sábado, 28 de abril de 2012

Understanding Exposure Compensation - Sunny 16 Rule - A Practical Guide

I originally was posting about the Rollei EV scales but then it grew more complex and I full post about Exposure and EV and LV were needed in a way they preceed the actual Rollei Exposure Table post I'll post after.

I am not a pro but rather a very interested guy! I just started shooting FILM and home developing with Caffenol and it came to my full attention that I will never get good results if my manual exposure isn't right...Well, shooting film requires 100% manual exposure... Then I better learn it, well and quickly!

Let's start!

The Famous SUNNY 16 Rule

In very simple terms -> in a sunny day, with very bright natural direct sun light and no or almost no clouds, the Earth is lit uniformily from 10am to 5pm. In such a day you WILL get a great photo (exposure of your photo will be very correct, showing a good amount of contrast and details, light areas and darker areas) if you set your camera to do the following:

Aperture: F16 (the name of the rule is Sunny 16!!)
Shutter speed: 1 over the ISO (ASA) of your film. That is: I shoot ISO 100 film = 1/100 shutter speed OR the closest you have.
Why is the above in red, you ask?? Because not all cameras have ISO 100, but 125 instead! Just like digital usually has ISO 200 but shutter speeds on cameras are usually 250. 125 is the closest to 100, and 250 the closest to 200. Got it? You will set your shutter speed to the closest speed number your camera has to offer you for your film ISO.

Making it visually easier: The "natural ONE FULL STOP shutter speed scale", goes like:

Faster                                                     ----> slower shutter
Less light                                                 ---_> more light

1/1,000 - 1/500 - 1/250 - 1/125 - 1/60 - 1/30 - 1/15 - 1/8 - 1/4 - 1/2 - 1" - Bulb

your mileage may vary.... your camera might have a couple numbers different, but in general that is what you get. If they are different, it doens't matter because what the specific scale on your camera will tell you is that each preceeding  (right to left - or smaller denominator to bigger denominator) number allows twice as much light into the camera as the next on the left. So changing from 1/60s to 1/30s allows 2x more light in. Or, cocking from 1/30 to 1/60 cuts the light in half and therefore your picture will be darker.
Every one of the examples above equalled ONE FULL STOP change = more or less light.
Same way changing from 1/250 to 1/15 means 4 full stops change for more light (brighter outcome) or 4x2 = 8 times more light coming in.

Terminology and Practice

EV means Exposure Value - Exposure Compensation

No Correction == No Compensation == EV 0 , or (+/- 0EV)

EV Compensation of -1 EV = making UNDER-exposed by one stop = Darker = image is too bright and needs to be darkened.
EV Compensation of +1 EV = making OVER-exposed by one stop = Lighter = image is too dark and needs to be brightened.

1EV == +/- 1 f-stop change == half / double shutter speed or light-in allowance. So 125s (1/125) F8 +1EV == 60s F8 OR 125s F5.6

Let's remember (know by heart, don't you!?) the True APERTURES scale:

They are "F/"s: 1, 1.4, 1.8, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45 (...)

Going from F8 to F5.6 allows 2x more light in. Going from F4 to F16 allows 4x less light in - or minus 4 full stops of light.
How do we count that? Simple.
Find F8 then count how many full stops until F5.6 (the above table only show full stop changes to make it easier). F8 is on the right side and F5.6 is the one left to it. So, ONE stop change.
F4->F16: Find F16, then count until F4 by full stops: 11, 8, 5.6, 4 - that is 4 f-stops change. Got it?
From F16 to F4 = +4 EV = 8x brighter = 4 f-stop more light.

Sunny 16 Rule is EV0 by default! So -> F/16 - 1/ISO - EV0.  You will see why this is EXTRA important.

* Adjusting Sunny 16 Rule * to ANY exposure need - Here the fun begins

Very often you hear people saying you need a +1EV compensation on the photo because the subject is in the shade, or because of too many light clouds, etc. That means you need to either change your aperture (right to left) by one or your shutter speed left to right by one full stop (ex. F8->F5.6 or 500s -> 1,000s).
Real life example: you're hiking. Shooting some of your friends under the bright sunny day in an open area. Shades are disctinct around you and them. That's perfect for the Sunny 16, right! Of course. BUT, you notice that their faces are in the shade. Perhaps the orientation of the sun makes their face come into their caps shade, whatever, you want their face to be clearly exposed and visible. Alas, if you shoot +0 EV "Sunny 16 straight" (F16 - 1/100 - +0EV) you'll expose all correctly but their faces might come too dark. Your girl\boyfriend has lovely eyes and you want to be able to see them. WHAT DO YOU DO??
Well, you re-expose your frame, making the darker areas a bit brighter/lighter. Not too light that all the rest is blown up in and white aura, but just a tiny bit, enough to make a shaded spot a smidge brighter. How? You add +1EV stop, to over-expose an area with shade.
Easy option are: F16->F11 (one stop brighter); 125s->60s (one stop bringhter). If you do both then you'll get TWO stops brighter and could ruin you exposure.
There you go. You'll get more details out o the shades and it's unlikely that +1EV will ruin the rest of the exposure of your photo.

<< Always keep in mind that the Sunny 16 relates to the amount of light incident on the subject. So take your measurements accordingly >>

Now the BIG SECRET CONCEPT: The Sunny 16 "straight" is the STARTING POINT. By that I means you should set your camera to F16 1/ISO and from there add or subtract EVs to reach any exposure you'll ever want. I'll show you how.

Memorise these quick settings - Sunny 16 Short and Quick Daytime Table

F-number                Light Conditions                                Shadows                                                
F22                          Snow\Sandy w/reflections                                 Dark shadows with sharp edges
F16                          Sunny \ beach\mountain\squares etc         Distinct
F11                          Slight Overcast                                       Soft around the edges
F8                            Overcast                                                                               Barely visible
F5.6                         Heavy Overcast                                                                               No
F4                            Open Shade / Sunset\rise                                                              No

-It's heavy overcast. You set your camera to 1/ISO speed and F5.6 then you get about perfect exposure.
-You're on a sandy beach, blue sky, very bright. Set to 1/ISO and F22 !
-It's slightly overcast. One f-stop will do the trick. You just need +1 EV, so set 1/ISO and F11. Easy

You will have noticed that the part of Sunny 16 Rule concerning the ISO over speed (that is shutter speed) NEVER CHANGES. That's right, you can get most exposures 'ok' by changing the aperture alone in a regular lit day.
There will be times when only the aperture will not be enough! Then you'll also change the speed of the shutter. Although your ISO will be the same (talking about FILM here - you can't change ISO like on digital. You have to replace the whole roll).
In the quick table above we just changed the F-stop. But we could have changed the speed too. Remember, from F16->F11 is one stop more light (=double of light) so instead of F11 you may keep F16 but dial 1/50 and not 1/100. Doubling the light only changing the shutter speed and not the aperture.

Film ISO for ISO's sake

ISO is the film's sensitivity to light. A higher ISO (ISO number >) means nore light will be caught on film for the same f-stop and speed. And so,
ISO 100 -> ISO 200 is a 2x increase of sensitivity.
ISO 400 -> ISO 1600 is 4x as much. And ISO 400->ISO 100 is 4x LESS light.

It's importante because we now know the third way of getting the desired exposure. ISO ! 
Even if you need to change your film it might be the case if the settings for the exposure you need are infeasible. I'll show a simple table capable of solving that question soon, but giving an example for now, imagine you want to catch a lowly lit scene of action. You know that without a tripod and in order to stop action you want at least 1/125 sec speed (125s) and you check all exposures for your slow ISO 100 film and they make you want to cry....ISO 100 is too slow and light sensitive to catch anything. But hey: if it takes you for ISO 100 1/8 - F8, if you change your film ISO to 1,600 you'll only need F8 - 1/125 !! Done! 
A 4x increase in ISO = 4x increase in light in without changing the other settings!

Time to go back to the EV Compensation, and expand it

Now it's time to learn to read and use the EV chart. The one below for what I call the Sunny 16 Rule EV Chart because it only goes up to F16. BUt you now know how to expand it one stop up if you need. Or more.

It introduces the ISO speed, EV Compensation, Shutter Speed and Aperture in a same table \ chart. And here's how you use it, in an easy way:

Since I don't know how to make Google Docs turn into Pictures, I'll post a link. Please forgit me, open the link and follow through.

What you have to do is simple find the ISO number of your film on the far left column, then the F-number you intend to shoot. The lines under the F number column show you all the shutter speeds available for that F number.
To use this table you need one more information, that I add now:

The EV number - or put differently - EV compensation form the scales under each ISO number (column).
Take a look at the EV Chart above. Let's find Sunny 16 there!
Look for "f/16" (F16) on the Exposure Setting columns. Now look under Exposure Value Numbers for your ISO number, for example 100. Now look down until you find the number 15 under ISO 100. Got it? What is the shutter speed for the intercept of ISO 100 at line 15 EV and f/16 ? It's 1/125, or the closest speed to 1/ISO ! There! F16 - 1/ISO. That's because the 15 is actually the LV or Light Value of Sunny 16 which translates into ZERO Compensation!

Below the LV / EV chart with light value and compensation for each exposure

LV Chart  - GoogleDocs link

Look for LV 15. You'll see that it is actually ZERO ("0") compensation. That is exacly what we've been saying, right. For a Sunny day, bright and with hard shadows you'll set your camera correctly exposed @ 1/ISO - F16 and +0 EV.

Although EV and LV are not the exact same thing they are pretty close and, we'll use them exchangeably here for ease&clarity's sake.

Reading the LV Chart:
- LV value 15 - Subject medium coloured in bright sunlight
-LV value 10 - Landscapes just after sunsets\rise, and I also find this "EV" adjust very good for taking pictures from behind a subject against a window in a heavy overcast day with very bright white clouds coming into a room.
-LV 0 - dim interior
and so on.

NOW LOOK: The LV scale is next to the Expusure scale. What does it translates into?

If you read LV 8 you have E (Sunny 16 Exposure) -7 -- that is -- from the starting poing 15 you need to add 7 stops of light in order to be able to capture on film what you see, inside a house lit by lamps.
Seven stops,,,,,,Let's say we choose F5.6. Count with me:

1 stop - 500s - EV 14
2 stop - 250s - EV 13
3 stop - 125s - EV 12
4 stop - 60s - EV 11
5 stop - 30s - EV 10
6 stop - 15s - EV 9
7 stop - 8s - EV 8   --->  LV 8 and 7 stop brighter!

We'd call that spot EV 8 on the chart.  Don't confuse the add\taking stops with the numbered EV. It's easy if you practice a bit with the charts to get the hang of it. You will always look for the LV number and then call it EV. Read down the ISO and Aperture lines to get your shutter speed.

USING both EV and LV Chart together:

Now we can add both info together and use in practice. Ask me the chart in excel or word file if you want.


1] Look on the LV Chart for the kind of light on the subject you are likely to be trying to shoot. Say it's a white car in a very bright sunny day :) - The LV value is 17, over 15 by two (second column, right next to the LV one) so you need 4x less light coming in to correctly expose the car,
2] Note that your film ISO is 200,
3] Go to the EV Chart and chose an Aperture, say F16,
4] Find the line under ISO 200 & F16 corresponding to EV 17 ==> 1/1,000 sec shutter speed.

of course 1,000s is higher than some cameras can do, especially older film ones, but then you're shooting ISO 200 in a bright sunny day, dumbass! ;)
Change your film to ISO 100 or lower ---- or,,,,,,, try F22 (= 1/500sec) or even higher, if you have it available.

Another example: You're bored in your flat, it's incoveniently overcast outside, looks like it might rain. No need to say there's not much light out there....AND it's night time....PLUS, you only have ISO 100 film.
Annoying as it may be you want to take a picture of the lovely outside lit by all the neighbouring buildings, lamp posts and cars. Can you do it? Can you still get the trees and the details of things in such low light? You can try! And it will work. See how:

EV 2 will help us. Look in the chart - you see under ISO 100 that the options available are dim....I mean...... you can get F4 - 4" (four FULL SECONDS!); F5.6 8"; F8 - 15" or F11 @ 30" (WOW). F16 is .... do the math.
Of course with a good tripod those 4 full secs or even 15 will not be a problem. So there you have it!
The bad part is that your DoF (Depth of Field) and resolution are going to be less than perfect. F8 is ok though.....
You can also move your ISO up and get better shutter speeds. Or even, a faster lens, say F2 and so have the 1" (one second only) option....
But really dark conditions are tricky anyway.

This is it. I'll add some pictures when I revisit this post.

Cheers peeps!

3 comentários:

  1. Estudando muito, né? É um mundo de conhecimentos. Óptica, mecânica, electrónica, química, há de tudo na fotografia.

  2. Sim sim! Escrever isto me ajudou a concretizar o conhecimento. Aprendendo também que fotografar à 'moda antiga' era muito difícil! Digital é muito fácil. LCD faz tudo ser imediatista e descartável.

    Como pode?? Eu estou com um rolo de 120mm há umas 2 semanas ou mais. Tirei 6 fotos e tive que tirar foto de qualquer coisa pois descobri que é extremamente difícil fotografar com comprometimento, querendo obter um resultado que não pode ser verificar imediatamente, mas tem que pelo menos servir um propósito científico; prático para o estudo da fotografia e do caffenol concomitantemente.

    O que entendi é que sem uma perfeita composição de exposição, mesmo que minha revelação e fixação estejam perfeitas, os resultados finais não serão bons de modo que preciso antes ter certeza que as composições foram boas e assim poder avaliar o resultado do processo de revelação e, se o caso, poder corrigir os erros - sabendo aonde os erros ocorreram....

  3. Exactamente! Sua interpretação está correctíssima. Eu, que tenho já uns aninhos a mais (60) cresci fazendo fotos analógicas e ansiando ver o resultado para poder ir corrigindo. Nós usávamos fotómetros de bolso para saber aberturas e velocidades, era tudo pensado e estudado antes de se apertar o gatilho. Com a prática a gente vai sabendo mais ou menos regular, a regra do f:16 é óptima para ser seguida de cabeça. Tenho um filme de 100 ISO, está Sol claro, coloco f:16 e velocidade 1/125. Cena mexida, subo para 1/500 desço dois na abertura para f: 5,6 ou mesmo f:4 ou subo para 1/1000 e desço para f:2,8.
    Pratique bastante e escolha horas em que o Sol está a 45º de altura. Sol a pino deve evitar-se, em paisagem o horizonte deve ficar abaixo ou acima do meio, nunca ao meio, enfim, há um sem número de coisas na fotografia que faz dela um hobby por excelência.
    Abraços e se divirta aprendendo.