View Full Version : Shutter speed or projector speed??


Tom Blizzard
July 8th, 2007, 09:58 PM
I'm recording some old 8mm and super 8mm home movies with my GL2. My searches on the many topics here on the forum don't seem to be working.

Would someone kindly suggest a shutter speed that will help eliminate the flashing or flickering I see when I play back my recordings. Maybe it's the projector speed that needs to be tweaked??
Thanks, Tom B.

Chris Harris
July 8th, 2007, 10:41 PM
At the very end of the spectrum of shutter speeds, after 1/10000, there's something called a clear-scan mode or something. It should eliminate the flicker you're seeing.

Graham Bernard
July 9th, 2007, 01:47 AM
At the very end of the spectrum of shutter speeds, after 1/10000, there's something called a clear-scan mode or something. It should eliminate the flicker you're seeing.

Hmmm? I'm really not sure that this IS the same thing as the "flicker" produced from a projector?

I say this for 2 reasons:

1 - Clear Scan:
The CLEAR SCAN option is for PCs or other screens that produce the black banding caused by the differences in field frequencies of screens. Projectors produce moving images from, for our purposes here, single field information that is projected onto a screen.

2 - Frequency Spectrum
My Users Manual for the XM2 states that: "You can select between 170 frequencies between 50.3Hz and 200.0Hz" As far as I know projectors are running around 25fps? Something like that? But, in any event, this IS erroneous for me to state as what is trying to be achieved is NOT about the field differences and but the diferential of phase scanning of the camera creating the black banding and NOT the flickering of a projector.

Maybe there is another flickering-reduction/removal method available? I really can't see the CS as being an option? From what I read CS is about field banding and not about flickering.

Grazie

Richard Alvarez
July 9th, 2007, 08:00 AM
The 'flicker'you are seeing is the result of seeing a 'darkened' or 'black' frame in the midst of the projection recording. This happens when your camera picks up a moment when the shutter blade of the projector is covering the frame.

8mm films typically run at 16 or18 fps. Super 8 ran at either 18 or 24 fps. The shutter on your typical projector has THREE blades.

Therefore;

EVERY time a frame is moved into position it is 'flashed' on the screen three times. 3 x 18 = 54 "Images" a second, flashed on the projector screen. Your camera records 60i = 60 interlaced fields per second. Since those numbers (54 and 60) are not evenly divisible, one or more frames/fields will show the shutter 'dark' - hence the flicker.

(3x24 = 72 also not evenly divisible by either 60i or 30fps.)

A simple trick, is to use a variable speed projector, and 'tune' the speed of the projector untill the flicker is gone. So 18fps film, sped up to 20 fps, will yield 60 IMAGES a second flashed on the screen - exactly matching 60i or 30fps. (The reason old home movies look a little fast.) Likewise slowing down 24fps to 20 will yield flickerless results, but slightly slow motion.

You can try and tune your CAMERA shutter to match the frame rate at 24fps, or 18fps but it might not work, depending on how your camera processes the fields. (even at 24fps, digital videocams are capturing 'two fields' so you are back to matchng 48 fields)

You can try and find a professional telecine projector, which has FIVE blades in it. (5x18 = 90 evenly divisible by 30 fps. 5x24 = 120 evenly divisible by 30 fps.)

Or you can send it off to be transferred professionally by digital capture, where each frame is held in place and 'captured' as a single frame of digital information... then reassembled into the sequence.

Search this forum for 'poor mans telecine' for more advice.
Also google rank cintel services.

Good luck.

Tom Blizzard
July 9th, 2007, 08:33 AM
Thanks Chris and Graham. Thanks for your suggestion Richard. I noticed your name in those topics many times in answering my question over and over to other forum members. You are one very patient fellow.

I searched over an hour last night and never found those good suggestions.
Thanks again, Tom B.

Richard Alvarez
July 10th, 2007, 09:31 AM
Not a problem. I used to shoot quite a bit of Super 8. Used it to teach filmmaking to kids. I've transfered a lot of S8 and R8 using a variable speed projector, and the results can be satisfactory for most uses. Not the best, mind you, but for teaching purposes more than adequate.

Janssen Herr
July 10th, 2007, 09:08 PM
Richard Alvarez made some really good points.. I will re-iterate his thoughts on getting a hold of a projector with variable speed control. Variable speed contol is different than set speed control which often is set (depending on projector) at 8, 12, 16, 18 or 24fps. Since I have had my XM2 I have not transferred any S8, but in the past I have. So here is a little about what I did to get the best transfer.

This is my own method of capturing S8 footage to DV- it may not be the best way but it certainly is the cheapest and gives results which is *almost* indiscernible from professional production houses using the telecine method.

If you have footage initially shot with 18fps, you can set the projector to 24, adjust the variable control speed to match. Over here in pal land it works really well as one can go from 24fps film to 25 PAL Video easily. For NTSC you would want to try and crank the projector up to 30fps. Once you have captured the footage you can slow it down on your NLE. There will of course come artifacts from this procsess (ghosting) though the pulsing black to white flicker will not be present.

I made a film in 2002 which used both a Super 8 camera (a wonderful canon 814) and a DV camera. The film, HOTEL, was based on the myth of Orpheus and his descent into hell to retrieve his dead wife. I used the different acquisition formats as a way to express the two worlds- above and below. All the Super 8 footage was shot at 24-fps NOT 18-fps - a big importance when one wants to match the film stock and DV. This may be a personal choice as some people may want the 'artifacts' and 'stuttery look' of footage shot at 16-fps or 18-fps.

Link to the promo of film 'Hotel'

http://www.janssenherr.com/hotel.html

I used a PAL Sony VX 2000 to capture black and white super 8 footage projected onto a screen. The main thing one has to concern oneself with here is the type of Super 8 projector used. The minimum requirement is to use a projector with variable speed adjustment control. Because we were capturing on PAL the frame rate being 25-fps and the projector (ELMO GS-1200) being projected at 24-fps i was able to adjust the speed of the projector incrementally until the frame rates matched. I also recorded on the VX 2000 using a higher than average shutter speed (around 100-150) this is because the motion blur 'was not needed' as it was already in the S8 footage.

Another consideration with the projector is to get one of the 'high end' S8 projectors which use a 200w light bulb- much better 'dynamic range' and throw in a theater! And also to use a DV camera which has very good low light performance with as little grain as possible- at the time the Sony VX 2000 was perfect for this use. An XM2/GL2 would be fine as well especially considering that one has FRAME MODE to use as well.

Super 8 is still a wonderful and viable (though not always accesable) medium. All my work is digital now (DV), but I have 10 rolls of B&W Kodachome in my closet and a Canon 814 which sits proudly on a shelf above my editing bay reminding me of the 10 rolls in the closet!

Janssen Herr
www.janssenherr.com

Richard Alvarez
July 10th, 2007, 10:17 PM
Jansen is correct, if your variable speed projector will allow speeding up 24fps to 30, then again you have a match. Either slow it down by for frames per second or speed it up by six... and you can alter the speed once again inside the NLE.

All of this dependent upon having a variable speed projector, and an NLE with good speed manipulation software.

Tom Blizzard
July 11th, 2007, 04:00 PM
Amazing. Richard, as you said, you can see the flashing go away on the GL2 LCD screen. Such an easy solution ...
Thanks so much. I taught Geometry for 30 years...
Regards, Tom B.

Richard Alvarez
July 11th, 2007, 04:21 PM
One more tip. Depending on the variable speed 'settings' on your projector. Here's how I do it.

I aim the projector and camera at a screen, and start the projector running WITHOUT FILM.

I white balance on the light hitting the screen. I also 'tune' the projector untill the flicker dissappears. Wait a few moments, as you might have to tune it back down a bit... back and forth untill the shutter speed and camera are in synch. MARK the spot on the dial. Load the projector and fire it up. IF the projector's belts are strong, then the film should transfer without flicker straight away. If the belts and drive are a little weak, you might have to 'tune as you go'.

R

Tom Blizzard
July 12th, 2007, 08:21 PM
Hey that's the kind of advice and suggestions that I can understand. All very practical. Just what I was hoping for. I'm printing your sugestions.
Regards, Tom

Hans Ledel
July 13th, 2007, 12:06 PM
The normal projector speed in PAL and 50i is 16,66 fps, when capture from a screen without getting any flickering., hence as been said you need variable speed
I guess you can make some calculation from that regarding 60i

Do not make the screen to big, you will not get as sharp if you have to big.
I normally have a screensize around 30-40 cm

Good luck

Hans