DZ's camera 101 - The Aperture, shutter speed and ISO balancing act- DRAFT

[DrunkenZombiee]

I have had 30 mins or so tonight and with some of Pen's comments I realised how useful some of the fundamentals may be to some of you when using your compact, bridge or DSLR camera. This is a very rough draft and I will ad pictures and diagrams to help explain the concepts better.

DZ’s Camera 101


There are three main fundamental settings to balance out on a camera to control the picture you are taking. These are universal for all cameras Digital or non-Digital.

1.   ISO â€" this is the sensitivity of the film/sensor in your camera. The Lower the ISO the less sensitive it is to light meaning that lots of light is needed to get a picture (or a longer exposure to the light). Lower ISO’s suffer from less noise as the film/sensor needs to be less sensitive and it more tolerant to noise. The higher the ISO the less light is needed (or less exposure time) however the more noise will be present in the picture.
If using film this will be the sensitivity of the roll of film you are using but if working with a digital camera you can change the ISO before taking each picture.
2.   Shutter speed â€" This determines the length of the exposure and in turn the amount of light per picture that the film/sensor is exposed to over time. Shorter shutter speeds will freeze the action dead, while longer shutter speeds will add blur to a moving subject.
Think of your film/sensor as a bucket and the shutter speed the amount of time that rain is collected into the bucket. The longer the rain falls the more that is collected, the principal is the same for light particles called photons.

Pictures to be added of shallow and wide DoF.

3.   Aperture â€" This is how wide the lenses diaphragm blades are. This controls the amount of light being let into the camera but also this can control the depth of field (the amount of distance that is in focus). This can be a complicated concept to get your head round but I find the best way to explain this is to look at a diagram of what the lens does (below).

Diagram to be drawn and added

When the diaphragm has a very small hole only light from a more acute angle is allowed through the lens. When this is projected on film at the back this allows more of the image to be in focus as the acute angle gives a higher focus plane.

Diagram to be drawn and added

When the diaphragm is wide the opposite is true and the more obtuse angle gives a shallower plane of focus.

Managing the Aperture, ISO and Shutter speed together is important to achieve a good picture. All three must complement one another so the sum of their parts adds up correctly to achieve correct exposure.
Scenario one : I am taking a photo of a car driving fast on a track. I have a shutter speed of 1/50th of a second, and ISO of 400 and a aperture of f/8. All of these setting are in roughly in the middle of an SLR’s capabilities. After taking the photo I notice that the car is blurry as the exposure time is too long to get a crisp clear image. I decide to increase the exposure time to 1/200th of a second so there is less motion blur. After taking this photo I notice that the image is far darker than the last and it is very hard to see the details as all of the dark pars have merged into black blobs. I do however see that the shutter change in shutter speed has got rid of the motion blur and I want to keep the higher speed but make the image lighter like before. This is the balancing act that we talked about earlier. We need to change the ISO, Aperture independently or both together to get the brightness where it was before. A compromise if you like has to be made for the shutter speed increase. We can either increase the ISO which adds noise as the film/sensor becomes more noisy or increase the aperture which lets more light into the camera but gives us a shallower depth of field. I decide that the depth of field can be shallower and I will still get the result I want to I increase the Aperture to f/4 (yes it’s a lower number when increasing) to let more light in. I take another photo and it is still not bright enough and I cannot increase the aperture any more as my lens is as wide as it can go so I have to up the ISO and run the risk of adding noise. I up the ISO to 1600 and take the photo again. This time the photo is perfect.

Scenario two : Its Christmas and David has just proposed to Tina under the Christmas tree. The entire family are so happy and they want some nice portrait photos taken of them to show off the new ring. Tina loves the idea of having the Christmas tree lights out of focus in the background to bring emphasis on the ring and the soft glow of the light behind to add colour to the shot.
You set up your camera beginning with your camera set up on ISO 400, f/8, 1/50th as before. The shot is alright but you want more out of focus as the multiple light sources are not as creamy and soft as you want. You increase the aperture to f/2.8 and take a photo. You live the soft and blurry lights behind but the shot is too bright and overblown with all of the details gone. You increase the shutter speed to 1/400th of a second and take the shot. This time it is perfect with the soft background and correct brightness. When loading the picture onto the computer you looked at the 1/50th of a setting shot and compared it with the 1/400th of a second shot and noticed another benefit in that the shot was more crisp thanks to the shorter shutter speed meaning that the action was more frozen and there was less camera shake and less noticeable movement from the subject to cause blur.
So these two scenarios equate to modes on your camera. These modes are called Aperture Priority mode (Av on your camera) and Time priority mode (Tv on your camera). Instead of having to change the setting yourself your camera when in these modes will change the other settings available to attempt to give either the time or aperture priority over the other settings.
For example if I want to shoot at 1/200th of a second and with the current aperture the scene is judged to be too dark by the camera it will automatically decrease the aperture to ensure correct exposure (brightness).
So with these three settings all need to add up correctly and compensate for each other to achieve correct exposure.