A slightly different 35mm adapter concept
 

THE IDEA

I was thinking about 35mm adapters and it occured to me that there is a simple commercial device that already does what is needed. I had one of these laying around so I thought I would try it.

End result: It works nicely. It cost me nothing. And it would cost anyone about $20 to make from scratch.


THE DEVICE

What I am talking about is a slide viewer. Its a "small" device where you insert a 35mm slide into de device and you can see the projected image on a large lens on the other end. It is designed to take a 35mm wide transparency which gets illuminated from behind and show it evenly lit over a large end lens. Sounds very convenient, doesn't it? :)

The one I have is old so it still has decent quality crystal lenses (not plastic).

What I did was cut a circular hole on the back to that I could mount a Nikon 50mm f/1.4 lens, then made a simple screen that slides where the 35mm slide goes. The Nikon lens is mounted such that its focal plane is right where the screen-slide is positioned.

The optics are already placed at the right distance to show the full image on the large lens on the other side. This large projection allows the DV camera (in my case a GL2) to focus easily.

I have done some tests and the illumination is really uniform and my only two complaints with the device are static grain (obviously) and the bulk of the device.


THE SCREEN

My screen is pretty good I believe, it has very little grain (although it can still be apparent) and it has great light transmission. Best of all it can be made in 5 minutes with readily avalible materials (well, it may depend on geography).

I will reveal my screen method after I post some result images. (But you have to promise not to laugh at what my screen is made out of :)


THE OPTICAL SETUP

Now, the viewer device uses 2 Plano Convex lenses. The first one is placed at a distance from the screen (not close to it as other designs have suggested), and the other PCX seems just to serve as a magnifying glass.

The setup is like this:

NIKON || |) |) DVCam

There is quite some space between each optical element, and the lenses are large and rectangular. The final lens (the one close to the DV cam) is about 6 inches wide.


THE QUESTIONS

What I would like to ask is, if this design has any virtue over the typical
|||) () setup, where the first lens is close to the screen. Or should I go into the usual setup?

Also, what would you recommend in order to convert this setup into a compact design?

I will post some images of the results shortly.

Images
 

Here are some sample shots:

http://mentemagica.com/AdapterTest9.jpg
http://mentemagica.com/AdapterTest12a.jpg
http://mentemagica.com/AdapterTest12.jpg

Keep in mind I build this thing just for fun and because it was so easy.

http://mentemagica.com/Adapter1.jpg

Nicely converted! I dont see any vignetting or colour seperation. Well done!

I haven't exactyl understood how the device looks like, would you mind ´sharing some more pics? I did try a similar setup with a slide viewer with a built in lamp, but it didn't give me any good results.

What is your emulsion (GG)? How does it look when you pan?

This is probably the device he's refering to: A Halina Viewer

http://www.danbbs.dk/~mikael/search/halina.htm

I don't know what gg he is using.

What a great idea....everything's in place already! Just add GG.

It looks wonderful. A microwax glass would get rid of most of that grain.

<<But you have to promise not to laugh at what my screen is made out of >>

Hmm...did you accidentally spoil milk in the adapter..right onto one of the lenses? No...did you blow a bubble of chewing gum inside the adapter?
(if so, you're pretty close to a microwax screen. Bubblegum is made of microwax...really)

You have to tell us! This is driving me crazy... I promise you no one will laugh.

THE SCREEN

When I was thinking about what to use as screen, I had multiple ideas but all of them seemed like too much work for the quick test I wanted to do.

So what materials could be diffusive enough to work for this purpose? Well, first of all not all whitish semi-transparent materials are diffusive. Most of them absorb lots of light and that's it. What I was looking for is something whose microscopic structure would act as a bunch of prisms that redirect light randomly but would not absorb it. This is how a ground glass or microcrystaline wax work.

I thought that some polymers could be structured in such a way as to observe diffusion properties, in particular polyethylene. But where do you find a polyethylene piece whose polymer strands are aligned so as to produce diffusion?

It turns out that there is a thin-film polethylene material that is highly diffusive and can be found easily. In some supermarkets it is used for wrapping food (sliced ham, turkey, etc.) and also it can be found in some sandwich plastic bags.


RECOGNIZING THE MATERIAL

This type of plastic is very thin, and it is completely non-shiny. It makes a noise when you crumple it, and it creases easily when you do. If you place it flat on top of a printed page it is totally transparent.

http://mentemagica.com/35mmAdapter/Screen-Flat.jpg

But if you raise it above the page just 1 inch, you will not be able to see the text below it. That's how diffussive this material is.

http://mentemagica.com/35mmAdapter/Screen-Halfcm.jpg
http://mentemagica.com/35mmAdapter/Screen-2cm.jpg

In contrast, non-aligned polyethylene plastic can be semitransparent but not diffusive. When on top of a printed page it will not become more transparent, and even if you raise it several inches above the print, you will still be able to see the text clearly.

So you have an idea of what you are looking for, it is a form of the same material found on 3M's Magic Tape, or Invisible tape. This is the non-shiny whiteish type of tape.


GRAIN GRADES

So far I have found that this thin film comes in a variety of "grades" when it comes to grain. The finer structure ones I have obtained from the sanwich bags, but your local products will vary. As with ground glass, the coarser the grain the more light goes through. But not that much more.


CONSTRUCTION

What I did to construct my screen was a simple procedure of selecting an area, stretching it and then gluing it to a frame.

First, cut a frame of your desired size on some sturdy material such a cardboard, metal sheet, or plastic. Then, select a piece of thin film that has no defects in the forms of scratches or creases (some creasing is acceptable since we will stretch it). The material you select must be much larger than the size of your frame. Lay the film flat on a piece of glass and stretch it using tape from all sides. Take the frame and either add glue to one side or double-stick tape. Place the frame on top of the stretched film and press all sides, making sure you don't touch the inside of the film as it is very delicate. Finally cut around the frame and you should have a usable screen.

To make a more durable screen, replace the frame with a piece of glass, and then use another similar piece on the other side such that the film is sandwiched (and thus protected) between the two glass pieces.


ADVANTAGES

I have found, that while the grain grade I am using still is a bit visible, the light transmission of this material is just unbelievable. It is so thin that it does not show any softening of the image, and lets most of the light through.

I will keep in the search for a finer grade before I turn my attention to wax based screens.


OTHER APPROACHES

While thinking about the screen and discussing it with some friends, a potentially useful idea came about: Liquid. A colloidal suspension could act as a great diffuser, and because of it being colloidal, the suspended mollecules will not sink to the bottom. Also, the grain can be as fine as a single molecule, and even if it is not, the brownian motion of the mollecules should ensure a grainless appearance.

I have not experimented with liquid suspensions but I may just give it a try and wanted to inspire others as well.

Please let us know if you find a finer grain grade polymer.

Enjoy!

Alain,

Im impressed with your diffuser material. Love the test with the book and text.

Would like to see some frame grabs though.

About this colloidal liquid diffuser idea, sounds very interesting, would love to know more.

Nice work. It's always nice to see someone try something new and in a different direction. Don't worry, Alain- if anyone laughs, Chris will put his/her head up on a stake next to Shannon Rawls'.

My question is, if you crumple the material in the forest and no-one is there to hear it crumple, does it make a sound?

You might even try the intenscreen that Oscar just bought and that Dan has always been raving about. It should really brighten up the footage without the fuss.

It does seem there are better solutions appearing then actual glass. I have found a pre ground/frosted material that seems to have a better diffussion to light loss ratio that im thinking of using in the SG35, as the tests appear superior!

Thank you for your comments.

I don't think I will spend lots of money on a screen (intenscreen or any other) just yet, instead I would like to get better optics first, once I decide if this setup is the best one. The current thin film I use has so little light loss that I would be very surprised if even the commercial ones are better in this respect. Then again, I would like to get rid of the grain :)

Here are some more pictures:

http://mentemagica.com/35mmAdapter/AdapterTest20.jpg
http://mentemagica.com/35mmAdapter/AdapterTest20a.jpg
http://mentemagica.com/35mmAdapter/AdapterTest20b.jpg
http://mentemagica.com/35mmAdapter/AdapterTest22.jpg
http://mentemagica.com/35mmAdapter/AdapterTest22a.jpg

PS. Bill, no it does not make a sound, but still makes a good screen.