What the heck is an f-stop?

Started 5 months ago | Discussions thread
Paul Anderegg
Forum MemberPosts: 71
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Re: What the heck is an f-stop?
In reply to bobn2, 5 months ago

Thanks for the reply Bob, the math formulas were informative.  All broadcast video cameras rate their s/n ratio at 0db.  My f13@2000 2/3" standard definition Panasonic is rated at 65db, and my f10@2000 2/3" high definition Panasonic is rated at 54db.  Obviously those big SD pixels play a role in that!

My problem with the current selection of new and used 1/3", 1/2", and 2/3" cameras, is there ability to obtain luminance in very low light.  I am a news shooter, so I rely on each 6db (1 stop) I can get my hands on to boost the picture.  The Panasonic HPX600 referenced above, will only gain up to 18db, or roughly 3 stops above 0db gain.  The JVC will gain up to 24db, which would be roughly 4 stops above absolute 0.  Obviously, in a news environment, being able to click that one extra 6bd doubles your picture brightness, an can mean the difference between seeing the SWAT officer hiding behind a bush, and not.  The JVC can go down to 1/4th sec shutter, the Panasonic only down to 1/15th.

I guess my main question would be the following.  At 0db, with identical shutter speed, which camera would provide the most luminance at wide open (f1.4/f1.8) aperture?  Second question, at full telephoto, with the 1/3" at f1.4 and the 2/3" at f2.3, what would be the luminance difference between the two cameras?  90% of what I shoot at night is shot wide open, and exposure is adjusted by gaining up.  Night is night, you work with what you have in news.  Thanks!

Paul

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