Understanding Exposure

‘Exposure’ is, in very simple terms, how light or dark a photograph is. 

Too light, and we say it is over exposed - too dark and it is under exposed.

If you get this wrong, you will not get good photos. Period. It is the building block of all photography.

(Technical stuff – skip if necessary! The reason it's called exposure is because it refers to the amount of light that the film is exposed too. The more light that hits the film, the more “exposed” (and the lighter) your photographs will be)

With any camera there are three things that affect the exposure of a photograph:

1. The Light Sensitivity

2. The Aperture

3. The Shutter Speed

We’ll cover what they are, and then look at how they work and what they mean on a day to day basis when you are taking your photos.

Light Sensitivity

On film cameras light sensitivity (sometimes called ‘ISO’) is controlled by the film you use, so you won’t need to worry about it when taking the photographs themselves.

However, you will need to know about it when selecting your film. Luckily this is easy. The higher the number on the film, the higher the light sensitivity. This means you will find it easier to take photos in dark conditions with film with a higher ISO rating.

You might ask why not just use film with high ISO all the time. Well, there is a trade off; the higher the ISO, the more grain your photos will have. Of course you might intentionally want some grain in your photos - that is after all part of the fun of shooting with film – but generally a lower grain will give you a crisper, sharper photo.

But what does all this mean in practical terms?

Films tend to come in the range of 100-3200 ASA/ISO. If you think you are going to be shooting outdoors and in good light, then 100 will work well and give you sharp photos without lots of grain. However, once you are indoors or conditions are overcast, or you’re in shadow, you might struggle with ISO 100 film.

If you use 400 ASA film you are going to be ok in most scenarios; it’s a good all rounder and lots of colour film is sold at this rating. If though you are, for instance, shooting at gigs, or at night time, you are going to need some really high ISO film – you can get them going into the 3000+ range and these can produce some really atmospheric photos, but will not do their best work in the day time!

We refer to higher ISO films as being “faster” and low ones as “slower” rather than high or low ISO/ASA.

Aperture

Whereas ISO is controlled by the film, Aperture is controlled by the lens and it is something you will need to think about when taking your photos.

In simple terms the aperture is the distance the inner blades on the lens are open.

Take your lens off the camera and play around with the dial towards the back of the lens. This is the aperture ring. You’ll see that when you line up the lowest number on the aperture ring lens with the little arrow mark, the blades inside the lens are wide open. When you go the other way, to the higher numbers, they are almost closed.

Unsurprisingly when the blades are more open you are exposing the film to more light. So, a wider aperture (and lower number on the aperture ring) will increase exposure. Go the other way, towards the higher numbers, and you are exposing the film to less light.

Yes, it’s confusing that a lower number lets in more light. You soon get used to it though!

We tend to talk about “fast” or “slow” apertures rather than ‘lower/higher aperture numbers’

But what does all this mean in practical terms?

You know those photographs where the subject is lovely and crisp and the background is all dreamy and out of focus? Those are taking with wide or ’fast’ apertures.

If you’re taking a landscape shot, or something where you want everything in the frame to be nice and sharp, aim for a higher number (i.e. a ‘slower’ aperture).

If you set your aperture ring on your lens to something in the range of 8 that is going to be a good “allrounder” to start with and you can then tweak it from there.

Shutter Speed

In simple terms, when you take a photograph the shutter will open – to expose the film to light – then close again – to stop that exposure. This is, effectively, the time over which your photograph is taken. So the longer the shutter is open, the more exposed the photo will be.

If though the subject is moving too much, or the shutter speed is too long, you will get blur in your photographs.

Shutter speeds are typically measured in fractions of a second. Confusingly, on old film cameras they tend to just be written something like this;

8,4,2,1,15,30,60,125,250,500,1000.

The numbers in bold are in whole seconds; you won’t ever use them for handheld photographs. The other numbers are in fractions of a second; so 1/15th, 1/30th, 1/60th and so on. The higher up that scale you get, the faster your shutter speed.

But what does all this mean in practical terms?

Unless you are using a tripod or a steady surface (like a table) to take a self-timer shot, you want to try and avoid using anything below 1/60 if you can help it. You might get away with 1/30 occasionally, but you’ll probably get a shot that isn’t quite as sharp.

As a good “allround” speed, aim for 1/125 in most scenarios. That will give you good sharp photographs whilst also letting in a good amount of light. If you are taking photographs of a moving subject you should aim for 1/250 or 1/500 if you can get there. Obviously when you increase the shutter speed (and reduce the amount of light getting to the film) you may need to increase your aperture (i.e. use a lower number on the aperture ring) to compensate and allow more light in.