“There is no such thing as a perfect exposure!”

There were a few shocked faces on Tuesday night when I said this. Some people clearly think that taking a photograph is a process of science. I want to qualify my position.

Ray kindly posted a link to the site that examines ETTR… Expose To The Right when shooting RAW. The link makes my case in many ways. Here is the important point from the article…

“…if the contrast range of the scene you are shooting is less than the dynamic range of your camera’s sensor, you can increase the quality of the capture by adjusting your image to be further to the right on your camera’s histogram display.

The ETTR article is about noise management at the sensor. The sensor, NOT after the camera has done any noise control or conversion to JPEG. Creating a JPEG can be extremely damaging. The camera dumps all but a limited range of data either side of the visible range. JPEGs can contain 200 times less data than the original RAW capture. So this article does not apply to JPEG users – the file is ruined once it is in JPEG.

So, in RAW, you capture all the data the sensor collects. The article rightly explains why an optimal ETTR gives you more control over noise or loss of detail at the extreme ends of the histogram. Great!

You might remember I mentioned that the camera sensor is roughly half as sensitive to contrasts compared to the human eye. The eye sees about 16 to 20 stops of light (individuals vary). Recent cameras see between 7 and 11 stops, depending on model and sensor (about the same as film). The eye detects this deficiency and overcomes it. From early childhood we learn to ‘see’ and interpret photographs. We create a perception of the scene. That is not what the camera records.

The purpose of a camera exposure meter is to establish the subjects mid-tone luminance (brightness). In auto-functions, the camera then sets the range it can work within. This is about three stops either side of the mid-tone – that’s your histogram. It aims to work in that range without clipping details at the extreme ends of the graph.

You can capture a scene with a glowing bulb and it will blow out (loose all detail in the white). The rest of the scene will be fine. The camera can also successfully photograph the bulb, capturing the glowing filament, without blowing out – but not see the rest of the scene. The camera adjusts it’s sensitivity to a light range, but can still only see 3 stops(ish) either side of the mid-point it picks. Pick for the scene and blow out the bulb. Pick for the filament and lose the scene in darkness. Humans have a fixed ISO – a glowing filament is too bright. If we artificially adjust our sensitivity (wear welding goggles) we can see the filament glowing too.

Using full manual mode WE determine the important mid-tones to work with. By adjusting the light input on all three aspects of the exposure triangle we are juggling the mid-tone view according to our interpretation of the scene and what we want the image to look like. It is different for every photographer. Adjusting settings to ‘see’ the scene depends on the eye, artistic impression, our artistic goal and scene characteristics. When we line up the camera exposure meter in the centre, and shoot, we agree with the camera calculations. When following the principle of ETTR we are deciding to ignore the camera. We are compensating for its inability to cope with detail clipping at the sensor. I have a stylistic preference for dark tones. This means that I often deliberately underexpose certain scenes. I get the exposure I want for the purpose. It is certainly NOT as calculated by the camera.

Exposure may be defined as ‘the total amount of light allowed to fall on the sensor’. What the light meter tells us is a good exposure may not be what I want. And, my preference for a shot will be different to yours. The camera has its ‘ideals’ based on its programming – I have mine. In the end I allow the light to fall on the sensor. In manual, my decision is final.

The camera tells you what is a reasonable exposure, calculated on its mid-tone reading. If that is not what I want then it is NOT a perfect exposure for me. Some people may accept it. Or on another occasion I might accept the cameras advice – where someone else might not. A correct exposure could be said to be ‘an exposure that creates a photograph as you intended’. Other people may not agree! But it is still correct for your interpretation.

It’s easy to dress up a machine in technological mythology. Cameras are sophisticated computers created by technologists in such controlled conditions they must be RIGHT! The sensor is dedicated to image creation according to specific parameters – calculations are absolute! Or not! We should remember that we control the technology. Not the other way around. We can be seduced into the technological fascism of ‘calculations and machinery logic’. I prefer to decide how I want my picture to come out and set up my exposure to achieve that. That is why the exposure triangle is a guide and not a calculation.

Being a good photographer is not the same as being a calculator. Using the camera metering system requires skill and interpretation. However, in the end it is only a guide to how you should start thinking about your exposure. The end result of a calculation might be the same. But whilst doing the calculation you have missed the shot. Going manual is about going intuitive – not about getting out the spreadsheet. An intuitive understanding of the exposure triangle helps you think about the relationship between the critical exposure factors. No amount of calculation in the world will do that, or tell you how to interpret a scene. Calculation might help you to think about the scene and your final exposure. It will not teach you to intuitively take a correct exposure.

An interesting quote… A member of the Adobe Photoshop team was talking about an aspect of photoshop and said:
“…it can give you the exact mathematical design, but what’s missing are the eyebrows.”

We can say the same about a scene we are photographing…
The camera/spreadsheet can calculate an exact exposure for the parameters supplied, but is that what I really feel about this shot?

Have fun with your camera!
By Damon Guy
Profile on Google+
Editor – Photokonnexion.com
Netkonnexion on 365Project.org


“There is no such thing as a perfect exposure!” — 3 Comments

  1. Tuesday evening clinic “Principles and the use of Digital Histogram”, taking Damon’s comment and detailed write up re “There is no such thing as a Perfect Exposure”
    On my first read through, initial thought a bit of a heavy read, best have a cup of tea and maybe a lie down before contemplating a second look. Well, have to say several reads later the modern sophisticated computer camera Damon speaks of, with more experimentation on my part, it’s all beginning to make a little more sense.
    Highlighting a number of key words used i.e. Contrast, Calculation, Feel, Sensor, Light Intended, Dynamic Range Light Meter, Photo as you intended, etc. one other word that perhaps springs to mind and often used describing photos, Subjective.
    I have had my current camera two and a half years and was considering upgrading later this year to yet more computer wizardry
    sophistication, clearly still have some way to go understanding and maximising to benefit what I already have.
    Damon’s Tuesday evening half hour hands on camera clinics I’m sure when I say is not only enlightening, from the regular attendance and interest shown very much appreciated by members for it’s presentation style breaking down in such descriptive terms the mysteries of digital photography.

  2. I came in half-way through, but I caught on quickly. I have been exploring the use of the histogram since I learnt about it through a Photoshop course. I really like this approach. Now I have found out how to call it up on my new (2nd hand) camera and see how useful this feature is. It was wonderful to hear that there is no such thing as perfect exposure, but the histogram helps you get within the right bounds.

    Another revalation from Damon! Thank you so much.


  3. I came in half-way through, but I caught on quickly. I have been exploring the use of the histogram since I learnt about it through a Photoshop course. I really like this approach. Now I have found out how to call it up on my new (2nd hand) camera and see how useful this feature is. It was wonderful to hear that there is no such thing as perfect exposure, but the histogram helps you get within the right bounds.

    Another revelation from Damon! Thank you so much.


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