BobDiaz
The Professor
Many years ago when I video taped a friend's wedding, I faced a nasty little problem. Not that it was unexpected, because the night before during the wedding rehearsal the woman coordinating everything went over the details of what would happen. The problem was the fact that after the bride entered, most of the lights would be turned off. I tried to explain to the woman why she should NOT turn off most of the lights, but I knew it was all in vain when she answered, "I can turn off more lights if you want." The night of the wedding, the bride came in and most of the lights were turned off. I had 3 choices: (1) Leave the gain at +0dB and have a very dark picture. (2) Kick the gain to +12dB and have a lighter image, but a ton of noise. (3) Go for the midpoint of +6dB and have some noise and a bit of darkness in the image. The point of my little story is the fact that for some of us, there are times when we have no control over the lighting and have to deal with bad lighting.
Given the same shooting conditions, the Panasonic HVX-200 would do much better then the Panasonic D-5000 I used back then. Still, as the light is reduced, the iris in the lens of the camera opens up allowing more light to enter. This works very well until we reach the limit of the iris and no additional light can enter.
The Gain Switch can be thought of as a volume control for the video signal. When you play music on the stereo and the music comes to a soft quiet spot, you turn up the volume to make the music louder. In the same way, Gain increases the voltage level in the video signal making the image look brighter. Voltage Gain is calculated as follows:
To save everyone a lot of trouble, just remember, a +6dB Gain is equal to a 2x increase in the signal. A +12dB Gain is equal to 2 x 2 or 4x increase in the signal. A +18dB is a 2 x 2 x 2 or 8x increase in the signal. When we express Gain as dB, every +6dB increase represents another doubling the signal. Another way to think of it as F Stops. If I open the lens from F8 to F5.6 (1 F Stop), I double the light. If I open the lens from F8 to F4 (2 F Stops), it's 2 x 2 or 4x increase in light. You could say it's like this:
Sadly, we can't get something for nothing and increased Gain results in increased noise. How much noise is acceptable is subjective and depends on each person's views. When you first get your camera, play with it and try shooting in a darkened room at +0dB, +3dB, +6dB, +9dB, +12dB, and +18dB. Maybe you'll find that +3dB or +6dB is acceptable to you and some may find the higher dB settings create an effect they like.
SLOW SHUTTER
The other possible solution for low lighting is the slow shutter. If the normal shutter speed is 1/60 of a second, switching to 1/30 of a second is like adding +6dB of Gain (1 stop). Going from 1/60 to 1/24 of a second is like adding +8dB of Gain (1 1/3 stops). Going from 1/60 of a second to 1/15 of a second is like adding +12dB of Gain(2 stops). Going from 1/60 to 1/12 of a second is like adding +14dB of Gain (2 1/3 stops).
For fast action sports, using a slow shutter may be a bad idea, but what about my friend's wedding? Given the same conditions, most would say that 1/30 to 1/24 is OK. This is subjective, some may not agree with that. Going to 1/15 of a second is about as low as I would want to go with normal movement. Again, this is VERY subjective and I'm sure there are those who will say that such a slow shutter produces strobe like action. At 1/12 of a second my guess is that most would see this as too strobe like, but this is something you would need to see to decide for yourself.
Going to slow shutter may add a little bit of noise to the image, but not as much as using the Gain switch. Keep in mind that I don't have an HVX-200 yet to try this out, so I can only guess. (When you get your camera, try it and find out.)
NOTES ON F STOPS:
The F Stops from F1 to F16 are: F1, F1.4, F2, F2.8, F4, F5.6, F8, F11, and F16. This may seem like a strange set of numbers to chose, but if you take the number, square it, and round it to a whole number, the sequence looks like this: F1=1, F1.4=2, F2=4, F2.8=8, F4=16, F5.6=32, F8=64, F11=128, and F16=256. (Yes, I know 11 x 11 = 121, but it represents the value of 128.)
At every Stop, the value calculated doubles. The higher the number the less the light. Think of it as F2=1/2, F2.8=1/4, F4=1/8,... In a way, you could think of each F Stop as -6dB of Gain; where -6dB equals 1/2 the signal. Close down the iris by 4 Stops and it's the same as saying (-6dB) + (-6dB) + (-6dB) + (-6dB) = -24dB. This is more engineering math than you really need to know, but I just thought I'd point it out.
1/3", 1/2", AND 2/3" CCDs:
Assuming the resolution is the same and the CCDs have 100% fill ratio, a 1/2" CCD has ROUGHLY twice the area per CCD pixel than a 1/3" CCD. Likewise, a 2/3" CCD has ROUGHLY 4 times the area per CCD pixel than a 1/3" CCD. There are many variables that come into play here, so only take this as a general idea and not a cold hard exact number. As the area per pixel increases, more photons land on the larger area and this acts like increased Gain, without the increased noise.
The bottom line is that if you shooting must include low level lighting, you will need to decide between the following: (1) Increased Gain. (2) Slower Shutter. (3) Larger CCD. (4) Have a "friend" stand by the light switches to gag and hog tie the offender before she turns off most of the lights. :grin:
Bob Diaz
Given the same shooting conditions, the Panasonic HVX-200 would do much better then the Panasonic D-5000 I used back then. Still, as the light is reduced, the iris in the lens of the camera opens up allowing more light to enter. This works very well until we reach the limit of the iris and no additional light can enter.
The Gain Switch can be thought of as a volume control for the video signal. When you play music on the stereo and the music comes to a soft quiet spot, you turn up the volume to make the music louder. In the same way, Gain increases the voltage level in the video signal making the image look brighter. Voltage Gain is calculated as follows:
Gain (in dB) = 20 x LOG(Voltage Out / Voltage In)
To save everyone a lot of trouble, just remember, a +6dB Gain is equal to a 2x increase in the signal. A +12dB Gain is equal to 2 x 2 or 4x increase in the signal. A +18dB is a 2 x 2 x 2 or 8x increase in the signal. When we express Gain as dB, every +6dB increase represents another doubling the signal. Another way to think of it as F Stops. If I open the lens from F8 to F5.6 (1 F Stop), I double the light. If I open the lens from F8 to F4 (2 F Stops), it's 2 x 2 or 4x increase in light. You could say it's like this:
+6dB = Adds 1 F Stop of light
+12dB = Adds 2 F Stops of light
+18dB = Adds 3 F Stops of light
If +6dB is like adding an F Stop, +3dB is like adding 1/2 an F Stop of light and +2dB is like adding 1/3 an F Stop.+12dB = Adds 2 F Stops of light
+18dB = Adds 3 F Stops of light
Sadly, we can't get something for nothing and increased Gain results in increased noise. How much noise is acceptable is subjective and depends on each person's views. When you first get your camera, play with it and try shooting in a darkened room at +0dB, +3dB, +6dB, +9dB, +12dB, and +18dB. Maybe you'll find that +3dB or +6dB is acceptable to you and some may find the higher dB settings create an effect they like.
SLOW SHUTTER
The other possible solution for low lighting is the slow shutter. If the normal shutter speed is 1/60 of a second, switching to 1/30 of a second is like adding +6dB of Gain (1 stop). Going from 1/60 to 1/24 of a second is like adding +8dB of Gain (1 1/3 stops). Going from 1/60 of a second to 1/15 of a second is like adding +12dB of Gain(2 stops). Going from 1/60 to 1/12 of a second is like adding +14dB of Gain (2 1/3 stops).
For fast action sports, using a slow shutter may be a bad idea, but what about my friend's wedding? Given the same conditions, most would say that 1/30 to 1/24 is OK. This is subjective, some may not agree with that. Going to 1/15 of a second is about as low as I would want to go with normal movement. Again, this is VERY subjective and I'm sure there are those who will say that such a slow shutter produces strobe like action. At 1/12 of a second my guess is that most would see this as too strobe like, but this is something you would need to see to decide for yourself.
Going to slow shutter may add a little bit of noise to the image, but not as much as using the Gain switch. Keep in mind that I don't have an HVX-200 yet to try this out, so I can only guess. (When you get your camera, try it and find out.)
NOTES ON F STOPS:
The F Stops from F1 to F16 are: F1, F1.4, F2, F2.8, F4, F5.6, F8, F11, and F16. This may seem like a strange set of numbers to chose, but if you take the number, square it, and round it to a whole number, the sequence looks like this: F1=1, F1.4=2, F2=4, F2.8=8, F4=16, F5.6=32, F8=64, F11=128, and F16=256. (Yes, I know 11 x 11 = 121, but it represents the value of 128.)
At every Stop, the value calculated doubles. The higher the number the less the light. Think of it as F2=1/2, F2.8=1/4, F4=1/8,... In a way, you could think of each F Stop as -6dB of Gain; where -6dB equals 1/2 the signal. Close down the iris by 4 Stops and it's the same as saying (-6dB) + (-6dB) + (-6dB) + (-6dB) = -24dB. This is more engineering math than you really need to know, but I just thought I'd point it out.
1/3", 1/2", AND 2/3" CCDs:
Assuming the resolution is the same and the CCDs have 100% fill ratio, a 1/2" CCD has ROUGHLY twice the area per CCD pixel than a 1/3" CCD. Likewise, a 2/3" CCD has ROUGHLY 4 times the area per CCD pixel than a 1/3" CCD. There are many variables that come into play here, so only take this as a general idea and not a cold hard exact number. As the area per pixel increases, more photons land on the larger area and this acts like increased Gain, without the increased noise.
1/2" Has ROUGHLY +6dB Gain Compared to a 1/3" CCD
2/3" Has ROUGHLY +12dB Gain Compared to a 1/3" CCD
As you know, larger CCDs are provide better low light performance and sharper images compared to the 1/3" counterparts, BUT there's a significant increase in cost for the camera.2/3" Has ROUGHLY +12dB Gain Compared to a 1/3" CCD
The bottom line is that if you shooting must include low level lighting, you will need to decide between the following: (1) Increased Gain. (2) Slower Shutter. (3) Larger CCD. (4) Have a "friend" stand by the light switches to gag and hog tie the offender before she turns off most of the lights. :grin:
Bob Diaz
