help. You can't use the center anyway, so there may as well be a tiny axle there to spin it. -Les

September 29th, 2004, 12:44 PM	#175
Brett Erskine Major Player Join Date: Dec 2003 Location: Anaheim, CA Posts: 445	Jim- I undestand what your trying to say and IF you put the motor in the middle with a axis right there then yes it could be too large and cause a line of sight problem. IF you want to rotate the GG from the outside like you mentioned I might recomend the smoother, quieter option of using large ring bearings. If you havent heard of them before image a sealed ball bearing thats as large as say a CD but has a inner hole just a few mm smaller than the outer diameter. In other words the bearing is the size of a CD but only a few mm wide and deep leaving a huge opening in the middle for you to see your image. By mounting your GG to something like this you dont have to work about it shaking at the edges and ruining focus. Its definately easier to build than a oscillating GG mechanism BUT your setup will be at least twice as big as it would have been if you had oscillated it. Also there could be a small chance that the "vortex" grain problem will still be there if you rotate it. Personally I would oscillate it but if you dont have access to precision tools to make a oscillating adapter then the ring bearing is going to be your second best choice. -Brett Erskine

October 1st, 2004, 03:11 AM	#176
Anders Floe Regular Crew Join Date: Oct 2003 Location: Copenhagen Posts: 91	To Les Dit I just read about the 4 shaft 12 ball bearing offered kit, with motor,belt, misc parts to make a complete GG orbiter for $350, Is that offer still there? If it is - could you then please send me some further info to my e-mail?? Thanks

October 1st, 2004, 03:56 AM	#177
Les Dit Major Player Join Date: Oct 2003 Location: Southern Cal-ee-for-Ni-ya Posts: 608	Email sent. I'm trying to see if at least 4 people need these kits. Then it's a go. -Les

October 5th, 2004, 09:09 AM	#180
Anders Floe Regular Crew Join Date: Oct 2003 Location: Copenhagen Posts: 91	To Rai Orz Have you made a working relaylens for the XL-1???? <<<-- Originally posted by Rai Orz : Justin, in principle yes......Arround the 35mm solutions, i think this products are possible: Prism-Set, suitably for the backside for UP-Side-Down correction Relay-Lens-Set for XL1 or other The products are here on my table, but yet i dont know details about prices or delivery. -->>>