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Help! Can’t understand “Understanding Exposure” by Bryan Peterson
- Thread starter Bruceter
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I'm reminded of a comment made to Stephen Hawking* when he was preparing his book "A Brief History of Time". The author himself notes in the book's acknowledgements that he was warned that for every equation in the book, the readership would be halved, hence it includes only a single equation: E=mc^(2). https://en.wikipedia.org/wiki/A_Brief_History_of_Time
Also I'm reminded of the archetypal picture of the Englishman abroad, who when not understood merely shouts louder. Some very knowledgeable folk in their field simply cannot understand those that don't have the same grasp; for all their knowledge they have a poor understanding the way others learn or comprehend concepts and in this case those who may be very artistic, and/or are beginners. The fact that Peterson's book has gone on to a 4th edition indicates that he has got the level(s) right (I say this only have read the early editions).
If I wished to do a degree in digital camera science I would want the likes of Illiah Borg as a lecturer. If my non-technical granddaughter wanted to take photos with a DSLR then I'd recommend Peterson. My sister, who retired as Head of Special Needs at a well respected secondary school (ie up to 18yr old) commented "Perhaps he just isn't a teacher" when shown some of this discussion. She goes cold the minute I start talking percentages, or try to explain a simple equation. Put her on Dante's Inferno and she'll explain it to me at 3 different levels depending on where I'm coming from.
*By way of a snippet of my background it was in doing that bit of research that I noted the person who made the recommendation was a fellow physics school pupil in the final couple of years prior to going to university. He never struggled with any of the those lessons!
sybersitizen
Forum Pro
Here's a go:
To better understand changes in ISO, recognize that they actually take effect only after the image has been captured. Successively raising ISO values in order to use a faster shutter speed or smaller aperture causes successive underexposure of the captured image. That underexposed image must then be boosted to create the final image with the brightness level you expected. The higher the ISO value, the greater the required boost. The predicted effect of the boost on the final image is typically previewed for you by the camera for your convenience.
Of course that's not the full explanation either, but it's not too difficult as a starting point for further details ... and it's not nonsense like the bee story.
Iliah Borg
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Exposure is Photography 101.
Iliah Borg
Forum Pro
You seem to mistake me for someone who hasn't grasped the concept.
Photography 101 starts with the triumvirate you detest.
Iliah Borg
Forum Pro
Detest? Emotions? Why?
It is simply wrong, while the right is simple enough not to start on the wrong foot.
“Also I'm reminded of the archetypal picture of the Englishman abroad, who when not understood merely shouts louder.”
As a general rule I see that more in my fellow Americans, once accompanied by “don’t you people know how important I am?!”
(And yes I have actually heard someone - a very well known Southern Baptist Televangelist - bellow those very words to some young women working an airline’s ticket counter at the airport in San Pedro Sula when they would not let him board a flight that was already pulling away from the terminal.)
As a general rule I see that more in my fellow Americans, once accompanied by “don’t you people know how important I am?!”
(And yes I have actually heard someone - a very well known Southern Baptist Televangelist - bellow those very words to some young women working an airline’s ticket counter at the airport in San Pedro Sula when they would not let him board a flight that was already pulling away from the terminal.)
riveredger
Senior Member
Iliah Borg
Forum Pro
Another off-topic.
Shutter-speed and f-stop determine how much light reaches the sensor, in a digital camera the ISO setting determines how much gain is applied to that initial signal.
Changing the ISO setting does two things:
1) tells the meter what the metering system’s engineers think a good exposure will be and that solution is heavily influenced by other algorithms that the system’s engineers have built based on experience of feedback from photographers so the meter more or less recognizes the likely content and lighting conditions.
2) Tells the A/D processor in the camera how much gain to apply to the analog signal while converting it to the digital form that is recorded.
Now obviously the ISO setting on the metering side can comes up with a very different exposure (f-stop and shutter speed combination) solution than if only the base sensitivity for the sensor was used.
Changing the ISO setting does two things:
1) tells the meter what the metering system’s engineers think a good exposure will be and that solution is heavily influenced by other algorithms that the system’s engineers have built based on experience of feedback from photographers so the meter more or less recognizes the likely content and lighting conditions.
2) Tells the A/D processor in the camera how much gain to apply to the analog signal while converting it to the digital form that is recorded.
Now obviously the ISO setting on the metering side can comes up with a very different exposure (f-stop and shutter speed combination) solution than if only the base sensitivity for the sensor was used.
photonut2008
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Yet another tortured and inaccurate analogy.
photonut2008
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In many digital cameras, and up to a point.
Not with Spot or Center-weighted metering.
See above. At some point in practically every camera this ceases to be the case.
Same as with setting exposure compensation, but (as I've stated numerous times) with ISO the effect on the image is done after the exposure rather than before the exposure.
yes. There are hard limits to what is done.
with every camera by every manufacturer? Can you cite some technical sources for that? I am genuinely interested.
As I said, there are limits.
That was point 2 but you restated it with greater clarity than I did, so thank you.
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photonut2008
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Spot metering sets the exposure so that middle gray is in the middle, and I'm reasonably certain that is the way all cameras do it. The area that is spot metered may vary, and how middle gray is determined will be dictated by the camera's defaults on how to process the data to JPEG, but it isn't influenced by algorithms that change because of content and lighting conditions.
I can't speak for all systems, and I have no technical sources to cite here, but the entire concept behind Center-weighted metering is much the same as it is with Spot metering. I do know that with Nikon we can weight the metering between the entire scene and different sized diameters of what constitutes the center, or we have the option to average the entire scene (my favorite, in large part because it eliminates the vagaries of undocumented algorithms that change with each metering system iteration).
Iliah Borg
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Yes, one needs to define "middle". Calibration varies from 6% to 22% for raw, and is typically between 9% and 13%.
It isn't indeed.
True.
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mamallama
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justinwonnacott
Senior Member
Please post your own untortured analogy.
Iliah Borg
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Omnis comparatio claudicat nisi in puncto comparationis.
Before resorting to comparisons and analogies, why not to try without them?
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