As you would be aware every lens has a focal length or focal range and is suited to different styles of photography. For instance, wide angle lenses are great for landscape and long telephoto lenses are ideal for sports, action or wildlife photography.
Wide Angle Lenses are best for Landscapes
The size of your image sensor can actually alter the dimensions of the focal length. This is because any sensor smaller than full frame is technically cropping the width of the image circle. As such, the smaller sensors such as APSC or Micro Four Thirds have what is known as a crop factor.
As an APSC is approximately ¾ of the size of a full frame sensor the crop factor is worked out to be 1.5 times. On micro four thirds the crop factor is 2 as the sensor is half the size of a full frame.
It’s easy to work out how the focal length will differ on a 2 x crop factor. A full frame focal length of 50 mm will become 100mm on a micro four thirds sensor. (These are found in many Olympus and Panasonic DSLRs)
When the crop factor is 1.5 times you need to halve the focal length and then add that amount onto the original focal length. For example a 50mm full frame lens on an APSC sensor would be have an equivalent focal length of 75mm. (50/2 = 25, 25 50 =75). (Nikon, Pentax and Sony use a standard APSC size sensor with a 1.5x crop factor, whereas Canon APSC actually has a crop factor of 1.6)
So, what does this all actually mean for us in practical terms?
APSC sensors are ideal for telephoto lenses
As the smaller, cropped sensors end up with longer equivalent focal lengths, they are ideal for sports or wildlife photography where you need an extra long telephoto lens. For instance on a Nikon APSC sensor, a 300mm lens will have the equivalent focal length of 450mm.
The smaller sensors are not so useful for landscape photographers who use ultra wide angles, given that the sensor is cropped to be less wide.
To address this problem most camera manufacturers have come out with lenses designed for the smaller sensors that actually have a much wider focal length than was traditionally used on film cameras.
The problem with making lenses this wide to accommodate the smaller sensors is that there is a much higher likelihood of distortions in your image.
The lenses also need to be made with very wide and large in diameter so are often heavier and need larger filter sizes if you want to use filters. They are much more expensive to make and hence expensive to buy.
Filters are Expensive on Wide Angle Lenses
For landscape photographers, the full frame cameras are a better option as they can use a standard wide angle lens and have it capture the angle it was designed to.
The opposite problem occurs when you want to use a full frame camera for sports or wildlife photography. You need to buy an extra long lens to reach the distance, and they are heavy and expensive.
At the end of the day though, it still comes down to how much you can afford to spend, and your skill level as mentioned in the previous article.
If portrait photography is your area of interest you may already know that a standard lens of around 50mm is the most suitable for capturing flattering shots of people. This is because standard focal lengths reproduce everything more or less the way it appears in real life. So no facial or body features are distorted unnaturally.
Focal Lengths other than Normal (around 50mm) Distort Perspective
However, if you use one of these lenses on an APSC sensor you will be actually capturing more of a telephoto view or around 75-100mm. It may be more suitable to buy a lens that is marked as 35 or 40mm for portraiture.
In the final part to this series we will look at the importance of good quality lenses for image quality.