Sprocket Registration


#6

Cross-posting some posts from another thread that are better categorized here as Sprocket Registration. CLICK THEM TO EXPAND.

http://forums.kinograph.cc/t/film-advancement-moving-the-film/43/2?u=matthewepler
http://forums.kinograph.cc/t/film-advancement-moving-the-film/43/3?u=matthewepler
http://forums.kinograph.cc/t/film-advancement-moving-the-film/43/4?u=matthewepler
http://forums.kinograph.cc/t/film-advancement-moving-the-film/43/5?u=matthewepler


#7

This is great, thanks! Any idea what component parts are used, exactly? Maybe I can order one and do some tests. Do you have a link?

Does your Point Grey camera require a frame grabber?
What “mechanical method” of counting sprockets are you referring to?
What’s a “flashscan type light source?” Link?

Forgive me if I’m being nosy. You have a lot of great advice on the forums, just trying to figure out what machines you’re using/building/etc. If you’re keeping some trade secrets for your business, I can understand, however.


#8

No, the camera just streams via USB, so no frame grabber required.
The mechanical method is using tiny neodynium magnets on a sprocketed wheel with a hall effec sensor.
A flashscan style light source refers to an LED array that is pulsed for a few milliseconds up to about 300 milliseconds for each frame, rather than staying on constantly. You can flash each colour for varying amounts of time to adjust the colour mix.

It might be worth talking to these guys re sprocket sensing:
http://www.balluff.com/balluff/MDE/en/products/selector-photoelectric.jsp#/PHOTOELECTRIC?SAP_ZD_017=Slot%20sensor&Range_max.=up%20to%2050%20mm&page=0
The slot or angle sensors would most likely work.


#9

Yes Matt, by dumbed down I meant a cheaper low res sensor/camera just used for the openCV frame boundary registration. Although the reflective sensor control parts you attached could provide this functionality in a simpler solution, only requiring film base density calibration on each newly loaded roll.


#10

Hey @matthewepler I was reading about acetate blocking IR light. Apparently US soldiers with IR night vision cameras couldn’t see through acetate signs. If you were to get an IR-only laser of the right wavelength, you might be able to use it as you first thought, even though lots of film appears clear to visible light around the perfs.


#11

I have a scientist friend who can do a spectral analysis of a film sample very easily. Maybe there’s a specific wavelength of laser that will be blocked inherently by all acetate film regardless of whether it appears clear in visible light. I’ll keep you posted.


#12

Hi @MikeThibault,

do you already have any news about your analysis of the film sample and what light might be blocked by acetate film or a film with polyester base?

Thanks!


#13

I’ll be giving samples to my friend this week; she says that it’s a pretty straightforward process. I’ll be out of town until after Labor Day but I imagine I’ll get results fairly soon!


#14

I’m sending some film samples to a sensor company in Melbourne Australia to test, hopefully they can give us some feeback on the best solution for sprocket sensing.


#15

@MikeThibault and @Peter
Great, thanks a lot! Really looking forward to hear what you find out!


#16

Long time lurker, first time poster. Please be kind !
I have built the machine ( in my mind’s eye ) from end to end many times and the " Frame " accurate positioning remains the main challenge for a given budget.

I am considering the digital options. The first contender would be " mocha " by Imagineer. Mocha is a powerful, frame accurate tracking software and more. We could give the " eye " of mocha something to cling onto for registration each frame and let it go to work.
I understand the issue of dependency to third party resources, but hey this will get the cart out of the barn sooner.
I am planning a short test with a few off registration scanned frames that tacked with mocha. I’ll post the results soon.


#17

Hi Claw, welcome on the forums!
I’m experimenting with a photoresistor for frame counting at the moment. So far I get good results.
Thanks for the link!
Please keep us updated! Thanks!


#18

Looking forward to your test results! We’ve had someone else do tests with Blender and Fusion 7. Would love to see the workflow for Moca in a similar video if possible. Thanks for doing this, @Claw_No_More (nice name btw).

Links to the tests:
Fusion
Blender


#19

I can confirm that IR is significantly attenuated by transparent film stock. I have an IR thermal temp sensing gun, which cannot see a soldering iron through it.

My guess a simple ‘clipper’ circuit, used to detect zero-crossings in waveforms would do the trick if the IR detector was AC-coupled. Also, I would suggest an IR led as the source, like those used in surveillance cameras.

Jeff


#20

The IR absorption may vary across film stocks, I did a quick measurement between the sprockets of a film I had on hand and it is pretty transmissive in the IR:
so you would have to be careful about the diode/wavelength selection.

I think a visible wavelength would be fine and would make alignment easier, even if the film stock is transparent there would probably be a detectable difference between the sprocket hole and film.

I came across this system which uses a red laser (3rd pic in the slideshow):
http://www.filmfabriek.nl/muller-hds.html

Will


#21

Beautiful machine. I think the best place to start is by people doing some tests. You up to it, @everlastgobstopp? @VitalSparks? @Peter?

I can do some here. I don’t have any fancy testing equipment. Any suggestions beyond reading values out of a serial port?

Perhaps we should start a document that lists the light source, type of sensor, etc. so we have a way to keep track of the test variables and results. If you guys and gals are game, I can start that up.

Also, what should we be testing? Types of lights/sensors…I have the common off-the-shelf LEDs and light sensors. But that’s it for right now.

M


#22

Black and white film blocks most of the IR spectrum, different colour stocks block from almost none to around 30% in various areas of the frequency.
Other manufacturers have had better results with Blue LEDs on the sprocket area, and placing them before the camera sensor so that there is no light bleed.

If you are going slow (1-3fps) almost any sensor will work, once you get up to speed it becomes a problem. It might be worth playing with polarisers to see what effect they have - anything that might magnify the difference between the clear stock and empty space is worth investigating. However remember that every stock type has different properties.

BTW, the Muller uses the same triggered light source for capturing that I have outlined in other posts designed by Frank Vine.


#23

Hi I’m new to this forum. I’ve be working on an 8mm project. I have used the
mechanism of a film editor, and modified it by removing the four sided prism. I then fitted a four blade shutter and photo-interrupter to give the trigger signal.Whilst this did work,it produced a lot of bounce. The bounce had a beat of four. It had to be the shutter. So to test the theory I made a thin metal finger that drops in and out of the sprocket holes. An electrical connection is made between the metal gate and the finger,providing the registration signal. Here is a youtube link. https://www.youtube.com/user/whoam42a1?feature=hovercard
It’s a very crude method, but it works very well. Its an ongoing project that need more work.


#24

@whoam42a1 thanks for sharing your project with us and for the documentation. It looks great!


#25

Hey, I had a friend do a UV-Vis-IR absorbance spectral analysis on some film. I had her do three samples, one Polyester and two acetate, labeled “Scrappy” and “Black” (I have no access to nitrate and I doubt too many of us are interested in handling it). Something that might be of interest to us here is that they both fluoresce at ~300nm. Check out the UV tab on this spreadsheet:

Instead of an expensive laser, it might be possible to shine a cheap UV LED to fluoresce the film and look with a visible spectrum camera at where the sprocket holes are.