Two projectors optical printer for S8 special effe

[sasounet]

Hello,

Sorry for the bad english... you have been warned!

I finally decided the time was right to start my own hardware project. I want to built an optical printer. But, contrary to many forum reader need, this one will have nothing to do with video transfers. (The reason I shoot super 8 is to be able to project the films on a big screen with no loss in quality. In other words, for the fun of looking at it. I have no fun looking at videos)
So what I want to do is to be able to combine two images from two projectors and shoot the result in super8. Why ? To do some nice special effects !! I know that some high end cameras can already do double exposure to a limited amount but this optical printer will be more versatile. Let me explain:

In camera double exposure is limited to a short amount of time. And if you miss your takes .. well too bad, you have start from scratch. With a optical printer you can do unlimited double exposure and more importantly, you can choose your takes for the effects: i.e use the ones with the best lighting, best acting, coming from a different roll of film or even different type of film.

So with this in mind, an optical printer like that will allow me to do :

1. Very long lap dissolve not only at the end of shots but also in the middle (for flashback or dreaming type of stuff)
2. Tile and credits over live action. (This is for me the most interesting)
3. Combine two parts of the images over each other black areas (the black areas have to match perfectly) and do some StarWars type of effects :-)

As you can see, hours of fun for the whole family...

Now, the projector and camera needs to be synchronized. I plan to do this using computer controlled actuators and motors. The computer and control part is easy. Modifying the projectors will be more tricky but as I am aiming at a transfer rate of one frame per second, it should be doable. (I know Roger would probably be able to built a complete working unit in the same amount of time I will take to unscrew my projector casing!)

So far so good, I am a mechanical engineer so I will have fun. However, I am NOT an optical engineer so I have a question (for Roger ??): What kind of condenser lens do I need ? I was planning to buy the lens # NT32-510 from Edmund-Optics but I'm not sure it is the right kind. As for the beam splitter and first surface mirror I think I know what to buy.

Anyway, I hope I was not too boring. I know the message was very long but I'm really looking forward to start building that beast. I you have any suggestions, please let me know !

Sasounet

[#Pedro]

Very, very interesting! Finaly a cool idea that is not related to video tansfer. When everything is possible, there is no fun anymore.
Years ago, I did experiments with that in a rather primitive way, using a ground glass screen (with hot spot) and a 45degree glass plate for superimposing titles into the running film. With flicker and without any syncronisation.

I am wondering, how you resolve the superimposing of two projectors without screen, only with direct shooting like in Roger?s work printer?

For syncing, my double system sound solution would work, sensing the flash contact pulses from the camera to feed two synconizers, each for one projector (DC-motor required). Both projectors would start/stop together with the camera trigger and keep in sync with the camera, frame accurate.

The shutters of the projector probably would have to be modified.

Good luck!

Pedro

------------------

[MovieStuff]

<BLOCKQUOTE><font size="1" face="Courier, Arial">quote:</font><HR>Originally posted by sasounet:
I want to built an optical printer. So what I want to do is to be able to combine two images from two projectors and shoot the result in super8. Why ? To do some nice special effects !! <HR></BLOCKQUOTE>

Hi!

A noble project, to be sure. I built my first double headed optical printer for a pal back in the late seventies. He had a tiny budget and we ended up combining the images on a small rear screen off two super 8 projectors using beam splitters. It actually worked pretty good. I wanted to replace the rear screen with a condenser lens but he never got the budget to do it and lost interest.

<BLOCKQUOTE><font size="1" face="Courier, Arial">quote:</font><HR>Originally posted by sasounet:

Now, the projector and camera needs to be synchronized. I plan to do this using computer controlled actuators and motors. The computer and control part is easy. Modifying the projectors will be more tricky but as I am aiming at a transfer rate of one frame per second, it should be doable.
<HR></BLOCKQUOTE>

Your biggest problem is going to be rigging a mount for the projectors so that they can be aligned and moved in small increments. Also, registration on super 8 is pretty abysmal, when it comes to layering up two super 8 images. With one image, you don't really notice the breathing. With two images, they breath relative to each other and the end result can be pretty disturbing. Fine for dissolves or title work but horrible for super imposition or other type compositing work. Plus you have the natural breathing of the super 8 camera that is copying the footage.

I would also suggest that you add a slide projector to the set up and align it on the same axis of the beam splitter like such:



The slide projector will make burn-in white titles super easy as you can shoot them on high contrast Kodalith or Agfa stock and mount them in glass mounted slide mounts. Also, the projector makes it easy to create effects like animated laser hits, explosions, etc, without having to shoot them first on super 8 and wait for processing. Handy to have.

Make sure you use a flat field projection lens. Navitar makes some excellent lenses for Kodak projectors. A flat field lens will have "ff" on it as opposed to "c". The light sources in all projectors will have to be reduced in intensity and diffused. The gates will need to be enlarged in the super 8 units, as well.

<BLOCKQUOTE><font size="1" face="Courier, Arial">quote:</font><HR>Originally posted by sasounet:

However, I am NOT an optical engineer so I have a question (for Roger ??): What kind of condenser lens do I need ? I was planning to buy the lens # NT32-510 from Edmund-Optics but I'm not sure it is the right kind. <HR></BLOCKQUOTE>

Well, you'll want a fairly large condenser lens; at least 3-5 inches. About a 3 diopter or better or the image will be too tiny to use. I would tell you where I get mine BUT I have a special deal with the supplier! Don't want to rock that boat so you'll forgive me if I don't share that trade secret! However, I'd be happy to sell you a condenser lens at my cost.

Good luck! Post photos of your progress!

Roger


------------------
Roger Evans
MovieStuff http://www.afterimagephoto.tv/moviestuff.html

[This message has been edited by MovieStuff (edited January 17, 2002).]

[sasounet]

Hi again,

> I am wondering, how you resolve the superimposing of two projectors without screen, only with direct shooting like in Roger?s work printer?

Yes that's it.

> For syncing, my double system sound solution would work, sensing the flash contact pulses from the camera to feed two synconizers

Clever idea... however I have no flash on my s8 camera :-( But as I said that sync part of the job is no problem.

> The shutters of the projector probably would have to be modified.

Why ???

Regards,
Sasounet

------------------

[sasounet]

Hi,

> Also, registration on super 8 is pretty abysmal, when it comes to layering up two super 8 images.

I'm aware of this. But I am not looking for the best quality result. Remember this is just for fun !

> Slide projector addition...

Good idea, I will see that the layout is compatible with an additional projector. (slide or even third super8 !)

> The gates will need to be enlarged in the super 8 units, as well.

I ask again why do I need to do that ?

> Well, you'll want a fairly large condenser lens; at least 3-5 inches. About a 3 diopter or better or the image will be too tiny to use.

The one I'm looking at is 6 inches in dia. But I don't understand your comment about the diopter value; don't this only change the camera position relative to the lens ?

> Good luck! Post photos of your progress!

I'll try. But don't expect progress reports to soon as I don't even have the second projector yet !

Regards,
Sasounet

------------------

[MovieStuff]

<BLOCKQUOTE><font size="1" face="Courier, Arial">quote:</font><HR>Originally posted by sasounet:

> The gates will need to be enlarged in the super 8 units, as well.

I ask again why do I need to do that ?
<HR></BLOCKQUOTE>

Well, here's a pretty good example of why:



Projectors crop the image tremendously. Since the camera will have to crop in as well, the final image will be double cropped, as seen in the left photo.

<BLOCKQUOTE><font size="1" face="Courier, Arial">quote:</font><HR>Originally posted by sasounet:

> Well, you'll want a fairly large condenser lens; at least 3-5 inches. About a 3 diopter or better or the image will be too tiny to use.

The one I'm looking at is 6 inches in dia. But I don't understand your comment about the diopter value; don't this only change the camera position relative to the lens ?
<HR></BLOCKQUOTE>

Yes but you really want the camera further away to reduce chromatic aberations. The closer the camera is, the shorter the focal length lens you must use. This not only increases chromatic aberations such as rainbow edges but also adds a certain "pin cusion" effect. The condenser lens I use is a 3x lens that forces the camera to be about 30-40 inches away; even further with larger format cameras.

Think of copying footage from a television screen that's curved: Would you use a short or long focal length to counter the effect of the curvature? You would use the longest lens you could get away with. The same holds true for shooting off condenser lenses. Longer focal lengths are better.

Roger

------------------
Roger Evans
MovieStuff
http://www.afterimagephoto.tv/moviestuff.html

[Matt Pacini]

Once again, my actors from Lost Tribes are web-famous!
Har har!
I should give Christopher Andre (the actor in Lost Tribes) this link, so he'll get a big head, thinking he's all over the internet now!

Matt Pacini

------------------

[#Pedro]

remark to the foto examples from Roger:

Looking at the fotos, I cannot help thinking on some special effects included in photo sofware like Adobe Photoshop I am working with... I don?t doubt that a condensor lens /areal image transfer is superior to a screen transfer, but the published fotos for me are a little bit suspect.

Concerning the frame criping, I?ve made my own tests in order to check the alignment of the viewfinder mask of my camera. I did not use the well known method to project a frame thru the camera and compare it with the viewfinder, I shooted a testing sheet with a two-dimensional scale with cenitmeter marks in vertical and horizontal direction.
The sheet contains a rectangular in 4:3 ratio and the 16:9 markings of the camera?s viewfinder.
For shooting this, I adjust as exactly as possible this two rectangulars (4:3 and 16:9) into the viewfinder.
Afterwards I look at the film with a magnifyer (microfiche monitor) to see, if the result came out centered and parallel. This alignment is very important for title shooting.
When projecting the film in the Elmo GS machine, I can see nearly exactly the same size that was in the viewfinder of the camera during shooting, the cm scales cannot lie.
However, without projector, there is a little bit more that the projector doen?t show. But with my equipment, this is quite as much as the camera?s viewfinder doesn?t show, too. And what?s really covered by the projector?s gate or not shown in the camera?s viewfinder, is far far away from the imense difference that Rogers fotos are showing!!!
So, excuse me Roger, I cannot help, the Photoshop manipulations of the second pic (sharpening function) together with the totally differnt size and ratio, give me some serious doubts...


Projector gate:

Depending on the projector type, I can only say: BEWARE from any manipulations of the gate! For this transfers I would prefer a quality projector and not a plastic toy, and quality projectors have usually a polished steel gate and pressure plate or even a diamond grinded gate made of special material. Does anyone believe, that one can enlarge this hi-precision parts with do-it-yourself methods, without totally disturbing parameters like friction, pan focus, surface smoothness etc.? Remember, in S8 even changes in 1/100 mm can have extreme effects!
However, who has the mechanical setup to make these changes and the projector does not matter, why not?


Projector shutter:

I think, that for optical printing to film, a 3-bladed shutter is not neccessary and complicating exposure, synchronization and flicker. I would cut away 2 blades and only leave that one blade that covers the film forewarding. Totally I would not remove the shutter. With one blade and a Beaulieu camera for shooting, I could check if there is any flicker, only looking thru the viewfinder and shift the phase of the setup in order to avoid flicker. Without any pojector shutter, I would have the risc shooting the transportation phase, too.


Pedro

------------------

[MovieStuff]

<BLOCKQUOTE><font size="1" face="Courier, Arial">quote:</font><HR>Originally posted by #Pedro:
And what?s really covered by the projector?s gate or not shown in the camera?s viewfinder, is far far away from the imense difference that Rogers fotos are showing!!!
<HR></BLOCKQUOTE>

Well, for starters, not all projectors crop the same; some crop more than others. This is a fact. Second, the images I used were only for the convenience of illustrating that cropping does occur, since many people don't even realize that ANY cropping occurs. Third, the image on the left clearly says it is from a "projection method"; not directly from the gate using the condenser lens. That means that there is a certain parellax that has to be cropped out or the frame will be skewed. This diminishes the amount of usable area for the left photo. Fourth, if you are doing any kind of optical printing work, you can not really assume that the amount your camera crops is the same as what your projector crops and, even if it did, you are STILL losing image on the edges. I don't find having a black border on the edges acceptable, even if you feel it MIGHT be cropped the same later on on a different projector. Of course, this is highly unlikely since, as we all know, every projector crops differently.

So, in the end, there are really three levels of cropping that occur.

1) The projector crops

2) The copy camera crops

3) The projector used to show the copied film crops

Unless you start out with the full image, you will lose resolution and information.

<BLOCKQUOTE><font size="1" face="Courier, Arial">quote:</font><HR>Originally posted by #Pedro:

So, excuse me Roger, I cannot help, the Photoshop manipulations of the second pic (sharpening function) together with the totally differnt size and ratio, give me some serious doubts...
<HR></BLOCKQUOTE>

Regarding the image on the left, you have to take into account the fact that ANYTHING you crop with the camera will then be re-cropped during projection. Therefore, the minimal cropping I did in Photoshop to square up the corners is doodly-squat compared to the potential cropping that would occur in any given projector. Again, not all projectors crop the same and the original GAFs crop quite a bit.

As far as the image on the right is concerned, I asked my wife about it, since she was the one that did the Photoshop work on it, and she does not recall adding any sharpening to the image at all as I made it a point to NOT do that. To my knowledge, the image on the right was not processed in any way other than color correction in Premier. Of course, even if it was sharpened a bit, that has nothing to do with the discussion at hand since the image was used to illustrate cropping and nothing more.

Regarding your doubts about the validity of the cropping, I offer this image taken directly from the condenser lens which clearly shows the entire frame, including sprocket holes:



Now, compare that image to the image on the right of the previous post:



You will see that the condenser lens photo and the right photo are identical. If anything, the image on the right was cropped too much in Photoshop on the right hand side, thereby losing even more information!

I can understand your confusion over the differences in ratios between the left and right picture. After all, that's the whole POINT! They DON'T match and rarely will because the ratio of the gate isn't always the same as the ratio of the raw frame. Therefore, if you DON'T start with the uncropped raw frame, then your re-cropping will be determined by the parameters of the gate ratio and not the frame ratio, as seen in the left photo.

Roger

------------------
Roger Evans
MovieStuff http://www.afterimagephoto.tv/moviestuff.html

[This message has been edited by MovieStuff (edited January 18, 2002).]

[sasounet]

Hi Roger,

Well the pictures are convincing... I will have a look at the projectors gates.

Regarding lens diopter:

> Yes but you really want the camera further away to reduce chromatic aberations. The closer the camera is, the shorter the focal length lens you must use.

Ah OK , when you said in your previous post that the lens diopter should be 3 or better , I though you meant 3 or higher.
For what I understand, the higher the diopter number, the shorter the focal length.
So tell me if I understand well... I need the camera as far as possible from the lens so the lens needs a long focal distance i.e. a small diopter of 3 or less. Is that right ?

Regards,
Sasounet