70 mm Adapter

[Jim Post]

Hey guys, great work on the 35 mm adapter. I ran this over at work by one of our engineers and a DP. This is what we all came up with:
1. Use a medium format camera. You'll get the quality of a 70 mm film. The depth of field will be very shallow. You'll use a second camera, or the same one, without the adapter, for wide depth of field shots.
2. The medium format camera will be more forgiving to imperfections in the ground glass.
3. You'll be able to use the larger ground glass easier with an HD camera.
4. The medium format camera will probably have the condenser lens built in.
5. You can pick up an older SLR camera with a few lenses under $1000, even for $500. Check ebay. Excellent lenses; surely many times cheaper than buying 35 mm cine lens.
6. The set up will be larger but you'll get 70 mm film depth of field.
7. You'll be able to focus the camcorder easier on the larger target area.
8. To improve the image, you can rotate, vibrate, etc. the ground glass. Our engineer recommends a motor or a piezoelectric drive. Both are inexpensive, but he prefers the piezoelectric one.
9. Patent and intelectual property issues. If you make the camera with the screen vibrating for the purpose of seeing the image better, then there is no problem. If another individual makes an adapter for this to fit a camera, there is again no problem, plus you've just created a combination of a still medium format camera and a camcorder. If it can be used to mount also a camcorder that take stills, you have a tripple system combination, something totally different from Mini35. You could even patent the various combinations.
10. Our engineer calaims that there are plenty of inexpensive piezo elements available that are efficient and powerful.
11. You could manufacure simple kits for Pentax 6x7 camera, for old Bronica 6x4.5 cm camera, etc.
12. When made in quantity in China, it would cost well under $500. Add the cost of the medium format camera and lenses. You'll have HDV camcorder that will give you a better performance than Pro 35 mm adapter. And medium format cameras are very rugged.
13. So there would be the DVinfo 35 mm static adapter, 35 mm dynamic adapter, and there could be couple of 70 mm adapters.
14. I don't have the expertise, time, or patience to do this. But if you could make 1000 adapters and make $300 on each, it is $300,000 total. I'd buy couple of them myself.

Keep the good work,

Jim

[Brett Erskine]

These are all real good concepts for the reasons you mentioned but I personally abandon using medium format lenses early on because of these issues:

1)Theres exponentially more 35mm lenses versus medium format lenses

2)Medium format lenses are quite a bit slower (usually about a f/3.5 and if you find the rare f/2 your going to pay BIG money

3)There are deals on both type of lenses but your best buys by far are still 35mm lenses

4)A adapter designed to work with medium format lenses wouldnt allow you to use 35mm cine lenses with their well designed zoom/follow focus optics. And dont forget the PL mount anamorphics that will allow us to double the verical resolution of our DV cameras.

5)The adapter would be longer and heavier with medium format lenses.

On the other hand the good thing about medium format lenses is that they give you twice as much DOF for the same f/stop on a 35mm but with cheap 35mm lenses with f1.4 aperatures your back to square one.

Then theres 4x5 cameras. Even bigger ground glass (little/no grain). You can use Bosscreens. Swing/Shift ability and cheap lenses. But even 35mm has swing/shift lenses so if someone asked me personally...35mm.

Brett Erskine
Director of Photography
Premiere Visions
1761 W. La Palma Ave., Suite #302
Anaheim, CA 92801
www.CinematographerReels.com
BErskine@CinematographerReels.com

[Jim Post]

35 mm format 50 mm, F1.4 lens would have the same DOF as 70 mm format 100 mm, F5.6 lens.

The 70 mm format with 2 f stops slower lens will have a 2x shallower DOF for the same angle lens.

The condenser is built into the camera body. The image is large. If nothing else, then a perfect scenario for a static adapter for HDV. There is no reason to go to a large format. And the medium format lenses have a real nice feel, good for follow focus, etc.

Don't discard the concept yet.

[Brett Erskine]

Just offering my personal opinion and a few more facts for everyone to consider as a whole before they spend a lot of time and effort in this direction. There are definately benifits for both formats. The more facts the easier it will be for everyone to make a choice. Heres the conversion numbers:

FIELD OF VIEW
50mm lens (35mm) = 82mm lens (2 1/4)

DOF
50mm lens @ f/1.4 (35mm) = 82mm lens @ f/2 (2 1/4)

[Jim Post]

I am not an expert on this, and I may be wrong.

I believe that 35 mm frame is 36 mm long. 6x7 camera camera would have 35 mm long frame. In the HDV format you need to be concerned with the length only. HDV is narrower than the still camera frame.

So with 6x7 camera, the equvalent focal length would be double of 35 mm. There is no reason to use a diagonal for comparison of equivalent focal lenth.

For all things being equal, the depth of field of a 2x longer lens becomes 4x shallower. All you need to do is use one of the formulas that are avilable on various websites.

If you use different circle of confusion for the various formats, then you could come up with 2x DOF difference, but I believe that in our case we shouldn't. Can someone else, who knows more than I do comment on this?

In a static adapter the medium format would make a lot of sense, especially for HDV. You would have higher tollerances, etc. Maybe someone could actually take e.g. 6x8 cm camera (Fuji makes one) with 200 mm lens and 35 mm camera with 100 mm lens and looks through the viewfinder to see when the DOF becomes equal, if it is at 2 F stops or 4 fF stops.

If it is 4 F stops, then I think that any medium format will look a lot more artistic because you will be able to achieve shallower DOF. Some of the most artistic photographs were taken with 8"x10" cameras, with very shallow DOF, I think. But I may be wrong.

[Jim Post]

I would like to stress again one more point. You make the static or the dynamic adaptor, and you may infringing on someone elses patents or intelectual property. If you make a different concept that will supposedly be for taking both video and still pictures, it is different than the other adapters out there and you're off the hook. You can even patent this yourselves.

If the meduim format camera has the condenser lens built in, it would be very easy to just make an adopter for the camera to see the ground glass. If you would use a miniature motor or piezoelectric drivers to shake the ground glass, you would hava a smaller, and a lot more reliable system than what you have now with a CD player mechanism attached. If nothing else, you would make this concept 100 legal, legitimate, kosher.

You could try to do it with a 35 mm camera, but the tolerances would be harder to achieve. The medium format camera has available 35 mm backs, so you could say that you're making a combination multiformat film camera, digital still camera, and a video camera, plus if you make the GG vibrate, you make also a better medium format camera, because the image will look better.

A lot of different things could be patented here. I am sure someone could make this concept not only good but also very profitable. I am just giving hints here after talking to an engineer about it. I am not interested myself in doing any of this.

[Brett Erskine]

Download "pCAM" - DOF, FOV, etc calculator software for your Palm Pilot here----->http://www.davideubank.com

Nearly all still, video, and motion picture formats are covered.

[Brett Erskine]

I've also been wondering about the patent issue but because were basically talking about a camera obscura (and trust me that pantent ran out a-long-time-ago) there may not be an issue.

[Charles Papert]

Gents, all really cool stuff. However:

I sound like a one-trick pony on this issue, but I do feel it's always worth mentioning: --achieving shallow focus is one thing; delivering footage that actually keeps the subject in focus is another. Consider a 100mm closeup of a face. Given a shooting stop of f2, there's one inch of depth of field forward and one inch back. If that person suddenly leans one way or another, they will be out of focus. Now that's with 35mm Cine, which means that 35mm still photo format will have even less depth of field, and medium format...how small is your ruler?!

The point is: it takes a lot of skill to shoot moving images and keep them in focus with these formats. A lot. Consider that you see occasionally see soft shots in movies with veteran camera assistants at the controls wielding all the appropriate tools and techniques.

Let's say you have 30 setups planned for your shooting day; how many takes can you afford to "do over" until you get useable focus? What about a stunt, or working with kids or animals?

I'm not trying to talk anyone out of making an adaptor, but unless you are planning to shoot still lifes or tableaux, this could be a can of worms...

[John Jay]

Charles,

Do you know what gate size is used on academy 70mm? I was thinking imax projection

[Jim Lafferty]

Jim Post:

With the latest adapter designs, moving the glass is a non-issue -- static solutions are all the rage now :D

Here's some sample footage from the static glass solution pioneered by Alain.

- jim

[Roman Shafro]

2 Jim Post: I was thinking about a piezo ever since I looked at the Agus35 for two reasons: first, it'd be a more elegant solution, no real moving parts, except for the diffuser mount, and nothing to break down, like a flying CD or a burnt-out motor. Secondly, I was uneasy about the spinning disk idea because of copyright and patent issues, precisely as you've mentioned. BTW, I don't see anything patentable in a static adapter, since ALL components had been used in other devices for SAME purposes, like producing the image on the GG, using a macro lens, etc.

The only potential problem I see with the piezo is how to isolate the vibrating diffuser from the rest of the assembly.

Since Alain had demonstrated a very decent home-ground GG, the need to spin or vibrate is no longer there: there are no large specks on the GG to hide, and as far as film grain is concerned, there are plenty of software packages that can take care of that in post-production.

[Jim Post]

The principle itself may not be patentable, but the application may be, since you bring new element into it. How about the Movietube, do they have a patent? Someone should do a search. But I don't know much about it. If someone starts building it, I'd buy a couple.

Now, if you could make it for CineAlta and Varicam, you'd compete with Pro 35 that is very expensive, and patented, but the principle is different and there is definitely profit in it.

Pro 35 is made for 35 mm cine lenses. The pros would welcome the opportunity to use 6x7 cm format lenses, or even larger. They would be able to control DEF better. Video DOF without adapter, Cine DOF with 35 mm cine lenses and Art Photography DOF with medium or large format lenses. You would have a better artistic control.

[Jim Post]

Pro 35 costs over 20,000 Euro and has a problem on long shots with vibration. If someone could make a static adapter for CineAlta and Varicam, it could be a good money maker. I believe that P+S sold about 400 of the Pro adapters. A staic adapter could make them absolete.

An adapter that would accept 35 through large format lenses would be a killer. If someone could make 10,000 Euro on each, it could make him rich.

[Brett Erskine]

I just altered my design so that it has a adjustable flange focal length. I guess we dont have to choose what lens we are going to stick with. Use them all. Same goes for camera too.