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Rate the ISO of HD111


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#1 Sivanesan

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Posted 17 December 2007 - 03:01 AM

Hi All,

I am about to Shoot with this JVC GY-HD111E.
http://www.jvcpro.co...?item=GY-HD111E

I would like to know what is the ASA for this Camera at the following Condition:

FPS 25
Gain 0 DB
Shutter Speed 1/50
ND ilter NO

Also i would like to know stop compensation for increase in DB.

The camera specication says
Sensitivity : F8, 2000 lx


2000 lux = 185.8 FC

This gives me roughly 400 ASA at the following setting :

Light 2000 Lux
Shutter Angel 180
FPS 25

Is my rating is correct?
what is the exposure compensation for increase or decrease in DB?

Regards
Siva
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#2 Adrian Sierkowski

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Posted 17 December 2007 - 10:21 AM

from my experience you really can't rate the "asa" of a video camera. it'll vary depending on a lot of things. Your best bet to get close would just be to expose a greycard to your liking on a monitor, and then meter that. fiddle with ASA on the meter until it matches with the F stop you're reading from your camera.

For example, the HVX "rates," at about a 250 asa. But, often i'll have to rate my meter @160 to get what the HVX sees, and other times I'll be rated at 320. It depends on what's in the scene (with 80% zebra on white spots.)
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#3 Sivanesan

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Posted 18 December 2007 - 02:59 AM

thanx for the reply adrian,

yes ofcourse like u said it varied a lot........ i was very confused while metering and comparing........
although i checked it with close shot only....... to get a proper skin tone in various light conditions like:

full Shadow
Shadow in Foreground
full top light
direct sunlight

im very confused........ it was not reacting well with exposure marks in the lens.....

finally i think i should rely only on monitor....... that is tweak the exposure ring till i get the right one.


ANY HELP ON exposure Compensation of DB (+ or -)
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#4 Michael Nash

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Posted 18 December 2007 - 04:25 AM

Every 6dB gain = approximately one stop
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#5 Andrew Koch

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Posted 18 December 2007 - 05:08 AM

The ASA constantly seams to be slightly to sometimes significantly different depending on shooting situations. The only way to really know where you are at is to use a waveform monitor to figure out where your exposures are. If you are like me and still like to use a lightmeter, you can use the waveform to figure out the ASA. After your white balance has been set, expose a greycard and adjust the camera's exposure until the card reads at 50 IRE on the waveform. I think some people like to set middle grey to 40. Anyone on the forum with a lot of experience with this, I would love to hear your info on this. (The DIT I talked to about this said it should usually be 50). Take a reading with your meter, then adjust the ASA of your meter until you have the same T-Stop on your meter as the one on the camera. That is APPROXIMATELY the ASA/ISO of your camera. I use the word APPROXIMATELY because there are other variables. I don't know particularly about your particular camera, but this issue has come up for me several times. What I am about to say is not necessarily about this camera in particular but still something worth thinking about. If you are shooting for a film out and are trying to have as much latitude as possible for more options with color grading, then the IRE settings are going to be different than if you are shooting high contrast with the intent of going straight to tape with no correction whatsoever (two extremes). Basically what I am saying is that once you know the approximate ISO, don't rely solely on the light meter. You still should check the waveform and field monitor as well. I am saying this because I have been guilty of some of these mistakes and I hope that by admitting to them that others won't have to endure the same pain and embarrassment.

Sometimes, it can be too difficult or expensive to get a waveform monitor. The solution to this is the DVRack software. It gives you a bunch of monitors and scope that you can view on a computer.

If you already know this info about waveform monitors, then please ignore the post, but if not, I hope this helps
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#6 Sivanesan

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Posted 18 December 2007 - 06:37 AM

thank u nash for the DB....

Hi Andrew,

i do not hv acess to waveform monitor. I will be using a computer monitor (with a tv tuner box to convert VGA to composite or S-video). The DVRack is now shifted to Adobe premeier CS3. Although we have acess to Adobe premeier CS3, i dont't want to go that because of the short Firewire cable and also i have to use to my laptop. The LCD will most of the time give wrong colour info, particulary black and shadows.

Regards
Siva
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