As you can see, a beam of reflected light from the top of the fish passes through the pin hole and hit the film near the bottom; in the same way, a beam of light from the bottom of the fish would pass through and hits the film near the top.   The image of the fish created on the film would therefore be upside-down, and it would also be inverted left-to-right.

    This inversion also happens with regular cameras, and even with the human eye - but our brains automatically uninvert the image for us, in the same way that they filter out the capillaries on the retina!

    What's true for pinhole cameras is also true for other cameras.   If the lens on a regular camera is set to focus at 10 feet, then everything which is exactly 10 feet from the camera will be clearly focused.   However, everything which is less than 10 feet or greater than 10 feet away will be less focused, and the larger the aperture, the less focused they will be.   The size of the aperture therefore directly determines the depth of field, which is the depth of the viewed image which is well-focused.   If all other things are equal, then a lens which is set to f4 will always have a "shallower" depth of field than the same lens set to f22.

    The third factor which affects depth of field is the focal length of the lens.   A telephoto lens with a focal length of 300mm or 400mm has a much shallower depth of field than a wide-angle lens of 15mm or 20mm.   The telephoto lens might have a depth of field of only 10 feet for a subject which is 100 yards away, whereas the wide-angle lens might be able to clearly focus all the way from flowers a yard from the camera to mountains several miles away.   Many digital cameras have sensors which are smaller than regular 35mm film, which means that they need only very short focal length lens to cover the same angle of vision.   Since the lens has a short focal length, this means that the depth of field is much deeper than for a 35mm camera covering the same angle of vision.  For instance, a Canon G2 digital camera has a very small sensor and a 7 - 21mm zoom lens to cover it.   This lens covers an angle of vision which is equivalent to a 34 - 102mm lens on a 35mm camera, but because it's the actual focal length of the lens which determines the depth of field, the G2 has a much greater depth of field than a 35mm camera which is shooting exactly the same scene with a 34 - 102mm lens.   This increased depth of field is a particular advantage in macro photography, so this is one area in which a point-and-shoot camera has advantages over a more expensive SLR camera.
 

   Macro photography is one specialized area where photographers constantly struggle to get more depth of field.   Bugs are often very small, so bug photographers rely on special equipment such as extension tubes or macro lenses which allow the camera to focus closer than it would normally be able to.   A telephoto lens might not be able to focus on anything closer than 10 feet from the camera, but a dedicated macro lens can focus on something which is less than a foot away.   By getting closer, the insect becomes larger in the photo, but the depth of field also changes.   The further the camera is from the subject, the greater the depth of field is, and the closer the camera is, the shallower the depth of field is.   Therefore, if the subject is 8 inches away from the camera, then even a macro lens which is set to f32 might have only an eight of an inch depth of field.   This is why macro photographers often use a tripod or flash to decrease the size of the aperture and increase the depth of field, even if there's enough light for a photograph to be taken at a more normal aperture setting.

    When you become serious about photography you'll need to get a better understanding of the lenses which are available.   The rule of thumb is this - always buy the most expensive lens you can, without risking divorce or estrangement from the other people around you!   The reason for this is that you're almost certain to go through several camera bodies over time, but a good lens will last you for ten or twenty years.   The lens will also usually have a greater effect on the amount of detail in the photo than the camera body.

    Nowadays, most people who buy an SLR get a zoom lens thrown in with it.   In the 1970s the quality of zoom lenses was truly awful, because it's difficult to make the lens work well both at the short end and the long end.   Since then, a lot of technology has been applied to the problem, and for almost everyone a zoom will provide all the quality they'll ever need.   However, there's no denying the laws of physics, and a good quality prime lens, which has a single fixed focal length, can still achieve better results than a zoom lens.   For some work like portraiture a certain amount of softness can actually be desirable, but where detail is critical, such as in macro photography of bugs and other small objects, a prime lens is always used.   Indeed, macro lenses are almost always the highest resolution lens in any manufacturer's catalogue.

    Usually, the first new lens someone buys is one which goes beyond the range of the zoom lens they started with.   If you want to photograph architecture or landscapes then often you'll need a wide-angle lens in order to fit everything in.   Nowadays, these lens are becoming wider and wider, but something like a 15-30mm is very flexible and will suit most people.   Wide angle lenses have several inherent problems, the main one being distortion.   The shorter the focal length becomes, the wider the angle of view becomes, but also the more curved everything becomes.   Even straight lines become curved, the ultimate example being a fisheye lens, which produces a circular photograph rather than a rectangular one!   Fisheye lenses can produce some interesting results, but they're very specialized and not a good purchase for most people.   Instead, you should buy a rectilinear lens, which uses a variety of optical techniques to keep straight lines as straight as possible.   Even so, there's likely to be some amount of barrel distortion or pincushion distortion in very wide angle photos, but it can often be fixed using digital photo manipulation software.

    At the other end of the range is a telephoto lens, which is a name usually applied to lens with a focal length of about 150mm or more.   This allows you to take photos of birds, other wild animals, or distant objects like aircraft at an airshow.   However, the greater the focal length becomes, the more the laws of physics start to take over.   In particular, it becomes more and more difficult to gather enough light from that distant bird or aircraft to get a good exposure.   The diameter of the lens must be made bigger to allow more light to be gathered, which increases the weight of the lens.   Making the large pieces of glass required for such a lens also becomes more difficult, and therefore more expensive.   Finally, it becomes harder and harder to handhold the lens, or even to mount it on a tripod.   This is because of the weight of the lens, and also because the field of view is so narrow that any little movement has a big effect.   If you're pointing the lens at a small bird 100 feet away then even a tiny movement will move the bird out of the shot.   To overcome this, you have to set the shutter speed higher.   As mentioned in the intermediate photography essay, the usual rule of thumb is to set the shutter speed to the inverse of the focal length.   If you have a 500mm lens then the shutter speed should be 1/500th of a second; if it's windy then you might need to make it 1/750th of a second of even 1/1000th of a second.   Many telephoto lenses now have image stabilization or vibration reduction, which helps significantly, but this issue is still a major problem.

    Another type of lens to consider is a fast lens.   Many kit lenses sold with a camera body are cheap and therefore very slow, with a widest aperture of f5.6.   This makes it virtually impossible to take a photo inside without using flash or a tripod.   Both of these solutions have problems, and sometimes it's not possible to use either of them, for instance inside many museums.

    In this case you can buy a fast lens with an aperture around f1.8 for a reasonable price.   These lenses are often primes of about 50mm, because it's much easier for a manufacturer to make a fast prime than a fast zoom lens.   A 50mm lens is called a normal lens, because it provides the same field of view as a normal person has.   That makes it fairly flexible, and able to handle most situations except where the subject is very large or very small.

    Lenses aren't the only piece of advanced equipment you should consider.   We've already mentioned tripods and flash units, and there's a wide range of choices and prices to consider there.

    If you're doing nature photography in a shaded area under a forest then you have two main choices - use a tripod or use a flash.  But sometimes it's an advantage to use both a tripod and a flash!   I always do this when photographing mushrooms in a jungle or forest.   The problem with using a tripod by itself is that the photo you get will often look dull and flat, because the yellows and reds of sunlight are missing in the shade.   The light of a flash is designed to provide light at a temperature which mimics the warmth of sunlight, however if you use a flash by itself then you'll end up with strong shadows and if the background isn't close behind the subject then it will turn black from under-exposure.   Depending on your taste, these black backgrounds can be a good thing or a bad thing, but the shadows are certainly bad.   The solution is to take the photograph using a tripod, but to use the flash to pop the colors and bring life into them, without creating harsh shadows.   This is done by setting the power of the flash low, perhaps to only 1/16th of normal power, so that most of the light is coming from natural sources, with the small burst of flash providing the color boost.

    If you're photographing moving water like a river or waterfall, then using a tripod and a slow shutter speed usually gives a much more pleasing blur than a high shutter speed which freezes the water motionless.

    Professionals doing portrait photography often use a white umbrella to diffuse the light from a flash, and multiple light setups are also a staple of studio photography.   Outside, large flat sheets of cardboard are often held close to the subject to diffuse available light, and if the panels are colored then it can be used to make the light warmer and more like Golden Hour light.   Amateurs who don't want the expense or inconvenience of carting around the professional's studio equipment can use diffusers such as embossed clear plastic fittings which fit in front of the flash, or pieces of white cardboard above and in front of the flash, or relatively cheap commercial units like the Stoffen Omnibounce which fit over the front.   Even a handkerchief placed over the front of the flash can be used to soften the light.

    If you're using flash to illuminate a moving subject then it's helpful to know about first curtain and second curtain operation.   This refers to the timing of the flash relative to the curtain movement.   In first curtain operation, the flash is fired as soon as the first curtain has finished moving, and before the second curtain has started moving.   In second curtain operation, the flash is fired just before the second curtain starts moving.   This is important in situations such as photographing a racecar in a floodlit stadium at night, where lighting is provided partly by the flash and partly by the floodlights.   If you use first curtain synchronization then after the flash has finished, ambient light will continue to illuminate the car, creating a blur in front of the image of the car which was magically halted by the flash.   If you use second curtain synchronization then the ambient light will create a blur behind the frozen image of the car, which gives an interesting impression of speed and generally looks better.   It's always seemed to me that second curtain operation is more useful, but for some reason most camera manufacturers set the default to first curtain.

    In the intermediate photography essay we discussed using a cable release to avoid vibration of a camera mounted on a tripod when the shutter is released.   Another source of vibration which affects a camera on a tripod is called mirror slap, which occurs when the mirror inside an SLR camera swings up as the shutter is released, directing light away from the viewfinder and towards the film or digital sensor.   This is most often a problem when you're using a telephoto lens and is usually worst when the exposure is around 1/10th of a second in duration.   The solution in this case is to enable the camera's mirror lockup feature; you then push the shutter button, the camera swings the mirror up and then a few seconds later, after the mirror slap vibrations have died down, the camera automatically takes the photo.
 
 

Composition

    Most people who take snapshots always put the subject at the center of the photo, even if that means cutting off Aunt Selma's feet while leaving a lot of empty space above her head.   However, if you place the subject slightly off-center then this adds some amount of interest to the picture, by forcing the person to decide for themselves what is of most interest in the shot.

    The rule of thirds suggests placing the subject a third of the way in from two edges of the frame.   In this shot of ferries on Sydney Harbour, there are two subjects at these rule of thirds positions, and there are also curved lines leading the viewer's eye around the picture, all of which enhances the photo considerably compared to a more static shot of a single ferry moving in a straight line.   On a slightly different topic, I once sold a print of this photo to a lady in Scotland who used to live in Australia and regularly used these ferries - she even named her son Alexander after the ferry in the background!   I guess the kid's just lucky he wasn't called Golden Grove!

    If the subject is moving then you should usually leave more space in front of the subject than behind it so it doesn't look crowded, but has room to move into the picture.   Similarly, if your subject is a person or animal which is looking towards the side of the shot, leave more space in front of its head than behind it, so it has some space to look into (see the bird photo below).    Flying planes or birds should be placed slightly nearer the top of the frame than the bottom, to give an impression of lift.

   Once you're consistently following the "rules" of composition described in these essays then you can start to break them!   Try tilting the horizon to produce a dramatic effect, or doing other things which would ruin an ordinary snapshot.   Don't do these things just to be different, but find something which appeals to you and provides an emotional impact.