008 - Focal Length

Last time I said that I was going to talk about aperture settings next but then it occurred to me that the focal length has a bearing on the aperture setting so I had better cover the focal length first. Simplistically I guess the Focal Length can be thought of as a measure of the magnification where 50mm is somewhere around the base line which is why it is classed as normal. If the focal length is less than 50mm then it is effectively a negative magnification where things start looking further away or smaller and if the focal length is above 50mm then things will look closer or bigger.

The normal range is anything from around 35mm up to say 70mm where you have a bit of positive and negative magnification around normal.  So when the focal length is below the normal range we're considering this to be wide angle, down to 10mm or even 8mm where we are at a very wide angle. Above normal we start at short telephoto up to around 120mm or 150mm, then long telephoto around 200mm to 300mm and above that we're into super telephoto territory.

If you have a DSLR you may well have had a kit lens in the package that you bought and these tend to be somewhere around 17mm or 18mm up to 55mm or 85mm. If your DSLR has a cropped sensor then you will need to apply the crop factor to the focal lengths on the lens to get the equivalent full frame focal length. A cropped sensor is one that is smaller than a full frame or 35mm sensor and will be what you'll find in most 'prosumer' cameras (i.e. non professional cameras).  The crop factor is usually about 1.5 or 1.6 so an 18mm to 55mm lens becomes 27mm to 82.5mm when the crop factor is 1.5. That makes the camera and lens goes just a bit either side of the normal range so is classed as a normal zoom. Some kit lenses do go a bit longer and reach well into the short telephoto range. Also the four thirds standard cameras have a crop factor of 2.0 which means you'd need to double the focal range marked on the lens.

Why have a cropped sensor? Well a cropped sensor camera start off as far cheaper than professional cameras and can use smaller and less expensive lenses. The price of the cropped sensor cameras start around £300 and can go right up to almost as much as a full frame camera which you'd be expecting to pay well over £1,000 for the body only and anything above that.

If you have a compact or point and shoot camera the focal length range will be something similar to the DSLR with the normal kit lens. That is starting at somewhere around 24mm to 28mm and going up to anything around 3 to 7 times zoom or about 75mm to 200mm as equivalent to a full frame DSLR.

In general you would be using a wide angle where you were wanting to get a lot of the scene into the frame or where your not able to stand far away from a large object that you were trying to photograph.  This would be mainly wide panoramic landscape shots or maybe architectural images. A problem you may find with wide angle shots is the tendency to get distortion, particularly towards the edges and also if pointing the camera upwards or downwards. Things close up also tend to look disproportionately large to taking portraits with wide angles would tend to make the subjects nose look quite large. Perhaps not a good idea for serious photographs but could be used for fun shots.

Photographs taken in the normal range are just that, they would be how you would normally see them. This is why kit lenses are favourite as a starting point for your photography because it can be used for all types of photographs.  Even now, when I have four other lenses in my bag, I will use the kit lens for about 75% of my shots because of the versatility. I take mainly landscape shots but the lens is well capable of good portraits and it is even quite good for close up photography.

The short telephoto range is good for getting closer when you can't physically get closer to your subject or want to stay a little further back. For example taking photos where there is some barrier to getting closer or if you taking people photos when you don't want to invade their personal space.

The longer telephoto ranges are used when you can't get anywhere near your subject. So this would be where things are very far away or very small (or a bit of both). The obvious use would be wildlife where generally, in the wild, the subject doesn't tend to come close up to you, or maybe you don't want to get too close to the subject.

These uses are, as usual, not hard and fast rules so you can mix it up a bit to make the images you want. I hope this post has been useful and next time I will definitely get onto aperture settings and depth of field, promise.