For those of you who don't know, it is a proven that you can now make an adapter that will allow you to use 35mm lenses of any type, movie primes or still, of any mount. The specifics are not important, only the theory is, and the theory works.
I may or may not cover the history of this adapter in detail here, but that is not whats important, what is important is how it works.
PART I. Intorduction and theory
You may have seen the PS Technik Mini35 adapter for sale or for rent and you may have realized that it is priced so out of line with typical budgets for DV productions that it really is cheaper to actually shoot in 16 or possibly even 35 for real. Nevertheless, their product opened the door for the internet community to brainstorm and determine how their system works and how to build their own for much much less.
The first I heard about this adapter was actually the fan film Marla marlathemovie.com . Their system I tried first, basically taking the viewfinder off of a SLR, and shooting the focusing screen with my video camera. Surprise, it works! But its impracticle. One, the camera needs to be mounted at a 90deg angle to the SLR, which makes it totally impractacle for anything but totally stationary shots. Two, there is too much variables to consider, its tough to clean, it wont work particularly well on anything but a Nikon F3.
So then it dawns on me to find out how it works. And here's the theory.
The prime works like this. The image comes through the front, through the lens, and is projected out the back, but the projection is not linear. The image only forms at approxamately 2" behind the rear element on the lens (which is just magically where the film is located behind the lens in an SLR, or the mirror that sends the image up to the viewfinder. ). It is crucial that whatever is to capture this image is in the EXACT position where this image is projected, because 1 mm either way means that the focusing will move too far towards the close up, or too far past infinity. So in other words, it must be perfectly spaced for the focusing to work correctly as it is indicated on the focus ring of the lens.
So now we just hook up the lens 2" away from the video camera lens, right? No. You will technically see through the 35mm optics but that is not going to take advantage of the DOF or FStop of the lens at all. Not to mention the image would be too small to do much with at all. So what then? Well remember how it works in an SLR. The projected image coming from the lens actually exposes the film, not the image in the lens itself, the film cannot "see" it only is exposed by the light that hits it. So we must STOP the projected image where the film would be. Seem hard? Don't worry, I did the work for you. What you need is the same principle as the Large and Medium format cameras, stop the image with some type of Ground Glass.
Ok so now we project onto SOMETHING at about 2 inches back from the lens (try it if you want, it will work no matter what you use). But how do we get the image into the camera? Here's where it gets a little tricky.
C. Why you can't just hook up the lens to the video camera
See the image needs to hit this plane of material to be stopped. But it would be impracticle to shoot the image from the side where the lens is. So we need to make this whole thing inline and use a ground glass as I said. In order to do this effectively we need two things out of the ground glass or whatever we use to stop the image.
1) High light transmittance. If the glass is too opaque, you wont hardly see the image because it will be too dark. But it cannot transmit too much light straight away otherwise we will just see the camer lens through the ground glass. So it needs to be diffused heavily on one side, but thinly.
2) Low Grain. If it is too visible with grain, you will see it in your final image every time you move your camera, and if its real heavy you will see it in static shots too. Its not like ever moving film grain, it looks like a thousand specs of dust that someone forgot to clean on the lens.
So it has to be a uniform, finely grained, diffused surface on one side of the ground glass, and the actual glass has to be thin enough to let a lot of light through without losing much.
Here is where the static and moving GG (Ground Glass) adapters diverge.
D. Static GG's and Moving GG's - the difference
Static adapter creators have tried everything from Beatie Intenscreens to acid etched glass to aluminum oxide scratced glass to just about anything you can think of. So far the BEST success I have seen has come from the Beattie Intenscreen, but I have only seen what was posted from Steev as mov's. I have been using a Nikon Type D Focusing screen. They are basically an all in one magnifier (plano convex lens which I will talk about in a moment) AND ground glass. It is very efficient, but semi costly @ $30 per one, if you can find it. It is the same size as a 35mm frame, which is not by coincidence, which again I will explain in a moment. HOWEVER, the ground glass is incredibly thin coating so it does not withstand much wiping of any type or it will start to lose its coating. I have also found a perfect piece of injection molded plastic that seems to do maybe even a better job than the Nikon with eliminating grain, but the light transmittance is probably 1 fstop worse.
Moving Adapters incorporate a portable cd player motor, a clear or frosted cd or GG spinning on the portable cd player instead of just the static GG. This radically eliminates any grain, but introduces many new problems such as vibration, size, and necessity to understand basic soldering etc. Personally, I don't see advantage to it only because I have had so much success without needing to do that. Believe me, when all is said and done I think either I or someone else will find the perfect GG or equivelent that will eliminate the need to get rid of grain because there won't be any to be seen.
Play around with different materials to understand what all of this means, particularly clear materials.
E. Lens to the Ground Glass, now what? Plano Convex.
Where are we now? Well we have the image going through the lens, hitting the ground glass at a precise distance that is approxamately 2" away from the rear element of the lens. Open up the aperature completely on the lens and check it out, its an image! How cool! If you can, try and focus the lens, and OMG it focuses! We're close to having the whole adapter now!
Well, there a slight problem. Remember the magic size of the 35mm frame and the focusing screen being the same size? Remember how I said we need a magnifier (actually a plano convex lens)? Well its not by accident. See, every 35 mm lens projects an image that is actually round and takes up a much larger size than the size of the 35mm frame. But only the size of the 35mm frame, in the center of the projected image, is usable. The surrounding area of this, all the way to the outside of the image, gradually loses its light intensity, and is more or less unusable. This is called Vignetting. This is not good for your image, it looks very poor. You can *spread* the light, with a plano convex lens, and slightly magnify the image itself, making the whole image bigger for your video camera to capture, but you will not be able to pull *all* of the frame. This is exactly why I use the Nikon focusing screen. The size is exactly the maximum size you can get from the projected image, and the plano convex lens on the front of it maximizes the light all the way around the image. Not to mention it is already 4x3, so the camera frames perfectly.
F. Hey its a nice image now, we're ready to shoot it right?
Pretty close. Now you have to determine the capability of your camera as fas as what the minimum distance it can focus on is, ie. macro. Can you put something right up to the lens and focus on it? If you can then you are ready to read part II and start building the adapter. If not, you will need a macro lens. At minumum you should get a +4. A great one to get to start is the +4 +2 +1 Hoya kit that is relatively inexpensive. Or you can get a +10 Hoya which I just bought. So now I have +17 but I think it may be overkill. But wait until you read Part II so you know exactly what you need.
Sidenote: Wideshot, what sort of 35mm adapter did you make?
Static, kind of custom, but nothing is really different from the traditional design.
+1+2+4+10 Macros > Plano Convex > GG > Lens