I wrote this as a practical guide to cameras. If you are after a tiny ‘point and shoot’ then you don’t need this guide. I’m going to be looking at cameras with bigger sensors, from ‘one inch’ and upwards.

‘Point and shoot’ cameras don’t weigh much, they are tiny, and will slip in a pocket. They may have a zoom that will reach further than a camera on a phone. In fact that is not always true with the recent phones that have more than one lens, with one of them a longer focal length lens for portraits.

One thing about a ‘point and shoot’, is that you can shoot hundreds of pictures and store them on the SD card in the camera so you don’t clog up storage like you would if you shot with a phone.

The downside is that the tiny sensor in a point and shoot makes photos that are no better than you can get out of a phone camera. In fact the computational power in a phone means that the image will almost certanly be better than you can get out of a ‘point and shoot’.

With that out of the way, let’s look at everything practical there is to know about digital cameras with bigger sensors, from ‘one inch’ and upwards.

Size And Weight

If I had a pound for every person I have heard say that they want a lighter camera because the one they have is too heavy, I would still be no richer. That’s because I have done it myself. I lost money selling a heavy camera to buy a lighter one.

So where is the weight?

Fixed lens cameras are cameras with a lens that you cannot take off the body. The lens may be a zoom like on the Sony RX100 series, or it may be a fixed focal length like on the Fuji X100 series. Either way the lens is permanently attached to the body, so obviously the weight always remains the same.

With interchangeable lens cameras where you can switch lenses, then the weight depends on what lens you stick on the front of the camera. So in looking at what makes cameras heavy, we have to know what makes lenses heavy.

Sensor Size

Not all sensors are the same size. I am going to stick to looking at four sizes because they account for at least 95% of the consumer, semi-pro, and pro market. The four sizes are full frame, APS-C, Micro Four Thirds, and one inch.

Full frame, APS-C, and one inch sensors all have the same aspect ratio of 3:2, which is the same aspect ratio as 35mm film.

Here is a diagram shows the relative sizes of the four sensors.

relative sizes of camera sensors from one inch to full frame

What you may not know is that the increase in quality between one sensor and a bigger one is not a function of the area of the sensor: It is a function of the linear increase of the frame.

Let’s look at APS-C versus full frame. A Nikon APS-C sensor measures 23.6×15.6mm. That gives an area of 368.16sq mm.

A full frame sensor measures 36x24mm. That gives an area of 864 sq mm. So the area of a full frame sensor is 2.3468 times the area of an APS-C sensor. But as I said, that does not mean the image is 2.3468 times as ‘better’ because image quality is a function of length. So we are looking at the ratio of 36 to 23.6, which is 1.5254 times.

Still, we have still said that full frame is better than APS-C, but there are other factors besides size that affect the quality of the image. Read on!

When you think about it, camera manufacturers could have made their sensors any size and any aspect ratio they wanted. They weren’t bound by the size of film rolls that came before digital cameras arrived on the scene.

Instead, they followed the tradition of film, and that’s why the first good quality digital cameras had sensors that were in the same 3:2 aspect ratio as 35mm film. And they still dominate the market today.

And here is a diagram showing the template or model that governed the decision by the first digital camera manufacturers when they were deciding what size sensors to use. As you can see, they based the sensors on the size of a frame of 35mm film.

Micro four thirds came along later, and it broke the mould and its sensor is 4:3 aspect ratio – more boxy and less long and thin that 3:2.

So to get back to the original question about size and weight, the image cast by the lens has to cover the sensor. And it is pretty obvious that the smaller the sensor, the smaller the diameter of the lens that covers it can be. So score one for smaller sensors because they can use smaller diameter lenses. And smaller diameter means smaller diameter glass. And glass is what makes lenses heavy.

Of course, if it was that simple then everyone would be shooting cameras with one inch sensors.

Bigger sensors in a camera means the lens glass that has to cover a bigger image circle. Longer focal length also means more glass in the lens. Bigger maximum aperture also means more glass in the lens. Let’s look at these in turn.

What Is A Sensor

First, what exactly is a sensor? It is something that records light and is able to recognise colours. It is made up of an array of micro-lenses in a grid stuck on the chip. It is the chip that begins the process of converter the light to an electrical signal.

The sensor in a twenty-four megapixel APS-C camera has twenty-four million micro-lenses stuck on it. That’s twenty-four million micro-lenses stuck on a chip two thirds the size of a single frame of 35mm film. Pretty impressive, eh?

If a manufacturer were to put the same number of micro-lenses on a bigger chip then the micro-lenses could each have a more gentle slope on them because they have more room to spread out. And the angle is important, because the shallower the angle at which light hits the micro-lens, the cleaner the signal.

Still, it’s also true that the micro-lenses at the centre of the chip will receive light more directly.

What does it mean? It means that bigger sensors receive a cleaner light signal, but not as much as you might assume, because the important micro-lenses are the ones nearer the middle of the sensor.

In practical terms it means that full frame sensors are better than one-inch sensors, but full frame sensors are not massively better than APS-C sensors. And APS-C sensors are not massively better than micro four thirds sensors.

And the comparison probably stops there, because in my own experience, micro four thirds simply are noticeably better than one-inch sensors. And unless you have a really compelling reason for choosing a camera with a one inch sensor, I would recommend you go with a bigger sensor than that every time.


There is one fact that has emerged in the development of sensors and that is that the more micro-lenses the better. It used to be thought that fewer micro-lenses on a big sensor, with each micro-lens having room to be designed to capture light at the best angle, was the optimum design. Now we know that smaller, squashed together micro-lenses BUT MORE OF THEM, can match bigger sensors with fewer megapixels.

Photographers and reviewers complain about the never-ending push by manufacturers for more megapixels. But the fact is that we got here precisely because manufacturers made cameras with more and more megapixels.

So what is the limit? You could say we have now reached a point that with the right lens, a camera with enough megapixels can resolve light as well as anyone could want. The limit now is our eyes. We simply don’t need anything more because we can’t see the difference. We already have incredibly good cameras.

Lens design is computed and lenses are built to a standard that only used to be dreamed of. So here is a tip – if you want the best out of your camera, get the very best lens or lenses you can.

ISO and Noise

Everything I have said about image quality 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 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 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.

You may be old enough to remember film being rated in ASA. Well, now it is ISO – same (almost the same) thing and it is the standard that is used all over the world today.

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.

How did I calculate ‘eight’ times? Well, you double up from 100 to 200. Then double up again from 200 to 400. And another from 400 to 800. So that’s 2 x 2 x 2 = 8.

As with all things, there is a penalty to pay for making a film more sensitive, which is that there is more grain. I won’t go into the chemistry of film emulsions, but it is so.

The ISO standard has carried over into digital cameras. And almost all digital cameras have a button or a dial to increase sensitivity, starting from the base sensitivity of 100 or perhaps 200 ISO, and going up to insane numbers. Certainly 400, 800, 1600, and 3200 ISO are now considered ordinary.

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 you can’t really. Instead, you get more more signal but you also get 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. Digital noise looks like tiny, dirty yellow-ish and black blobs in the shadows

In fact, camera manufacturers put a lot of effort into making noise as unobtrusive as possible. They can’t eliminate it for photos taken at higher ISOs, but they can play around with the signal to make the noise less ugly.

The other downside of higher ISOs is that the vibrancy goes out of the colours. Again, camera manufacturers put a lot of effort into making colours continue to be vibrant at higher ISOs.

Here’s the bottom line: bigger sensors have less noise than smaller sensors. But the difference is not that great – maybe one stop between a full frame sensor and an APS-C sensor. And of course this is only a factor at higher ISOs.

Wow, I have only covered sensor size in this discussion of what makes lenses heavy. Still two to go – focal length and maximum aperture.

Focal Length

If you want to ‘reach out’ to a distant subject, as it were, with a long focal length lens then the lens itself is going to be longer because that’s the way light works when it focuses. It’s as simple as that. Ask Isaac Newton because he did some great experiments on the subject.

And the lens at the far end is going to have to be a bigger diameter because again, it’s the laws of physics, and that’s how light works. If the lens at the far end was a smaller diameter it would not cast an image circle big enough to cover the sensor or it wouldn’t let in enough light to to the sensor.

Also, no one wants to walk around with a lens that is three feet long. So in order to keep the actual physical length of the lens as short as possible, manufacturers use combinations of lenses within the lens to collapse the length needed to focus with a narrow field of view at a far distance. That keeps the lens shorter, but it means that with all that glass, it is also heavier.

Maximum Aperture

The lens element at the far end of the lens is what determines the maximum aperture of the lens. And the bigger the aperture, the more the glass and the heavier the lens. The advantages of a bigger aperture are that it lets in more light and it allows a smaller depth of field. That means that the front to back distance of the subject that is in sharp focus is smaller than when the lens is set to a smaller aperture. If a photographer wants good separation between the subject and the surroundings then a shallow depth of field is good. It would help, for example, to isolate a bird on a branch from the tangle of branches behind the bird.

We’ve established that smaller sensors mean smaller diameter lenses, which means lighter lenses. And we’ve established that larger aperture lenses are heavier but they can separate subjects better and are better in low light because they let in more light. And we’ve established that more megapixels means better quality images and that at higher ISO, full frame cameras are better, but not that much better than smaller sensors.

So now let’s talk about the camera body, and different kinds of body and those that are best and enabling you to see what you are trying to photograph.

The Camera Body

I’m going to talk about mirrorless cameras, rangefinders, and SLRs.

With an SLR you put your eye to the optical viewfinder, and 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 mirrors and prisms. The hump at the top of an SLR is the box that contains the mirrors and prisms.

The advantage of this mirror and prism arrangement is that there are no parallax errors. You see what the camera lens sees. And it is a true optical viewfinder. You see down through the lens. Compare that to mirrorless cameras that I will come to in a moment where you look at a digital representation of the scene.

The reason that SLRs are called ‘reflex’ cameras is that the mirror that sends the light into the viewfinder, has to flip up out of the way when you take a shot.

It has to do this because in its rest position the mirror covers the sensor, so it has to flip out of the way to let light fall onto the sensor when you take the shot. Then it flips back down again. That’s the reflex. The downside of this is that no matter how well damped the mirror is as it moves out of the way, it causes some vibration. Ad it is noisy. Of course ‘noisy’ is a relative term, but in a quiet church for example, people will hear the noise.

The other downside is that 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. But even with 1/500 second you lose sight of the subject for a moment and it cuts you off from the action. When the ‘light comes on’ again, you have to reorient yourself. It’s not a big deal, and photographers get used to do it, but it is something they have to learn because for a moment or a long moment, the scene goes black.

There are other ways of seeing the scene. Rangefinder cameras have their viewfinders to one side of the camera and there is nothing connecting the viewfinder window to the lens so nothing to obstruct the view of the scene..

Because that viewfinder window is half-an-inch to one side of the camera lens, however, you see the scene from a slightly different vantage point to what the lens sees.

You may think having the viewfinder an inch or so to the side the line of the lens wouldn’t make much difference. But for subjects that are close to the camera it causes parallax error. In other words, you see one thing and the camera records another.

To test that yourself, hold your finger in front of your eye and then moving your eye 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 to compensate for parallax error as the photographer focuses the camera. That way they show you what the camera will actually see.

One advantage of rangefinder cameras is that because the viewfinder is to one side of the camera, you can look outside the edge of the camera with the other eye. On the other hand, rangefinders are not good to use with long lenses because the lens obscures part of the viewfinder.

So why mention rangefinders at all? Well, we are getting an idea of what works and what doesn’t work in camera design. Being able to see without parallax error and to use long lenses are big pluses for SLRs. So why are nearly all the new cameras mirrorless?

Mirrorless Cameras

When you think about it, describing a camera as lacking something is a funny way to describe it. Obviously it is meant to distinguish these cameras from SLRs.

There are other messages implied in the description. One implied message is that not having to have a mirror is good. Another implied message is that mirrorless cameras are on a par with SLRs, suitable for professional use.

So what are the advantages and disadvantages?

The are lighter because you don’t need hump of the mirror box or the the prisms and mirrors and mechanisms for flipping the prism up and back again that are inside the mirror box.

The whole of the sensor is used to measure exposure and focus. That’s unlike an SLR where only a tiny space in the middle of the sensor is dedicated to focusing and calculating exposure.

Mirrorless Camera Viewfinders

The viewfinder through which the photographer looks to see the scene and to see where the camera is focusing, can be very big. That’s because it is an electronic representation of the scene, so there is no limit (other than unwieldiness) to the size of viewfinder and of the image in it that manufacturers can make.

Compare that to SLRs. Top of the range SLRs have big viewfinders, but lower end SLRs have tiny viewfinders. And you can see that for yourself if you try a few cameras in a shop.

So what are the downsides if any to electronic viewfinders? Well, some people don’t like looking at what is effectively a real time video of what they are photographing. Another downside is that the view can look very contrasty with dark blacks and blown out whites. And thirdly, there is lag, which is where the scene lags behind the actual scene so that your are always a bit behind the curve of whatever is happening in the scene.

How bad are these issues with mirrorless cameras? I think the contrasty image problem is still there a bit. Lag is pretty much nonexistent in good cameras, and the whole business of looking at a streaming video of the scene (because that is effectively what it is) is something you just get over.

If you cannot get over it, then maybe look at a hybrid viewfinder that one can find on the Fuji X1oo series or the Fuji X-Pro series. With those you can change at will between an optical viewfinder and a digital viewfinder with just the flick of a lever. Or try a rangefinder but check your piggy bank before you do because Leicas are hideously expensive.

No Viewfinder

Before I get off the subject of viewfinders, a word about cameras that don’t have a viewfinder at all. We know that most compact ‘point and shoot’ cameras don’t have viewfinders, but there are some cameras with bigger sensors that also do not have a viewfinder. The Nikon Z30 has an APS-C sensor. It is promoted as a ‘video first’ camera, but it is also a stills camera just like any other camera. So 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.

There are two problems., though. 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 some shade so you can see the LCD properly. The other problem is seeing where the camera is focusing. Some cameras that don’t have a viewfinder have eye focus, which means they hunt out an eye, and if they find one they focus on that. All of which is great unless you want to focus somewhere else or there are no people in the scene. It’s not impossible, but if you want to enjoy homing in on a subject, there is nothing like the real thing – whether it’s an optical or a digital viewfinder.

Beyond Size and Weight

I think I have covered size and weight pretty well, but to sum up

  • More megapixels is good
  • Bigger sensors are better than smaller sensors but not by a huge margin
  • Bigger sensors mean bigger diameter glass, which means more weight
  • Longer focal length lenses means more weight
  • Mirrorless bodies are lighter than SLRs because they don’t need a prism housing
  • Mirrorless cameras have bigger viewfinders than the lower end models of SLRs
  • Whether mirrorless or SLR, with a bigger viewfinder it’s easier to see where the camera is focusing
  • Some cameras don’t have a viewfinder, and it can be a problem to see the LCS in bright sunlight

A Conclusion

The good news is that cameras from the leading manufacturers – Canon, Nikon, Fuji – are so good that any of them are capable of good quality photos.

Once you have decided how much weight you can carry comfortably, spend some time handling different cameras. It’s important that a camera feel right in the hand. It is also true and very important to understand that a good lens is the key to getting good shots. Spend your money on good lenses.