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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.

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