Getting the Down Low : Low light shooting terms, definitions and the exposure triangle in operation.

Getting the Down Low
Part 1


Hopefully I whetted your appetite for learning how to shoot in low light with the intro to this three parter.

In this part i’d like to talk about some of the terminology used and some examples from above and below the water.

The final part will analyse some more specific examples and I’ll share some tips about getting these type of shots in the bag.

Taking pictures using the available light is one of the mainstays of underwater photography, and also one of the first things that people pick up before they start shooting using strobes, so this weeks visit to the tool bag of   tricks is how to best shoot in very little available light, and the best practices to manage the balance between quality and being able to get shots in these conditions.


At first glance a shot like this may seem pretty straightforward, until I tell you that it was taken at first light. So I've had to juggle the exposure a bit, to make sure i'm able to record a nice deep blue, rather than black background. Which has meant in this case that i've traded a low ISO to keep the image noise free, but had to use a slower shutter speed (1/15), which thankfully wasn't too much of an issue as I knew that myself and my model could each hold ourselves rock steady in the water.
So whilst this was a textbook example of the exposure triangle in action, it was equally a test of diving skill and buoyancy control.



Best gear for the job?


Sensor size, it’s all down to sensor size, combined with advancing technology.

A cameras ability to deal with low light has little to do with how many megapixels it has, in fact it’s often a case that less is more.

Digital cameras have advanced a lot in the last few years, and whilst people where caught up in the megapixel race for more and more, the smart money has been on the actual physical size of the sensors being used to capture the light that makes up the picture.
And it’s a simple fact here that bigger is generally better.

So the larger the surface area that the cameras digital sensor has the better it is able to gather light.

Recently though we’ve had access to compact cameras that have had larger sensors, some of them the same size as sensors used in DSLR’s but without the cost and weight penalty.

So don’t think that you definitely need a more bulky camera rig to shoot in lower light and get great results.

All of the shot’s i’m sharing in this blog series have been taken on a micro4/3 camera.

This has a sensor not much bigger than our current favourite compact camera the Canon G9Xmk2 which if carefully handled can give equally impressive results.

And modern sensor technology gets better and better each year, so it’s a win win, as we can now get results on compact cameras that would have been unheard of even a couple of years back.


First though we need a little primer in the camera controls…..



The Exposure Triangle


There are three ingredients that you need to combine in order to get correct exposure in photography, they are the aperture (F number) , the shutter speed, and the ISO.

And in one way or another juggling this three controls to decide the exposure  and artistic content of our shots hasn’t really changed since photography was first invented !

This trio of settings is called the 'exposure triangle' and I plan to do a really in-depth post about these in a dedicated blog for the future.

So this is really just skimming the surface, it’s a big subject, and deserves a thorough look, just not now.

If you're thirsty for knowledge right now about the Exposure Triangle then please have some fun, and Google the terms, there are hundreds of Infographics explaining it in greater or lesser detail.
And im sure that folk will find one explanation that resonates and sticks with them.


If you’re feeling impatient and want to get a fuller grasp on the exposure triangle, then there’s a great app for your desktop, tablet or phone called CameraSim which I use a lot to teach with.
Or just Google exposure triangle and see what comes up.

Briefly though aperture, shutter speed and ISO all have two roles, one is in controlling the exposure, and the other allows you certain artistic freedoms, depending on the shot in mind.

The most important thing to remember with the exposure triangle is that if the light remains the same, and you change one of the options available to you, then you will need to move one or both of the other settings to counteract and keep things correctly exposed.

So with the scene in front of you, you need to work out if the shutter speed is more important, the aperture, or the ISO, and this will be defined based upon the outcome you’d like and how much light you have at your disposal.
It’s quite easy, and I can usually teach people the fundamentals of the Exposure Triangle in a very short time, but they then need to put in the practice time. It’ll make a difference guaranteed.


Aperture or F Stops

Aperture is defined as F numbers or stops, and it works a bit like the pupil in your eye, and opens and closes letting more or less light onto the camera sensor.
When the camera is in Program or Shutter Priority then this will open or close all on it’s own as the light changes.
Or preferably in manual or Aperture Priority you decide on the setting or F number, which will allow you total or some control over exposure and creative freedom.

It’s artistic role allows you to control a photographic phenomenon called depth of field (DOF) which is how much you want in focus front to back in the shot.
It’s how you get those shots where only the subject is in focus as an example.

This little fish was set against the background of a muddy Indonesian bottom. So these examples are to show how you can isolate your subject or have more in focus by altering your aperture.
Exactly what you set depends on how close you are, and the type of lens you're shooting with.
Broadly speaking though, all else being equal, if you choose a smaller aperture (bigger number) you'll have greater Depth of Field, more in focus, than if you'd chosen a wider aperture (smaller number) less in focus.
Your choice though, and yet another example where understanding the exposure triangle will empower you.



Bear in mind that in underwater photography if using a fisheye lens behind a dome, you’ll be restricted to a degree what apertures you can realistically choose, because of certain optical limitations. 

So actually you’ll more than likely find the optimal settings to be around the middle of the range around f5.6 to f16 depending on sensor size. Full frame sensors using fisheye lenses behind big domes like smaller apertures, around f11-f16 to maintain quality.
You can get away with more in this regard with 1” or micro4/3 Sensors and shoot behind a small dome and still get good results at as wide an aperture as f5.6

This technique is equally valuable and affords you artistic control on land for portraits and any other subject where you may want to keep everything in focus, or just a bit in focus. Again it's your choice. Very liberating to be able to make these decisions though, and it's a skill you can learn like anything else.


Shutter Speed

Shutter Speed allows you to decide for how long you want to leave the shutter open, and also controls the light, as if you leave the shutter open for twice as long, then twice as much light will onto the sensor.
This also has an aesthetic advantage in that you can deliberately freeze the action or introduce motion blur into the picture.

You might have seen those pictures of star trails, or car lights at night? or waterfalls and clouds given a dreamy look? this has been done using very slow or long shutter speeds.

Being able to utilise the slower shutter speeds and understanding how that effects the aesthetic outcomes and the way you'll have to compensate your exposures, will teach you a lot about the exposure triangle, and whilst this type of shot is considered cliched in some snobby circles, it's an important path to go down to expand your overall understanding of photography. So fire away and the haters can bog off!!





ISO this is how sensitive the digital sensor is to light, and raising or lowering in your camera will also allow you to control the amount of light and the overall exposure of your pictures

It’s secondary, aesthetic job is more in support of the other two controls allowing you leeway to adjust shutter speeds or apertures to your liking as the light level changes, and it’s this facet of it’s usefulness that we are going to look at more closely in part two of this series.

There are also some quality considerations too, if you have a large full frame sensor then you can get away with shooting at ISO’s from 800 to 6400, and still get acceptable results, the higher the ISO the more noise or grain you get in your shots.

This shot wouldn't have been possible to take without resorting to a very high ISO. In this case I was shooting at a very high ISO. I also made sure that I exposed to keep the highlights in the shot from blowing out, which meant that the picture in camera was very very dark on the screen. Luckily though I knew that I could push my camera ISO much further than was thought possible, and it meant this enabled me to use a shutter speed that I could get away with hand held, as you can't normally use a tripod underwater!
This was a gamble, but it paid off at the time, as I was able to recover the shadow information in my processing software afterwards, without too much of a quality hit.



The most difficult question I get asked most regularly


"What were the settings you used for this picture?"

When this question is asked by people that haven't yet fully got the 'exposure triangle' then i'm always a bit torn. As usually if they do understand the concept of the 'exposure triangle' they most likely wouldn't have asked me so the reason being is that my answer comes loaded with the realisation that if they don't understand the exposure triangle then what , aperture shutter speed and ISO's I chose for that picture, really only have relevancy in those exact same circumstances that I was in.

And by this I don't mean, in a Mexican Cenote, or on the Thistlegorm.
What  I mean by 'exact same circumstances' ie depth, distance to subject, exact time of day, position in relationship to the sun, and a whole handful of other variables that render me giving out the camera settings as being virtually meaningless, unless they fully understand the 'exposure triangle' as it's something which is very context dependant.

Even turning 90 degrees from the original shot may well mean that I need to alter or tweak something.
So im always wary about giving out the settings as if people were to not get the shot they wanted with my 'magic settings'  they'd think I was giving them duff info.

Once you know the exposure triangle, and have used and manipulated it for the best outcomes in your shots, you'll realise why just giving out the data means nothing without the context.

I know some photographers that for an easy life just show people a 'go to' bunch of settings, and instruct the shooter to keep the subject matter to a metre away, and to shoot between 10am and 3pm, this will work to a degree until the person wants to shoot outside of these parameters.
So it's way better to take the time to learn this as it will give you better skills and greater confidence, and you'll know why some shots have turned out and others haven't so you'll learn and progress.

I was shooting here at dusk, not a great time for shooting if you're using the standard settings of f8@1/125sec@100ISO. If I had this shot would have had a totally black background, which is not what I wanted, and I could see the lovely blue at the time.
So I had to reduce my shutter speed to 1/10sec considered to be too slow to get a successful shot in normal cases, however I'm also using a strobe ( flashgun) and they fire at very short durations, so anything they light up will be frozen in motion.
So using this knowledge and the exposure triangle, I was able to keep the background a nice blue, freeze my friend Reda in the foreground and surround him with a blurry dreamy background, helping to focus the attention on him.


How does knowing all this help in a cavern beneath the Mexican Jungle? or inside a Wreck?

Well it will enable you to understand exactly what is possible and what isn't using your skills and your camera. Not what the review sites say what is and isn't possible.

Don't get me wrong, I love Dpreview and PetaPixel but i'm very aware that they can't always answer all the questions, particularly when it comes to underwater photography as it's such a small section of the photography world, and what works well topside, doesn't always translate well to underwater.

So in the final part in a couple of days time, we'll look at some real world examples shot in various conditions and locations and why I've used the camera settings that I have.



If you want more specific advice or have a suggestion for a blog subject feel free to get in touch, details on how to do this are on our contact page. Do the same if you'd like a quote for equipment or to book on one of our courses or workshops (dates are on our Events page). Anyone with an interest in photography is welcome to join the Alphamarine Photography Q and A