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Topic: Mk3 8mm Transfer machine.
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Martin Jones
Phenomenal Film Handler
Posts: 1269
From: Thetford , Norfolk,England
Registered: May 2008
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posted August 13, 2008 04:01 AM
I've prepared a reply to you James, so am going to post it here. Only hope its not too large!
James,
First and foremost, you will have to reduce the projector lamp wattage to a very small level because your camera will not cope with the brightness using the normal bulb. I use a 10 watt halogen capsule lamp running from a 12 volt supply, with a diffuser between it and the gate.
You have no doubt already discovered that the lens on your Sony has not got a powerful enough telephoto to directly fill the monitor with an 8 mm or super 8 frame when pointed directly at the film in the gate. Some degree of magnification will be needed. The obvious thing to try is to leave the projector’s own projection lens in place and point the camera into the front of it. If you have tried this you probably will get a small image of the frame in a sea of black at the wide angle setting of the camera lens and a magnified image of part of the frame at the telephoto end, with nowhere in between giving just the frame cleanly filling the monitor. This is because the small diameter of the projection lens coupled with its relatively short focal length is the wrong combination for the job.
In order to magnify the frame to fit the sensor in the camera you need to use a supplementary lens on the front of the camera lens situated at a distance equal to its focal length from the film gate. This enables you to set the camera lens to infinity and then vary its focal length (zoom) to the frame size. In order to do this, you have to choose a combination of camera lens focal length, supplementary lens diameter, and supplementary lens focal length that will not only give you the magnification required but also avoid any vignetting due to the camera lens angle of view being too great for the diameter of the supplementary lens.
The problem is; how does one decide what to use as a supplementary lens?
Getting back to basics, what one has to achieve is to create an image on the camera sensor of the film frame in the gate, no more, and no less. Since different cameras use different size sensors, manufactures not only quote the actual focal length of their camera lenses, but also the “equivalent 35 mm still camera“ focal length. This is the focal length that would give the same field of view if the camera was a 35 mm still camera with a “sensor” width of 36 mm (the width of the frame in a 35 mm still camera). The magnification of a supplementary lens/ camera lens combination is given by the ratio of camera lens focal length to supplementary lens focal length.
So, for Standard 8, which has a frame width = 4.8mm.............. .
In order to enlarge this onto a 35 mm still camera frame, one would need to magnify it 36/4.8 = 7.5 times. So if your projector lens (used as a supplementary lens) is 25 mm the camera lens would have to be set to 187.5 mm (35 mm camera equivalent). The chances are that the field of view at this setting of the camera (which is actually having to work at more than 25 mm from the gate because of the length of the lens barrel) is too great to cover only the frame in the gate, and a circular vignette due to the small diameter of the lens barrel will result.
So what we need to do is to increase the camera focal length to a value that produces the correct field of view, at the same time increasing the focal length of the supplementary lens in the same proportion to keep magnification the same. The camera will move away from the gate as these focal lengths increase, affecting the field of view to some extent.
I found, by some trial and error, that a supplementary lens of 75 mm focal length placed on the front of my camera lens and situated 75 mm approximately from the gate would give me the magnifications I required for both Regular and Super 8 by adjustment of the camera zoom setting coupled with minor adjustments of gate to lens distance and camera lens focus. The required focal length of the camera lens was adequately within its range. If I could have physically accommodated a lens of shorter focal length and sufficient diameter closer to the gate that would also have been OK, using a shorter focal length on the camera lens. The amount of space available precluded this, however.
The problem then was to find a supplementary lens of 75 mm focal length of good enough quality, and large enough diameter to match the camera front element. I could have employed a lens from a 35 mm still camera, reversed and attached to the camera lens front. This is a standard practice amongst still photographers, but the problem in this application is that the diameter of such a lens at the end furthest from the camera (i.e. nearest the gate) will usually be too great to get it near enough without drastic mutilation of the projector, as mentioned in the previous paragraph.
My own solution was to use a projection lens from an old B&H sound projector which has a large front element, and a much smaller rear barrel which fits into the projector (which of course is what it was specifically designed to do!). Being for a 16 mm machine it has no difficulty in handling the 8 mm frames throughout its length. This lens attached to the camera lens is shown in the attached enlarged picture, which also shows it fitted to the projector, with the gate on the left. I had to remove only a very small part of the lens barrel housing of the projector to allow the lens to come back far enough towards the gate.
The sequence for set up is:
1. Set camera lens focus to infinity. (I set to infinity then back off very slightly, to allow fine adjustment later).
2. Adjust distance of lens assembly from the gate for best focus.
3. Adjust zoom setting to fill monitor with film frame, focus will be lost.
4. Repeat 2. The size will change.
5. Keep repeating 3 and 2, until size and focus are correct. Progressively smaller adjustments will be needed as the correct point is reached.
6. Once this is set and locked off, any slight focus changes due to film thickness can be accommodated by adjustment to the camera lens focus (see 1. above).
It depends, of course, on the projector you wish to use. If there is plenty of width forward of the gate (the distance between the optical centre of the lens and the main mechanism plate) so a large diameter lens could be located close to the gate, then a shorter focal length lens could be used and you would have a wider choice of lenses, but trial and error would still be needed to avoid vignetting if the camera lens is used at too short a focal length. The ratio between the focal lengths would still remain the same, 7.5 times for Regular 8 and a little less for Super 8. The camera zoom deals with that difference.
The principles would remain the same with 9.5 or 16 mm, but the lens diameters would probably have to be greater; trial and error again! The magnification would be less, of course (around 3.75 times).
OH, nearly forgot... you'll have to invert the result in Edit software.. or mount the camera upside down and flip left to right in Edit software!!!!
The following link may prove of interest as it deals with this subject in general way
http://www.srb-griturn.com/about-coupling-rings-386-c.asp
That covers the specific question you asked; other details of my machine, as it stands, are on my webpage (PLEASE NOTE: NO LONGER AVAILABLE THANKS TO UNSOCIABLE AOL) I’m happy to answer any other questions. I only wish I had access to a 3-CCD camera to take my experiments further in that direction, but I’m looking into possibly using a 2 mp webcam or a high quality CCD chip camera.
Regards,
Martin
[ August 29, 2010, 10:56 AM: Message edited by: Martin Jones ]
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Retired TV Service Engineer
Ongoing interest in Telecine....
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Martin Jones
Phenomenal Film Handler
Posts: 1269
From: Thetford , Norfolk,England
Registered: May 2008
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posted February 03, 2010 03:18 AM
John,
The CineCap approach (CineCap is no longer available as a stand alone Software, but other similar ones are) is based on capturing each single frame of film as a separate complete frame of video and then "stitching" them back together as a continuous movie file in a computer. It works by sending a pulse from the projector, timed just after the film has been pulled down and is stationary, to the computer, which then captures the next available COMPLETE video frame (e.g. two interlaced fields of PAL video) from the camera. The software then, again for example, takes a second's worth of frames, say 18 or 16 or whatever the original film was filmed at, and recreates them as a 25 fps (or 30 fps) video file ready for recording (perhaps after editng) to a disc or tape.
The clever bit of this is that it can ensure that even if the film was originally made at an odd speed (21fps?) it can be effectively shown at that speed. The Software has many other features, incidentally.
There are limitations to the speed at which the Software can perform its tasks, and because there are time delays involved in the Capture process, both due to the computer and the exposure correction in the pickup camera, there is a limit to the number of frames that can be captured each second, so 6 fps is generally considered a very reliable speed to use. Higher speeds are possible, and there are other methods, including real time capture, but the great beauty of the Frame by Frame method (animation in reverse!) is that it lends itself to ensuring that each successive frame is treated identically, both from the registration and exposure points of view.
I am currently working on the construction of my MK. 4 machine which will have facilities for using other methods as well.
Martin
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Retired TV Service Engineer
Ongoing interest in Telecine....
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UBBFriend: Email this page to someone!
![[Big Grin]](biggrin.gif)
) reversing the image would be no worry at all in Adobe PE3 which although an old software is super-stable on my XP and gives me pretty good results consistently.
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