This article covers the basic components of a modern digital camera. It will also touch on the terms used when describing features and functions and why they matter.
The three main properties that affect image quality from a sensor are resolution, physical size and dynamic range. High-ISO performance is the fourth factor that determines how well a sensor captures and processes images in dim light. A sensor is made up of an array of photosites. A photosite is basically equal to one pixel of the final image. Each photosite has a tiny lens, a color filter and a photosensitive semiconductor (think of a tiny solar cell). On most digital sensors, the photosites are arranged in groups of four with two green filters and one each of red and blue. This is called a Bayer Filter Array. When the sensor is exposed to light, each photosite converts the light that it receives to an electrical charge. After the exposure, the sensor passes the measurements of all the collected charges to the camera’s processor where the brightness and color of the light that struck each photosite is calculated by comparing it to adjacent sites and assembling the data into an image.
Resolution:
What is a pixel? A pixel is the basic unit of current digital photography. Each pixel is one photosite on a sensor that measures the amount and color of the light that hits it when exposed and combined with the measurements of all the other pixels on the sensor, the camera records the image that was focused on the sensor when it was exposed. Since it takes a lot of little dots to make a clear image, sensors have millions of pixels which is why the resolution of a camera is measured in megapixels. A megapixel is one million pixels.
Ask yourself, what are you going to do with the pictures? If you plan to store and view them on a computer, a TV or online, even 4K screens are only a little more than 8MP, so how much more than that do you need? Will you print them? 4×6 prints are cheap and are the most popular size for scrapbooks and physical albums. If you plan on elaborate albums with enlargements, keep in mind that a 300dpi 8×10 print is only a little over 7MP. These reasonable numbers have been inflated by the megapixel wars, so let’s look at it another way…do more megapixels make a better picture? Maybe. Viewed on most media other than maybe a gigantic print, it’s hard to tell the difference between a quality 12MP image and a quality 50MP image. The advantage of a higher resolution original is that you can crop (cut) a section of the image out to remove unwanted clutter or “zoom” in on a subject and it will still have enough resolution to display a quality image. This is how the “zoom” feature works on almost all phones and cameras with a “digital zoom” feature. It doesn’t change the focal length of the lens, instead it takes part of the image on the sensor and enlarges it. FYI: Digital zoom on a camera is never a better alternative to an optical zoom. Personally, I have always turned the feature off on my cameras.
I go into more detail on image quality and file formats in my article Viva La Resolution.
Physical size: A bigger pixel count isn’t always better. There are other factors such as the size of the pixels. In good light and assuming quality lenses, an image viewed on a web page will appear about the same whether it’s from a camera with a Full-frame sensor, APS-C 
sensor, a compact camera or even a top-end phone. When the light gets dim, the difference starts to show. A sensor detects the light level by measuring the charge created when the photons strike the photoelectric material in each photosite (pixel). In low light the camera will need to amplify the measured signal and as the amplification increases, the signal gets distorted and the measurement becomes less accurate. The inaccuracies show up in the picture as spots of random color (chroma noise) or as spots that are brighter or darker than they should be (luminance noise) and reduce the clarity of the image.
Assuming the same number of pixels, the larger the sensor, the larger each individual photosite will be and it will gather more light at the same exposure settings (see illustration). The larger number of photons doesn’t make the image brighter but creates a larger charge at each photosite that requires less amplification to be readable and can be measured more accurately. Fewer errors means less noise of both types. There are dozens of sensor formats for a wide range of purposes from
security cameras to specialty units used for astrophotography, but consumer cameras only use a handful of them. The three main formats across most ILCs are Full-frame, APS-C and 4/3 (pronounced “four-thirds”). The 1” sensor was used in Nikon’s short-lived 1-Series cameras but is thriving in high-end compacts and bridge cameras. Compacts use a few formats but are mostly around the size of the 1/2.3 sensor illustrated above. Smartphones with sophisticated cameras use sensors like the 1/3” format with less expensive models using even smaller ones.
Dynamic Range: Dynamic range is a measure of how well an image captures all levels of light in an image. When the photosite receives too little light to measure, it reads as black. If a significant area of the image is below the minimum sensitivity it records a black area with no detail at all. This is often referred to as a blocked shadow. One way to picture this is to imagine a cave that is too dark for you to see the cave walls. If there is a hole in the wall that is even darker, it looks exactly the same as the wall because both are dimmer than you can see. The same is true when a photosite is exposed to light levels above what it can accurately record as anything other than white. This condition is referred to as “blown highlights”. Too 
bright to look at is indistinguishable from way too bright to look at. Dynamic range indicates the range between the lowest amount of light a sensor can detect without reporting “black” for everything below that and the highest level beyond which everything reads as white. A wide range will record an image closer to what your eyes see without too many dark shadows or half the sky being white because the sun was bright that day.
High ISO Performance: ISO stands for the International Organization for Standardization. (Yeah, I know it’s out of order.) ISO as it applies to cameras refers to the sensitivity of the sensor. ISO sensitivity follows a simple scale that increases arithmetically. In other words, ISO 200 is twice as sensitive as ISO 100 and ISO 800 is 8 times as sensitive as ISO 100. Way back in the early days of mass-produced film, there was a need to standardize film so if you bought two different brands with the same ISO rating (ASA or DIN back in the day) and exposed them using the same settings, both would produce a properly exposed image. The ISO rating of digital sensors follow this standard. If you expose ISO 100 film with the same settings as a sensor set to ISO 100, the results will be pretty much the same. This is true for images taken with different digital cameras (sort of the point in having standards). Here’s where digital photography really has changed things. In the film days, if you had your camera loaded with ISO 100 film for daytime and wanted to shoot inside at night, you had to rewind the film into the cartridge (wasting the remaining film) and load a different roll. Digital cameras have a dial. That’s better, right? Another is the amount of sensitivity available these days. I remember when ISO 400 was amazingly fast and ISO 3200 B&W film was really only good for surveillance or artsy shots that looked like they were printed on 80 grit sandpaper. Newer Full-frame cameras can produce excellent images at ISO 25,000 and useable images at over ISO 100,000. Back to that dial. One shot can be at ISO 100 and the next at ISO 1600 and in most cameras, the ISO will automatically adjust shot to shot. Some more sophisticated cameras offer features that will analyze hundreds or even thousands of areas in the image at the moment of exposure and adjust sensitivity up in deep shadows and down in bright highlights to increase the dynamic range. That’s what I call progress.
The Lens and Stabilization:
This is an overview with some detail. For more on the subject of lenses and stabilization, see my article about Adding Lenses to your ILC kit.
Without a way to focus light on the sensor (or film), a camera is…well, it’s not much of anything. The lens, therefore, is an important thing to consider when choosing a camera.
The most common lens question I see is about the “X”, as in “WITH 30X ZOOM!” Right behind that is “Equivalent” as in “24mm-720mm Equivalent”. Another popular one is “Crop Factor”. Following those is a smattering of “Fast”, “Wide”, “Long”, “Normal”, “APO”, “Macro” and so on. I’ll do a brief rundown here. If you want more specific info, take a look at my Adding Lenses chapter.
“X” Marks the Spot: Zoom lenses on Point & Shoot cameras, Superzooms and camcorders often offer lenses with significant zoom ranges covering moderate wide angle to telephoto. Sometimes a lot of telephoto. This will be advertised as a 15X, 24X or more. The X-number by itself is sort of meaningless without a reference point. It’s like algebra with only one known value: 24 * y = z. If you have ever owned a pair of binoculars or a spotting scope, the “X” means how many times larger an object appears in relation to the naked eye and a lot of people confuse this with the “X” on cameras. What the camera “X” refers to is the ratio between the shortest focal length of the zoom and the longest; 100mm / 4mm = 25. That’s a 25X zoom. You will seldom see a camera with a fixed lens (non-interchangeable) advertised with its native focal length. That brings us to the next subject. Equivalence.
Equivalence: “24-2000mm 35mm Equivalent Focal Length…” So sayeth the advert for a popular superzoom. The blurb actually explains the equivalence but not very clearly. The actual focal length is 4.3mm – 357mm, so why not just say that? For one thing, 2000mm looks a lot bigger than 357mm. Marketing, eh? The 24mm-2000mm numbers refer to the equivalent focal length of the lens with reference to a full-frame digital camera where the sensor is the same size as traditional 35mm film. The 35mm frame size is used as a base simply because it was the dominant standard for many decades leading up to the advent of digital and it provides a mental reference to photographers used to the popular focal lengths used on 35mm cameras. A Full-frame sensor (same as a 35mm film frame) has a diagonal measurement of 43.3mm. The diagonal measurement of the smaller 1/2.3” sensor in the superzoom is 7.66mm. 43.3 / 7.66 = 5.65. That means the smaller sensor captures a 5.65x smaller slice of the lens’ projected image than it would on a 35mm frame. The result is called the Crop Factor.
Crop Factor: If I were a math teacher, I would call the Crop Factor a variable used to solve for Equivalence. But I’m not. So, in plain terms, it is the ratio between the diagonal measurement of any non-full-frame sensor and a full-frame sensor. It is called a Crop Factor because the smaller sensor’s coverage area performs a cropping of the 35mm image area just as if you edited a 35mm image and cut or “cropped” the edges from the whole image and kept a smaller central section. Using the lens specs from above, taking the 4.3 – 357mm focal length and multiplying it by the Crop Factor of 5.65 (5.65 x 4.3 = 24.3 and 5.65 x 357 = 2017) yields an Equivalence rounded to 24-2000mm. Crop Factor became a “thing” then the first Digital SLRs came out with non-full-frame sensors but accepted lenses from 35mm film SLRs. Most of the early DSLRs had APS-C sensors with a 1.5x or 1.6x crop factor. To a person who was once a 35mm film camera user just moving to a DSLR with an APS-C sensor, multiplying the focal length of their existing lenses by the crop factor would tell them what familiar field of view their film camera’s wide or telephoto lenses would cover on their new digital cameras. The words “Wide” and “Field of View” provide a handy segue to the next subject.
Normal, Wide, Telephoto, etc.: Now that we know that everything in the photo universe relates to 35mm film, we will explore what Wide, Normal and other lens descriptions mean. Let’s start with “Normal”. In the olden days, a camera body was seldom sold without a “standard” lens which was almost always 50mm -55mm. A “standard” 50mm lens on a 35mm film camera presents an approximate visual equivalent to what the human eye sees (sometimes referred to as “normal field of view”). A shorter than 50mm focal length will capture an image wider than your eyes see, bringing more of the scene into the image frame as if you had backed away from the subject. If it is longer than 50mm, it will capture a narrower view as if you had moved closer. The term, “Field of View” is another complicated-sounding bit of jargon with a simple explanation. It is the angle created by two imaginary lines radiating from the camera to points at the extreme right and left of the image viewed from above. Picture yourself in a field with a view (free pun included) looking at trees and mountains in the distance holding two sticks. Hold the ends of the sticks right under your nose and point them forward straight at the horizon. Spread the sticks at a 39.6° angle keeping the ends under your nose. Everything inside of where the sticks are pointing is the field of view of a 50mm lens. Or you can look at the illustration.
We have already determined that “Normal” is generally considered a 50mm lens on a full-frame camera. A “Wide-angle” lens is from 35mm down to 24mm. Below that is considered “Ultra-wide”. On the other end, anything between 70mm and 105mm is considered a “Short Telephoto”. From there up to 300mm is a “Telephoto” and above that is a “Super-telephoto”.
As we discussed earlier, fixed lens cameras typically advertise focal lengths in Equivalent values. If you are in the market for a lens for your ILC, keep the Crop Factor in mind. A 20mm lens is considered Ultra-wide on a full-frame camera but its field of view is the same as a wide 30mm lens on APS-C and a near-normal 40mm on a 4/3 camera.
Stabilization: Stabilization used to be a luxury found on only the most expensive telephoto lenses that were out of the reach of the average photographer. As the technology matured, it gradually made it’s way to consumer telephotos and zooms. Still a more expensive option, but within the reach of non-professionals. Lens-based stabilization was the norm until about 2004 when Minolta released a camera with stabilization at the sensor level. This meant that all lenses attached to the camera were stabilized, not just the expensive telephotos. Whether lens-based or sensor-based, stabilization really works and very few fixed-lens cameras or ILC body/lens kits come without some form of it.
The LCD
I couldn’t think of a digital camera that didn’t have an LCD screen on the back to review images, so I did a search and found the $12,000+ Leica M Edition 60. I’m sure someone out there is clapping slowly, overjoyed at the return to the “good old days” of guessing how the shot came out until they got it “developed”. In my opinion “Good old days” for me started around 2000 A.D. and include the best and most basic feature of digital, namely you take a picture and can see immediately how it came out. The range of sizes of LCD screens grew with every generation from a dim, grainy 1.5” screen in the dinosaur days of digital to where bright, clear 3” or larger displays are fairly standard, even on some compacts. There are all types of screens with a wide range of both brightness and resolution. If you can, check the LCD out in the sunshine before you make up your mind some models without a viewfinder offer a Sunny Day mode that brightens up the screen. If you are looking at a SuperZoom, Digicam or mirrorless ILC, pay attention to the viewfinder. They aren’t optical but contain a tiny LCD screen that replaces the prism and mirror of an SLR. These too vary a lot in resolution and viewability. Electronic viewfinders (EVFs) have come a long way and the best ones are as good or better than the high-end optical ones in viewability with far more information available at a glance.
Memory:
Some cameras used to have a base amount of dedicated Internal memory so you could take a few images without a memory card. I didn’t try too hard, but I couldn’t find that feature on any current or even recent camera. If the two-decade-old compact you’re shopping to replace had it and the lack of this feature is a deal breaker, my condolences. You need to buy memory.
Most of the memory card formats from the early years of digital have followed the Passenger Pigeon and the Dodo into extinction. The SD form factor has become the majority standard with Compact Flash hanging on by a thread as newer, faster formats like C-Fast and XQD are appearing to support huge resolutions, insanely fast burst shooting and 4k or 8k video.
Cameras no longer come with a card in the box, but retailers often bundle a cheap card (and even cheaper accessories). If the bundle costs any more than the camera alone from somewhere else and the memory card isn’t a recognized brand, pass on it. If it doesn’t cost more, go ahead but toss the card when you get it. EBay has determined that 90%+ of brand name cards sold at a substantial discount are counterfeit. Save yourself some grief and stick with the major brands from a reputable supplier.
Memory may seem like an expensive accessory but using an average file size for a 16MP JPEG image, a $15 16GB memory card will hold the equivalent of eighty or so 24-exposure rolls of film. At $3.50 per roll plus, say, $7.00 to develop and print, you would have $800+ sunk into the same number of conventional photos, including the ones that sucked and were tossed in the trash. The keepers would put in albums (another expense) or boxed in some obscure closet shelf. Another consideration is that you can’t scrape the image off of a roll of film and reuse it. That little feature makes “expensive” digital storage cheaper every time you offload your images, reformat and reuse it.
When you fire up the new camera and get it all set up, put the card in and see how many images is says it has room for. The number will be an approximation but good enough for estimating. If you plan on taking video, do a test run and see how much memory is used for a short clip of a minute or so. Take a guess as to how many images and how much video you will collect on your next trip and if the card won’t hold two or three times that number, but more cards. An unused card in your bag isn’t a crime. Running short on storage during a memorable trip should be.
Memory speed: Memory card speed was another overly cryptic standard. Until recently you would be bombarded with more “X”s like 133X, 300X, etc.. If you still have old cards rated in “X” numbers, the base is the playback speed standardized for the CD-ROM which is 150 kilobits per second. That means that a 40X card could be read at a maximum of 60 megabits per second. Note the “bits”. Files are measured in 8-bit bytes so a 40X card could, theoretically, transfer about two 3mb files in a second. Though some still include the “X” number, most reputable manufacturers’ current practice is to label CF, CFast and XQD cards with a simpler MB per second (MB/s) rating which indicates transfer rate. Unfortunately, along with MB/s rating, SD cards have another set of ratings to contend with. The Class system
indicates minimum sustained read/write speeds that a card is capable of. Class 4 will maintain 4MB/s, Class 10 will do 10MB/s, etc. UHS is a newer standard with the slowest U1 cards being able to maintain at least 10MB/s and U3 rated at 30MB/s “V” ratings are like the Class ratings but geared toward video. V30 cards will read and write at a minimum of 30MB/Sec. and so on. There are also ratings for different bus speeds (the bus is the memory pipeline that the card communicates through), but thankfully they can be ignored as all cards I was able to find using the newer UHS-II bus use MB/s ratings. SD cards that read and write at less than 30MB/s are getting rare and the latest and fastest ones can read and write at 300MB/s. Announced in 2017, the UHS-III bus promises twice that. above. Keep in mind that a camera may not be able to take advantage of a higher speed card due to in-camera bus and processor limitations and buying one won’t likely make your camera write or review images any faster. That said, if the difference in price is reasonable to you, get a faster one. All SD cards are backwards compatible (with a few limitations), so high speed cards aren’t completely useless if your camera can’t make full use of them. With a fast card reader, you can really see the difference in while downloading images to your computer!
Memory capacity: Memory card speed isn’t the only thing that has increased. As file size grows, so must the camera’s ability to store them. I’ll concentrate on SD since it is overwhelmingly the most common and the capacities of the other formats are uncomplicated.
There are four types of SD cards but since one with the original spec is as rare as an honest politician, I’ll cover the latest three. The basic SD card (SDSC – SD Standard Capacity) has a maximum capacity of 2GB. SDHC (SD High Capacity) supports 4GB to a maximum of 32GB. SDXC (SD Extended Capacity) supports 64GB to a maximum of 2TB. The various spec cards are compatible, but there are restrictions imposed by the device they are plugged in to and actually make sense. Any device that supports SDXC (latest format) can use any previous version (the UHS-II cards with the extra row of pins can be used in non-UHS-II devices that support SDXC and vice-versa). A device that supports SDHC can use SDSC cards. Check the manual for your camera before running out to buy a bigger card to see what they can support.
Memory card philosophy: This section is just an FYI passing along some thoughts on dealing with memory cards when travelling. One school of thought is to buy the biggest card your system and budget will support and shoot away until it’s full then load a new one. Another plan is to carry a bunch of smaller cards and put a new one in daily so if there’s a card failure, you don’t lose all your images. Which one suits you is a personal decision. I have never had a card fail and statistically it’s rare. On the other hand…you never know.
Batteries:
Cameras use power. This has been true since someone decided to put the exposure meter inside the camera. That took a teensy amount of power and a $3 battery would last for years. Digital cameras use a lot of power. You are holding a tiny digital device with the computing power of a 1970s mainframe! A very few off-brand models still use AA batteries, but most use proprietary lithium-ion power packs. These usually cost from $30 – $100 each but can be recharged hundreds of times and can last for 2-3 years with normal usage. You will need at least one extra battery if you plan on using the camera much. Trust me! If you think that nothing could be worse than that once-in-a-lifetime shot getting away because you left the camera at home, try missing it because a dead battery has transformed your camera into an expensive necklace.
Rule-of-thumb; stick with buying the camera maker’s battery unless the camera model is popular enough that you can buy a major-brand third-party replacement. Proprietary lithium-ion batteries will self-discharge between charges if not used, but do so very slowly and will hold a charge for several months to a year. Always remember to check the batteries left in your camera and any spares in the bag before an outing to see if they need to be charged. The better chargers will charge the batteries quickly and then switch to a light “trickle” charge. That lets you leave batteries in the charger so they are always ready to go.
In Conclusion…
Remember what you read earlier: Cameras, like most electronics, suffer from rapid upgrade cycles and it’s easy to be stricken with feature envy when the “next big thing” comes out a month after you buy yours. Most cameras, again like most electronics, are obsolete as soon as they hit the stores. I have found that unless you truly need that new super-feature, buying a generation back from the cutting edge can save you a lot of money and give you equipment that has been blessed with the long list of fixes that those brave buyers going before have shed sweat and blood to get released. Why do you think it’s called the cutting edge?
At the risk of being repetitive, I will end this article with what has become my standard advice to anyone buying a camera: