Exposure Basics, lesson three?

Started Mar 18, 2013 | Discussions thread
Great Bustard Forum Pro • Posts: 40,681
Quick question:

Najinsky wrote:

By the end of the course they would know that Light Exposure is the amount of light falling on the recording surface controlled by the Aperture and Shutter Speed and that ISO is a setting that controls how the camera processes that light into their image.

The exposure is the density of light falling on the sensor, which is all together different than the total amount of light falling on the sensor:

Total Light = Exposure x Effective Sensor Area

and different from the total amount of light used to create the photo:

Total Light Collected = Exposure x Effective Sensor Area x QE

where QE (Quantum Efficiency) is the proportion of light falling on the sensor that gets recorded.

For example, four times (two stops) more light falls on a FF sensor than an mFT sensor for a given exposure. A sensor with a QE of 50% records twice the light as a sensor with a QE of 25% for a given exposure.

It is the total amount of light used to make the photo, not the exposure itself, that is the relevant measure in terms of the IQ of the photo that has to do with exposure. In short, exposure is relevant only insofar as it is a component of the total amount of light that makes up the photo.

If we are working with a single camera, there is no need to make the distinction between exposure and total light, just as there is no need to make the distinction between mass and weight when in the same acceleration field.

However, if we are comparing different formats and/or sensors with different QEs, then the distinction is rather central.

And that's why techies should't try to teach beginners.

Alternatively, it's why beginners often stay beginners, more often than not, at least so far as technical understanding goes. They start out learning something wrong that seemed to make sense, and leads to comments such as "Total Light = Total BS", "f/2 = f/2 = f/2", "larger pixels means less noise", etc., etc., etc., that, try as one might, they cannot let go of the dumbed down incorrect version they "learned".

Do you honestly believe that the concept of exposure as the density of light falling on the sensor is too hard for a beginner to grasp? Do you honestly believe that the concept that the more light a photo is made from the less noisy it will be is too hard for a beginner to grasp? Do you honestly believe that the idea of sensor efficiency, in terms of the proportion of light falling on it that is recorded, and the additional noise added by the sensor and supporting hardware, is a concept too difficult for a beginner to grasp?

Myself, I tend to think that the correct understanding is the more simple understanding:

  • Exposure is the density of light falling on the sensor.
  • Wider aperture and/or longer shutter speed means more exposure.
  • Greater exposure, larger sensor, and/or more efficient sensor means more light recorded.
  • More light recorded means less noise.
  • Sensors can absorb only so much light, beyond which you will get blown highlights.
  • Camera's ISO setting adjusts the brightness of the LCD playback and/or OOC jpg, as well as influencing the camera's choice of f-ratio, shutter speed, and/or flash power depending on the AE (auto exposure) mode you are using.
  • Image files have a limited bit-depth, so increasing the ISO may push portions of the photo outside the range of the image file, resulting in blown highlights.

Is it really that confusing?

Try it. Offer your services to a local college. Put the course together and get it approved by the college. Get them to include the course in their night class program, see if people want to sign-up and pay money for it. And if it all goes ahead, deliver the course and get a critique about how well the course was received.

It's really great fun, you meet interesting people, and it's one way to know for sure.

But to give some partial answer. I believe if I submitted a beginners course with terms/equations like Total Light Collected = Exposure x Effective Sensor Area x Quantum Efficiency, the course would be rejected as having missed the brief that it is aimed at complete beginners.

So, I take it that your opinion is that saying that the total light collected is the product of the exposure, effective sensor area, and the QE is too much for a beginner.

How would you teach "stops"?  Explain to me, if you would, why f-ratios, in one stop increments, go: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, and 32.  Would you just have the class memorize these numbers or explain the numbers to them?  Or would you just tell them not to worry about the numbers all together, and just move the dial left or right?

I'm a little different than many in that I have some experiences that are not at all common. I was the advanced programming course designer for Hoskyns. I was also the chief trouble-shooter consultant, meaning my name was listed in the experts directory, known as the "Oh shlt, who we gonna call, guide" (it was the post Ghost Busters era). That would be me. I solved issues with IBM Systems that IBM had failed to solved, "dam, who we gonna call now?". I was called on to out-geek the geeks who were hiding stuff from their bosses. I was the sole representative of the UK (in my specific field) invited by IBM to attend their technical seminars at their labs in Italy. One each from certain European countries, two from America and one from Canada. A small group the IBMer insisted on calling the elite.

I don't say this to brag or elevate myself, I say it because I want you to understand, I can do techie. I was, in that career, the techie's techie. However, I am somewhat different because I can also do beginner and this isn't all that common. The intro lecturers didn't have the knowledge for the advanced courses, while the advanced lecturers didn't have the patience or dumbed down (simplified, being more polite) vocabulary to keep the beginners on track. They would sometimes try if the scheduled lecturer was off sick, but it would more likely lead to 'brain-dump' tactics and end in tears. Yes, both delegates and lecturers do end up crying when faced with a group situation that overwhelms them into feeling they can't cope.

An insurance company client ran an annual program taking six virgins; people with a degree in anything other than computer sciences. If could be Business Administration, Medicine, Legal, Drama, Languages, Photography and Media, whatever, just so long as it wasn't Computer Sciences. These would then be trained to become computer programmers, by me, in a 6 week intensive course (30 full days) over an eight week period.

Their rationale was that Computer Science Geeks were in general, geeks, and didn't make particularly useful additions to the business, lacking both business and communications skills. Dismissive, aloof and intolerant. More likely to hold the business to ransom than help drive it forward.

As an honorary computer science geek I was naturally a little skeptical, but we ran it for three years before the recession hit and they stopped the new hires. It was hugely successful.

The point of all this rambling is, teaching beginners is a lot more than just having the knowledge they lack. You need empathy and imagination to put yourself into their position, to understand where they struggle. A little psychology to figure out a way to help them over their hurdles. You need to pace the learning so people don't get bored while others struggle. And the biggest mistake the more techie lecturers make in this situation is in believing it is easy. Some even make the mistake of saying it in just the wrong way, directly at someone who is struggling, in the innocent hope it will help. Might as well just light the blue touch-paper.

So what do you think, are techies dismissive, aloof and intolerant? Seen any evidence of it here in the m43 forums?

In my opinion, the people who are dismissive and intolerant are those who actively resist learning, and those who want to "protect" the ignorant masses for getting confused by "geeks".

Either way, from the vast majority of photos I see here on DPR, this would be my recommendation:


Shut the camera down (Mute/Natural) -2,-2,-2,:

Shoot complete Auto, and the camera will be right more times than you with all your adjusting machinations and bracketing;

relax, enjoy the Image !

and this has much to do with why I think most would be best served with a good compact, like the RX100.

However, these people are not my target audience, nor is taking a good photo the point of my posts.  I simply explain to those that wish to understand how things work.  Those who have no interest can simply skip my posts, but what I find "entertaining" is those who fight my posts.

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