- Created on Wednesday, 08 October 2008 15:40
- Last Updated on Friday, 14 December 2012 20:15
- Written by Patrick Steele
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Gary Elmer's 2M Intervolameter
This past February, a surprising and enlightening email arrived on the Topica listserv; seems a camera guy out of Ontario by the name of Gary Elmer adapted a Tobin Cinema Systems intervolameter to his 2M. I contacted Gary after reading his posts and requested photos of his rig. He kindly obliged, and I now post them here along with two of his messages from the [Konvas] group. If you have any specific questions, please contact Gary directly via his email, garyelmer at sympatico.ca, or his website. Also the thread regarding his intervolameter is quite long; I direct interested parties to the [Konvas] listserv to read the entire exchange.
If you require more info on the intervolameter, a link to Tobin Cinema Systems is present on the Services and Accessories page.
Hi everybody. Just new to the list and thought I'd share how I converted my Tobin TTL Intervalometer (time Lapse motor for a Bolex) to work with my 2M. The Tobin motor is a great little unit and I believe under $500US. (saw a couple lately on ebay... sold for about $350). It will do from 1 frame every second right down to one frame every 60 minutes. Short or long duration shutter. mmmm. 5 second per frame car shots. It's very good.... and the Konvas (at least mine is) rock solid in the registration.
Here's what I did:
Took off my motor ;
Made an aluminum bracket that starts under the camera and comes up the right hand side of the Konvas in a 90 degree angle. Cut a hole for the motor mount to slide through. The bracket is supported by the screw underneath and resting snugly around the motor mount. I drilled and tapped some holes into the bracket to match the configuration of a Bolex. (had to turn the intervalometer 90 degrees clockwise because of space issues)
With a small piece of brass and a Dremel I carved out a Konvas-Bolex "Key". It's about the size of a thumbnail at the thick Konvas end and the size of a thin pencil at the other. This lets the Tobin believe it is driving a Bolex and the Konvas believe it is being powered by a mighty motor from Mother Russia. It's actually not as difficult as it sounds. the Tobin has a great spring suspension on it's drive shaft so the actual key fabrication doesn't have to be a major work of art. Personally I liked the kind of hacked homemade nature of non-engineers anyway. It works.
For battery power, there is a space under the Intervalometer that I have mounted a 12volt NP1 style battery so the entire unit is self contained. The Tobin uses a standard 12volt 4 pin XLR connector.... so any 12volt juice is good. It takes NO POWER and can chug away for hours and hours. This motor only works because the Konvas and some Bolexes have a 1:1 drive shaft on the side of the camera. Each one rotation of the shaft exposes one frame... same in both cameras.
The tobin motor spins opposite to the way the Konvas wants but you just have to reverse the leads on the motor -- you don't even have to take it apart and it will spin correctly. The Tobin easily has enough torque to drive the Konvas and pull some primo stock through the camera. She'll even run comfortably for hours at -20 degrees Celsius. (that's below zero F.)
mmmm...35 time lapses... there is absolutely nothing finer. (certain activities excluded naturally).
His musings on the technical side of using a 2M with an intervolameter:
I've just had a beer and with your indulgence hatch some fresh theories about time lapse fogging from mirror shutters. Thought I'd break the problem down into three chunks and then do some tests on the tricky guesses.
Instances where fogging would not be a problem at all.. Any situation where the shutter speed is very close to the duration. So for instance a 4 second exposure in a five second duration would be more than fine. This would apply to Night or other long open shutter exposures. In the real world the camera shutter does actually spend more time closed than open when shooting at cine speeds so this would be no different.
The fogging levels will turn out to be primarily a ratio between the length of exposure and how long the camera must sit in standby mode collecting fog. If it's a good ratio the fog will be non existent, a halfway decent ratio will be correctable in the transfer. A nasty ratio would be a situation with a 4 minute duration and a 1/50 second exposure --- it would definitely touch the fog.
Personally I've found that most of the exciting day time lapses can be had between 1-10 seconds per frame. Time lapses that use durations much over 60 seconds are actually kind of rare. Even stars look great at 60secs and that's with a long shutter anyway.
The Tobin uses a 1/2 second exposure as it's shortest shutter speed which as it turns out really helps with the fog issue. It puts a lot of light on the film as a "I'm here first fog protection scheme" so even if the camera is going with a 16 second interval between frames that's only about 5 stops different. If you contrast this to an animation use where there would be lots of time to accumulate the fogging followed by a quick exposure not nearly bright enough to overcome the contamination.
I'll do some tests this weekend and try to figure out what the envelope is for the Mid and nasty zones and let you guys know. but if I was a betting man, and I am, I think that the Tobin Mod will turn out to be useful 9 times out of ten. I hopped over to the Norris Intervalometer site and they recommend using a capping shutter for any exposure duration over 10 seconds on an Arri. This is probably a safe interim number for us as well.
FYI technical spew:
I took some quick measurements with my Konvas 2M. Using a Dedolight I was able to get 1200foot candles of light through the lens and through the gate with the shutter open. When the mirror swings in front of the gate in a darkened room I can visibly see some light seeping in around the grand exposure hole but it's not bright enough to get a reading? which means that it's under .1fc. So worst case scenario it's only a 13 stop difference between open and closed shutter. (but I'll bet it's better than that) Does anybody know if there are real stats for this?