"Water is not light" contd. :-)

Started Mar 6, 2013 | Discussions thread
GaryW Veteran Member • Posts: 8,541
"digital is not film" :-)

wcdennis wrote:

...What you need to be comparing when comparing different sensor sizes is how each camera system creates the same photo (same shutter speed, same FOV, same DOF, and same SNR). Keeping exposure constant is an arbitrary gain adjustment at the end.

...You're done. You'll notice that even ISO is not comparable between systems with different sensor sizes. In this case, the larger sensor has more highlight headroom.


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You are right, I’m done, I give up.

It just struck me that there is now no need for anyone to understand the fundamentals of exposure. For those of us who are old enough to have worked extensively with film, there was no such thing as an “arbitrary gain adjustment at the end” as you put it.

It can't be completely arbitrary, though.  There is an optimal set of parameters which partially fill the photosites without blowing out too many of the highlights.  But if you severely underexpose, you can just pull it up in the RAW converter.  The gain adjustment in the camera is still done before the photo is taken because you want to optimize the capture into the sweet spot; too low of a signal and it'll be harder to bring up the signal without bringing up the noise.  Or am I thinking of analog tape?  Anyway...  But this gain is sensor-specific.   Since it's just a gain control, you can gain however much you want, so any ISO-equivalent is possible.  It is possible for them to accurately match standard ISO values if they want.

I've seen posts in the past with people claiming that in the future, we might be "ISO-less".  No ISO needed.  Just pull up the exposure as-needed as post-processing.  (I assume that there is still some amplification gain necessary, set by the manufacturer.)

Ansel Adams, who taught us the finer points of exposure and film development never mentioned an “arbitrary gain adjustment at the end.”

I've read that he did a lot of adjustments in the darkroom.  Did he "push" or "pull" the entire exposure?  If so, then now we're just talking about doing even greater pushes and pulls, but I'm not sure it's such a crazy difference.  But film does behave a bit differently as well....

I now realize that you mainly see the aperture setting as a method to adjust depth of field. You have to understand that all my life I used a light meter to set the correct f-stop and shutter speed. For this to work, one of the fundamentals is that the aperture setting meant the same thing on every lens I owned. Now that cameras have instant review and allow you to dial in any ISO you want, all the things that we old-school photographers learned has become practically irrelevant. The laws of physics haven’t changed, but have become obselete. So, keep in mind that we old folks are coming from a very different perspective, where exposure had to be carefully calculated in advance because film couldn’t be “gained up” (although someone will probably jump in here and mention push-processing).

Well, you can underexpose and bring up the exposure in the RAW converter.  Is it the same as using a higher ISO?  In the past, you'd pull up more noise, but with better electronics, I think the results are closer now.

It does make me think that the main thing is to choose your shutter, for digital.  Aperture may be limited by your lens if light is low enough.  Now ISO is "whatever".  But many of the old rules still apply.  You'll still have more capability to keep the shutter speed up with a wider aperture lens, for another example.

But at the end of the day, all that matters is whether I can tolerate a certain level of noise.  If I have a smaller sensor but somehow I'm happy with the image, it really doesn't matter how it got there, how much gain, etc., but I think in general, larger sensors are going to produce nicer looking photos with less noise, with diminishing returns as you get larger.

May your signal always be greater than your noise.


Now, If we can get that rain gauge discussion sorted out, maybe we can put this thread to bed.

Oh no, now we have the "how is digital different from film?" thread.  

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Gary W.

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