ISO Rating for Movietube with HVX200

Christian

Christian

Member
Hello,

I'am going to shoot a short in 1 1/2 weeks. Today i've been to berlin, to have a look at the Movietube. What I saw there was both, good and bad. Though the Movietube delivers a stunning image quality, it takes almost 2 stops of light, plus the amount the lense consumes. With a given ISO of 250 - 300 from the raw HVX200 there isn't too much left. Round about 80 ISO or something like that.
Does anybody has a precise ISO Rating fpr the Movietube bundled together with the HVX200? Unfortunately they hadn't a waveformer, so I couldn't measure it.

greetz
Christian
 
You're right

You're right

I just used a movie tube & HVX combo and I pegged the ISO rating right at 80. I think you've got it right.
 
lighting package

lighting package

We shot a series of interviews for a television project here in NYC. I had some Alzo Digital soft boxes and a variety of tungsten lights. We picked a shot that had a large background with plenty of available light to put our interviewee into.
 
How do you go about rating the iso of the camera + 35mm adapter? What's the process?
 
You'll need an accurate light meter, and preferably a waveform monitor to connect to the camera

A way to ball park this measurement is to light an 18% gray card, to an arbitrary value.

Set a shot of the gray card up on the camera and look at a waveform. This obviously assumes you know how to read a waveform....
Or you can set your zebras to 50 percent in the VF. Or you can turn on the marker function and fill the box with the gray card and that will give a very accurate numerical value of the video level under the marker box.
Now their is some discussion as to what represents a proper exposure of a gray card, 50% is kind of a traditional video value, 40 to 42 percent is generally agreed as a exposure value for high end HD cameras.

Adjust iris so that you get 50 ire on the waveform or just a tickle of zebra starting to come in on the VF. Note your iris setting at this point. Now take a light reading, placing your meter in front of the gray card but as close to the plane of the card as possible. Shutter speed setting for the meter should be a nominal 180 degrees or double the frame rate, so that if you are shooting 24fps , your exposure would be 1/48. Double check the shutter setting on the camera to make sure it matches what you set on the light meter...
At this point you can adjust the ISO setting on the meter unit the f setting on the meter matches what you observed on the camera.
This will get you in the ball park with a more or less repeatable ISO setting.

Some Caveats: You don't want to get your iris reading from the camera if you are zoomed in all the way on the lens, virtually all zoom lenses exhibit fall off in sensitivity at the long end of the lens.

Your gamma setting will affect overall exposure. On an HVX there is a considerable exposure difference between cine like V and video gamma. You should spend time exploring gamma settings as they really do have an effect on exposure. Learn what effects they have. If you are shooting in a Low con situation, you might want to use a more contrasty gamma setting, or if you are in a high con situation, you could very well go the other way with the gamma to a low con setting.

The difference between 41% exposure and 50% exposure is almost a stop so you have to decide what you like in terms of how exposures for skin tones.
 
Ah, that makes perfect sense to me. Thanks so much Mark. Thanks for the tip on the zoom and gamma settings.

To clarify further, if I'm doing this with a 35mm adapter in front of the HVX, like the movie tube for instance, I'd set the 35mm lens wide open and adjust the aperture on the camera? or vice-versa?
 
Its a little more complicated, but I would set the lens on the camera to wide open, then set the taking lens on the movie tube or red rock or what have you to a stop that gets you to the 50% OR 40 % value on the grey card as described. Personally I find 40% ~ish caucasion skin tones on the the HVX to be in the right ball park. 50% is geting a litttle high but is still ok. It really depends on what the ultimate use is. If you are shooting dramatic stuff go lower, like with the 40% number & if you are shooting interview based material, go higher. Once you have established a base line ISO , you can go a head light scenes and meter set ups like you would for film and that will get you very close to where you need to be.

If you are shooting HD, you can use a flatter gamma knowing that you can always do a readjust of the gamma very easily in post and crank the contrast as desired. If you don't have a great viewing situation on the shoot, its safer to go this route, knowing you'll be able to readjust gamma at a later point under more controlled condtions.
Be more careful if you are shooting DV . Your post options are more touchy, and while you can still make adjustments, the range of adjustment is much more limited than with DVC pro 50 or DVC pro HD material.
 
Movietube sucks at least two stops. Used it on a video recently and it was a pain since the HVX isn't that sensitive to begin with. When I removed the Mtube it took me 2 stops plus on my camera's iris to get it back to the same exposure.

Also, I find the system is unacceptably soft.

Eitherway, test it before using it.
 
We did a test with the movietube last weekend on a soundstage. I calculated much more than two stops light loss. At 0dB the system is at ~20 ASA. You can push 3dB to get it to 30 ASA. Compared to a 320 ASA without the adaptor.
The image was very good though.
Another problem was that the distance markings on the lens would not work. To focus at 4 m I had to set the lens to 5m. I don't know if this was a problem of this unit or if this is a genenral problem. In our case this would mean that some poor assistant would have to recalibrate all the lenses in our kit.
We were using Zeiss HS lenses and they were slightly soft if the f-stop is below 2. If it's above 2.8 you start seeing the ground glass. So you only have a narrow range where you can use your lenses.
You will need a good 1st AC because you are going to be shooting at f/2 most of the times when inside.
 
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