TRUE ASA rating for DVX100a

crazymcnutjob

crazymcnutjob

Active member
hi, I know this has been brought up before but I can't find it anywhere on these forums. I was wondering what the true ASA rating for the DVX100a (on 24p) was, I've heard something like 620, but others say it's somewhere between 320-400, and I'm getting really confused as to which one is really true. Please help me out! thanks!
 
There is not an answer. Video does not expose linearly, it responds differently depending on how much light is available. So the answer is usually 640, but under different lighting conditions the answer will be 400, and other under lighting conditions it could be 800 or 1000.

In other words, don't try to equate it to a specific ASA, because it doesn't respond in a linear fashion. There is no one "right" answer. It all depends on the amount of light entering the chips.
 
Barry_Green said:
There is not an answer. Video does not expose linearly, it responds differently depending on how much light is available. So the answer is usually 640, but under different lighting conditions the answer will be 400, and other under lighting conditions it could be 800 or 1000.

In other words, don't try to equate it to a specific ASA, because it doesn't respond in a linear fashion. There is no one "right" answer. It all depends on the amount of light entering the chips.
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Hey, I'm sure you hear this all the time, but you wrote a great book. You really managed to keep it both interesting and informative....that's all :)
 
And don't use the term ASA. There is no such thing as ASA for video. Exposure index EI is the correct term.
 
Yes they mean the same thing but the term ASA (American Standards Association) is a still film term and if you wanted to be technically correct you'd be more accurate to use EI (exposure index) as we do with motion picture film.
 
I'm well aware that ASA doesn't apply to video (hence: FILM speed, not 'video' speed). I didn't wanna say EI because light/spot meters adjust accordingly to ASA. Taylor - I guess you can't, your meter is the LCD screen because what you see is what you get. I was interested in spot metering with the DVX which is why I wanted to know it's ASA equivilent.
 
Barry_Green said:
There is not an answer. Video does not expose linearly, it responds differently depending on how much light is available. So the answer is usually 640, but under different lighting conditions the answer will be 400, and other under lighting conditions it could be 800 or 1000.

Could you expound on the different lighting conditions that alter the EI? I've read rather complex formulas using waveform monitors and gray cards for determining the effective rating. Under what situations might those methods be useful?
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Here's my 2 cents: I have found that at f stops between f4 and f5.6 (no gain), the DVX has a comparable ASA of 500. When I light, I put the 500 ASA slide in my Spectra Pro and light up the set so I can set my aperture between f4 and f5.6. Plus, this setting keeps critical focus off of the front element, thereby getting rid of all of those little specks of dust with the camera's huge depth of field. ASA 640 also works, but it made images about a half stop dark for my taste (in that exposure range). To Barry's point, however, when I ventured outside of those apertures, the ASA would change.
 
crazymcnutjob said:
I'm well aware that ASA doesn't apply to video (hence: FILM speed, not 'video' speed). I didn't wanna say EI because light/spot meters adjust accordingly to ASA. Taylor - I guess you can't, your meter is the LCD screen because what you see is what you get. I was interested in spot metering with the DVX which is why I wanted to know it's ASA equivilent.
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This is a kind of unrelated point and un-technical point, but for the other less-than-consummate-professional video guys/gals out there (like me), I discovered the hard way that the LCD is not your meter! The factory brightness on the LCD is IMO set deceptively high. A few hours of run and gun doc shooting taught me that judging exposure by the LCD was giving me underexposed footage. I was used to regular visits to Video Village complete with production monitors, etc. The viewfinder is a better judge of exposure, but I eventually lowered the LCD brightness settings to get them to be a better estimation of exposure. For what it's worth.
 
The LCD is not your meter. The ZEBRAS are your meter. If you're not using zebras to monitor your exposure, then you're flying blind and probably getting worse video than you otherwise would.

Don't even try using a light meter with video. Video doesn't respond linearly, it's all up to the gamma curve that you're using. If you change your gamma curve (and nothing else, just the gamma curve) you'll change your perceived ISO from 640 down to maybe 400. And you'll change your shadow response, and your highlight response.

Then, factor in that the light performance does NOT perform linearly at the most-open iris settings. A stop = a stop up to about f/2.4, but above there you can't count on a linear response. Opening up to f/1.6 doesn't result in 1.3 stops more light coming in, it results in a little more light coming in. That has to do (apparently) with the way the microlens works on each CCD pixel, or (more conspiracy-theorist) with the notion that maybe the lens isn't truly f/1.6, and the marketing department just marked it optimistically?

Either way, it doesn't matter: the light response isn't mathematically linear, so you can't count on that.

Ditch the light meter, learn to use your zebras. A waveform monitor is the ultimate tool for working with a video image to determine proper exposure, and zebras are the quick 'n' dirty substitute for having a true waveform monitor.
 
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