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Old December 22nd, 2005, 04:31 AM   #1
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light metre for hdv

can anyne tell me how to use a light meter with hdv. For example I have the hd100. When I take a light reading I am suppossed to enter the film speed and the meter tells me my f. stop (I think). What i'd lik eto know is what film speed do I enter or do I need some kind of special light metre.

Thanks Greg Corke

P.S. can anyone reccomend a good meter for this purpose
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Old December 22nd, 2005, 04:51 AM   #2
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I wouldn't bother with a light meter as the camera's built in one should be perfectly adequate. Of course it's a reflected light meter which means it's easily fooled by large areas of light or dark, but you can overcome that by metering off a standard grey card. If you use a grey card it's almost as good as using an incident light meter, and should stop you over exposing in the woods and under exposing in the snow.

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Old December 22nd, 2005, 08:49 AM   #3
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Quote:
Originally Posted by Greg Corke
can anyne tell me how to use a light meter with hdv. For example I have the hd100. When I take a light reading I am suppossed to enter the film speed and the meter tells me my f. stop (I think). What i'd lik eto know is what film speed do I enter or do I need some kind of special light metre.

Thanks Greg Corke

P.S. can anyone reccomend a good meter for this purpose
There's nothing special about HD that makes light get measured differently. Whether you're shooting video, film, or stills, a light meter is a light meter. I'm a big fan of Gossen meters but there are a number of good one's out there. If you want to use one, spend some time experimenting to come up with an effective film speed equivalent for your various camera settings. Where the meter will be most useful is probably not so much in setting the camera's exposure but in setting lighting ratios where you're working in a controlled situation. OF course with video, unlike film or still, you can get much of the same information just by eyeballing in the viewfinder or monitor prior to rolling.
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Old December 22nd, 2005, 09:40 AM   #4
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Greg,

If you are trying to find out what the ASA for your camera is. Light a gray card, allow the camera to auto-expose the card to 50IRE, and note the F-stop it is using. Then take a reading on the card with your light meter, and adjust the ASA setting until the F-stop readout on the meter matches what the camera came up with. That's your ASA.

However, I know in another discussion (possibly on another board), people couldn't get a fix with one of the new HD cams. It varied across the range of F-stops in the camera. So, depending on how brightly you illuminate the card in the first step, you'll get a different reading. Not sure if that was the HD100 or not. Try the calibration illuminating the card at least two different levels and see if you get a consistent ASA.

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Old December 22nd, 2005, 10:10 AM   #5
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Originally Posted by Joshua Provost
...
However, I know in another discussion (possibly on another board), people couldn't get a fix with one of the new HD cams. It varied across the range of F-stops in the camera. ...

Josh
Could that be caused by some exposure automation being turned on in the camera?
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Old December 22nd, 2005, 02:35 PM   #6
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Yeh, definitely. Something was going on with the A/D or DSP in the camera, where the iris and sensitivity just wasn't linear.

I found the thread. Looks like this is the behavior in the HD100 and the DVX100.
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Old December 23rd, 2005, 01:10 AM   #7
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Also, the lenses are not necessarily calibrated accurately enough that you can rely on the markings.
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Old December 23rd, 2005, 02:51 AM   #8
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That's very true Charles. The marked maximum apertures are mathematically calculated, they're not T stops (True Transmission). And the aperture values as they appear in viewfinder readouts are only ever to the nearest half stop.

I makes a lot of folk think their lens hangs onto f/1.6 for some way into the zoom but of course it doesn't. The speed starts dropping immediately uou leave wide angle, it's just the display that's taking its time to display the next nearest half stop figure.

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Old December 26th, 2005, 11:44 AM   #9
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"However, I know in another discussion (possibly on another board), people couldn't get a fix with one of the new HD cams. It varied across the range of F-stops in the camera."

This is true of any video camera. Video cameras do not have very linear MTFs across the exposure range so if you try this trick outdoors, then do it at a different f-stop indoors your camera will register two completely different exposure indexes (EI). Video cameras are not measured in ASA so it would be incorrect to use that term. Exposure index (EI) would be more correct. You could get an estimate for proper exposure index at any one f-stop but that will not mean it will be as accurate once you go a few F-stops higher or lower. And HD cameras are no different than standard definition cameras so there would be nothing special to do and special result that would occur. Only with a chip chart and waveform can one get a more accurate reading and measurement translation for a light meter. ANd even then some interpretation must be done by the user.


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Old December 31st, 2005, 08:23 PM   #10
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You'd probably be better off hauling out a carefully set-up production monitor and checking your exposure and image quality directly off the screen.

Light meters were originally intended for film work where it would be impossible to predict the results without careful measurements prior to tripping the shutter. You might be able to determine if your general exposure is close but you won't be able to tell if you've blown any highlights within the entire scene.

With video you can get immediate feedback, seeing precisely what you'd get as a final product, provided you use an accurate monitor and view it under reasonable conditions.
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Old February 13th, 2008, 01:30 AM   #11
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Any recommendations for such a monitor? THANKS!
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Old February 13th, 2008, 01:44 AM   #12
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Since you have the HD100 here is a thread about ASA for that camera, with posts by some experts with the camera:
http://www.dvinfo.net/conf/showthrea...&highlight=ASA

Similar comments to what are made here are made there, but there are also specific ASA numbers used by some people in defined situations.

Here's another thread:
http://www.dvinfo.net/conf/showthrea...&highlight=ASA

If you go to the HD100 forum and just search for ASA you will get a lot of information and comments about people's experience with ASA and light meters.
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Old February 13th, 2008, 08:07 AM   #13
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Quote:
Originally Posted by Dean Sensui View Post
You'd probably be better off hauling out a carefully set-up production monitor and checking your exposure and image quality directly off the screen.

Light meters were originally intended for film work where it would be impossible to predict the results without careful measurements prior to tripping the shutter. You might be able to determine if your general exposure is close but you won't be able to tell if you've blown any highlights within the entire scene.

With video you can get immediate feedback, seeing precisely what you'd get as a final product, provided you use an accurate monitor and view it under reasonable conditions.
While a properly setup video monitor along with a waveform monitor & vectorscope are invaluable tools, I still find that the first two tools I use on a set or location shoot are my light meter and color temp meter.
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Old February 13th, 2008, 09:04 PM   #14
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well back in the days of Sony D-30's I could light with my meter, and then iris the cameras when they came into the studio and be within a 1/2 stop of ideal between what I metered and what worked on the monitor. what I used the light meter for was balancing all the keys out to within .1 stops ( dimmers :) ). the video engineer's loved me because they didn't have to ride iris on a show :) set it and forget it.

the new camera's with all sorts of DSP now though change so much that a light meter is pretty much useless for setting exposure because of how they fiddle with the incoming light. then go and adjust the gamma curve and knee point and you are back in new territory again. the HD100 can vary from maybe ISO 100 to maybe 500 depending on the scene setup.

I still use a light meter when doing chroma key work. basically I want the FG light level to match the BG light level and that the BG is lit evenly to within .1 stop. useless for setting camera iris though.
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Old February 14th, 2008, 06:52 PM   #15
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Quote:
Originally Posted by Steve Oakley View Post
what I used the light meter for was balancing all the keys out to within .1 stops ( dimmers :) ).
I'm also using a light meter in our studio to adjust key and fill intensity in the sets. I basically go from chair to chair in a talk set and check the intensity of the keys and fills to get all the positions to the same level (key1=key2..., fill1=fill2...).
I'm using a digital Minolta lightmeter and I just set it to the standard setting: 100ASA. There's a table in the manual where you can look up the according lux values in this 100ASA setting but I don't do that because all I need is the differences between positions (or, the lack thereof)

The f-stop is much more easily adjusted using a monitor and a waveform monitor.
An eng camera like the HD100 has zebras to help you with correct exposure, you can set them from 70-100% usually, each having it's own benefits. 70% is pretty good for the brightest parts of a caucasian skin tone, good setting for talking heads set-ups. 100% shows what parts of the frame are beginning to blow out. Some cameras like the good old DXC-D30 are able to show both zebras at once, but the HD100 isn't, as far as I know. However, with what you see in the viewfinder and one of the zebra settings (or cycling between them) you can achieve a pretty good exposure real quick, no need for a light meter.

Quote:
Originally Posted by Steve Oakley View Post
the new camera's with all sorts of DSP now though change so much that a light meter is pretty much useless for setting exposure because of how they fiddle with the incoming light. then go and adjust the gamma curve and knee point and you are back in new territory again. the HD100 can vary from maybe ISO 100 to maybe 500 depending on the scene setup.
Studio cameras are usually still set to straight manual with no knee or other auto-functions. We recently worked with some guys with an eng truck who had all new DXC-D55 cams with full digital ccu's and their video engineer adjusted everything just like I learned it a few years ago (as far as I could see)

Last edited by Heiko Saele; February 14th, 2008 at 07:34 PM.
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