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-   -   Mini 35 Competing Unit for a Lot Less $ (https://www.dvinfo.net/forum/techniques-independent-production/10532-mini-35-competing-unit-lot-less.html)

Joseph George June 6th, 2003 12:55 AM

Mini 35 Competing Unit for a Lot Less $
I have a cousin that heads development for one of Thompson divisions and because of that now lives in Europe. Anyway, to make the story short, we hired couple of guys and were able to use a different principle for the ground glass to move. It does not spin; it vibrates. The problem with the spin is that in the center the movement is too slow. We used 4 piezoelectric elements to make the screen vibrate at quite a high frequency -- installed the screen at focal plane of 35 mm camera. The movement was quite small and insufficient to fully get rid of the ground glass "dirty" look. We'll need to increase the deflection by using more powerful drivers. There was a guy on this forum -- from Australia -- Zac -- I think. He wanted to do create a Mini 35 equivalent by spinning the ground glass. I gave him info on the piezo drive system, but he thought that I'll give him 1/2 the world market for verifying the principle. Is there anyone who would be interested in working on this project?

Robert Poulton June 6th, 2003 01:24 AM

Interesting. I wouldn't know where to start, other than giving you my support for the idea you presented. Keep it up and you got any links or any other information about the vibration of the glass?


Alex Knappenberger June 6th, 2003 01:37 AM

Suspend the glass with rubber bands, or another form of rubber suspension, and then make a 12VDC motor off-balanced and connect it to the glass. No small vibrations there.

Send me the materials and i'll make one for you, heh...

Cosmin Rotaru June 6th, 2003 08:29 AM

That idea crossed my mind to. But not with piezo. Neither off-balanced motors... More like this: http://www.tecnohuila.com/Mecanismos/Topic39.HTM
I gave up on the idea. I think you end up with allot of vibrations in the system. The mini35 spins the ground glass and that gg has to be very well calibrated NOT to add vibrations in lens and such...

I'm very curios about this project.

Maybe you can connect the ground glass to an electromagnet that is also able to vibrate! So the electromagnet pushes the gg but it will also push itself back (action-reaction) so that the forces are absorbed into the unit and not transferred outside, to the camcorder's lens or body.

Joseph George June 6th, 2003 10:36 AM

The vibration problem: This is a non-problem so far. Since the ground glass and the piezoelectric moving portion have nearly no weight compared to the rest of the structure -- the 2 cameras and the 35 mm lens, plus the fact that the vibration is somewhere in the middle of the structure -- it so far did not introduce any vibration problem in the image at all. The frequency is just too high. Sound attenuation is the only concern so far.

Piezo elements are used in some tweeters, and were used in the past in phono cartridges, plus there are industrial applications also. The drivers are attached to the body and the screen is attached to the piezo elements. The piezo element is extremely efficient and reliable.

If vibration would become a problem, which is extremely unlikely even with extreme telephoto, counter mechanism can be installed with 4 more piezo drivers moving a counter balance in the opposite direction.

The advantage of the piezo system is increased reliability, a lot simpler mechanism, and highly decreased cost over the rotary system.

The HD version of the Mini 35, I heard, has a problem on high-resolution systems (CineAlta) near the middle where the speed is too slow. On Varicam it supposedly works fine.

Yang Wen June 6th, 2003 03:42 PM

Why do you need to spin the ground glass? Something about burning it up or somethin?

Elmar Tewes June 6th, 2003 04:10 PM

I'm very curious about that kind of thing too...
let me say the following and tell me if i'm right or wrong- i'm really no technican, so perhaps i made it a little bit easy in my mind ;-)

you make a kind of box, like the one from the original mini35 (aluminium or metal) and construct it that way that you are able to attach it to the xl-1 without the lense. it must be a fix construction.
then construct something inside the box.
a mirror that throws the picture from the 35mm lense on a milk like groundglass that is spinned with a small motor.
everything done, make the box that way that it is kind of sealed and has a lets say pl mount fixed on it so you are able to attach pl mount lenses on it.
last but not least, costruct something like you see on a original mini35, the "cage for the camera and the mini35 system, so it is everything fixed and stable.

correct me if i'm wrong. is that the way to go (i'm not sure if the mirror is needed) ? when thats everything it doesn't seem to be a real problem for someone who has some mecanical and optical skill :-/

by the way, someone from germany here who thinks who has such skills ? especially from the region about frankfurt ? when i would like to get in contact with him, perhaps were able to try some things

Joseph George June 8th, 2003 09:49 AM

Went to Cinegear Expo; talk to the P+S people from Germany, and also with one of the guys in Germany on the phone. The high def unit costs about $25K and works on a different principle. The ground glass does not spin but vibrates. to the sides and up and down, creating small circular motion. They use a motor as a drive.

They have a number of patents on the various principles and are very well covered so there is no way around it to create anything like this on your own and market it without a patent infringement.

They tried the piezoelectric drive with the same drivers we did; also could not get sufficient amplitude; there is no more powerful piezoelectric drive according to them -- and we could not find one either.

You could create something like this for personal use but not to sell to others, except maybe some tight-lipped friends. If P+S would find out, they would try to shut you down.

They sold 200 of the SD units and 60 of the HD units worldwide.

The Japanese studied their unit extensively for about a year, apparently trying to get around the patents, but then gave up.

It all started when an American DP approached them about this and they thought that he's crazy. They then made one unit and saw the dramatic results.

Panasonic worked hard with them on developing a unit for the DVX. JVC has no interest on developing one for the HD1/10. But P+S will make one regardless, unless there are some problems with the JVC lens, etc.

Elmar Tewes June 8th, 2003 09:55 AM

sure for personal use. it's clear that you can't rebuild something that was developed by someone and sell it

Cosmin Rotaru June 9th, 2003 02:46 AM

Joseph, I have to ask you: use a fresnell lens, right? Where do you put that? Is it sandwiched with the gg? If so, the fresnell would also move and the focal point would move to - leading in some vignetting problems? Or is the fresnell fixed? If so, I guess is not placed between the gg and camcorder's lens, because it would show up on image... Could you share a comment, please? Maybe you know how P+S do it.


Martin Munthe June 9th, 2003 09:25 AM

Please don't lock it down to the Canon XL1. If it is at all possible to make it fit most standards you'll have a sure fire hit. You could base it on some type of step down ring priciple. The trick is of course to make it focus properly on most major camcorders. Perhaps you could supply it with a calibration tool?

Joseph George June 9th, 2003 09:28 AM


You don't use Fresnell lens, only ground glass. You have the 35mm lens, oscilating or rotating ground glass, and the camera lens that may need additional close up lens to be able to focus on the ground glass.

Cosmin Rotaru June 10th, 2003 01:32 AM

Have you try that, joseph? And you have a clear pic all over the gg? No vignetting?! Can you explain how does that work without the fresnell?


Jaime Roman June 17th, 2003 10:04 PM

Joseph could you elaborate on how you would vibrate the glass to go both up and down, and side to side?

Istvan Toth June 17th, 2003 10:50 PM

Is it so dificult to find an excentric rotation for that spinning gg? In the case of vibration there is always a moment where the gg stops before going into the opposit direction and this would disturb the image. I remember it was the center where the mini35 had the problems.

Joseph George June 23rd, 2003 07:23 PM

Hi guys, I'm back from my trip. There is no vignetting. You use the GG in the film plane. There is no vignetting on film either. You vibrate the glass to the sides only. The image will not be perfect; you can claim it is a film look -- some of the grain. The vaibrations need very high frequency so the video frame sees always more than one spot. But we tried it and piezo drive does not work.

Cosmin Rotaru June 24th, 2003 02:43 AM

Whell, in film there is no vigneting but you're not interested in the light that passes throu the film...
Could you give me some info on the gg you use? Maybe the manufacturer? Thank you!

Jaime Roman June 24th, 2003 09:12 PM

Hey joseph,

Why a piezoelectric drive as opposed to a vibration motor? What would you consider a high frequency (rpm)?

Cosmin Rotaru June 25th, 2003 05:39 AM

Hi all,
This is my own attempt, my little experiment on this mini35 homemade stuff...

This is the 50mm lens I use. For this test the iris was wide open at 1.8. (quite a fast lens - very narrow DOF at this opening)

This is the fresnell I use. Is a book sign...

The little GG. I cut it from a fake CD. The kind of unusable look alike CDs that you find in bulk CD boxes. They're at the bottom and on top of the bulk, for protection.

The GG and fresnell makes a sandwich. There's about 2mm space between the two. If there's no space between them, the fresnell's rings becomes visible.

I use an old electric razor as a means for vibrating the GG/fresnell sandwich!

Here are all parts in an improvised homemade mini35 adapter. I'll have to do more experiments until I decide if it worth doing something stable and usable.

Now for the tests:

This is a pic using the camcorder's lens alone (canon XM2 - European PAL version)

Here's a pic using the homemade adapter with the GG not vibrating. Very grainy. I think I need a better GG.

This is a pic with the homemade adapter. The GG is vibrating. I also modified a little the color curves.

Here you can see a little demo clip (you need WMP9) that starts with a grainy look and than the GG starts vibrating and the grain almost disappears. I modified the color curves also, for the part were the GG vibrates. :)

Din anyone tried something else?

Chris Hurd June 25th, 2003 05:45 AM

Cosmin, these aren't loading for me. If you can send them to me by email, I'll be happy to put them on the DV Info server for easier access.

Cosmin Rotaru June 25th, 2003 05:51 AM

I don't know... I can open the pics but the video is totaly unaccesible...
I'll send you an e-mail Chris, if you can help me with this.

Cosmin Rotaru June 25th, 2003 06:02 AM

I've sent you the pics and the clip.


Chris Hurd June 25th, 2003 06:38 AM

See http://www.dvinfo.net/media/cosmin/ -- this should provide a clickable directory listing of these images and the video clip. It'll have to do until I can put a page together; I'm leaving momentarily for the L.A. Entertainment Technology World trade show.

Cosmin Rotaru June 25th, 2003 07:35 AM

Have fun there, Chris!
And thanks!

I have updated the links on the original post. I hope now they're working!


Joseph George June 25th, 2003 09:07 AM

Edmund Scientific sells ground glass. The piezo elements would make it a nice reliable design. The image stays o the GG. It does not go through the GG. Frequency? I would say as high as possible -- couple hundred Hz and up.

Zac Stein June 25th, 2003 09:33 AM

Not exactly quiet heh heh, looks cool though.


Cosmin Rotaru June 25th, 2003 09:35 AM

Hi Joseph,
have you seen my "setup"? You're probably doing it in some other way... In my setup the light has to go thru the GG. Some GGs would make smaller vigneting at the expense of loosing much of the light. If the GG is not that dense (it is more clear) it would transmit more of the light but with more vigneting. The fresnell always helps in the setup I'm testing...

Cosmin Rotaru June 25th, 2003 09:41 AM

Well, it is an electric razor, Zac! :)
My wife didn't like the noise either! (It was like 2 o'clock in the night when I finally pushed the button!) I think it vibrates at 50Hz. This is what we have here: 220V at 50Hz. So the ancient razor I think it goes 50 cycles/second!
I'll do more testing. I'm not going to use the shaver in a final setup, though. :)

(is it "razor" or "shaver"? - English is not my native language...)

Zac Stein June 25th, 2003 09:45 AM

They are called, electronic razors/shavers here... but I don't speak 'yank' so I am not sure what they call it. We already had quite a large discussion about flip flops.

I would love to see a schematic of this thing... i have a lot of parts sitting around, and am meeting with an engineer first thing next week, would be great to knock this thing together.


Cosmin Rotaru June 25th, 2003 10:13 AM

Hey, I thought the pic would be enough to see what I did!
Just ask what is not clear from the pic, ok? I'll be happy to answer your questions!

O! The lens I'm holding goes on the camcorders lens. As close as posible. So I could zoom al the way in to the GG and still focus. If I just bring the camcorder close to the GG (in macro), I'm to close to the fresnell and out of its focal point. Way out! So that's translated into a BIG vigneting problem!

Cosmin Rotaru June 25th, 2003 10:21 AM

Zac I understand you've seen the clip? Anybody else? Elmar has reported me that he has troubles playing the clip even though he has WMP9...

Keith Loh June 25th, 2003 11:23 AM

I've seen the clip. That thing is LOUD.

Robert Poulton June 25th, 2003 12:00 PM

looks good. I wonder if you are able to more the piece that creates the horizontal lines in the image near the top and then also near the sides. Granted that is from it moving from side to side but just wondering.


Joseph George June 25th, 2003 12:09 PM

Cosmin, could you please write to my email address Film2000@aol.com. I want to send you some more info in the suppliers.

Jaime Roman June 25th, 2003 10:53 PM

Cosmin what type of lens is that in the back of your setup? Is it a magnifying lens? What magnification is it? And what exactly are you using the fresnel lens for?

Joseph do you have a dealer for the piezoelectric drives?

Cosmin Rotaru June 26th, 2003 03:34 AM

Hi all,

Keith, I know it is LOUD! :) Is true that the shaver is maybe 15Cm in front of the mike, but even if you'd use an extra mike on the actor you'll still be hearing this thing. It is just for a test. I wouldn't use it in a final setup. Anyway, I'm more interested in what you think about the image. It seems a little to soft more me... Part of it because the GG/fresnell sandwich is not to well constrained to follow the pan axis that I choused for vibration. So it also vibrates back and forth.

Robert, It is possible that the shooter sped got synchronized with the frequency of vibration. I left the camera on auto but I should have try different shooter speeds. I had plenty of light so the camcorder maybe went over 1/50 (PAL camcorder).

The lens in the back of the setup, that goes directly on the camcorder lens is an ordinary philatelic X5 lens. Without the fresnell I got dark corners on the image. I use it to obtain an image evenly lit. There are plenty of sites on the net that deals with homemade medium and large photo cameras. You use a GG on this cameras to focus. And there are basically to types of GGs: the simple ones, without fresnel were you have most of the light in the middle, if you look straight on the GG. Most of the light is were the line between the eyes and the lens intersect the GG. The second type of GGs have a fresnel attached and this makes the GG evenly lit. Is hard for me to explain it in English. But search for those sites on the net and you'll find more info.

Jaime Roman June 26th, 2003 06:57 AM

I understand Cosmin, i was asking cause i read this on edmundoptics.com:

"Fresnel lenses are most often used in light gathering applications, such as condenser systems or emitter/detector setups. Fresnel lenses can also be used as magnifiers or projection lenses; however, due to the high level of distortion, this is not recommended."

Joseph do the Mini35 or Pro35 use fresnel lenses?

Cosmin Rotaru June 26th, 2003 07:14 AM

You don't use it for magnification... I'd like to make a small draw. Chris, could I send you a litle draw to host it on DVInfo so I could show it and explain what I do with the fresnell? Could someone tell me a site were I could upload the pic and link it here?

Chris Hurd June 26th, 2003 08:47 AM

Cosmin, go ahead and email it to me. I might not be able to put it on the site until later today though.

Kai Leibrandt June 27th, 2003 10:29 AM

Just a quick question reg. the ground glass; I am starting an experiment myself this weekend with a number of lenses (including an Angenieux 12-120, some Olympus 35mm still lenses and the Canon manual 16x) and an XL1, and am actually making my ground glass myself. So.... is it ground on both sides or is one side left shiny?
Many thanks in advance,


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