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Old July 31st, 2002, 12:37 AM   #1
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basic questions : What is gain? & zebra settings

Would someone please explain what is happening when you increase the gain.

Are you just increasing the sensitivity of the chip? and what is the penalty for increasing the gain.

Would a good analogy be a faster film speed in a still camera?

Zebra settings, what do they represent 85, 90, 95 what? What setting should I be using and how do I decide?

Thanks for the help.
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Old July 31st, 2002, 03:01 AM   #2
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I might not be able to answer everything, but I can give you
some basic explenations.

Gain: gain is an electronic amplifier. It amplifies the signal by
a given amount (making it thus lighter - if you have a +db). The
downside is that this introduces NOISE. Which you can easily
see and test for yourself. I always shoot at -3db to get the
cleanest image possible.

Zebra stripes: these stripes are here to warn you of overexposed
parts of the image (ie, too bright). You can set your own level.
If you choose 95 or 100 everything above that will be CLIPPED
HARD (since digital can not go over 100). I have it set at 90 as to
have a bit more headroom. I know when I start to see zebra
stripes that I must be careful (unless I want to have blown out
parts) but that I'm not loosing any information... YET.

Some other people will tune in with exact discriptions and such,
I hope this will help in the mean time.
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Old July 31st, 2002, 08:34 AM   #3
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Hi Rob,

now you've got me........always shoot at -3db. Could you please elaborate for me.

Thanks
Andrew
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Old July 31st, 2002, 08:47 AM   #4
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You want the cleanest signal possible, so that is why you want
-3 dB gain (less noise as possible!!). I usually shoot at a shutter
of 1/25 or 1/50 and adjust my iris for different amounts of lights
(I also have ND filters to help). I'm starting to use additional
lights as well. Basically I do not touch my gain knob (unless it
is the absolute last thing I can do to get the image brighter, which
happened only once). The more you dial up the gain, the brighter,
but also the more grainier the image becomes. It might be a look
your after, but I'm not. If I want grain I'll ad it later during editing
and post processing.

Just play with the settings and see what you like. Everyone
agrees on -3 dB gain though, as far as I know.
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Old July 31st, 2002, 10:46 AM   #5
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Now unless I'm missing something the GL2 lowest setting for gain is 0. Is that correct?

You shoot at 1/25 and 1/50? that seems slow to me but I'm thinking in terms of stills does this create a particular effect you like?

Where do most people judge their image a computer screen, studio monitor, TV screen is there an actual standard?

Thanks for the help!
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Old August 1st, 2002, 01:19 AM   #6
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To judge you video properly you should use a hi res CRT studio monitor that has bean Properly calibrated. I find it hard, and next to impossible to judge my footage on a standard TV. Usually if your footage is being seen on a computer monitor then it (the footage) has bean compressed which dose not give a you the viewer a true view of what the footage will look like uncompressed.

alex
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Old August 1st, 2002, 01:32 AM   #7
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Hi Rob,

now you've really got me.

I thought dB was related to a reference signal level of 0. Any +dB setting would amplify and any -db seting would attenuate a given signal. Further to this, as dB is plotted on a log / lin graph it stands to reason that the function is based on the principal of the square, this applies to both lighting and audio. Generally a change of 3dB would represent a halving / doubling of the signal. So in mind I am trying to understand why by attenuating a signal you would get a better picture.

You also seem to intimate that a slow shutter speed will also help matters. How so? Do the same principles as for 35mm photography apply i.e. the relationship between shutter speed and aperture. F5,6 at 1/125 is the same as F8 at 1/250.

Could you please explain in a bit more detail, my fundemental beliefs are being rocked.

Thanks
Andrew
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Old August 1st, 2002, 02:22 AM   #8
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Correction

F5,6 at 1/125 is the same as F8 at 1/60. DUH

Cheers
Andrew
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Old August 1st, 2002, 03:34 AM   #9
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Well... I'm not an expert on dB's by a long way. So I cannot tell
you what it means exactly. I just know that everyone is shooting
in -3 dB and that it is what is advised. Ofcourse you lose 1 or
more stops of light. The advantage is that you are reducing the
noise the CCD chips are producing, ie, you get a cleaner image.

Just try it for yourself. That works the best! As far as I understand
the shutter issue (and remember, I'm not a professional) you do
not want to change your shutter speed. Set it at something and
keep it there. Otherwise you will see different motion signatures
when the camera or something moves. Keep in mind that this
is a VIDEO camera not a STILL camera. You can get away with
changing shutter speeds in between photo's, but not whilst your
shooting video (in my opinion). I choose 1/50 or 1/25 because
that closely resembles a FILM SHUTTER and I like the motion at
the moment (I'm in a PAL country... hence the 25 and 50 instead
of 30 and 60). I'm still experimenting with things though....

What shutters is everyone else using for movie making?
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Old August 1st, 2002, 03:35 AM   #10
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Addendum:

" F5,6 at 1/125 is the same as F8 at 1/60 "

This might yield the same photo image regarding with how much
light enters etc. But it will definitely not produce the same motion
signature on video.
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Old August 1st, 2002, 05:40 AM   #11
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"What shutters is everyone else using for movie making?" (Rob)



Normally I try to get away with shooting at 1/60. It's not always possible, though.

1/30 is just too slow if anything in the shot is moving.
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Old August 1st, 2002, 07:58 AM   #12
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Hi Rob

OK things are falling into place....to some degree. I understand what you are saying and what the general practice is. Why did'nt Canon just produce a -12dB setting, think of the quality then....Ha Ha.... yeah I know how many stops you would lose.

I still would have thought that in terms of dB (in my poor understanding that is ) that the best setting would have been 0 i.e. no boost and no cut to the signal. I hear what you are saying and will certainly set mine to -3dB.

As with you, I too am a PAL man. Had never thought of the 25 / 50 speeds for the film look. Would you suggest this for all filming like wildlife doccies?

I have tended to shoot on aperture priority as a result of the diffraction issue (As documented on the watchdog under Soft Focus and Workaround). Can't figure out how to get 1/50th at F5,6 in the bright African light. Argh..there ain't no such thing as a free lunch.

Cheers
Andrew

PS: Anyone out there with an understanding of the dB issue?
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Old August 1st, 2002, 08:46 AM   #13
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Andrew,

Well... experiment. Best way always. I do think that low
shutter speed helps in a more movie kind of look, since they
use a slow shutter too (after frame doubling it is effective 1/48 ???)

You should be able to get 1/50 F5,6 in bright african light with
the help of ND filters. I have one in the lens and I can screw
an extra one on if I need too. A circular polarizer might help
too. For a documentary or wildlife documentary it is probably
better to go with a higher shutter speed, because:

1. you want to see the animals perfectly sharp, not blurred
2. it doesn't have to have the "feel" of a movie. It is meant
to be a documentary to watch on TV and get see as much
as you can....

But as I said earlier, I'm no professional and am still fiddling with
this myself. Just try and see what you like. Both with low and high
shutters. Watch it on a TV (or high res monitor) though, do not
depend on your viewfinder to see the difference. After a while
you'll start to like a certain look and you can just leave it at that
setting.

0 dB will get the closest original signal as possible. Look at -3 dB
as an ND filter with noise reduction filter. And again, play with
what you like. In the bright african sun you should not need
anything higher than -3 dB anyway, which will give you very
nice pictures.

Good luck
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Old August 1st, 2002, 08:55 AM   #14
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Hi Rob,

yeah...had not thought of additional filters, good point. Will be playing a lot in the next few weeks. Pity this thread was not 10 days ago as I have just returned from a week in the Kruger National Park where It would have been great to have tried these things out.

Got some incredible sunrise footage which I now have on my desktop...as do another 20 odd people in my business. Would have been nice to have got it better with the tips.

Thanks and cheers
Andrew
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Old August 4th, 2002, 07:32 PM   #15
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Sorry for the dumb question. Maybe I should check this out on www.canondv.com

The GL1's lowest manual shutter setting is 1/60. Does the new GL2 have lower manual shutter speeds? (1/30 and 1/15)?

Thanks!
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