ISO expansion

Having earlier written in my blog that my canon 500d had ISO settings from 100 to 3200, I have now found out that the range is from 100 to 12800. I subscribe to PhotoPlus magazine and it was here that I found this out, basically the higher ISO's are hidden in the default settings so you have to unlock them through the camera menus. I will take some pictures in very low light conditions to show the differences up to this range now.

Shutter speed examples

Below are two photographs taken at different shutter speeds, the ISO was set to 100 and the aperture to f3.5. The top photograph is taken at a 1 second shutter speed and the bottom photograph is taken at 1/4 of a second.

You can see quite clearly that the top photograph is brighter than the bottom photograph and this is due to the fact that the extra length of time the shutter was open for has allowed more light onto the sensor. I will post some more shutter speed photos later showing movement.

ISO examples

Below are two photographs taken with different ISO settings. These pictures were both taken using a shutter speed of 2 seconds and aperture of f3.5

The top photograph is taken with an ISO setting of 100 and the bottom photograph is taken with an ISO setting of 400. It is clear to see the bottom photograph is very over exposed as the 400 ISO setting has made the sensor too sensitive for the light conditions.

Aperture examples

Below are 2 shots showing different aperture settings taken from my set of test shots the top one is taken at an aperture setting of f3.5 (large aperture) and the bottom one at a setting of f14. The two main differences in the photographs are as follows.

1. The bottom photo is darker than the top one this is because the shutter speed on both photos is set the same 1/20th second so as the bottom photograph has a smaller aperture than the top one this means not s much light has got into the lens and onto the sensor
2. The writing on the "Black Grouse" bottle is out of focus on the top picture (big aperture) but it is in focus on the bottom picture (small aperture) this is because the depth of field is smaller for the bigger aperture.

Understanding Aperture, ISO and Shutter speed

From taking test photographs this week and from the ideas given to us by Steve in the lesson and also what I have read about on the internet this is what I understand about the following.

Aperture

This is basically the size of the hole in the lens used for taking a photograph, it is measured in "f numbers" and just to confuse matters the smaller the "f number" the larger the aperture. This means an aperture f22 is a smaller aperture (or hole) than f5.

The larger the aperture in the lens means the light will get in the lens quicker than a smaller aperture. This means in theory that if you are using a fast shutter speed you will need a larger aperture to let as much light in as possible so the photograph is not under exposed.

Another area that aperture will change is the depth of field of a photograph, this means how much of the photograph is in sharp focus. A large aperture such as f2.8 will mean a shallow depth of field meaning only a small area of the photo will be in focus and the foreground and background will be out of focus. However if you use a smaller aperture say f22 then most of the photograph will be in focus from foreground to background.

Shutter Speed

This is how fast the shutter opens and closes to take a picture. the shutter speeds range from (on my canon 500d) 1/4000th of a second to 30 seconds. I can take this higher than 30 seconds to "bulb" setting which means that the shutter will sty open for the length of time I keep the shutter button pressed down (my remote shutter release has a lock setting so can leave it open as long as I need to.

For shots showing movement such as water moving in a waterfall using a slower shutter speed will make the water look as if it is moving, however a faster shutter speed will make the water look like it is frozen in time. When using slower shutter speeds you will need to use something to help steady the camera such as a tripod otherwise you will get camera shake/blur. Shutter speed is related to aperture and need to be adjusted accordingly as using a fast shutter speed with a small aperture will lead to under exposed shots as the shutter speed is not allowing enough light into the camera to take the photograph.

ISO

ISO is basically how sensitive the sensor is, the smaller the number say 100 is less sensitive than 400. The good thing of DSLR over 35mm SLR is the fact you can change the ISO for each shot. Whereas when using film and you loaded a 400ISO film you were stuck with that until you had used all the film. The issue with ISO is the larger the ISO number the more light noise you will get on the photograph. Ideally you need to set the ISO as low as you can for each set of photographs. This means on a bright sunny day you could use an ISO of 100 or 200 however for a dull overcast day you may need an ISO setting of 400 or 800. My canon 500d has ISO settings from 100 upto 3200.

There are times that when taking photos in low light that you may need to use a low ISO and I will try to show these later.

Here are a few links for areas on the internet explaining ISO, Aperture and Shutter Speed (click on the links below)

ISO

Aperture, depth of field & shutter speed

In my next few blogs I will show examples of these areas.

The pictures above show changes in ISO settings starting from top 100, 400, 1600, 3200 all the above were taken at 2 second shutter speed and aperture f3.5 to see the full album click here . When looking at the photos in Picasa if you click on the photo then on the right hand side of the page it shows photo information then if you click on the more info button this will show the setting used for ISO, Aperture and Shutter speed.

Test Shots for ISO, Aperture and Shutter speed

I set up a simple method for taking some test shots of still life under constant light conditions to go through variations of ISO, Aperture and Shutter Speeds.
I set up two bottles of whisky (as they were near to hand) but also as they have writing on them would hope this woud show any blurring up due to depth of field changes (aperture).

I set everything up as follows to ensure the best test I could

1. Two bottles up on a small coffee table at a diagonal.
2. Set my camera up on my Velbond tripod to ensure the camera position was constant.
3. I used my remote shutter release to make sure there was no camera movement.
4. I set up the central focus point only and set focus on the label of the nearest bottle.
5. I used the pop up flash on the camera

I then took a series of shots at one ISO setting then changed the shutter speed starting at 2 seconds and moving down by halving this till I got to 1/200 of a second (so 2 secs, 1 sec, 1/2 sec, 1/4 sec etc) Once I had done this I move the shutter speed to 1/30 sec and then went through a range of aperture (f numbers) starting at f3.5 down to f22.

After this I then moved the ISO to 400 and repeated the above process, then did the same for 1600 and 3200 ISO.

As a test the last shot I put the camera in full auto mode to see what the camera though the best settings were.

I will post a few pitures in my next blog, to see the whole session click here.