GG demos and how to spot useless ones
 

Jesse,
I am sorry that you wasted your money on some of the other GG attempts.
Let me just say something about evaluating them:

1) Posting still images of a GG video is WORTHLESS for evaluating the grain. Period. You need to see a slow panning shot of the GG in use, preferably with some of the scene out of focus a bit and shadows and highlights. Only then do you have a chance to see the grain pattern because it remains in the same place on your monitor while the image moves past it.
So you shouldn't ask for frame grabs of the GG for evaluating it for grain.

2) Posting tiny video of some highly compressed format is also worthless for seeing grain effects. The first thing that a compression codec throws away is the grain pattern! The poster should use a 7 megabit mpeg4 or Media9 video to show the details. Then you can see possible fixed pattern grain effects.

OK,
Having said that, how about I post a small demo video, at a high bit rate Media9 ? My camera is an HD-10 JVC, if it works for that, it will work for DV res. no problem. The HD video will be 1280 X 720 pixels. I can also crop into it and make a smaller version for playback on slower computers. I'm open to suggestions on what to do for the Mac. I hear they play media9 now, but with some difficulty.
So, isn't the proof in the pudding, as they say? ( when the pudding is properly compressed )

-Les

Jesse: I understand exactly where you're coming from. Although you don't see many posts from me, I have been following developments and have spent money on glass, aluminum oxide, wax, etc... only to discover a couple of days and few posts later that there's a better way to do something.

HOWEVER, Les does have an actual device (not just something on paper), and I think the price he's asking is easily justifiable for the parts and labor involved, even if it's not in a housing. I don't see a reason why a 5 micron ground glass mounted on a rotating device would not work. However, I am building my own since it is just fun.

Les, have you tried advertising this on other forums where there are less technically minded people? (ie. consumer type people) Well, I don't mean that in a bad way. I just mean...people that don't like to build these things themselves, since that is what a majority of us guys in this thread are, I think.

Les-

A video clip would be great. I can handle high-res.
Also how big is the target area? Is the vibration isolated in the adapter? Does it shake the camera at all?

thanks
-jes

The cutout size right now is about 42mm X 30mm, but I want to switch to a 4 shaft system that will leave a little larger area. Right now the hole is not centered top to bottom either, another reason I want to change the design. The motor seems to run fine on 6V , four AA batteries are adequate.

There is a small amount of vibration, it's impossible to get rid of it all. I'm going to soft mount it in the housing, to minimize external vibrations. This must be done in such a way to avoid any z axis motion, which would ruin focus.
I haven't attempted to advertise anywhere, as this is really more for the type of person that can adapt it to their own use. It would not ship with a GG, for legal reasons.
I'll try to make some demo video in the next few days.
-Les

Les do we all get royalties for our contributions? ;-)

Im only kidding. Good luck.

-Brett Erskine

my roller ball
I will try to get more of them.
http://www.giroud.com/minidv/roller.jpg

Where did you pick up your bearings/pulley wheel?

frankly , i do not know.
i got a friend who got a box full of this, a few month ago, a take five of them to see if they could fit my needs for my video crane.
since the crane is going to a no-cable version, i will probably use these little marvels to the vibrating gg project.

Les,

How's that video clip coming? I'm anxious to see it.

It's finally the weekend, I'll get a chance to work on it!

-Les

<<<-- Originally posted by Jesse Rosten : Les,

How's that video clip coming? I'm anxious to see it. -->>>

Update: I tested with a lens and GG and discovered a very slight ( about 0.0015 inch ) off axis motion that causes the image to move laterally a little. I think one of the shafts is off center, I have to take it all apart and check, I'll probably make a new backing plate for the bearings. This thing has to be very precise for sure to get a good image. Also, I think that a fairly slow rpm will work, the grain moves by fairly fast with my 1.5mm radius.

So no video clip yet.
-Les

Les.

If your device is floating on rubber mounts, you may find you need counterbalance on either side of load centerpoint on each shaft, not just one side, otherwise the counterweights themselves may be creating the abberant motion you describe. It may not be a shaft running out.

Depending on how much of the oscillating mass you manage to balance out you will still get vibration but it will occur directly and not obliquely across the image axis. Make sure wires and other attachments come off at the load centre as well.

If your device is rigidly mounted, then you may have clearance in the bearings being taken up, again by the same offset counterbalance problem.

I am assuming that the bearings are a secure fit on their shafts and crankpins and the housings they fit into and cannot float. If not then you will need to limit movement along the image axis with some sort of guide frame. If this is already part of the design then ignore this commentary.

Don't take my ramblings too seriously as I am not an engineer. I do know that small 2 stroke engines with a half-crankshaft (like the oscillating groundglass devices) vibrate cruel-bad compared to a full crankshaft version of the same power and cubic capacity.

Les -

I'm still interested in your oscillator. If I disappear for the next three weeks it's because I'll be on location in Africa <plug plug> :)

peace
jes

Jesse,
I worked on it a bit this weekend. It still has some Z axis deflection that I'm trying to minimize. I can test it by looking at the mirror reflection of the GG shiny side, at a grazing angle. Even the smallest deflection, under 0.001 inch is enough to move the image around, indication that there is some Z axis motion. I'm thinking one of my eccentric shafts is off, I think I'm going to remake them, out of brass this time ( easier to machine ).

I want to post some tests soon. HD is very demanding, I don't want to diminish it's sharpness with my DOF adapter!

Africa... be safe, it's rather lawless in many places!

-Les

<<<-- Originally posted by Les Dit : Jesse,
. I can test it by looking at the mirror reflection of the GG shiny side, at a grazing angle. Even the smallest deflection, under 0.001 inch is enough to move the image around, indication that there is some Z axis motion.
-Les -->>>
Les,
Try to use a small laser pointer and look at the reflection on a screen or surface away from the disk. The "amplification factor" will make the measurement of the deflection easier.
Good luck

0.001... laser...
you start to understand now why these gadget cost the hell to build. I think we reach the point were the usual workbench in the garage is not more of any use.
try some small springs to keep all the stuff in place.

<<<-- Originally posted by Giroud Francois : 0.001... laser...
you start to understand now why these gadget cost the hell to build. -->>>

Giroud,
A laser pointer can be purchased from gift shops or night market stalls for ~3-5 dollars or for less euros. They come in various flavors, even as keyrings.

... and i already got so many of them.
They are fine to kick the cat, but i doubt they can be of any use
for chasing the .0001 inch.
When you start to deal with real fine mechanics (i used to deal with micron when i was in tool machining), you need some serious tools.

The laser idea is good. Just looking at a distant object using the GG shiny side does the same thing, really, but the laser would make it easy to actually measure the thing.
Springs: I am already taking the bearing lash out by using a pair of magnets and steel disks.
I don't think I need 0.0001 tolerance. Just a bit better than what I have now.

-Les

ground glass
 

hi everyone I just recived a piece of 5x9 ground glass from ebay seller .It looks real good. he has quite a few pieces. my winning bid was about ten dollars. I tried to have a circle cut once ,it has to be perfect. but maybe this could be of use. please let's share this.




http://cgi.ebay.com/ws/eBayISAPI.dll...830724092&rd=1

I now have my GG orbiter working. I redid the shafts and made them longer. There is no noticeable image vibration or shift, and it looks like it holds HD focus now. My GG has some rather gross pits in it when viewed static, but those look like they are gone when it's moving. I have no corrective optics to minimize the center hot spot, and I flip the image in the computer.

This weekend I will post a link to some video which I'll shoot on Sat.

-Les

Les-
Whats the target size your actually focusing on?
It should be 36mm X 24mm but without corrective optics you might have to zoom in farther than that.

here is my first test.
 

OK, my first test footage is up. Media9 and Mpeg2, both the same test. See the new thread:
http://www.dvinfo.net/conf/showthrea...863#post209863

-Les

Heey!!

I'm preparing to give this oscillating adapter a try, but I'm unsure if it's possible to oscillate my GG condenser, since it might be too heavy..

.. but let's say I get around this somehow ( a more powerful motor ? ), do you think I would see some wierd optical distortion because I'm oscillating my last condenser? .. I'm thinking it will scatter the incoming light all over the place .. resulting in a hotspot .. but I'm just guessing! .. anyone know for sure?

Martin-
Yes it will. Dont do it.

alright, brett, thanks for clearing that up!

by the way, do you have any footage with your orbiter in action ? I'm very curious!

I've been too busy to work on it lately. Trust me as soon as its done I'll post it for you guys.

About vibrating the condenser dont do it for all the reasons you mentioned. The way to do it is make the GG and the Condenser two seperate pieces and rotate the GG only. This will solve all of your problems. This is also how the Mini35 works.

Counterbalances
 

How have you guys been working out how much mass to be offset for the counterbalances? What are you basing these calculations on? As small as they seem to be, it seems too easy to over compensate and cause instability and vibration.

Re: Counterbalances
 

I just guessed on my first pass. I could see calculating the correct amount, but there are other things I would redesign before I make a new version.
The vibration I had on my first test, which I posted a while ago, is reduced when it is mounted in a more secure manner.
-Les



<<<-- Originally posted by Brandt Wilson : How have you guys been working out how much mass to be offset for the counterbalances? What are you basing these calculations on? As small as they seem to be, it seems too easy to over compensate and cause instability and vibration. -->>>

Is it possible to mount the motor on the same stationary plate as the three other bearing/shaft/counterweight assemblies? Sort of taking the place of one of the corners in the 4 shaft design. One possible problem is that the motor may get in the way of some of the optical components. You could always make the spacing between shafts a bit larger, but because of the larger overall design, that may defeat the purpose of having all of the stationary components on a single plate. I'm also assuming that the motor would have to have an offset shaft, or be fit into some sort of pin which would offset things appropriately so that the motor wouldn't get beat up. P+S probably went through all of the variations that have been talked about in this thread, and ended up with the one they're using because it seems to be the most efficient and stable design.

Les, your footage looks really nice. Especially under the conditions which the assembly was mounted. Are you using a condenser in that shot, or are you just shooting through your GG and primary lens?

Ray, I just used the GG and 50mm lens, no condenser lens used. It does get a tad darker on the edges, but not much.
My assembly is only 3.5 inches in diameter, so the motor has to be offset with a mounting plate.
-Les

Les.

Did you receive the DVD+R disk yet?

Yes Bob, Sorry, I meant to reply but I was sidetracked!
The footage looks great, there is really no grain or other artifacting going on. Good work!
Thanks again!
-Les


<<<-- Originally posted by Bob Hart : Les.

Did you receive the DVD+R disk yet? -->>>

Les, could you email me a link to your footage?

film AT bigsmile.com

Also, do you have any photos of your unit? That would be very helpful too.

Thanks!

Hey Les,

I wouldn't mind seeing that footage of yours. Can you link me up?

elrosten@yahoo.com

thanks

OK, link sent. Let me know what you think!

Looks great. I see no grain. And I'm sure the jitter will go away when the unit is mounted solidly to the camera.

This may have been mentioned a while back, but by oscillating a focus screen ( like from a 35mm or medium format camera) with a fresnel already "built-in" to the ground glass, you should be able to do away with all the condensor madness. The fresnel lines should be invisible because the screen is moving.

anyways... What's the noise level on your oscillator?

It seems like the fresnel type ground glasses are built with the rings relative to the center of light, so that it distributes the light across the plane. Rotating a fresnel with the axis being along the center of the rings would work, surely, but would oscillating it work without having some jittery unevenness? Does this make sense? Sorry if I've confused anyone.

Jesse,
I didn't use a condenser on that test. Did you notice?
-Les

Yes, Les, The vignette was quite obvious. I wasn't trying to imply that you WERE using a condenser. - Just thinking aloud about the possibility of oscillating a fresnel-type focus screen.

peace
jesse