View Full Version : ISO for Canon XL1?


film8ker
03-18-2004, 06:13 PM
Hey hey. Just got a light meter, and I was wondering, does anyone know the effective iso of a Canon XL1 (not XL1s)?

Shot Renegade
03-19-2004, 04:16 AM
Hey Film8ker... take a look at the following link:

http://www.dvinfo.net/canon/articles/article75.htm

I think it says everything about XL1 iso typethings!

All very radical!

film8ker
03-19-2004, 05:40 PM
good article. I especially like this quote, "Bigger numbers mean there is less light reaching the sensor (f/11, f/16, f/22) and smaller numbers mean there is less light reaching the sensor (f/5.6, f/4, f/2)."

While this has some interesting ideas, the article prompted me to look through my ACC Video Manual (all I have is the second edition which is a little outdated, I don’t know if the new third edition has any other useful information) and I found the most concise answer to my question, and I thought I’d share it in case anyone else is interested.

Direct quote from page 147, “How to Establish an Exposure Index for a Video Camera by Harry Mathias. . . . Establishing an exposure index (EI) allows a light meter to be used meaningfully with a video camera. Assuming the camera is on a lighted chip chart and a waveform monitor is available, the procedure takes only a few minutes.
First open the iris until the crossover chip is at 55IRE units on the waveform monitor or the peak white chip is at 100. Check the f-stop on the lens, then take a reading with an incident meter at the chip chart. The photosphere on the meter should be pointed towards the camera. Change the slide on the meter until the f-stop reading on the meter coincides with the f-stop at which the lens is set. Once you have found the slide that results in the closest approximation to the f-stop on the lens, you have determined the effective exposure index of the camera. You need only keep that slide in the meter and use it as you would with the film.
Changing the gain boost setting, however, will alter the correct exposure index. If you want to know the camera E.I. at the +6db gain setting, for example, you must repeat the process with the +6db gain boost switched on.”

If you want to know what a “chip chart” is, (http://www.kozco.com/calibrat/gray3.html) but don’t try to print one out because the colors won’t be right. I couldn’t find any companies around me that rent (or would let me use one for 10 minutes) a waveform monitor, so I have a friend who works at a local TV station who’s going to let me come in and use one of their monitors and chip charts.

film8ker
05-27-2004, 10:14 PM
In case there is any other folks out there who want to use a light meter, I have calibrated my meter to my camera. I have a XL1a, and a Sekonic Multimaster L-408 with incident and spot metering. I set up the calibration in my office with a Colortran Minibroad, a 100% IRE white card (I got it when I bought some warmcards – they are all white on the back) and a 18% grey card. These are the same values for the white chip and crossover chip on a chip chart. I hooked up my XL to my Leader monitor/waveform monitor (LVM-5863A which I highly recommend). I set the light up so the camera was at F2.8, and the white read 100 IRE on the waveform. The 18% was hitting right on the 55 IRE line. I took a spot reading of the grey card with the meter set to aperture priority for 30 fps and ISO 400. It gave me a really high F stop, so I changed to ISO down until the F was close to 2.8. I then took another reading and adjusted the ISO until it read exactly 2.8 (ISO=160, EV=9). I then took an incident reading and found the F was low. I adjusted the ISO to 200, and it was right on 2.8 again. Just to be sure, I did the test again at camera F4.0, 5.6, and 10 by moving the light closer to the cards. I found that as I got higher, the grey card wasn’t quite hitting at 55IRE like the lower Fs. This may be because I was moving one light so close to the cards in stead of adding a second light. Of course, this may be because I’m not using a chip chart and a chip’s chart’s grey might not be exactly the same IRE as a Kodak Grey card 18%. The spot meter seemed to be right on at ISO 160 every time, but the incident seemed to be right on the cusp of ISO 200 and 250.

Just for S&G, I wanted to see what the F for the 100 was on the spot, so I could have a rough gauge for what the cutoff was for a bright spot, and it grew as the camera F grew. For instance, I set the camera at F2.8, and the spot read 2.8 @160 on the grey, and the incident read 2.8 @200, and the spot read 5.6 @100IRE. The EV was 11. When I increased it to F4.0, the spot and incident for the 18% stayed true, but the spot for the 100 read 8.0. The EV was 11. When I did F5.6, again the settings for the 18 stayed true, but the spot for the 100 was F11, EV=13.

Now, I expected the 100 IRE reading to stay consistent like the grey card reading, does anyone know why it grew? Also, does anyone know why the EV did not change from 11 on F2.8 to 4.0, but increased to 13 on F5.6?