Bigger the better for wildlife photography?

07th March 2013
I met a gentleman this week who was thinking about taking up wildlife photography, birds in particular. He was expounding his theory that bigger lenses are always better for wildlife. He told me quite bluntly that I should be getting a Canon 800mm lens because it was the best lens for the job. I told him that it was definitely not necessarily the best lens for the job. I find that the people who spout these theories are usually the ones who have no experience of using the equipment they are talking about and that in their mind bigger is always better.
There are a lot of people who justifiably swear by the Canon 500mm f4.0, it is a superb lens for bird photography, sharp, lightweight (especially the new model) and with a reasonably fast aperture it takes some beating.
By most peoples standards, me included, the 500 is a big lens, however, not this gentleman, his only consideration seemed to be focal length.
He did tell me though, that he thought a Sparrowhawk image I had taken was superb and that the Canon 600mm lens was a great lens but the 800mm was still superior! The old saying about giving someone enough rope to hang themselves is a very true one and he was somewhat taken aback when I told him the image was taken with a Canon 300mm lens.
I also told him that my latest Barn Owl shots could not have been taken with the Canon 800mm because I was already on an aperture of F4.0 and the ISO on my camera was already up to a high level, so using the Canon 800mm with an aperture of F5.6 would have been unsuitable in that situation. Also many of the shots that I take very early in the morning and later in the evening in low light would not be very good with a f5.6 aperture.
A lens with a maximum aperture of f5.6 is fine if you are living somewhere blessed with an abundance of good light, Norfolk for instance, or Lesvos or Cyprus. However, in most of the UK and especially in Wales for me f5.6 is too small for a maximum aperture.
Another thing I told him to consider was the corresponding decrease in Depth of Field as focal length increases. When an image is taken with a big prime lens there is very little DOF and most of the time part of the subject is out of focus. These lenses are very unforgiving in this area and unless the subject is 180 degrees across the focal plane then there is going to be some blurring, this blurring of your subject will magnify with an increase in focal length.
Another thing to consider is that if you add a 1.4 converter to a f5.6 lens you will lose auto focus unless you are using a Canon 1 Series camera body. You may say that with a focal length of 800mm you don't need a converter but a 1.4 converter on a Canon 600mm f4.0 lens will give 840mm of focal length and with the new converters there is not much difference in image quality to the bare lens. Add to this the cropping factor of 1.6 from eg a Canon 7D and you have 600 x 1.4 x 1.6 giving an equivalent focal length of 1344mm with auto focus, image stabilization and very good image quality indeed, this focal length should be more than enough for most wildlife.
Finally if you need less focal length then you can always remove the converter, with the 800mm lens that's it, that's what you are stuck with!
An interesting choice for some, but for me an f4.0 is always better than an f5.6!

However, an 800mm f4.0 now that's different, but the wheelbarrow you would need to move it around would be rather inconvenient!