----- Original Message -----

From: "Joe Sacher" <news@joesacher.com>

Newsgroups: rec.video

Sent: Saturday, July 12, 2003 2:43 PM

Subject: Re: Why would a large sensor give better low light performance?

> "RGBaker" <gb@bakerfilms.com> wrote...

> > > I just don't get it. If you have two sensors with the same number of

> > > pixels, but one is smaller than the other, why would the larger one

> > > give better low light performance? I would think the lens system takes

> > > care of it that all incoming light reaches the sensor. Then as I see

> > > it, all that matters is how many pixels the sensor has, the size of

> > > the sensor should be irrelevant. Right?

> > Picture a checkerboard sitting out in a sprinkly rain shower -- after a

> few

> > seconds count the rain drops that have landed in any given square of the

> > board. Now count the drops per square in a checkerboard twice as big

> > sitting beside it. You'd expect that four times as many drops of rain

> will

> > have landed in any given square in the board twice the dimensions.

> >

> > Same for CCDs -- each (large) pixel is more likely to have been struck by

> a

> > photon, or more likely to have been struck by more photons, than the small

> > pixels on a small CCD.

> In addition, it would be possible to have the same performance, if you

> concentrated the same amount of light on both (meaning higher light density

> in the smaller CCD). However, the opposite is usually true. The cameras

> with the larger CCDs also tend to have larger lenses, which will let more

> light in and improve the performance even better.

> --

> Joe Sacher

> Indianapolis, IN

> http://joesacher.com

UMMMM...! ;-)

Thought we had "killed" this misconception long ago, but I guess not...;-)

"Larger" lenses of the same relative aperture as "smaller" lenses, all else

equal, pass the same 'brightness" of light - and most small lenses are f1.6-1.8,

as are many big lenses (i.e., they pass the same brightness of light), though

some of each are a tad faster (not enough to get really excited about,

though...;-). The main sensitivity differences are with the CCD size and

type (and sometimes associated electronics).

---

David Ruether

d_ruether@hotmail.com

http://www.David-Ruether-Photography.com

Hey, take a gander at www.visitithaca.com, too...!