Using Aperture priority – Part II
Creative digital photography
In the first part of Using aperture priority, you saw that the depth of field is controlled – in part – by the aperture setting in AV mode.
Another factor that influences the depth of field is the focal length.
Put simply, the focal length is your zoom.
It is the distance in millimeter (mm) between the optical center of your lens and the sensor.
If you have a zoom lens, such as my 75mm – 300mm from the last post, you will notice a difference in depth of field depending on your zoom.
Distance from the object of your desire
Focal length is also connected to your distance from the object.
You must be further away from the object of your desire in order to zoom in on it.
This doesn’t change the depth of field much, but it does change the composition. Making it easier to get what you want in the image.
Distance between object and background
Another thing that influences the depth of field – indirectly – is the distance between the object and the background.
The further away the background is from the object, the better the blurring of the background.
Once again, this doesn’t change the depth of field exactly, but it can and does make it easier to get the composition you want.
These three factors;
- distance from the object
- distance between the object and the background
- focal length
have a combined influence on the image you create.
Some things to keep in mind when using AV mode.
- Since you have a shallow depth of field, you need to set your focus on one point and be sure you’re focused on what you want to be sharp.
- In low light situations, you may have to pop up your on camera flash, if you are close enough to the object.
- You can also turn up your ISO, but that’s a story for another post.
So now you can go back out and experiment.
Use a zoom lens and find an object that you can capture at 75mm and 300mm (or whatever limits in focal length your lens offers)
Set your aperture as low as possible and try to keep it that way for all images.
Back on PC you will see the difference in depth of field.