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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)

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.

Rob:D

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,


Kai.

Kai Leibrandt June 29th, 2003 10:29 AM

Sorry to reply to my own posting, but I thought I'd just give a quick summary of what I had achieved during my _quick_ experiments.
What I tried to do was to create a really simple, cheap (less than $5.00) proof of concept and experiment that would show me the various things that were involved in creating a homebuilt mini35.
I have an old, broken Olympus OM-2 from which I took the lenses, a wide angle 35-105 Tokina zoom and a 70-210 tele. I also have an Angenieux 12-120 16mm lens lying around that I put through the same treatment...
I used a bit of cardboard tubing as the envelope holding target, for I used a CD-case cover (the square front bit that is), This piece I initially sanded to make it opaque, but the sanding did leave streaks, so I used a piece of tracing paper instead, which has a very coarse grain but at least it was even.
The results were surprisingly good. I have just pointed the XL1 with my manual 16x at the "ground glass" and got some ok pictures, but nowhere near good enough to use of coarse. I used macro so that the lens was actually only an inch or so away from the target, and of course this would not allow the image to fill the viewfinder completely, but it did show some gorgeous depth of field, and also, surprisingly, the colours were gorgeous too. It was also very interesting to see what exactly it means when people say there 16mm lens will not cover a 35mm image; the diameter of the image the Angenieux projected onto the target was less than half of what the other lenses produced. At the same focal length however, items in view would be the exact same size on the image, only you'd see less the surrounding objects around it with the 16mm lens.
Also clearly visible was the vignetting that I was expecting as I don't have any fresnel lens or similar material. What I found out is that the ground glass of the OM-2 is in fact ground on a curved surface which points away from the lens, and the other side is flat (and shiny). I beleive this is to compensate for the light fall-off toward the edge of the viewfinder, and I will try to do something similar with my setup.
I will probably post some pictures sometime during the week, and until then I hope to be going around the local camera repair shop to hunt for some old lenses and bayonets to make something sturdier, plus I hope to find a ground glass similar to the OM-2's so that I don't have to take my camera apart, even though it is broken...

Kai.

Cosmin Rotaru June 30th, 2003 02:15 AM

just one side

Kai Leibrandt June 30th, 2003 05:15 AM

Cosmin,

yes I did discover that also. I did wind up taking my OM-2 apart and that little bit of ground glass is a real piece of magic. One side has a fresnel on it, so fine you can't even see it, you can only feel it if you (gently!) go over it with a finger nail. It's this frensle that makes it look curved while it is in fact perfectly flat. The other side (which points away from the lens) has the matte finish to it. Results were very promising and I am getting some more bits today to start building a more solid one.
Will report back when more interesting stuff happened...

Kai.

Cosmin Rotaru July 1st, 2003 03:00 AM

Hi again,
Jaime, here is what I understand about the fresnel:

In this first pic I try to explain what happens to the light when it hits the GG. Of course you'll have an image forming on the GG, the light spreading out. But the light tends to follow its original path, so a part of the light that hits a point on the GG would spread out but most of it will go straight ahead, as it hit the GG.
http://www.dvinfo.net/media/cosmin/gg2.jpg
The fresnel would concentrate the light before it hits the GG (or after - you could chouse to install the fresnel on the other side).
http://www.dvinfo.net/media/cosmin/fresnel&gg.jpg

I hope this helps!

What else have you guys try?
Joseph, have you found some other means to vibrate the GG?

Jaime Roman July 1st, 2003 03:26 PM

I will now be incorporating a fresnel lens in my configuration -- thank you Cosmin :)

Now all i need to iron out is my source for vibrating the GG.


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