What the heck is an f-stop?

Started Apr 25, 2014 | Discussions thread
OP Paul Anderegg Regular Member • Posts: 123
Re: Sensor size, f-stop, exposure, total light, and noise.

That does help, which brings me to another question.  Assuming the two f10@2000 1/3" and 2/3" models considered above..........that f10 isn't really the same is it?  I will give a hypothetical example based on two small camcorders I own.  Sony CX900 and Panasonic x920.  Both provide the same picture brightness (luminance, zebras set to 80IRE would zig and zag in the same spots) at wide open aperture and no gain (0db).  Both also provide the same amount of sensitivity boost, and provide comparable ability to discern (brightness-wise) a line of trees at night against a lit skyline.

The Sony has a 1" sensor, the Panasonic a 1/2.3".....it's actually probably 1/4", but that isn't completely relevant.  The Panasonic has a maximum aperture of f1.5, the Sony an f2.8.  Due to the larger chip in the Sony, that f2.8 "rating" is enough to provide enough light on the sensor to provide a brighter picture than the f1.5 lightfall on the tinier Panasonic sensor.  At all gain settings, the Sony is also MUCH cleaner.

Noise aside, please take the following hypothetical into consideration when answering the follow-up question.  Given as I said they produce the same luminance wide open at no gain/ISO boost, if the Sony was rated at f2.8@2000, and the Panasonic was rated at f1.5@2000, then those f10@2000 ratings for the professional camcorders would be similarly skewed?  If both cameras, 1/3" and 2/3" provide that critical measured 100IRE at f10@2000, then would not the 1/3" camera be able to provide a brighter image at wide open iris, because it could open past f1.8?

I just need to know if the 1/3" camera/lens combo first proposed would have a brighter image (more IRE's!) at 0db, no gain, lowest settings, boost set to off etc, at full wide, and then again at full telephoto, given the lenses listed in the B&H links.  I actually use the 18x4.2BERm lens every night for my job, and it doesn't get darker when you zoom in through to full telephoto.  All cheap 1/3" mount "pro" lenses do ramp the aperture down, as do all 2/3" mount lenses.  this little secret nugget of high end 1/3" lenses got me thinking they could actually beat out the larger sensor better low light sensitive 2/3" models simply do to the wins they see in the math game.


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