Revised and updated 23 April, 2019
This is a practical guide to buying a digital camera to help you know what to look out for in a camera before you buy it.
It will look at features like whether the camera can focus quickly enough to get the shot and how to test that, and whether you can see the subject clearly.
The Size And Weight Of The Camera
It’s been said before, but the best camera is the camera you have with you. That means you had better be comfortable with the size and weight of it.
Time and again I read about people who want a lighter camera to replace the one they have.
So they must have learned the hard way – after they bought the camera – that it was just too heavy for them.
How About The Camera In Your Phone
I shot this photo with an iPhone. For some subjects, mainly those that don’t move, it can do the job. Don’t let anyone tell you it can’t.
You can adjust the exposure on the iPhone by tapping on the lighter or darker parts of the scene. And there is a digital zoom on the iPhone, too.
But it is limited as a tool for serious photography.
There is always a trade-off in photography. A camera that can shoot a beautiful landscape and show the detail on every leaf is not going to fit in your pocket.
Some people have two cameras – one to have with them wherever they go and one for more ‘serious’ work.
I took this shot with a dSLR and I don’t think there is any way I would have got the shot without using a camera with a big sensor. A compact camera with a tiny sensor might take the shot, but the quality wouldn’t be there.
Seeing What You Are Shooting
SLR means ‘single lens reflex’. You put your eye to the viewfinder. The viewfinder is about half an inch or so above the lens. The light from the subject comes directly through the lens and is reflected up into the viewfinder via a series of little mirrors and prisms.
The advantage of that is that there are no parallax errors. You see what the camera lens sees.
Looking through the viewfinder of an SLR is like looking through a periscope in a submarine; it’s just that the periscope is only a half an inch tall.
SLRs are called ‘reflex’ cameras because of what happens to the mirror that diverts the light that comes through the lens and sends it up to the viewfinder.
The mirror flips up out of the way when you take a shot and then it flips back down again. That’s the reflex.
It has to do this because in its rest position it covers the sensor, so it has to flip out of the way to let light fall onto the sensor when you take the shot.
And when the mirror flips out of the way, everything in the viewfinder goes black.
How long it goes black for depends on how fast the camera shutter fires. It could be one five hundredths of a second or it could be two seconds. Of course, if it’s two seconds then you will probably have the camera on a tripod.
There are other ways of seeing the scene. Rangefinder cameras have their viewfinders to one side of the lens and there is no prism connecting the viewfinder window to the lens.
Because that viewfinder window is half-an-inch to one side of the camera lens, you see the scene from a slightly different vantage point to what the lens sees.
You may think having the viewfinder a half inch away from the line of the lens wouldn’t make much difference. But for subjects that are close to the camera it makes a difference.
This is parallax error.
To test that yourself, hold your finger in front of your eye and then moving your eye half an inch to one side. The view you see is quite different.
Some rangefinder cameras have frame lines in the viewfinder connected to the lens focusing mechanism and they slide across the viewing area as the photographer focuses the camera.
That’s how they compensate for parallax error.
The advantage of rangefinders is that because the viewfinder is to one edge of the camera, you can look around the camera with the other eye.
Let’s Talk About Henri Cartier-Bresson
Henri Cartier-Bresson, voted the world’s foremost photographer of the 20th century, used a Leica rangefinder camera.
No one claims that all of his shots were world-beaters, but in my opinion he understood the way three-dimensional reality translates into a two-dimensional image.
Maybe part of that was because he used a rangefinder camera and could see around the subject. It may have helped him to frame his subjects so well.
Looking through a book of his photographs (his book The Europeans is a good example), you can see shot after shot where he makes three dimensions come to life on the flat paper.
Leica and Fuji are the only current manufacturers of rangefinder cameras with optical viewfinders that I can think of.
There are other manufacturers that make cameras with electronic viewfinders, and I’ll say more about them later.
Compact Cameras And LCDs
With a lot of compact cameras, instead of a viewfinder, you look at the LCD – the Liquid Crystal Display on the back of the camera. And that is how you compose your shot. Which is OK if it suits you and if you can see the subject in the LCD.
When you think about it, that’s the way you see the subject with cameras in phones and tablets.
One problem with LCDs is that in sunlight they can be very difficult to see. And if you want to take a shot outside on a summer’s day, it’s no good if you have to find a dark corner to stand it to see the LCD properly.
Looking Through The Viewfinder
It’s time to put this into practise. Take a trip to your local camera store. Look through the viewfinder of an SLR at a general scene – nothing too close – a street scene is fine.
Choose something in the scene that you want to be able to see clearly. Imagine it is your loved one standing across the street. You want to see his or her face.
Now try the same thing with a compact camera.
Now your loved one is either a tiny dot at the end of a long tunnel (the view you get with the optical viewfinders on compact cameras) or he or she is a tiny figure in the LCD.
Either way, how are you supposed to check that he or she is smiling or is in focus? You can’t.
That’s not to say that compacts are no good. They can take some very good shots. But you should know their limitations.
Later on I will talk about how compact cameras with small sensors manage to get the subject in focus, and the advantages and disadvantages of this.
Shooting What You See
Being able to see the subject is important, but so is being able to shoot what you see.
That is easy enough if the subject is a vase of flowers. Then you can put your camera on a tripod or prop it on some books – which you might need to do if the light is low – and gently press the shutter.
But what if the subject is moving?
It is important then that you can choose a fast shutter speed (see below about sensitivity) to freeze the action.
However, it is also important that the delay between the moment when you want to take the photo and the time when the photo is actually taken is as near to instantaneous as possible.
The time lag between these two moments is made up of three parts.
The first part is the time you take to get your finger to obey you and start pushing down on the shutter button.
Then comes the time the camera takes to focus.
Finally, there is shutter lag, which is the time the camera takes to fire the shot after you press the shutter.
The time you take to get your finger to obey you and start pushing down on the shutter button is nothing to do with the camera of course, but you can get better at it with practise.
The second part is easy to check. Pick up a camera and point it at a variety of subjects in good light.
Does the camera ‘hunt’ in an out looking for the point of focus? Sometimes you can hear the mechanism moving back and forth as it hunts.
Does the focus perform in poor light as well as it does in good light? These things are easy to test for yourself.
You can test shutter lag by choosing something that is moving – say a person walking past. Press the shutter and see whether the person is in the frame or whether the delay was so great that they are out of the frame by the time the shutter fires.
Shot To Shot
It is not just the time to the first shot that is important. Some cameras are quite speedy in getting off that first shot, but then slow down to take a second, a third, and more shots. That is when the shot to shot lag is important.
We are not talking in seconds here. We are talking in milliseconds. Good quality SLRs might have a shutter lag of around 50 milliseconds. Some compact cameras may have a shutter lag of five or six times as long as that.
Would you be happy to have to wait half a second between the time you press the shutter and the time that the mechanism actually records the image?
That is why it is a good idea to pick up a good top-of-the-range SLR and focus and shoot with it in good light where you can see how fast it works.
Even if you have no intention of buying an SLR, using it will give you a benchmark for what a good camera can do.
Digital cameras have an array of micro-lenses that capture the light coming onto them. An ‘array’ is a collection of lenses laid out in a pattern.
Imagine a rectangle about as big as your thumbnail. That is about the size of the chip that holds the micro-lenses in a compact camera.
A six megapixel camera has six million lenses laid out in an array on that chip. Six million lenses cemented onto a little chip the size of your thumbnail, capturing light that comes into the camera.
How Micro-Lenses Work
Each micro-lens reacts to the light that falls on it. The bigger the micro-lens, the better it is at capturing a good signal. Of course the manufacturers can boost the ability of the lens to receive a signal but, along with the boosted signal comes more ‘noise’.
We see that noise as mushy, dirty, speckled, gritty-looking, yellow-black areas in the darker parts of the image and as little speckles all over the image.
Manufacturers sometimes process the images in the camera to hide that noise, but that also affects the signal and produces images that look less sharp – in bad cases they can look more like watercolour paintings than photographs.
You are not necessarily going to see this in a 4 inch x 6 inch print, but if make a bigger print you will see it.
The sizes for best micro-lenses are when they big enough to allow a nice gentle rake to the angle at which they receive light through the camera lens. And they work best when they are not boosted to receive a stronger signal than is optimal for their design.
If the chip is small, then there is less space for the lenses so the smaller each lens must be. That means the signal has to be boosted more. And that lowers the quality of the image.
Small Sensors And Large Sensors
SLRs have sensor chips with an area that is about fifteen times the area of the chip in a compact camera. And there are some SLRs on the market that have chips that are bigger than that.
They are called FX or full-frame sensor cameras because the chip is the same size as a frame of 35mm film.
And there are cameras with chips even bigger than that. But if you are considering one of those you need to know a lot more than is in this guide, and we are talking about cameras that cost tens of thousands of dollars.
More Microlenses Means More Detail
The more micro lenses on a chip, the more resolving power it has. That is, the more detail it can show.
Resolving more detail can outweigh the disadvantage of more noise that is caused by each micro-lens having to be smaller to fit on the sensor chip.
And there is a second factor and that is that lenses are at there best near the center of the lens. And if the micro-lenses are bigger, as they tend to be on bigger chips, then there are fewer ‘centers’ and more corners.
But all of this only holds true for shots taken at the lowest sensitivity of the camera, and that’s the next thing to talk about.
In the days of film, you went into the shop and bought a film suitable for daylight, and a different film for shooting indoors. The manufacturers understood that there was likely to be less light for those indoor shots, so they made film for indoors that was more sensitive than film intended to be used indoors.
The international standard for the sensitivity or ‘speed’ of a film is called ISO, and a typical low-sensitivity film would have an ISO of 100. And a ‘fast’ film with more sensitivity would be something like 800 ISO.
What does ISO 100 and ISO 800 mean? It means that to get enough light onto the film to expose it sufficiently for the image to be produced, you need eight times more light on the slow ISO 100 film than you do on the fast ISO 800 film.
As with all things, there is a penalty to pay for making a film more sensitive, which is that there is more grain.
The ISO standard has carried over into digital cameras. Almost all digital cameras have a button or a dial to increase sensitivity, from the base sensitivity of 100 ISO (or perhaps 200 ISO) up to 400 or 800 or 1600, 3200 ISO and beyond.
Each doubling of the ISO corresponds to twice as much sensitivity to light. Or one ‘stop’ of light as it is called (a carry over from the days of film cameras).
And you may wonder how it is possible to just turn a dial and make a digital camera more sensitive to light.
And the answer is that more sensitivity means more noise. And the noise problem is the same with digital cameras as it was with film cameras.
No matter how big or how small the chip used in the camera, The more we boost the sensitivity of the chip by turning up the dial, the more ‘noise’ we get. And digital noise is the digital ugly sister of film grain.
How Sensitive? And How Much Noise?
So how does this translate into something practical we can say about compact cameras compared to SLRs? The generally accepted word is that 800 ISO with an SLR produces the same amount of noise as 100 ISO with a compact camera. And that tells us a lot.
Because if I was thinking of buying a compact camera because it is supposed to give good exposures without too much noise, that isn’t such a big deal when I know that the noise on a compact camera is likely to be as bad at 100 ISO as it is with an SLR at 800 ISO.
Very few camera manufacturers make their own sensor chips and the fact is that there are very few chip manufacturers. So the differences between the cameras made by the various camera manufacturers is often down to the processing technology in the camera rather than differences in the chips.
Somewhere in all of this there is a trade-off but the bottom line is that bigger chips mean better image quality over a wider range of sensitivities. It’s as simple as that.
How Images Are Processed – JPEG and RAW
So what happens after the signal hits the micro-lenses? Well all cameras process the signal that come from the array of micro-lenses.
The technology is a fine blend of science and art – between what ought to look good and what people think looks good.
Once that signal is processed, we come to a big division between those cameras that allow you to capture and download the original ‘digital negative’ and those that don’t.
JPEGs and TIFF files are ‘processed’, finished files. They can be read by computers and photographic printing machines. They are universal formats.
RAW files on the other hand are ‘digital negatives’ and most camera manufacturers have their own proprietary RAW format. And without being converted to a readable format they cannot be read by computers or the web or whatever. They have to be downloaded from the camera and then processed (‘converted’) using a program designed for the job.
Some camera manufacturers make their own RAW converters but there are many programs made by other companies that are widely regarded as being as good as the proprietory ones made by the camera manufacturers.
Adobe Photoshop and Adobe Lightroom are probably the most widely known of the RAW converter programs.
Several cameras that produce RAW files also have in-built converters so that you can download a custom-tweaked jpeg right out of the camera as well as being able to download the RAW file.
As a side-note, if a camera has an LCD then it produces jpegs in-camera, because that is what you are looking at in the back of the camera when you review the shots you have taken.
Why You Want RAW files
One reason you want a camera where you can download RAW files is that you can alter a RAW image more successfully than a JPEG or a TIFF.
You can alter the exposure (in case you or the camera messed it up when you took the shot) and you can alter the colors or the tonal distribution from dark to light areas.
You can do that with JPEGs and TIFFS but with less latitude and more likelihood of degrading the image.
This is particularly true with JPEGs because of the limited range of colors of which they are composed. Change the exposure and color balance and the whole image suffers.
Which begs the question of whether you want to get involved with all this stuff.
If you don’t, then just know that to squeeze the best out of a digital camera you either want to be able to play around with RAW files, or you (or your camera) had better be pretty good at getting exposure and color balance correct when you take the shot.
There are many compact cameras that produce good photos when the scene is bathed in diffuse light and the distribution of dark and light in the subject is fairly even.
But there are limits to how well cameras are able to detect exactly what they are looking at, and that is what I’ll talk about next.
Difficult Lighting Conditions Or ‘A Black Cat At Night’
Imagine a black cat against a white background. Now picture a white cat against a black background. How about a white cat against a white background? You get the idea.
How is the camera supposed to know which one it is being pointed at?
It doesn’t, so it is going to get the exposure wrong.
In fact all cameras are standardized to expose every scene as though the subject is a specific internationally agreed shade of grey. But it is only a starting point.
Many sophisticated cameras have certain standard scenes programmed into them. If the distribution of shapes in the scene is like one of those in their memory, they will expose it accordingly.
But even the best of them are not always correct, and for certain scenes, ones that photographers learn to recognize, they are often wrong.
Some compact cameras or less ‘expert’ cameras go a different route. They ask the photographer to tell them what kind of scene it is by turning the dial to the appropriate ‘scene’ mode.
In fact ‘scene’ modes are often used in compact cameras for another additional reason and I will talk about that when we talk about other settings – speed and aperture.
The bottom line is that cameras have a limited ability to detect how light or dark a scene is. So they use one of the methods I’ve just described:
So with this knowledge you have got to expect that the exposure will probably be wrong in ‘difficult’ scenes.
The Quality Of Light – White Balance
The next thing the camera has to know something about is the quality of the light. It needs to know this so that it can reproduce the color in a natural way.
But perhaps the light is not natural – perhaps it is deficient in part of the spectrum.
Perhaps the scene is lit just by fluorescent light. Or perhaps there is more than one light source. Perhaps there’s a flourescent light and a halogen light and some daylight. That’s not an unusual mix. In fact it’s pretty typical in a household kitchen.
Or perhaps the scene is lit by natural light but it is in the glare of the sun at midday. Or perhaps it is bright natural light at midday, but under the shade of a tree; or perhaps it is at the end of the day when there is a pink glow in the sky.
Perhaps the scene is in Norway or Canada where the light is filtered through the atmosphere and creates a different light to the light in the tropics.
Again, the camera has to detect which of these it is looking at or it will get the color balance wrong. The color balance is called White Balance – setting the White Balance means setting the color temperature to show white correctly as white. All the other colors fall into place around this.
All digital cameras have what is called automatic White Balance detection but it is easy to show this is not foolproof.
Many cameras have manual settings for daylight, sunlight, shade, fluorescent, halogen, tungsten and others. Why have these if the auto White Balance gets it right all the time?
And this leads us back to look at RAW files. That’s because if the camera does not expose the subject correctly, or does not get the color balance correct, then someone is going to have to correct these after the shot has been taken. And RAW files allow more correction than JPEGs or TIFFs.
Printing The Image
Photo magazines run tests comparing the services of different photo labs.
They compare them for price, speed of service, and for how well they develop the digital file they are asked to process.
What this shows is that not all labs develop print digital files the same way or equally as well.
If you choose the cheapest service without color correction, then you are relying on a machine to correct the color and exposure in your digital image.
And these machines are very good at doing this.
But they vary between brands, and they vary depending on which engineer set them up and how well he or she checks and maintains them. And of course, how well you exposed the shot in the first place.
For a little more money you can ask the lab to manually color correct the images. Which means that a technician will sit and check the images on screen and correct the exposure and the color.
The point is that ‘somebody’ has adjusted and printed the images, and if the file is a JPEG, and the exposure or color balance is wildly wrong, even a lab will have difficulty correcting them to make a printable image.
Consumer photo labs will usually only handle JPEGs (or sometimes TIFFs). Professional labs will handle RAW files or other proprietary files. That gives them more scope for correcting exposure and color balance.
If you shoot RAW you can tweak and correct the RAW images and then save them as JPEGs, copy them to a CD and take them into your local lab knowing the files are ready for printing – color and exposure corrected. Just tell the lab not to apply any settings, and instead to print the images as they are.
The fact is that photographers who used film when that was all there was, could never achieve that kind of quality.