for Lens Settings, keep it as Wide open as Possible, until you got so much light, that your Image is getting too Bright. Meaning f/ 1.8 for that Lens or the Smallest Possible number for any other given Lens.
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To get the Image Brighter, try using Gain Settings.
Start to work your way up in that order:
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Digital Gain in steps up to 12dB (analog Gain at 0dB)
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if still not bright enough, Increase analog Gain to 6dB, and work your way up to 18dB Digital Gain in Steps
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If STILL not Bright enough, increase analog Gain to 12dB, and work your way up from 12db to 24dB digital Gain.
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If still too dark, increase the Analog Gain to 18dB / 24dB, and Keep the Digital Gain at 24dB
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the higher the Gain Settings are, the lower the Image Quality becomes, so ideally you would just have enough Light and keep the Gain at 0dB and 0dB for analog and Digital, but that is sometimes not Possible or Practical, especially for the Higher Framerates.
That way you will get an image that does not look as good, but you will usually at least see what is happening.
. For the Lens setting, given you have enough Light, closing the Aperture to an f-Number of 8 would also be Beneficial, as you get more of whats happening in Focus at once, but it also makes the Image much darker.
So, for as long as you are Struggling to get enough Light, you will need to keep it wide open, and only be able to see a very shallow Plane of Focus Sharp at once.
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Regarding Aesthetic Lighting Advice, if you need further Advice / Information about that, let me know I will PM you some.