Direct-vision finders are found on compact cameras – if they have a viewfinder at all; many digital compacts don’t bother. A direct-vision viewfinder is essentially just a small window. The window’s frame may correspond to the borders of the image you’ll shoot, or there may be a marked area within the window to show the actual picture area. In this case, round the edges of the finder you can see stuff which won’t appear in the final picture.
Because looking through a direct-vision finder is like looking through a window, your eye can adjust to focus on close or distant objects. Just as when you are looking around you normally, whatever you look at appears in focus, so you get the impression that the whole scene is in focus. However, it’s by no means guaranteed that everything in the final shot will be in focus: things that seemed clear in the viewfinder may be blurred, even blurred beyond recognition.
Ribblehead Viaduct, North Yorkshire (Jon) When looking at the SLR finder the eye stays focused at a constant distance. This can weaken our sense of depth, but the third dimension is always there and in some shots it’s immensely important
With a reflex finder, and with the LCD screen, you actually view through the camera lens – the same lens that takes the picture. In a single-lens reflex (SLR) camera the image is relayed to your eye by a mirror that flips out of the way when the shutter is pressed. We can lump reflex viewfinders and camera-screens together as ‘through the lens’ (TTL) finders. Surely TTL viewing means that what you see matches the photo you’ll get? You can certainly be forgiven for thinking that it should, but it’s not that simple. Sometimes it gets very close, but at other times it doesn’t.
Actually, the SLR finder image is a bit of an illusion. It is not a three-dimensional image; you aren’t literally looking through the lens. What you really see is the image projected by the lens on the focusing screen. When you look directly at the world, your eye has to refocus to look at distant or near objects (even although we often don’t notice that it’s happening). When looking at the SLR finder the eye stays focused at a constant distance (of course the lens may have to refocus to give a sharp image of things at different distances). And with your eye to the viewfinder of an SLR, the image becomes your entire field of view, and there’s a tendency to look at it piecemeal rather than in its entirety.
Next time you look into an SLR viewfinder, think about the fact that you are looking at a projected image which has no more real depth than the image on your computer screen. Let’s hope that this helps to focus the mind on the image as an image.
Another problem is that the viewfinder doesn’t necessarily show you the full picture area. Unfortunately, a true 100% viewfinder image is largely the preserve of professional SLRs – most others shave a good 5–10% off what you actually get in the image. Digital camera screens are much more likely to give closer to 100% view, but you should always check.
There’s an even more significant reason why what you see in TTL viewing isn’t always what you get. This is all to do with something called depth of field. We’ll explore this in more detail in Chapter 3, but for now, depth of field simply means what is in focus and what isn’t. If the image shows one object sharply focused, with everything else out of focus, depth of field is small. If, however, objects both nearer and more distant also appear in focus, depth of field is large.
Druidston, Pembrokeshire (Chiz) Focus is on the closest grasses, depth of field is small, and distant landscape soft
Focusing and depth of field: what’s sharp and what’s not
While a direct-vision finder gives you the impression that everything is in focus, with an SLR you can often see that some things are in focus and some aren’t. Focus on a nearby leaf and the distant landscape may well appear soft. This could be a good thing if you want to concentrate attention on that leaf. The problem is that when you take the shot, the background sometimes looks much sharper than it did in the finder or screen. In other words, depth of field in the shot is much greater than in your TTL view.
With direct-vision finders, the opposite is often true. When you view, everything appears in focus but this is rarely, if ever, matched by the final shot. With a little luck the main subject is still in focus, but foreground and background may not be. In this case, depth of field is much less than it appeared in the viewfinder.
It’s not hard to understand that a direct-vision finder doesn’t match the final photo. You’re looking through a separate window, not through the camera lens. But in TTL viewing you are looking through the camera lens, so surely what you see should match the final photo?
Well, no. You are looking through the same lens, but it isn’t necessarily doing exactly what it does when it takes the photo. Specifically, the aperture is often different. When you view, normally the aperture is at its widest and depth of field is minimal. When you take the shot, however, the camera often sets a smaller aperture, causing depth of field to increase. Camera manufacturers set things up this way as it lets the most light in at the viewing stage, and therefore gives the brightest image in the viewfinder (easier to see than a darker one!), regardless of the settings you use to actually capture the shot.
Once you know this, it becomes very easy to check the image on playback and change the aperture if required to reduce or increase the depth of field. Or even use a button called depth-of-field preview to check this before shooting (if your camera has this it’s usually found near the lens mount)
Exposure and contrast
The accuracy of modern autofocus systems means that the camera usually gets the main subject sharp – although this does require you and the camera to agree on what the subject is! Depth of field, however, means that there’s rather more uncertainty about whether other things in the shot are or aren’t sharp.
There’s a very similar relationship between exposure and contrast. Just as the human eye adjusts focus so fast it gives us an impression of immense depth of field, it can adjust almost instantaneously between deep shadow and bright sunlight. Most of the time we don’t see shadows as completely black or bright objects as totally white. We might call them black or white but we can still see detail within them.
However, digital images (like film before them) can’t always stretch this far. If the brightness range (sometimes called tonal or dynamic range) of a scene is too great, the most a camera can do is aim somewhere in the middle.
Again, we’ll go into more detail on this later on. The key point now is that this is another way in which what the eye sees can be different from what the camera records. And understanding that fact is the start of being able to deal with it.
Aperture and shutter speed
Some cameras now have more exposure modes than you can shake a trekking pole at: Landscape mode, Portrait mode, Night portrait mode, Party mode, Alpine bivouac mode (OK, we made that last one up)… And yet the most important task that all of these modes perform is to determine how the camera sets aperture and shutter speed. You might never set these manually but they are still key to every shot.
Aperture just means ‘opening’. There has to be an opening to admit light into the camera, to reach the sensor (or film) which captures the image. Varying the size of that opening is one of two ways in which we control the amount of light admitted.
Graphical display of aperture on screen of a Nikon D3100 (Jon)
However, varying the aperture also affects depth of field. This is a bad thing if it gives us results we didn’t expect, but it becomes a very good thing when we can exploit it to get more control over our results.