View Full Version : Canon XL1s and Spectra Light Meter


VPTurner
02-23-2008, 10:49 AM
I combined my XL1s setup with a Spectra Cine Pro IV-A meter to get more accurate control over light balance and exposure, but I can't seem to find a comprehensive breakdown of the ISO ratings for the camera at various gain settings.

During experimentation, at 1/60 shutter, zero gain, and the in-camera meter dead center, the Spectra (set at 30fps) showed the same F/stop as the camera while it was set to ISO 400. But I read elsewhere that the XL1s supposedly only has an ISO of 160 at zero gain. Of course, this may just be a difference between measuring at the subject versus the average of all light entering the camera lens. There was sunlight in the background that was blocked by the meter.

Has anyone tried the full range of experiments with the Canon XL series to accurately identify the ISO ratings? My first project was horribly underexposed. That will not happen again. I just need to know what to set on the meter for the ISO.

Thanks!

Edit: I just realized I had the circular polarizer on the lens and may have also had one of the ND filters set. I'll lose some light with those. That could explain the disparity. But I'd still like to find a chart if one exists. If not, I guess I'll just have to make one.

oakstreetphotovideo
02-23-2008, 11:17 AM
Find an 18% gray card (or make one), point your camera at that for setting the camera, then meter the light hitting the card, and your readings should align closely. One good way to get around a light meter, is to carry an 18% gray card and use that to set your camera. I don't do that, because the dynamic range of most scenes exceeds the range of the CCD, so I generally have to favor the highlights at the expense of shadows. 18% gray would center the exposure and there would probably be some blown out highlights in a HDR scene.

A technique I use shooting in wooded scenes where shadows are important, but I still may need some compromise, is to zoom into a shadowy area and set the aperature to give me just a little detail in the darkest shadows. Then I pull back and see where that leaves my highlights and if I can live with it, I go with that. If not, I'll darken slightly, knowing I'm losing subtle shadow detail, but also knowing that life is all about compromises! ;)

VPTurner
02-23-2008, 08:21 PM
Thanks for the feedback. The whole idea behind getting familiar with the light meter and not relying on the in-camera meter is to prepare myself for film cameras.

I'll get an 18% gray card and make some comparisons.

oakstreetphotovideo
02-23-2008, 08:50 PM
You are right that the meter is the only way for film. The good news is that film has a couple stops more latitude than video, and it's more forgiving in that it doesn't just clip at the ends of the exposure curve. You'll also be able to get 36 bits/pixel RGB and 4:4:4 color sampling. That would be sweet.

VPTurner
02-24-2008, 11:56 PM
I did some more digging tonight, and I believe I found what I was after:

Bill Pryor: You can use a standard gray bounce card to get a reading. Light it, zoom in and adjust aperture till you see the zebra pattern in your viewfinder. Let's say that it comes out to a f/5.6. Take a reading with your light meter and adjust it so you make it read at f/5.6 under the same conditions.

D. Gary Grady: The problem with that is the zebras indicate overexposure (brightness of 95 IRE or more), or roughly caucasian skin tone (70 IRE or over), not the middle of the exposure range which is what the light meter is going for. A better bet would be to set the camera shutter speed for 1/60 (or 1/50 for PAL) and use Shutter Priority automatic exposure (Tv mode in the XL1). Note which f-stop the camera uses, then find an ASA setting on the light meter that gives you the same exposure.

There are people who question the utility of using a light meter for videography anyway. Using it for setting exposure is certainly questionable. You're better off using viewfinder zebras to avoid any areas of overexposure (a few small highlights are okay), and then fill in to bring up the shadow areas.

Rather than use a light meter to determine image exposure, in video a better application is to use it when lighting a set. Periodically, someone will complain that it's a pain to have the camera shut down in standby mode while in the middle of setting up lights, because they want to check exposure with the camera. People coming from a film background chuckle at this, especially when the same video people insist that there is no possible application for a light meter in shooting video.

If you use a light meter (preferably an incident meter or a spot meter) for that, then you don't really care about the ASA equivalent of the camera... only its dynamic range in stops.

Finally, it's useful to read some basic information about the zone system -- not the darkroom part, but the basic ideas of mapping different brightness levels in front of the lens to brightness levels in the captured image. Once those ideas are understood, a lot of questions suddenly answer themselves.

Armed with all of this wonderful information from both you and elsewere on the web, it's off to the camera store to add an 18% gray card to my kit and do further study on the Zone System.

I made a trip to Ikea today and added some paper lanterns to my stash. Next stop on the lighting scavenger hunt is Home Depot to get ceramic light sockets and 200W bulbs for the lanterns.

knightly
02-25-2008, 04:45 PM
Please post what you learn about the zone system (or if someone else could post on it, that'd be spiffy too). I've been trying to figure it out, but it seems to be presented in ways that don't come across easily to me. Or perhaps, I'm just easily confused.

oakstreetphotovideo
02-25-2008, 05:26 PM
I am an Ansel Adams study. The zone system was the system I used to create my best black and white photos back in the day. It works on the premise that you can divide your image into 10 zones of luminance. The system was designed for computing optimum exposure to get shadow and highlight detail, and compute developing time to match the film latitude to the exposure latitude of the shot.

In any case, you could compute your exposure for shadow detail, then push or pull your film in processing to put the highlight detail exactly where you wanted it, as long as you had metered the objects you wanted in zone 10 (zero detail white, maximum negative density). Normal processing would yield 10 stops of dynamic range (1 for each zone). Your averaging light meter assumes the average luminance or a scene will land in zone 5, but this is seldom the case.

Since we don't develop each frame, or scene of our video to control the contrast it is hard to apply this to video. Furthermore, most video cameras don't have 10 stops of exposure latitude. If you did know the dynamic range of your camera's electronics, it may be useful to use something of a zone system to measure the range of luminance in your scene and adjust your lighting accordingly. It may also be possible that you could create a custom setup for shots with specific exposure ranges; assuming your camera has controls for it's gamma curve and dynamic range, so you could use the correct camera setup, based on the # of stops between the dark and bright areas of a specific scene.

In black and white, we also used color filters to darken or brighten certain elements in the photo, based on their color. e.g. To lighten green leaves you could use a green filter, which would have little effect on green and white, but would darken other colors, respectively. You'd use a red filter, generally with a polarizer, to darken the blue sky. etc.

We are really pretty limited shooting color video, as we do not process to control dynamic range, and if we did, we'd have to separate each scene onto a different tape for different processing. Ansel shot exactly one image on a sheet of film. Each image was developed based on the subject and exposure. If you're not planning to do black and white stills on sheet film, or very shot rolls, a lot of this is just not relevant. I loved Ansel Adams, and I studied everything he published, but his techniques have limited applicability to my work today.

In black and white photography, the old adage was "expose for shadows and develop for highlights", but with video I'm afraid it's "expose for highlights and pray for your shadows".

Doug