HV20 exposure overide at DVinfo.net

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Old August 22nd, 2007, 04:25 PM   #1
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HV20 exposure overide

I have been experimenting with the HV 20 for a couple of days and have been using the exposure lock/miniSD card trick to get the shutter locked to 1/48.
My question, and I know I must be missing something obvious, so apologies in advance, how do I control exposure once I have locked the exposure setting? I know I do not want to increase gain, and if I unlock the expousre and adjust f-stops then I quickly lose the 1/48 shutter.

but I still feel like I am missing something quite basic.

I hope that this is at least somewhat clear, I know I was not incredibly articualte, but hopefully this will at least point someone in the direction of my basic question.

Thanks

Sam DeWitt
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Old August 22nd, 2007, 05:28 PM   #2
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The short answer is that there is no perfect thing that you can do. You can try to avoid using gain, though:

- If you've properly "exposed" the sensor using the light trick, then you should be able to bump the exposure a couple of stops without introducing gain.
- If you use Tv mode, the cam is gonna stay at 1/48th no matter what.
- If you use CINE mode the cam seems to try to stay at a 1/48th shutter, and it also tries to avoid using gain, and has a gamma curve more amiable to low light.
- If too much light is the issue, then ND filters are your friend.
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Old August 22nd, 2007, 05:38 PM   #3
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I am trying to stay with Cine mode (to get the flattest gamma curve I can).

It seems to me that in cine mode I lose the 1/48th rather quickly, and unless I am missing something from this video -

http://www.dvinfo.net/conf/showpost....0&postcount=20


- I am going to introduce gain if I increase exposure (that is open up the lens, or decrease the f-stop).

Are you saying to add external ND's, or let the cameras kick in? ( I am acting like I know that the camera has a built in ND. although that is another thing I am not clear on yet either).

Thanks very much for your reply.

Sam DeWitt

http://www.obtuse-ny.com




Quote:
Originally Posted by Joseph H. Moore View Post
The short answer is that there is no perfect thing that you can do. You can try to avoid using gain, though:

- If you've properly "exposed" the sensor using the light trick, then you should be able to bump the exposure a couple of stops without introducing gain.
- If you use Tv mode, the cam is gonna stay at 1/48th no matter what.
- If you use CINE mode the cam seems to try to stay at a 1/48th shutter, and it also tries to avoid using gain, and has a gamma curve more amiable to low light.
- If too much light is the issue, then ND filters are your friend.
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Old August 22nd, 2007, 05:47 PM   #4
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- You need to experiment with how bright of a light source you lock your exposure against, relative to the overall brightness of the scene you are shooting. I wish I could explain this better, but I confuse myself when I try to explain it! What I've ended-up doing is loading-up my iPhone with a handful of different images from 100% white down to 50% grey. The brighter the scene I'm shooting, the brighter the image I use for locking my exposure.

- I'm talking about external ND filters, since the camera's aren't directly accessible.

- Yes, CINE will drop out of 1/48th, but it seems to only do so when it can no longer adjust the aperture, and at that point, your image would be incorrectly exposed, so you probably need to try to do something else anyhow (adding or subtracting light from the scene.)

PS. I'm approaching this from a narrative filmmaking standpoint. If your goal is run'n'gun or ENG shooting, there's not much you can do to control lighting ... you're gonna get into situations where gain is unavoidable.
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Old August 22nd, 2007, 06:02 PM   #5
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OK - this is actually helping me understand.

So say I am in a controlled environment (interioir), I point at a bright light source, get my 1/48th and I lock my exposure.
Now when I frame up to the actual scene I am underexposed and if I unlock exposure and get a decent exposure that puts me out of 1/48th shutter, what is the recommended "fix".

PS - I am also approaching from a more or less narrative viewpoint, but more to get backplates to enhance with VFX work and extensive color correction, hence the desire for the flat gamma.

PPS - I am not using the "cell phone trick", or in your case the "iphone trick" (that sounds quite clever BTW), but am simply using the ability you get with a miniSD card installed that lets you check exposure and shutter speed at any time.
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Old August 22nd, 2007, 07:51 PM   #6
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Sam,
In that case, you locked the exposure to something too bright. You'd be stuck pushing the camera into gain because it had already closed down the aperture to try to control the overexposure of the bright light. You need to lock it to something that more closely matches the overall brightness of your scene. That's why the cellphone, iPod, iPhone, whatever hack works so well ... the brightness of those devices is much more inline with natural highlights within a scene.
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Old August 22nd, 2007, 08:57 PM   #7
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OK - with this knowledge is it safe to say that once the exposure has been locked, there is no other way to manipulate the camera without increasing gain (or adding ND in the case of overexposure, or adding more light if that is an option)?

Thanks

Sam
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Old August 22nd, 2007, 09:12 PM   #8
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No. The aperture should have some room to open before gain needs to be added.

If you see the f-stops going down (using the photo button) then you're not peobably not using gain.
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Old August 22nd, 2007, 09:45 PM   #9
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right, but you can not see the f-stops going down if the exposure is locked, correct?

Sam
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Old August 23rd, 2007, 07:24 AM   #10
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I don't have it in front of me, but I think you can see it as long as you're not actually recording. The exposure isn't so much "locked" as it is "manual from a baseline."
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Old August 23rd, 2007, 09:35 AM   #11
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I simply mean that once you have locked the exposure, you would have to unlock it to manually change it again, up or down.
The main thing I am trying to confirm is that there is not another way to adjust exposure, since you want to keep the shutter at 1/48.

Thanks again for all you replies.

Sam
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Old August 23rd, 2007, 10:00 AM   #12
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I'm not sure what you mean by "locked."

Once you're in manual exposure mode you can adjust from -11 to +11. The baseline "0" (shutter, aperture and gain) comes from what you exposed against when you went into manual mode.

You don't have exact control over what the camera does when you step-up and down, but if you're in Tv or CINE mode, you can probably get a few steps in each direction without ruining the shutter speed or engaging gain.
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Old August 23rd, 2007, 10:35 AM   #13
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By locked, I mean you push the joystick up to get to the manual exposure mode, find the exposure you want, then click the joystick "in" to lock it.
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Old August 23rd, 2007, 10:38 AM   #14
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Yes, that's the only way to manually adjust exposure.
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Old August 24th, 2007, 11:32 AM   #15
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Quote:
Originally Posted by Joseph H. Moore View Post
Yes, that's the only way to manually adjust exposure.
I noticed the exposure setting is not remembered when you turn off the camcorder. Is there a way to do this? I know there's brightness setting in custom mode. Would that be the same as exposure?
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