My limited knowledge of bird photography leads me to say that 400mm is the minimum when using a 1.5X crop sensor body. It greatly depends on what size sensor they use. There is no formula involved.just seat-of-the-pants knowledge. But why not 300mm?īecause people who do this have empirically come to that conclusion. It is said that if you want to shoot birds, then 400mm is the minimum. Now that you know a bit more about what "Zoom" means, you should know that there is no answer to your question. When the image of the subject is the same size as the subject (IE, the magnification ratio is 1:1), both the subject ant it's image are 2FL from the lens center. This shows that when the subject (being imaged) is infinitely far away (IE, the light rays from it are collimated/parallel), the distance from the center of the lens to the image is one FL. That may not help if you don't have a clue what "Focal Length" is? FL is a key property of all lenses. "Prime" is a short way of saying "Fixed Focal Length". The opposite of "Zoom" is "Prime" for some long forgotten reason. "Zoom" is a short way of saying "Variable Focal Length". That's primarily because you don't know what some words mean. If you're good at sneaking up on birds, you can use a shorter focal length. For example, with a 400 mm lens on an APS-C camera at 40 meters, you will cover 100 X the sensor size, or 2400 mm X 1600 mm.Īs far as needing 400 mm to take pictures of birds, this comes from the experience of the people that do it. Or, if you want to know what your field of view is going to be at a given distance, just use similar triangles and multiply the sensor size by the ratio of the distance to the focal length. So to get the angle of view in either dimension, you need to solve the triangle whose base is the sensor dimension and whose altitude is the focal length. An APS-C sensor, commonly found in DSLR's, is 24 mm X 16 mm. First, you need to know your sensor size. A lens with a small angle of view will allow a small field of view at long distances.Īny focal length lens can take a picture at very long distances you can take a picture of the moon with any camera, but if you want the moon to take up a reasonable portion of the picture, you will need a narrow angle of view.Ī calculation you can make regarding the angle of view.
A zoom lens is one that can change its focal length, which has the photographic effect of changing its angle of view. The angle of view of any lens on a specific camera is controlled by its focal length. Your question does not in fact relate to "zoom" or distance but to the angle of view. However, you will want to use the maximum resolution and quality to make this effective - for example you may have got your bird in the central area of the picture, and want to crop out more than half of it in your image editor. One way around this is to crop the picture after you've taken it - that has the same effect as zooming in. On my camera I can go to 486mm and that's not nearly close enough sometimes.
This lets you think you are getting 'close' but all that's really happening is that the field of view changes.Īs for 300mm or 400mm - I assume those are 35mm equivalents? with birds you need the biggest zooms of all as you will be shooting from quite a distance. As you zoom in, the square will become smaller and smaller, as your field of view narrows.
At full wideangle it will be quite a large square. Imagine a square on your living room wall. As long as you are within your lens closest focus, you can zoom on something relatively close, but make it larger in your viewfinder. What you get close to depends entirely on where you are pointing your lens. What a telephoto zoom does is narrow the angle of your field of view which gives the impression of getting close up. Then there are the more recent 'superzooms' which go from eg 27mm to 400mm or even 600mm, in other words from wideangle to useful telephoto.Īs for 'how far', that's not really a useful term. It can be anything from a wideangle zoom (eg 18mm - 35mm in old 35mm terminology), to a telephoto zoom, eg 200mm - 500mm.
But why not 300mm? Thanks in advance.Ī zoom lens is simply one that's not one single focal length. how far away does a 200mm lens "zoom"? A mile? 1.5? Is there a calculation? I'm having difficulty understanding zoom lenses.Į.g.