Mini35 Oscillating Ground Glass Idea

Brett Erskine · July 8th, 2004, 03:06 PM

Rai-
Buddy you are DEAD on! Thats a perfect example of how to make a smooth, professional oscillator. Our designs are so similar its scary right down the where and how its counter weighted. I looked everywhere for off set shafts that are ready made but couldnt find them (at least not that small). You have to make me some of those. If anyone else has a idea of where you can get some let me know. I may have to have them computer lathed. My set up makes it oscillate alittle too wide.

Im on the hunt for a ultra quiet motor. What do you plan on using? Im hoping to find a tiny 7.2v DC motor so that I can just use another camera battery to run it. It would be nice to know what the RPMs of the P+S Technik motor but my guess is at around 1000rpm we shouldnt have any problem. Early on in this project people were using motors out of CD players but reported that they didnt spin quite as fast as they needed to. Then again back then people werent using quality GG or focusing screens so maybe it will be fast enough now. A CD player motor runs at 500rpm. Going alot faster will insure that you wont see the grain but you have to remember the faster the motor the noiser it generally is and you dont want to pic up the sound of the motor in your on camera mics. 1000rpms sounds like a good ball park because we are oscillating the GG instead of spining it. But the best solution would be to have a variable speed controler on a motor that can go alot faster than that. Why? Sometimes we shoot at 1/500sec shutter speeds instead of 1/48th. This quick shutter speed is sure to catch the imperfections on the glass if it isnt oscillating fast enough.

I wouldnt change anything on your design ;-) Everything looks good. I could only recomend that you add a few things that you havent shown yet. Make the mount the motor and the oscillating mechanism on the same plate and when it comes time to house everything in a project box have the everything inside attach to the project box by mounts that have rubber bushings. This is the best place for them. I noticed that you are using rubber bushings where the bearings sit. This is a good idea because you made your own off set shafts but if you switch to some that are precision made (all exactly the same) I would loose the rubber bushings because they cause a little slack in a system that doesnt need it at that point. It some speeds it might actually create strange vibrations if you have the bushings there. You want thoughs three points to be solid.

Lastly if you havent already made it you might find it alittle easier to build if you have 4 off set shafts instead of three. Its easier to find something ready made with 4 holes pre drilled equally apart than 3 holes in a triangle. But more importantly you can make your over all design smaller then. The reason is the off set shafts dont have to be set so far out from the ground glass in order for the O ring to clear it. This is even more aparent if you plan on using a rectangle shaped focusing screen instead of round GG. Personally Im going to go with a Beattie Intenscreen or a Minolta Acute Matte focusing screen. These screens are anywhere from 1 to 4 stops brighter than anything else out there and our adapters need all the light they can get. They do however use fresnels to focus the light instead of a optical lens but Im starting to get real tired of buying a bunch of different plano convex lenses trying to do the same job. As many of us know the optical quality of fresnels arent as good as a plain lens BUT these Minolta and Beattie screens use a much finer etched fresnel lens then others out there. You cant see it. They are perfectly calibrated to give you a even field without any hot spots as well. They are extremely light weight which is a must if you plan on oscillating it. Lastly the microscopic fresnel rings act to contain light that would otherwise diffuse alot more with traditional GG. The result is a sharper image with more contrast. On top of that you can increase most of these advantages if you use a medium format focusing screen instead of a 35mm screen. Grain gets smaller and image gets sharper and has more contrast by at least a factor of 4X. Now this is all true if you plan on using medium format lenses but you can also use 35mm lenses with at least some of the benifits mentioned. You cant use a 35mm sized focusing screen anyways on a oscillating style adapter because the focusing screen needs to be a bit larger than the target area of the lens because its oscillating. You can also get alot of them pre mounted in a frame. Perfect for attaching to your off set shaft.

Alright I better stop there and save the rest for later otherwise people wont want to read all of this info because the post is too long. Anyways Rai since we are working in the exact same direction we really have to work together on this. Email me and/or post info on parts and I'll do the same.

Brett Erskine
BErskine@mail.com

P.S. What camera are you using? I've got a source for $10 DVX100 battery docking mounts to power the motor.

Les Dit · July 8th, 2004, 07:16 PM

Funny, the drawing looks like what I built!
Form follows function!

I just got some GG, so I can finish it all this weekend.
I may use 4 shafts next time, because it's hard to get the GG size
to fit with the 3 shaft setup.

I'll post a pic of what I have tonight. It's all shiny still, but I'll matte black it as I finalize the machine work.

You can test the Z axis motion by looking at a reflection of the GG plane. It should be without warpage or image shift if it's perfect. Look at it at a 45 degree reflection. It's an easy way to test it out. The spinning CD people had a problem with the Z axis going in and out ruining the focus.
-Les

Les Dit · July 8th, 2004, 11:50 PM

Here is where I am at with my 'substrate shaker' .
http://home.earthlink.net/~lesd/hd/

Still needs a bit more work, like mounting the motor, preloading the bearings with springs or magnets, and milling out a hole in the lexan. I'm still thinking of where I want to put the counter weights, maybe in the pulleys. I hand held the motor and it drives it nicely. The whole thing fits in a PVC pipe coupling with the motor outside.
-Les

Brett Erskine · July 9th, 2004, 01:42 AM

Les-
You werent kidding. Join the club. Very nice work btw. Could you post a picture of your off set arm and tell us where you found it or how you made it. Also hows that motor working out for you? Is it quiet enough? Whats it's RPM's? Voltage?

I was thinking about the counter weight issue some more and you could also put it on the far side of the shaft. The opposite side than where Rai put his. That way when you add more or less weight its not only easiler but you arent changing the position of the GG. Either way will work though.

I remember someone mentioning the magnet idea before (maybe it was you). You may not need that if you switch to a micro sized bearing because the slack in those things are a fraction of 1 mm. Hobby store. 5 bucks a pop though. Let keep working and sharing ideas. Thanks.

-Brett Erskine

Bob Hart · July 9th, 2004, 05:38 AM

Brett.

Deceased video-cassette players might warrant investigation as a possible quiet longlife motor source. My understanding is that the drum motors are designed to slave to 60hz for US or 50hz PAL country. This may mean 1800rpm or 1500rpm if slaved to their reference.

They have to be powerful enough to drag a half drum past half-inch tape and for accelleration and retardation sharp enough to match the sync signal off the tape against a reference. Best of all, they have a miniature ball-bearing set, an inbuilt balanced flywheel and a nice thick robust precise shaft. They are a bit big and heavy however.

Earlier specimens used a separate high speed DC motor capable of more modest acceration and retardation which was made responsive and powerful enough by a high reduction ratio belt drive to the drum which was effectively an idler or contained a less powerful motor which contributed the final more precise accelleration and retardation needed. These drive motors may not be robust enough and more likely to have been the cause of the appliance failing.

Another source might be the mirror motors from fixed window - bench type supermarket checkout scanners.

Rai Orz · July 9th, 2004, 08:41 AM

Bob, Brett, Les, and all the others in this club...,

Look for (batterie) audio cassette player motors. Most work with 3 to 5 Volt and, with a pair of eletronic parts (poti, transistor), you can speed change simple on power change.

Les Dit · July 9th, 2004, 11:38 AM

No, why would I be kidding. Oh, thats right, this is the internet ;)
Anyways, as I mentioned before, I used a lathe to make the offset shaft. I was going to use a pin in the end of the shaft, but it's harder to do it that way. Without a lathe, I'd do a pin and put it in with some red locktite.
The motor is from a tape deck, it seems good, maybe a bit big. I'll have to see how fast it needs to run to motion blur out the grain. With a smaller radius the rpm has to be more to get the velocity. The closer you get the weights to the plane of the moving part, the less vibrations you will have. You have to think dynamic balance, CG is not the only thing involved, for this thing, any counterweight will help, it doesn't vibrate that much.
Is yours constructed yet?
-Les

<<<-- Originally posted by Brett Erskine : Les-
You werent kidding. Join the club. Very nice work btw. Could you post a picture of your off set arm and tell us where you found it or how you made it. Also hows that motor working out for you? Is it quiet enough? Whats it's RPM's? Voltage?

I was thinking about the counter weight issue some more and you could also put it on the far side of the shaft. The opposite side than where Rai put his. That way when you add more or less weight its not only easiler but you arent changing the position of the GG. Either way will work though.

I remember someone mentioning the magnet idea before (maybe it was you). You may not need that if you switch to a micro sized bearing because the slack in those things are a fraction of 1 mm. Hobby store. 5 bucks a pop though. Let keep working and sharing ideas. Thanks.

-Brett Erskine -->>>

Brett Erskine · July 9th, 2004, 12:56 PM

Audio cassette (Walkman) motors huh...Hmm interesting. I wonder how cheap and small they make AC/DC converters these days that would be to run one of thoughs 48X CD-ROM drive motors or a variable speed. Or perhaps a manufacture has the same motor available in a DC.

My mechanism is half built. I'll post something when I get closer.

-Brett Erskine
www.CinematographerReels.com

Giroud Francois · July 9th, 2004, 01:23 PM

you should try ultrasonic motor. that is what they use in autofocus lens like the canon EOS.
see http://www.photoscene.com/sw/tour/inside.htm
you can even see that this kind of motor is like a ring, so stacking two of them can give the ideal movement if they are not centered.
the first one is moving the second which is moving the GG, each one having different speed and are non centered so you obtain a kind of chaotic orbital movement
they run smoother and quieter than regular motor and offer a better torque/size ratio so you probably can have a real small (flat) one. you even can find linear motor that move along a straight line and can go back and forth at more that 100x/sec.
the only drawback is ultrasonic vibration can sometime be a trouble in fine mechanics.
The positive fact is it could help to keep your gg clean...
check too http://www.adaptronics.com/products/ultrasonic_motors/index.html
For instance i am pretty happy with my fixed gged condenser.
with good light, the grain in SD video is not really noticeable.
i learn from several test that a lens with relative aperture at 1.4 is a real plus. at 1.7 or 1.8 you still get vignetting too easily.
fortunately, this is just the kind of old lense with M42 mount you can find for cheap everywhere (mine is a revuenon paid 20$).
Unfortunately you are limited to FL at 50 or 55, because it seems unusual to find a FL under or over with such specs. anyhow 50 or 55 mm is still a pretty workable value, close to what you get from a video camera.
i solve the vignetting effect by using a lens that look like a huge contact lens. This totallly remove vigneting.. you find these lens into any photo or video lense , usually just behind the firste one.

Brett Erskine · July 9th, 2004, 05:40 PM

Giroud-
Excellent idea! Of coarse the ones used in EOS lenses are practical for a few reasons but I'll do some hunting around for a small DC ultrasonic motor. I think ultrasonics may be the answer guys. Thanks

-Brett Erskine

Brett Erskine · July 9th, 2004, 05:45 PM

I mean, "NOT practical"

Les Dit · July 9th, 2004, 09:36 PM

I wonder what voltage the cannon motors need? 50 or 100 volt driver at some high frequency ? I like the look of them !
-Les

Brett Erskine · July 9th, 2004, 10:51 PM

They are nearly the diameter of the lens - making them too large to use for our purpose. It would be nice IF they moved in a oscillating motion because we could just simply mount the GG in the center of one of them. But they only rotate and slowly at that.

On another note - Im killing myself here looking for a tiny offset shaft. Can someone pleeeease help me?

-Brett Erskine

Rai Orz · July 10th, 2004, 01:58 AM

Brett, you´r right. They only rotate... so you have a point in the middle with visible grid... and also it rotate slowly...

Find a company with repair parts for audio recorder and you find a lot of different motors, belt, etc., all for small $.

Tiny offset shaft? How much may they cost? How much may a complete set of parts cost? With or without motor, housing, etc.. Give me an idea. Maybe you have found a source...

Obin Olson · July 10th, 2004, 09:53 AM

brett, i love the opening shot on your demo reel...how did you get that look? it's high production value looking!

July 8th, 2004, 03:06 PM	#46
Brett Erskine Major Player Join Date: Dec 2003 Location: Anaheim, CA Posts: 445	To Rai and other Oscillating Designers Rai- Buddy you are DEAD on! Thats a perfect example of how to make a smooth, professional oscillator. Our designs are so similar its scary right down the where and how its counter weighted. I looked everywhere for off set shafts that are ready made but couldnt find them (at least not that small). You have to make me some of those. If anyone else has a idea of where you can get some let me know. I may have to have them computer lathed. My set up makes it oscillate alittle too wide. Im on the hunt for a ultra quiet motor. What do you plan on using? Im hoping to find a tiny 7.2v DC motor so that I can just use another camera battery to run it. It would be nice to know what the RPMs of the P+S Technik motor but my guess is at around 1000rpm we shouldnt have any problem. Early on in this project people were using motors out of CD players but reported that they didnt spin quite as fast as they needed to. Then again back then people werent using quality GG or focusing screens so maybe it will be fast enough now. A CD player motor runs at 500rpm. Going alot faster will insure that you wont see the grain but you have to remember the faster the motor the noiser it generally is and you dont want to pic up the sound of the motor in your on camera mics. 1000rpms sounds like a good ball park because we are oscillating the GG instead of spining it. But the best solution would be to have a variable speed controler on a motor that can go alot faster than that. Why? Sometimes we shoot at 1/500sec shutter speeds instead of 1/48th. This quick shutter speed is sure to catch the imperfections on the glass if it isnt oscillating fast enough. I wouldnt change anything on your design ;-) Everything looks good. I could only recomend that you add a few things that you havent shown yet. Make the mount the motor and the oscillating mechanism on the same plate and when it comes time to house everything in a project box have the everything inside attach to the project box by mounts that have rubber bushings. This is the best place for them. I noticed that you are using rubber bushings where the bearings sit. This is a good idea because you made your own off set shafts but if you switch to some that are precision made (all exactly the same) I would loose the rubber bushings because they cause a little slack in a system that doesnt need it at that point. It some speeds it might actually create strange vibrations if you have the bushings there. You want thoughs three points to be solid. Lastly if you havent already made it you might find it alittle easier to build if you have 4 off set shafts instead of three. Its easier to find something ready made with 4 holes pre drilled equally apart than 3 holes in a triangle. But more importantly you can make your over all design smaller then. The reason is the off set shafts dont have to be set so far out from the ground glass in order for the O ring to clear it. This is even more aparent if you plan on using a rectangle shaped focusing screen instead of round GG. Personally Im going to go with a Beattie Intenscreen or a Minolta Acute Matte focusing screen. These screens are anywhere from 1 to 4 stops brighter than anything else out there and our adapters need all the light they can get. They do however use fresnels to focus the light instead of a optical lens but Im starting to get real tired of buying a bunch of different plano convex lenses trying to do the same job. As many of us know the optical quality of fresnels arent as good as a plain lens BUT these Minolta and Beattie screens use a much finer etched fresnel lens then others out there. You cant see it. They are perfectly calibrated to give you a even field without any hot spots as well. They are extremely light weight which is a must if you plan on oscillating it. Lastly the microscopic fresnel rings act to contain light that would otherwise diffuse alot more with traditional GG. The result is a sharper image with more contrast. On top of that you can increase most of these advantages if you use a medium format focusing screen instead of a 35mm screen. Grain gets smaller and image gets sharper and has more contrast by at least a factor of 4X. Now this is all true if you plan on using medium format lenses but you can also use 35mm lenses with at least some of the benifits mentioned. You cant use a 35mm sized focusing screen anyways on a oscillating style adapter because the focusing screen needs to be a bit larger than the target area of the lens because its oscillating. You can also get alot of them pre mounted in a frame. Perfect for attaching to your off set shaft. Alright I better stop there and save the rest for later otherwise people wont want to read all of this info because the post is too long. Anyways Rai since we are working in the exact same direction we really have to work together on this. Email me and/or post info on parts and I'll do the same. Brett Erskine BErskine@mail.com P.S. What camera are you using? I've got a source for $10 DVX100 battery docking mounts to power the motor.

July 8th, 2004, 11:50 PM	#48
Les Dit Major Player Join Date: Oct 2003 Location: Southern Cal-ee-for-Ni-ya Posts: 608	A few pics Here is where I am at with my 'substrate shaker' . http://home.earthlink.net/~lesd/hd/ Still needs a bit more work, like mounting the motor, preloading the bearings with springs or magnets, and milling out a hole in the lexan. I'm still thinking of where I want to put the counter weights, maybe in the pulleys. I hand held the motor and it drives it nicely. The whole thing fits in a PVC pipe coupling with the motor outside. -Les

July 9th, 2004, 05:40 PM	#55
Brett Erskine Major Player Join Date: Dec 2003 Location: Anaheim, CA Posts: 445	Ultrasonic Motors Giroud- Excellent idea! Of coarse the ones used in EOS lenses are practical for a few reasons but I'll do some hunting around for a small DC ultrasonic motor. I think ultrasonics may be the answer guys. Thanks -Brett Erskine

July 8th, 2004, 07:16 PM	#47
Les Dit Major Player Join Date: Oct 2003 Location: Southern Cal-ee-for-Ni-ya Posts: 608	Funny, the drawing looks like what I built! Form follows function! I just got some GG, so I can finish it all this weekend. I may use 4 shafts next time, because it's hard to get the GG size to fit with the 3 shaft setup. I'll post a pic of what I have tonight. It's all shiny still, but I'll matte black it as I finalize the machine work. You can test the Z axis motion by looking at a reflection of the GG plane. It should be without warpage or image shift if it's perfect. Look at it at a 45 degree reflection. It's an easy way to test it out. The spinning CD people had a problem with the Z axis going in and out ruining the focus. -Les

July 9th, 2004, 01:42 AM	#49
Brett Erskine Major Player Join Date: Dec 2003 Location: Anaheim, CA Posts: 445	Les- You werent kidding. Join the club. Very nice work btw. Could you post a picture of your off set arm and tell us where you found it or how you made it. Also hows that motor working out for you? Is it quiet enough? Whats it's RPM's? Voltage? I was thinking about the counter weight issue some more and you could also put it on the far side of the shaft. The opposite side than where Rai put his. That way when you add more or less weight its not only easiler but you arent changing the position of the GG. Either way will work though. I remember someone mentioning the magnet idea before (maybe it was you). You may not need that if you switch to a micro sized bearing because the slack in those things are a fraction of 1 mm. Hobby store. 5 bucks a pop though. Let keep working and sharing ideas. Thanks. -Brett Erskine

July 9th, 2004, 05:38 AM	#50
Bob Hart Inner Circle Join Date: Dec 2003 Location: PERTH. W.A. AUSTRALIA. Posts: 4,476	Brett. Deceased video-cassette players might warrant investigation as a possible quiet longlife motor source. My understanding is that the drum motors are designed to slave to 60hz for US or 50hz PAL country. This may mean 1800rpm or 1500rpm if slaved to their reference. They have to be powerful enough to drag a half drum past half-inch tape and for accelleration and retardation sharp enough to match the sync signal off the tape against a reference. Best of all, they have a miniature ball-bearing set, an inbuilt balanced flywheel and a nice thick robust precise shaft. They are a bit big and heavy however. Earlier specimens used a separate high speed DC motor capable of more modest acceration and retardation which was made responsive and powerful enough by a high reduction ratio belt drive to the drum which was effectively an idler or contained a less powerful motor which contributed the final more precise accelleration and retardation needed. These drive motors may not be robust enough and more likely to have been the cause of the appliance failing. Another source might be the mirror motors from fixed window - bench type supermarket checkout scanners.

July 9th, 2004, 08:41 AM	#51
Rai Orz Regular Crew Join Date: Jun 2004 Location: Germany Posts: 136	Bob, Brett, Les, and all the others in this club..., Look for (batterie) audio cassette player motors. Most work with 3 to 5 Volt and, with a pair of eletronic parts (poti, transistor), you can speed change simple on power change.

July 9th, 2004, 11:38 AM	#52
Les Dit Major Player Join Date: Oct 2003 Location: Southern Cal-ee-for-Ni-ya Posts: 608	No, why would I be kidding. Oh, thats right, this is the internet ;) Anyways, as I mentioned before, I used a lathe to make the offset shaft. I was going to use a pin in the end of the shaft, but it's harder to do it that way. Without a lathe, I'd do a pin and put it in with some red locktite. The motor is from a tape deck, it seems good, maybe a bit big. I'll have to see how fast it needs to run to motion blur out the grain. With a smaller radius the rpm has to be more to get the velocity. The closer you get the weights to the plane of the moving part, the less vibrations you will have. You have to think dynamic balance, CG is not the only thing involved, for this thing, any counterweight will help, it doesn't vibrate that much. Is yours constructed yet? -Les <<<-- Originally posted by Brett Erskine : Les- You werent kidding. Join the club. Very nice work btw. Could you post a picture of your off set arm and tell us where you found it or how you made it. Also hows that motor working out for you? Is it quiet enough? Whats it's RPM's? Voltage? I was thinking about the counter weight issue some more and you could also put it on the far side of the shaft. The opposite side than where Rai put his. That way when you add more or less weight its not only easiler but you arent changing the position of the GG. Either way will work though. I remember someone mentioning the magnet idea before (maybe it was you). You may not need that if you switch to a micro sized bearing because the slack in those things are a fraction of 1 mm. Hobby store. 5 bucks a pop though. Let keep working and sharing ideas. Thanks. -Brett Erskine -->>>

July 9th, 2004, 12:56 PM	#53
Brett Erskine Major Player Join Date: Dec 2003 Location: Anaheim, CA Posts: 445	Audio cassette (Walkman) motors huh...Hmm interesting. I wonder how cheap and small they make AC/DC converters these days that would be to run one of thoughs 48X CD-ROM drive motors or a variable speed. Or perhaps a manufacture has the same motor available in a DC. My mechanism is half built. I'll post something when I get closer. -Brett Erskine www.CinematographerReels.com

July 9th, 2004, 01:23 PM	#54
Giroud Francois Inner Circle Join Date: Feb 2004 Location: switzerland Posts: 2,133	you should try ultrasonic motor. that is what they use in autofocus lens like the canon EOS. see http://www.photoscene.com/sw/tour/inside.htm you can even see that this kind of motor is like a ring, so stacking two of them can give the ideal movement if they are not centered. the first one is moving the second which is moving the GG, each one having different speed and are non centered so you obtain a kind of chaotic orbital movement they run smoother and quieter than regular motor and offer a better torque/size ratio so you probably can have a real small (flat) one. you even can find linear motor that move along a straight line and can go back and forth at more that 100x/sec. the only drawback is ultrasonic vibration can sometime be a trouble in fine mechanics. The positive fact is it could help to keep your gg clean... check too http://www.adaptronics.com/products/ultrasonic_motors/index.html For instance i am pretty happy with my fixed gged condenser. with good light, the grain in SD video is not really noticeable. i learn from several test that a lens with relative aperture at 1.4 is a real plus. at 1.7 or 1.8 you still get vignetting too easily. fortunately, this is just the kind of old lense with M42 mount you can find for cheap everywhere (mine is a revuenon paid 20$). Unfortunately you are limited to FL at 50 or 55, because it seems unusual to find a FL under or over with such specs. anyhow 50 or 55 mm is still a pretty workable value, close to what you get from a video camera. i solve the vignetting effect by using a lens that look like a huge contact lens. This totallly remove vigneting.. you find these lens into any photo or video lense , usually just behind the firste one.

July 9th, 2004, 05:45 PM	#56
Brett Erskine Major Player Join Date: Dec 2003 Location: Anaheim, CA Posts: 445	I mean, "NOT practical"

July 9th, 2004, 09:36 PM	#57
Les Dit Major Player Join Date: Oct 2003 Location: Southern Cal-ee-for-Ni-ya Posts: 608	I wonder what voltage the cannon motors need? 50 or 100 volt driver at some high frequency ? I like the look of them ! -Les

July 9th, 2004, 10:51 PM	#58
Brett Erskine Major Player Join Date: Dec 2003 Location: Anaheim, CA Posts: 445	They are nearly the diameter of the lens - making them too large to use for our purpose. It would be nice IF they moved in a oscillating motion because we could just simply mount the GG in the center of one of them. But they only rotate and slowly at that. On another note - Im killing myself here looking for a tiny offset shaft. Can someone pleeeease help me? -Brett Erskine

July 10th, 2004, 01:58 AM	#59
Rai Orz Regular Crew Join Date: Jun 2004 Location: Germany Posts: 136	Brett, you´r right. They only rotate... so you have a point in the middle with visible grid... and also it rotate slowly... Find a company with repair parts for audio recorder and you find a lot of different motors, belt, etc., all for small $. Tiny offset shaft? How much may they cost? How much may a complete set of parts cost? With or without motor, housing, etc.. Give me an idea. Maybe you have found a source...

July 10th, 2004, 09:53 AM	#60
Obin Olson Trustee Join Date: Jan 2003 Location: Wilmington NC Posts: 1,414	brett, i love the opening shot on your demo reel...how did you get that look? it's high production value looking!