Trying to perfect my Telecine (direct to gate) machine, help me understand shutters

[Paul Wende]

Hello everyone,

I built this machine 4 years ago with the help of you fine folks and converted a dozen 200' reels of my families old 8mm film. I just found another 2 400' reels whichI somehow missed, however, the machine vision camera I had used has crapped out since I last used it so I bought a new one and have it installed and working again. It's much faster than the old one and I'm able to capture at 6fps now vs 3 for the old one. I was happy with the performance of the old setup but while I was tuning the new camera white balance without any film in the machine, I noticed that some of the frames were darker, seems every 3rd or 4th frame was noticeably darker. It wasn't an issue while I was capturing as I think the camera exposure masked the effect, but being a perfectionist, I would like to figure this out.

My machine is driven by an Arduino ucontroller and triggers the cameras electronic shutter and LED light. There is a magnet and hall effect sensor for the trigger mechanism, the shutter wheel on the projector has 3 openings. I guess I gave you more info than needed but what I need to understand is how the old projector was designed to work, ie, why 3 holes on the shutter wheel, 5 on some projectors, why not just one for when the film is stationary in the gate? My projector shares the shutter wheel with the cam drive for the claw so eliminating it is not an option. I'm thinking I may be able to elongate the openings significantly to allow more "open" time for the capture without compromising the structure of the wheel. I'm trying to just capture one frame at a time, exposure is about 10-15mS.

I look forward to getting some some fresh ideas from you, I'll be working on it again tomorrow with a fresh brain, it all may make sense to me in the morning but thought I would ask. Here is a video of my machine shortly before finishing it 4 years ago and a sample of the finished, processed film, 1970.

Thanks all.

Paul

https://drive.google.com/file/d/1KWH...ew?usp=sharing

[Paul Adsett]

Home movie projectors, operating at 18 fps, typically have 3-blade shutters. One blade is used to block the light during the time the claw is actually moving the film down by one frame in the gate. The other two blades are necessary to remove flicker. If you are projecting sound film at 24fps you can get by with a 2 blade shutter (and gain 30% brightness), and some projectors have this kind of shutter, or even the ability to switch from 3 blades at 18fps to 2 blades at 24 fps.
There are some special projectors around such as the Bolex 18-5 which can automatically switch from a 3 b;ade shutter at 18fps to a 9 blade shutter for flickerless slow motion at 5fps.

[Nantawat Kittiwarakul]

Therefore, the shutter blades are no longer necessary in your telecine setup.

It is actually better to have them all removed, as that may cause issue if the timing between the camera & the projector isn't quite right. This might even be the cause of those darkened images that you get.

[Stan Jelavic]

Instead of trimming the blades you can try reducing the projector speed. The global shutter camera should not have this issue as much.

[Paul Wende]

Hi again,

Well a good nights sleep and some thinking this morning, I decided to play with the magnet placement on the shutter rather than timing in Arduino. It seems the new camera has slightly different delay than the previous one. I shifted the magnet about 1 cm and that helped the rolling dark frames. I decided to pull the shutter wheel off and take it to the shop for some surgery to see if I could eliminate it altogether, I used nibblers to remove all but 1 cm spokes, just got it back together.

I played with a couple of 7" practice reels this morning fine tuning all the settings and I'll be transcribing the first of the forgotten family films tomorrow. It's going to take a few days to remember how I did all the processing, thankfully the old computer is still as it was in 2019 and all the software is still on it, settings shouldn't have changed so it should be "plug N play".

I'll make a better video of my machine and post a clip of the results in the next week or so.

Thanks for the ideas!

Cheers

[Paul Wende]

It was a great day of discovery, and learning, and at this moment I am capturing perfect images at 4fps.

I tried removing material from the shutter with ZERO effect, there were still various dark frames. I moved the trigger magnet in small increments all the way around the shutter, no difference. I had eliminated everything to do with timing so I started thinking about other possible causes. Then I thought what if the PWM signal I'm driving the LED with is causing some flickering that our eyes can't see but maybe the camera can so I substituted a different LED powered from a lab power supply.....problem gone! YES! So I spent a few more hours trying to get the original LED working with the PWM circuit now that I knew the issue, couldn't get it to work so I gave up and put the lab power supply on the original LED and just left it on while I'm capturing. I already had a fan installed to keep it cool so I will stick with this until I get some time to make a proper switching circuit for the LED to flash at the appropriate time.

Glad I figured it out, took some thinking but I got it.

Here's a video I shot today showing my current setup.

Cheers

https://share.icloud.com/photos/006a...fN1QjbxWUcT_0w

[Alwyn Adkins]

Paul, out of interest, could you post a short clip of your captured video? Thanks!

[Paul Wende]

Paul, out of interest, could you post a short clip of your captured video? Thanks!

Yes I will, but it's going to take some time, days maybe, before I get a final product, right now it's just 36,000 tif images.

cheers