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Old January 23rd, 2005, 09:10 AM   #1
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Ultimate In Front of Camera System

I have been living and dying buy Alternative Imaging Forums for about 6 months now. It seems that all the major projects here (obin's, 35mm adapters, reel-stream?) are really getting to a point where they can be implimented. I am at a point where I am ready to start not only building a 35mm adapter (really loving the micro 35) but also a full in front of camera system. Here are my requirements for the ultimate rig to go in front of a camera.

- 35mm adapter
- anamorphic ability (16X9 and Cinemascope)
- MatteBox, sunshade, filter holders
- Follow Focus
- Universal design (I want this baby to fit on ALL of our cameras)

I am currently working on designs to integrate all of these things. I have a decent head for engineering but Lens physics are not my forte.

I am currently wondering if there is any reason putting a piece of anamorphic glass in front of or behind an achromatic adapter would or wouldn't work. Anybody know?
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Old January 23rd, 2005, 10:35 AM   #2
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Rob,

Yes it can be done. In fact it is something I have been working on, on and off, for a while now. I'm getting close to having it completed.

You would want to place the anamorphic after the 35mm lens and before the ground glass. This is one aspect that has to be precisely controlled and callibrated. If you are off by a little bit your aspect ratio will go to heck as well. It's looking like I'm going to need some custom designed parts made for me on this. It's not easy but it can be done.
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Old January 23rd, 2005, 11:31 AM   #3
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Based on my experience, introducing a new lens between the 35mm lens and ground glass will directly effect the focal length or flange-to-film distance. This doesn't really cause any problems until you want to switch to a different 35mm lens. In other words, if you make the adapter with a 50mm focal length Canon FD mount lens, and later pop on a 100mm focal length Canon FD, the back focus will be off due to the extra lens.
I'm not sure if an anamorphic lens will have a similar effect, but my guess is yes... a lens is a lens is a lens.

My intention isn't to discourage, because its a great idea, but rather to discuss another variable that will come into play with the final design.
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Old January 23rd, 2005, 11:37 AM   #4
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Completely understandable Nicholi. I am however, quite sure that this would not affect the focal length to any significant degree. The idea is known as a bravais system and has been implemented on many 35mm cameras before. It is designed to keep the image plane precisely in the same place - just expand the image.
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Old January 23rd, 2005, 05:37 PM   #5
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I'm wondering if you are making the lens your selves, and if so, how?
I've made a huge lens based on homemade anamorphics for projectors. Those are two straight triangles made of glass filled with water. I think the second lens is to stretch the image on one half (I'm not sure), but mostly to correct the color displacement with one lens. Here is a link (in German, but with images) to such a lens:

http://ww2.bepo.com/jochen/anamorph/Wasserprisma.htm


I must say, it works very well, but it needs to be very big to stay outside the image.

Reading this tread I thought: What would happen if you put one triangle lens in front of the 35mm lens, so it can be of acceptable size, and the other lens behind the 35mm lens to correct the color shifting. Maybe even behind the GG.

It could be made from lens protection glass (or UV filters) to avoid reflection.
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Old January 23rd, 2005, 06:28 PM   #6
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Yes and no. I'm finding as many stock parts as I can which will work for my design and then having the parts which I cannot find custom made.

I know the precise setup you refer to! It seems to be the most popular DIY projector enhancement :D. The problem with the idea as you have suggested it is this:

The anamorphic prisms need to work in conjunction with one another. If you rotate one of them or change the distance between them you will change the compression. For what we want, prisms aren't ideal.

The system I am building is known as a Bravais or rear anamorphic system. It is deisgned to allow standard 35mm film lenses to be used to create a widescreen image. These have been utilized in some 35mm films.

In it's most basic form it looks and works like this:

http://www.weet.us/anamorphic.GIF

The design effectively performs an optical equivalent of a digital in camera stretch. This is not the same as an anamorphic adapter which you would screw onto the front of your lens neither does it loose resolution like you would with a digital stretch. It in essence takes the middle 70% or so of the _projected_ image and optically stetches it vertically (yes, vertically).

Lets assume we start off with this image projected onto the ground glass (no recording with the camera is done yet):

http://www.weet.us/recon2_small.gif

Then optically we stretch the image so it appears like this on the ground glass:

http://www.weet.us/stretch.gif

What the camera actually records then is only the central portion of the image (though it uses the cameras full CCD block to do so - no res loss):

http://www.weet.us/stretch_crop.gif

Now ignore the resolution loss in the following image. This was done with a normally shot digital still so this process looses resolution in the demo pics (I didn't shoot it anamorphically to begin with). This is merely for demonstration purposes.

This then is what gets recorded to the full CCD block:

http://www.weet.us/cropped.gif

When you stretch this out in post you end up with an anamorphic picture that is the full resolution of your CCDs.

http://www.weet.us/stretched.gif

What you do loose is a little bit of light (the light that no longer falls on the actually imaged area. This is, however, a small downside given the great benefits. This system also has NONE of the limitations that an anamorphic mounted in front of the camera lens has.
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Old January 23rd, 2005, 07:21 PM   #7
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What if you'd bend acryl glass in the shape of the lens in your drawing and fill it up with (distillated) water or oil. Is it possible? I'd like to try, but do you have the exact curves?
Also, I see two lenses in the drawing, why is that?
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Old January 23rd, 2005, 08:01 PM   #8
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Yes that could work. It would be awefully big and unweidly but it would probably work. Now you wouldn't have a perfect surface either so you would have to accept the distortion that comes with a hand bent piece of glass.

Sorry about not explaining the image. I didn't do a good job illustrating the direction of the rays. The first lens brings the width of the light down so it can more easily be manipulated with the concave lens. You'll have less stray light that way.
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Old January 23rd, 2005, 08:57 PM   #9
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So am I correct in thinking that the anamorphic adapters for most dv cameras are just a piece of glass curved on one side to distort the image?

Century Optics offers 2 types of adapter. Unfortunatly someone just copied the same description for both. There is a 16x9 widescreen adapter and a 1.33 anamorphic converter. They both do the same thing but the 1.33 converter is $1500 instead of $900. I am not sure though what is different about them.

My thought on building this system would be as follows

French Flags - sunshade - filter holder - Anamorphic adapter - 35mm lens - Ground Glass - Achromatic Diopter - camera lens

slap a follow focus on the 35mm lens and put it all on a rail system. Then find a DP who can bench press a truck to use it ;)

I was hoping to just yank a piece of anamorphic glass out of an old ebay lens to put in front of the 35mm lens.
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Old January 23rd, 2005, 09:23 PM   #10
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Yes basically that is correct. However, these systems are usually designed very carefully to give:

1) The proper aspect ratio
2) Aberration correction

A bent piece of glass alone will have all sorts of aberrations unless you optically correct them.

I'm guessing here but the cost difference with the adapters is probably a quality thing.

You certainly could use an anamorphic which went in front of the 35mm lens but why? A rear anamorphic has none of the limitations that a normal anamorphic has and can be used with any lens. With one in front you would have to make a different lens for each lens diameter you used.
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Old January 23rd, 2005, 10:18 PM   #11
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Does anyone know of a commercially available 16:9 bravais component which would fit between a C-Mount 10x160mm Fujinon TV-Z and a 2/3" C-Mount JVC KY-F50 cam?
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Old January 23rd, 2005, 10:52 PM   #12
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The only commercial adapter I know of is made by Kish optics for 35mm film. It's far too expensive for our purposes though - about 6K.
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Old January 24th, 2005, 06:36 AM   #13
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Would this work?

http://s01.picshome.com/52a/anamorph.jpg

Those water prisms are made easily, I just donít have enough space to put two between the 35mm lens and the GG.
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Old January 24th, 2005, 11:28 AM   #14
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I honestly do not know. I suspect that you need both in front of the GG to get the full anamorphic image but that is just a guess.
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Old January 24th, 2005, 01:57 PM   #15
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We hijacked the tread a little with the anamorphic discussion, but the other points by LaPoint also interest me. I'm making the double camera system (no one is very interested, which I understand, but tests are going great) and I'll be thinking about the design to build around everything.
I'm also planning a filter or sunshade holder. I'd like to use the old material of movie cameras and projectors. Does anyone know the word? Itís a little rough, a bit irregular pattern.
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