Is it a good idea to use a low gain dB ? at DVinfo.net

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Canon XH Series HDV Camcorders
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Old February 7th, 2008, 03:50 AM   #1
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Is it a good idea to use a low gain dB ?

I've been experimenting with manual gain dB comparing it to auto, but was wondering whether there's a negative side to using a low setting, something like -6dB apart from the change in exposure. Are there any known bad artifacts in using really low settings.

Hope its not a daft question.

Mark.
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Old February 7th, 2008, 05:19 AM   #2
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Gain(+) = Grain .
In Canonland -3db gain is the cleanest noise free equivalent of "0 db gain."
The Canon's 0db setting produce noise.

I have been shooting for more than a year on -3db for noise free pictures.
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Old February 7th, 2008, 06:38 AM   #3
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Do alot of people keep the gain at -3 regularily? I've been just assuming 0 was good enough - and -3 if you needed to cut some light in big sun after you've exhausted ND filters.

Would -3 gain add any artificial smoothing?
Trish

Last edited by Trish Kerr; February 7th, 2008 at 07:55 AM.
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Old February 7th, 2008, 07:59 AM   #4
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The lower the better but i have shot +6 @ night and no problems, if your final output is dvd you will be fine.
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Old February 7th, 2008, 08:50 AM   #5
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One thing to keep in mind is that the nominal 0 dB setting is typically the manufacturers best compromise setting considering dynamic range (of the CCD), noise, linearity, sensitivity, etc.

Increasing gain increases gain-sensitive noise/grain in the image, and decreasing gain will result in less noise in the image. But there can be other artifacts as well. Decreasing gain requires more light hitting the CCD for the same image brightness, and pushes the highlights in the image closer to the saturation point of the CCD pixels. For example, the image may be somewhat more likely to develop vertical smear from hot spots in the image at a low gain setting.

Some shooters prefer -3 dB setting for minimum noise for their work. Some shooters find gain up to +12 acceptable for their work. And even +18 has a following with custom presets for certain shooting environments. There is no hard and fast fast rule for all situations. Bottom line is check it out with some tests and use what looks/works best for you and meets your clients expectations.

I would say that in most common shooting situations adjusting shutter speed, aperture, and using ND filters are the preferred way to manage image brightness, and play with gain only when you run out of range with the first three or need it for a specific gain-induced effect.

FWIW: camcorder white balance is typically implemented by internal gain adjustment.
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Old February 7th, 2008, 09:04 AM   #6
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Quote:
Originally Posted by Don Palomaki View Post
But there can be other artifacts as well. Decreasing gain requires more light hitting the CCD for the same image brightness, and pushes the highlights in the image closer to the saturation point of the CCD pixels. For example, the image may be somewhat more likely to develop vertical smear from hot spots in the image at a low gain setting.
[QUOTE]
this was the kind of thing I was wondering about - smear effects are similar to what I meant by smoothing (more a graphic term)
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I would say that in most common shooting situations adjusting shutter speed, aperture, and using ND filters are the preferred way to manage image brightness, and play with gain only when you run out of range with the first three or need it for a specific gain-induced effect.
So do you mainly keep it at 0 and use the filters - I purchased an ND and a polarizer after I discovered the onboard ND wasn't enough when I had to shoot a mini horse show for a friend in full noonday sun - however I didn't even think of reducing the gain to -3 as an option at the time.

I will have to test the two variations outside - when it gets decent enough to step outside - we're buried in snow in Toronto at the moment
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FWIW: camcorder white balance is typically implemented by internal gain adjustment.
how do you know these things??

anyway, thanks again for the info, as always.

trish
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Old February 7th, 2008, 01:29 PM   #7
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Thanks for the input everyone, its been a big help.

Mark
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Old February 7th, 2008, 01:46 PM   #8
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Quote:
[I purchased an ND and a polarizer after I discovered the onboard ND wasn't enough when I had to shoot a mini horse show for a friend in full noonday sun - however I didn't even think of reducing the gain to -3 as an option at the time.
What aperture and shutter speed were you using?
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Old February 7th, 2008, 04:23 PM   #9
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It's been so long - but I think I was trying to stick to 24p with 1/48 - which I should have abandoned at some point

and trying to keep the F below the 6 range whenever possible

I actually stayed relatively in shape but there was just a whole lot of harsh sun beaming down (no trees) - the field grass was practically bleached dry which didn't help - so a polarizer would have been nice

and then, upon viewing the footage realizing that I had way too many bum shots as the minihorse's heads come in around there on the handlers. Crazy sport really - a best in show on steroids

so in this case - is it better to add an ND filter, reduce the gain (-3), up the shutter speed, or close the aperture?

trish
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Old February 7th, 2008, 08:38 PM   #10
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Your pick, but not having been there, I would probably

1. Use internal ND as first option, then
2. Go with -3 dB gain,
3. Go with the smaller apreture as long as I was confortable with the result,
4. Increase shutter speed, (but this can give a different look to motion), and
5. Lastly add external ND filter.
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Old February 8th, 2008, 12:06 PM   #11
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Interesting - external ND filter last! I wouldn't have guessed that. Thanks again Don, for the primer - definitely great guidelines for those of us still in the learning curve.

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Old February 8th, 2008, 02:09 PM   #12
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External ND last mainly to avoid putting additional glass in the light path, with the possibilities for dust, additional reflections, etc. (IMHO, the internal ND is less likely to induce these concerns.)

However, if the change to the look/feel of motion caused by a fast shutter is objectionable, then using faster shutter might be last.

And we ALL are on a learning curve!
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Old February 8th, 2008, 05:28 PM   #13
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I usually use the 1/32 built in ND filter, 0dB and a manual Aperture of around f4.8. In most situations, which include shooting a lot of bright sky (air shows) I usually end up shooting with a 1/50th - 1/125th of a shutter speed. I can't imagine what conditions you'd be shooting in to need an external ND filter. I'm now going to try the -3dB, so that should help even more.

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Old February 10th, 2008, 03:25 PM   #14
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On auto in the bright southern hemisphere sunlight here the A1 calls for both internal filters and my B&W ND6. I shoot most airshows on auto because of the speed of the action. Flypasts, I'm working up my manual chops.

Piston engine props don't appear to be spinning right at anything other than 1/50th.
Cheers.
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