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-   -   Negative Gain (ie -6db) (https://www.dvinfo.net/forum/general-hd-720-1080-acquisition/130737-negative-gain-ie-6db.html)

Steve Phillipps September 13th, 2008 08:02 AM

Negative Gain (ie -6db)
 
The PDW700 has a -6db gain setting, and most pro camcorders have a -3. I think I read something about this elsewhere but can't recall, just wondering about the pros and cons of negative gain. Do I remember rightly that you get less noise (obviously) but also less dynamic range? I kind of always assume the less gain the better, so would tend to want to shoot -6db on the PDW700 (as it has such good light-gathering you still get plenty of exposure even at -6), but if it's going to lose out in DR or something else then it's probably not worth it as the 700 is so noise-free anyway.
Steve

Rick L. Allen September 14th, 2008 07:01 AM

Steve, I've never heard anything about the lower gain settings creating less dynamic range. Higher gain settings don't create more dynamic range just more noise. My $.02 worth. I generally like to run my cameras at -3 anyway. I really can't wait to get my hands on a 700!

Brian Drysdale September 14th, 2008 01:09 PM

Quote:

Originally Posted by Rick L. Allen (Post 934534)
Steve, I've never heard anything about the lower gain settings creating less dynamic range. Higher gain settings don't create more dynamic range just more noise. My $.02 worth. I generally like to run my cameras at -3 anyway. I really can't wait to get my hands on a 700!

Not well known, but it does reduce the dynamic range by reducing the headroom available for overexposure.

Understanding gain settings [Archive] - The Digital Video Information Network

However, many people do happily use -3 as a ND and for reduced noise.

Steve Phillipps September 14th, 2008 01:58 PM

Thanks Brian, was starting to think I'd imagined it!
It's above my head though, and I'm still no clearer as to whether it's a good idea or not.
Steve

David Heath September 14th, 2008 04:54 PM

Quote:

Originally Posted by Rick L. Allen (Post 934534)
Steve, I've never heard anything about the lower gain settings creating less dynamic range. Higher gain settings don't create more dynamic range just more noise. My $.02 worth.

Think of a chip as being a device for converting light into an electrical voltge. The more light you put in, the higher the voltage - up to a point. At a certain level the output of the chip will limit, no matter how brighter it gets, the voltage is constant.

That may be (say) 600% larger than the amount of light needed to produce a nominal white at the 0dB setting - but the chip output between 100% and 600% gets processed to put detail into the highlights, and stop them abruptly burning out.

Put negative gain in and you now need (say) 200% to produce the nominal white, hence the headroom necessary for processing highlights is reduced.

Those are the underlying principles anyway, in practice it's dangerous to generalise. Practically, a valuable use for negative gain can be to control depth of field, the NDs may give coarse ranges of iris, which gain settings can fine tune.


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