Hello, all:

Does anyone have any idea as to what the ASA/ISO equivalent
would be for the XL1s. In other words, if I wanted to use a light
meter to meter my subject, what ASA film speed would I choose?

Any help would be greatly appreciated.

Thanks.

Looking Glass

See the XL1 Watchdog at www.dvinfo.net/xl1.htm -- go to Articles Menu > Camera Head. There are two articles discussing ASA for XL1. I guess the real question is, how much does this change for the XL1S. Any takers?

As I've tried to determine the exposure index of my XL1s, I've read suggestion after suggestion on how to accomplish this (including that on the Watchdog site). As I've attempted this, it seems to vary under different lighting conditions. This is all being done without the benefit of a waveform monitor. Also, it depends upon the initial ASA setting on the light meter selected prior to the test. This has been my experience, anyway. There's an excellent chance I'm doing something wrong,too!

In my own tests, the XL1s has an ASA rating of 160.I should note, however, that this will hold for proper exposure in sunlight. Over/under exposure in less than ideal conditions and the ASA rating will not be 160. The in-camera lightmeter has a different responsivity curve than a still camera light meter.

Bill,

Your results are very close to result I get most often, that's an ASA 200.

Bill,

Why do you feel the XL1's internal meter has a different response curve? I'm going to run some tests in the next day or 2 and I'm trying to get different peoples ideas. I've read the articles here as a starter, but this subject has me intrigued.

Jeff

Jeff...

I've tried using a light meter, myself, for certain off-ideal lighting conditions and continue to have a problem if I don't double check it against the in camera meter. I read an article explaining that a video CCD has a different responsivity to light than film, accordingly, the light meter is designed to match. One must take caution when using a light meter designed for film on a CCD based device.

Bill,

In your last post, you said that an article stated, "...a video CCD has a different responsivity to light than film..." While that's true, all light meters are calibrated to properly render the 18% grey at the suggested exposure. The 18% grey is what it is, regardless of the medium recording it, isn't that true?

I don't understand what the difference in light meters would make.

Here's my ideas on running the tests. I'll use my Lux meter to actually measure the light levels falling on the 18% gray card. I will meter of the grey card with the XL1, XL1s, Nikon F5 and Seconic handheld meter in both incident and reflected mode. The measurments can be done in 5 or 6 different light levels as measured by the lux meter. The shutter speeds will all be set for 1/60 of a second. This will give me baseline data. But I'm not sure yet the best way to compare or plot the data. Any thoughts?

Jeff

Good dog....

Indeed, you're right....an 18% grey is used to determing correct exposure. However, that's just a design point. One point does not a curve make. There are off design conditions, as well...i.e. under/over exposure. While the meter is always right at a theoretically "perfect" exposure level, it falls down if you're intentionally over/under exposing.

Bill,

I still don't understand your point. We weren't talking about over/under exposure. We were talking about light meters responding differently and determing the exposure index of the camera. . . I thought.

well, if all you're interested in is using a light meter to determine a technically correct exposure, then none of this matters to you. If on the other hand you're doing some creative exposures, beware.

Bill,

I stand corrected. I went back and re-read your post and you stated, "...for certain off-ideal lighting conditions..." My bad, sorry!

NP.....;O)
Good luck!!

I'm not trying to put words in Bill's mouth but I think I understand his point. Film has a relatively linear response under most lighting conditions. But film is subject to reciprocity failure. It just doesn't occur under most lighting situations. For example in very low light the meter reads F2@60 seconds, but the correct exposure for the film is F2@120 seconds. Why? In low light the response curve of the film changes. The same must be true for CCD, except it occurs in more typical lighting situations.

Jeff

You're right on, Jeff. CCD's have much less "latitude" than film. That's why they blow out the highlights and muddy up the shadows so much more easily than film. Off of ideal exposure, we pay the price. In any given scene, the range of light to dark values may exceed the CCD's ability to respond linearly. That is to say a CCD is not as forgiving of contrasty scene conditions as film.

The contrast range could be measured too, using a grey scale like in the Zone System. I did all this 20 years ago when I shot out West with my 4x5. I don't know if I have a good grey scale any more, but I still have my densitometer. This might turn into a real challenge. This will take some thinking.

Jeff

The major reason for use of light meters with film is that there is no instant feedback to judge exposure. The video camera gives real time feedback as to exposure on the monitor or viewfinder. Zebra helps judge highlight exposure.

Thus a light meter is mostly useful for judging set lighting (e.g., lighting uniformity) before the videocamera arrives.

The 18% gray card means that no reflected (short of a mirror-like reflection of a lamp) highlight will be more than about 2.5 stops brighter (100% reflectance). This concept works well with the way film speed is rated and the typical exposure latitude of film.

Because CCD's have a different response (exposure latitude if you will) than film, the 18% setpoint for exposure will not yield the same relationahip between shadow and highlight detail and the primary items of interest in the scene (the reference to blownout highlights and muddy shadows).

Also, when playing wiht light meter readings, keep in mind that as processing is also a factor in film speed so gain is with video. With video 'gain' corresponds to push (or pull) processing. So check your gain setting as wellas the aperture and shutter speed. 6 dB of gain corresponds to a stop of push processing.

I'm sure i could amass a large amount of data but to what point would it be useful. Whenever possible, I try to use a waveform/vectorscope. It tells me a whole lot more than a simple light meter does. However, when I'm in the field a waveform/vectorscope isn't feasible. I depend on the zebra pattern now to aid in exposure (and 20 years experience in the field). But at times, I miss, and end up with shadows crushed or worse, highlights blown out. it would be nice to spot meter a highlight and accurately place it in a zone. But i don't think that's going to happen.

Jeff

Jeff...

For awhile, I tried using the Zone System. I found that my outside, naturally lit scenes changed too rapidly. The system works well indoors when setting up lighting, however. Indeed, the best overall system is the zebra display, I set mine to 90% which gives me about 10% headroom. When I get to my NLE, I might "tweak" certain selected groups of frames using a signal analyzer. Generally, correcting overexposed scenes works better than correcting underexposed scenes. Expose for the highlights and let the shadows fall where they may.