Selecting a Camera - Step One: Sensor Size

The original article that I wrote on buying a camera  (see it on Photo Writing) was written seven year’s ago. Surprisingly, and despite the rise of mirrorless cameras, not all that much has changed in the intervening years. My advice then, remains pretty much the same now. Still, seven years in the digital world is a lifetime when it comes to the hardware and software that we use to create images. Due to a recent spate of emails requesting advice on what camera to buy, here is our (the Nature's Light team) ‘updated’ thoughts on buying a camera (particularly as a first time buyer). Below is a brief synopsis in table form. More detail below.

Click on the image to see an enlarged view of the pros and cons of each of the sensor sizes.

Before starting on what’s out there, it’s important to realize that just about every camera available today is capable of producing superb imaging results when used properly (this hasn’t changed in the last seven years, and cameras that I wrote about seven years ago are still capable of producing excellent results). Smartphones are now so capable of producing images that rival photos captured on film 20 years ago, that the camera industry itself has contracted massively as a result. The era of the affordable point-and-shoot camera is over, as the cellphone cameras of today are as good as the entry-level point and shoot camera from five years ago. Still, the reality is that better control over the image can be had by using an interchangeable lens camera with full manual override than with a compact camera or phone, no matter how good their image quality. So, assuming the reader understands the difference between a camera where the lens can be swopped, and one that doesn't, below is the first consideration we would make in selecting an interchangeable lens camera.

Size Matters

The first major decision that a camera buyer usually has to make is what size sensor they are wanting to purchase. At the moment the standard choices are between Micro Four Thirds (M43), APS-C, Full-Frame (FF) and Medium Format (sometimes referred to as MF). More generally, the choice is between APS-C and Full Frame cameras. ‘Full-Frame’ refers to cameras with a digital sensor that is the same size as a traditional 35mm piece of film (so 24x36mm in size and 2:3 aspect ratio). APS-C refers to a 90’s era film type with dimensions of about 16.7x25mm (also 2:3 aspect ratio). Also available is the smaller format Micro Four Thirds sold solely by Olympus and Panasonic with a dimension of 13x17.3mm (3:4 aspect ratio)

The full range of sensor sizes from the tiny cellphone camera sensors to the large medium format sensors.

So first off, where is the image quality coming from? Simplistically put, the bigger the sensor, the better the image quality. It’s true that cellphone cameras have sensors with a huge amount of pixels. Several high-end cellphone cameras now sport 40MP sensors. However, the size of the actual pixel (or individual sensel to give it the correct term for the light gathering component) makes a difference. The larger the physical source of the pixel, the better the quality of the light that has been captured or recorded. With all things being equal, a large sensor (so think Full-Frame) with 24MP is going to produce a better image than a tiny sensor with 24MP. In actual cameras terms; the new Huawei P40 Pro+ with its 1/1.28” sensor is not going to produce an image of equal quality to even an older technology Nikon full-frame 36mp sensor.

In a very real sense, the size of the individual pixels impact on the light gathering ability of the camera. Generally speaking, larger sensors with larger sensels have better low-light ability than smaller sensors with smaller sensels. Camera’s like Nikon's Z6 and D780 are brilliant in low light with their relatively low 24Mp pixel count and large sensor design. Even they get trumped by Sony with its A7S mkiii with only 12MP on board. The large sensels on this camera mean that it can practically see in the dark.

However if sensor size were the only consideration we would all be walking around with Hasselblads (a medium format camera manufacturer) hanging from our necks. The thing is that there are other factors involved with the most glaring being that of cost. A Hasselblad has a starting cost of over US$10,000 (body, back and lens - the bare minimum you need to take a photo). In a nutshell though, image quality does improve each time the sensor grows.


The biggest problem with a larger sensor is that it requires larger glass components in the lenses that the camera uses. More glass means more expense. A lot more expense in some cases. If you consider four cameras and the equivalent focal length (so a scene shot on all three systems would look more or less the same when viewed on a computer screen or even an A3 print):

Putting megapixel count aside, the Fujifilm GFX camera with it’s ‘medium format sensor’ is expected to give the best image quality - and it does - but you’ll notice that the cost of the lens (as well as weight and size) is significantly greater than the cameras with the smaller sensor. The smaller the sensor, the less glass required, so in theory the price and physical size should be lower and smaller as well (note that the pricing of Olympus equipment is often at odds with the size). Simplistically this is usually the case, although variances are there based on the brands involved.

As this article concentrates on interchangeable lens cameras I am going to ignore the very small sensor cameras and look at the currently available smallest sensor interchangeable lens cameras upwards. Currently the smallest interchangeable lens system uses the Micro Four Thirds sensor since Nikon discontinued their smaller 1 inch sensor cameras a few years ago.

The cameras above, from Micro Four Thirds to the larger full-frame sensors have resolution stretching from 16MP through to 100MP. The current base resolution for full frame cameras is 24MP, and for APS-C cameras it’s either 20 or 24MP depending on the manufacturer.

All the cameras mentioned above are capable of excellent results and every single one of them would be able to produce prints of up to 13” on the long side without any issues. In fact, most of these cameras would be able to produce prints of 17” on the long side (with some post-production massaging all would and some of the higher resolution full-frame and medium format sensors will produce native resolution prints up to 24” on the long side). For many people, the question is really going to come down to, “how often do you print this large?”. If all you ever do is place images on the internet through sites like Flickr or 500px, and potentially want to print a book, then you don’t need a 36mp sensor.  Even 24mp is more than enough.

The Visual differences of Sensor Size

Some photographers like to talk about visual equivalence between the various sensor sizes. Lots of internet pundits split hairs over the focal length and and maximum diameter of the aperture in a fairly pointless exercise of trying to compare the image quality and traits between the different sensor sizes. It’s beyond this article to look at the physics behind apparent depth of field and focal length. If you really want to delve a little more into this you can read this article I wrote several year’s ago.

Looking at the sensor sizes more generally, the larger the sensor, the easier it is to generate creamy out of focus portions in the image.  This has to do with the physics of the sensor size compared to the actual size of the aperture diaphragm (aperture hole) in the lens itself.

A comparison between the field of view of a Full Frame camera compared to that of a APS-C camera fitted with the same lens (The APS-C view is the red bracketed area)

 So, generally speaking. The smaller the sensor, the greater the depth of field (or area from near to far that is in apparent focus) for a given lens. Similarly the same lens (say a 50mm f1.8) on two different sensor sizes is going to have a different view. A 50mm lens on a Full Frame sensor is going to give a roughly 46 degree field of view. Put the same lens on a APS-C sensor, and the field of view will narrow to about a 32 degree field of view. Put a 50mm lens on a medium format sensor (if the lens is designed for that sensor size) and the field of view will widen to about 60 degrees.

This makes lens choices more complicated based on the genre of photography you are interested in. In Wildlife photography we tend to want to have larger lenses that can get the view closer in of birds and animals. A Full-Frame camera with a 400mm lens has a tiny 6 degree field of view, but that same lens on a APS-C camera has an even narrower 4 degree field of view. So the same lens is effectively giving the photographer 200mm of focal length if used on a APS-C camera. If you travel a lot, you’ll also know that a 400mm lens is going to be big and heavy. So weight can become a deciding factor

As an example: A Fujifilm X-T4 with 100-400mm f5.6 lens weighs 1.93kg while a Canon 5Dmkiv with equavelent 100-400mm f5.6 lens has a a weight of 2.3kg. The Fujifilm combo has a 4 degree field of view (effective 600mm lens on a FF camera) while the Canon has a 6 degree field of view. The Fujifilm setup is also physically smaller, so easier to pack and carry. If you have to pass through multiple airports carrying a backpack of camera gear, the Fujifilm setup is going to be a lot easier to tote about than the Canon.

From www.camerasize.com

On the flip side, if you are interested in landscape photography, there are more and better wide angle lenses available for FF cameras, compared to APS-C sensor cameras. Although to be fair, now that there are more mirrorless FF cameras available, the weight and size advantage of the the smaller sensors falls away somewhat.  

So the size of the sensor impacts on cost, physical size of the lenses, light gathering ability (due to the size of the individual pixels/sensels) and apparent depth of field and focal length/field of view. As mentioned above, if image quality is the ultimate goal, and you have the funds as well as ability to carry all the equipment, selecting a medium format camera like the Fujifilm GFX-100s will net you the very best image quality available, but at a (significantly) increased financial cost and an increase in size and weight. At the other end of the scale within the same camera brand, the Fujifilm X-T200 will fit into a small handbag, produce decent prints up to A3 in size and costs literally one tenth that of the GFX system.  

Purely in terms of image quality, if you never print larger than A3 you do not NEED anything beyond the base-level cameras that are currently available. Obviously, other needs will impact on a camera decision, such as autofocus options, video abilities, weather-sealing and ergonomics, but at a base level, the size of the sensor dictates the first decision making when choosing a camera.  

A Nutshell Conclusion

If you already own a camera, or several for that matter, the above doesn’t really impact you as you probably already know what you need or want in a camera. For someone starting out, the sensor size is likely the first and one of the more confusing decisions to work around. So the table at the start of the article is our simplistic answer boiled down to a few bullet points (obviously this is a very basic overview, others might disagree, but from our experience it pretty much works).

To continue the simplistic view (please remember that one size does not fit all, and there are other criteria that also matter, which we’ll delve into in future articles):

• On a serious budget, just want an interchangeable lens camera to learn how it works and are happy to potentially change in the future: Go for one of the entry level APS-C DSLR packages from Canon or Nikon that include two lenses. The cameras produce decent results, and are really cheap in comparison to the rest of the market (older models usually marked down significantly, but still produce excellent images).
• Concerned about size and wanting to be more ‘future proof’: Look at the entry level to mid-range mirrorless cameras from all the manufacturers (Fujifilm have the best ‘cheapest’ models at the moment, along with Canon’s also excellent starter packages - bear in mind this fluctuates as new cameras hit the market).
• Wanting to take photography more seriously in the future and are prepared to put down a sizeable chunk of money in starting out: Any of the 24mp full-frame mirrorless cameras that are currently on the market.
• Most interested in travel photography and size is more important that image quality: Look at Micro four Third camera and some APS-C cameras (particularly those from Fujifilm as they have the broadest range of lenses available and are slightly smaller and lighter than the Canon and Nikon equivalents.

That’s the advice to someone trying to decide on a first camera to buy. It is not advice meant for someone who already has a camera and is wanting to get another. That’s a different kettle of fish as it delves into the pros and cons of mirrorless versus DSLR, which we’ll look at next month. However as a very basic bullet-point for those entering into photography but with the idea that they are likely to eventually earn an income with it (or take it very seriously as an art form)

• If you want to eventually do photography in a manner that earns an income, or are more serious about a future in photography, consider Full Frame. If you are on a serious budget look at DSLRs, first and then Mirrorless. If the long-term viability of your camera is very important to you, consider mirrorless over DSLR as that is where the industry is going. Also, consider secondhand as you will get more ‘value for money’ and features on the secondhand market at the loss of being on the ‘bleeding’ edge of technology.

Continue reading Part 2 - Selecting a Camera: Step 2 - DSLR or Mirrorless?