You can see directly and easily what upping the gain does for your image quality. Connect your camcorder up to a TV and point the lens at anything with some colour and detail in it. Switch the camera into full auto mode.
Now watch the TV picture as you simply up the gain. On the Z1 I have my 3 position gain selector switch set on zero, +9 and +18dB.
As I flip the switch the iris stops down to compensate so the exposure of my TV image remains constant. If I start at f/2 (say) flipping to the +9dB position automatically stops down to f/4.8 and at +18dB to f/8.
It's pretty difficult to spot that +9dB has degraded the image at all - even on a large screen LCD TV. At +18dB the image has softened slightly (some of which will be attributable to diffraction), the grain has begun to dance and the colour saturation has dulled - and the latter can be corrected to a certain extent in post.
The +36dB gain setting on the Z1 is for emergencies only, and I've never had call to use that.
It all goes to show how usable the gain-up settings are on modern camcorders. The PD150 may have been 'king in the lo-lite' but its gain-up settings were far less usable.
tom.
Gain gives you a trade off between depth of field and noise, all other things being equal. Your call.
Tom, I'm surprised that Sony have also introduced this method of selecting gain - 3 presets.
It's the one thing that I seriously don't like about my XH-A1's. Give me the 'ol wheel on the PD/VX's any day.
Maybe you can explain how there can be a -3 gain setting (as with the XH-A1. Don't know if your Z1 is the same). How can there be a minus setting for gain? If it's at zero, isn't that 'no gain' = nothing? How can you have less than nothing?? :confused: But then I confuse easily. :)
Some cameras have gain settings that will go down to -6dB. What it means is that the head amplifier gains are reduced, thus consuming the overexposure range by up to a stop (1 stop = 6dB). The reduction in gain comes with a reduction in noise levels, which is why we need it.
-3dB gain is the standard setting for shooting drama in most professional cameras, to get the noise level down.
0dB is only the reference level, at which the camera's sensitivity and noise are specified.
Along with various other settings (such as slightly crushed blacks), I tend to use -3dB as my standard setting for XDCAM HD when shooting corporate work; obviously not using auto. I find it also increases the colour saturation a little bit (esp. those close to primaries) which along with slightly less latitude at the lower end of the contrast range gives a more 'cinema' feel to the raw footage. :)
Arthur - it was only the VX (rather than the PD) that let you increase the gain level seamlessly via a wheel, the PD (I'm pretty sure) had the choice of three positions like the Z1 and your Canon.
The snag was you could only increase the gain with the VX2k1 when you were using maximum aperture, and my first posting in this thread shows that the gain switch can be used as an aperture control should you want to leave the shutter speed fixed.
Alan - did you mean to say one stop = 6dB?
tom.
Yes, Tom, ammended.
The reason why you get slightly cleaner colours at lower gain is that the noise level has gone down. That's why we do it :D Also, a little black crushing increases the saturation of already highly saturated colours, as you've noticed. None of this is mystery, it's all good common sense, and is mathematically correct as well.
Tom, My PD150 had 0 - 18db graduated. The VX as you say wouldn't let you loose on the gain until you'd reached max aperture.
Alan, that makes sense now that you've explained 0db is a reference. In other words, similar to 0db on my Home cinema amplifier. (but would deafen you if played it at that volume! :) )
Just to make clear how black crushing helps saturation:
A colour is fully saturated if one or more of the RGB components is already at zero% (or 100%, but let's forget that for now). So, I define a colour, a reddish colour with RGB signal levels of, say, 100%, 10%, 5%, so it's a deep orangy red. Now, if I do a bit of black crushing, say -5%, then my colour has gone to 95%, 5%, 0%, all the blue has gone, so the colour is more saturated. Also, the hue has changed a little, closer to the primary colour of Red. A bit more black crushing, say down to -10%, and we've got 90%, 0%, 0%, pure red. Not only that, but the noise from the low-level G and B signals has been clipped off, so the resultant colour is less noisy.
Generally, black crushing increases the saturation, reduces the noise in already saturated colours, and shifts the hues towards the nearest primary (RGB) or secondary (Yellow, Magenta, Cyan) colour. Note that this is a graduated effect, affecting highly saturated colours most, it has little effect on lower saturation colours, such as skin tones, because none of the RGB signal levels is terribly low. This also happens when the camera's gamma curve is less than ideal, you can't get the colours right unless the gamma curve matches the display curve.
Welcome to the wonderful world of non-linear colour science, it's great fun :D
Quite so Alan, not too sure "welcome" applies to me, but I have been aware of this since I was apprenticed in a studio in the early 80's, particularly noticeable when working with highly saturated Kodachrome. :D
...1 stop = 6dB....
Alan I wonder if you would be kind enough to explain the relationship between gain and f-stops.
I understand that doubling or halving the area of the effective lens iris (that is a 1 stop change) doubles or halves the exposure. I understand that doubling or halving the shutter speed also results in doubling or halving the exposure.
So continuing the logic I would have expected a doubling or halving of the gain - ie a 3dB change - would be the equivalent of a 1-stop change. But this isn't the case - a 6dB change is required to cause a 1-stop change in exposure.
Is this because a 1-stop change requires a doubling of the video amp output voltage which is a quadrupling of the power gain ie a 6dB change in power gain, which is where the 6dB per stop comes from?
Clarification would be gratefully received.
Thanks, NL