02 – What is a camera?

We’ll start this class with a rather gentle introduction, by asking ourselves what a camera really is, and what its different components are. Chances are that you will already know some of this, but going through it anyway will at least ensure that we have defined a common vocabulary.



In the strictest sense, it is simply a device which can record light. It does so by focusing light on a photosensitive surface. From this simple sentence, we can see the three main parts of any camera. 

The photosensitive surface reacts to light through either a chemical process (film) or an electric one (digital sensor). There are fundamental differences between these two, which we will cover in a subsequent lesson, but for now we can consider both of them to be identical: they are a grid of several million tiny dots (pixels) and each can remember how much light it received in a given period of time. There are three important qualities to each sensor: resolution, size and what we can call “quality”.

  • Resolution is simply the number of pixels (it is slightly more complicated with film, let’s forget about it for now). The more pixels you have, the more fine grained details you can theoretically record. Any resolution above 2 or 3 megapixels (i.e. millions of pixels) will be enough for displaying on a screen, but higher resolutions come into play for two important applications: printing and cropping.
    • In order to have a good reproduction quality, it is generally estimated that between 240 and 300 pixels should be used for every inch of paper (dots per inch, or dpi), which will give a natural limitation to the biggest size one can print. For instance, a 6MP image of dimensions 2000×3000 pixels can be printed at a maximum size of 12.5×8.3″ at 240dpi (2000/240 = 8.3, 3000/240 = 12.5). It is possible to print bigger by either lowering the dpi or artificially increasing the resolution, but this will come at a serious loss of image quality. Having a higher resolution allows you to print bigger.
    • Cropping means reducing the size of an image by discarding pixels on the sides. It is a very useful tool and can often improve composition or remove unwanted elements from an image. However, it will also decrease resolution (since you lose pixels), so how much cropping you allow yourself will depend on the initial resolution, which you want to be as high as possible. This is also what some cheaper cameras call “digital zoom”, which use should be avoided as the plague, as the same effect can very easily be reproduced in post-processing, and the loss of image quality is often enormous.
  • The physical size of the sensor is very important and will have an impact on many other parameters, most of which we will see in subsequent lessons: crop factor, depth of field, high ISO noise, dynamic range are some of them. Bigger sensors will also allow to have more widely spaced pixels (increasing image quality) or more of them (increasing resolution). Bigger is almost always better, and this is one of the main reasons that DSLRs (and medium format cameras) produce much better images than compact cameras. In tomorrow’s lesson, we will cover the different types of cameras in more details.
  • Finally, sensor quality is harder to quantify, but it refers to how well the sensor reacts to difficult light conditions: either low light which will require to increase ISO and for which we want the sensor to have as little noise as possible, or high contrast, which will require a good dynamic range to be recorded adequately.


The lens is the second component of any camera. It is an optical device which takes scattered light rays and focuses them neatly on the sensor. Lenses are often complex, with up to 15 different optical elements serving different roles. The quality of the glass and the precision of the lens will be extremely important in determining how good the final image is.

Lenses must make compromises, and a perfect all around lens is physically impossible to build. For this reason, good lenses tend to be specialized and having the ability to switch them on your camera will prove extremely useful.

Lenses usually come with cryptic sequences of symbols and numbers which describe their specifications. Without going too much into details, let’s review some of their characteristic:

  • Focal length refers roughly to the “zoom level”, or angle of view, of the lens. It will have its own lesson in a few days, as it can be a surprisingly tricky subject. A focal length is usually expressed in millimeters, and you should be aware that the resulting angle of view actually depends on the size of the sensor of the camera on which the lens is used (this is called the crop factor). For this reason, we often give “35mm equivalent” focal lengths, which is the focal length that would offer the same view on a 35mm camera (the historic film SLR format) and allows us to make meaningful comparisons. If there is a single length (e.g. 24mm), then the lens doesn’t zoom, and it is often called a prime lens. If there are two numbers (e.g. 18-55mm), then you can use the lens at any focal in that range. Compact cameras often don’t give focal lengths but simply the range, for instance 8x. This means that the long end is 8 times longer than the wide one, so the lens could for instance be a 18-144mm, or a 35-280mm, etc.
  • The aperture is a very important concept which we will talk about in much detail later on. The aperture is an iris in the centre of the lens which can close to increasingly small sizes, limiting the amount of light which gets on the sensor. It is refered to as a f-number, for instance f/2.8. To make things worse, it is quite counter-intuitive, as the smaller the number, the bigger the aperture! For now, we don’t have to worry about this too much. The important number on a lens is the maximal aperture, the lower the better. Professional zoom lenses often have f/2.8 maximal apertures, and cheaper consumer lenses have ranges such as f/3.5-5.6, meaning that at the wide end, the maximum aperture is f/3.5 and at the long end, it is f/5.6. Aperture can be closed to tiny levels, usually at least f/22.
  • Lenses also need a focusing system. Nowadays, most lenses have an internal motor which can be piloted by the camera: the autofocus. They also have a ring to allow the photographer to focus manually. There are plenty of options for autofocus motors as well, for instance hypersonic or silent ones.
  • Lenses are increasingly equiped with stabilisation systems (called VR by Nikon, IS by Canon). They detect small movements, usually handshake, and compensate for them by moving internally the optical elements in the opposite direction. Though no magic pills, those systems tend to work very well and allow to take sharp images at quite slow shutter speeds.
  • Finally, lenses can have all sorts of fancy options: apochromatic glass, nano-coating, etc, designed to increase the quality of the final image. You probably shouldn’t worry too much about those.


Finally, the body is the light tight box connecting the lens to the sensor, and ordering everyone around. Though some film cameras are just that, black boxes, most digital cameras are now small computers, sporting all sorts of features, often of dubious usefulness. Let’s review some of the components found in most bodies:

  • The most important is probably the shutter. Think of it as a curtain in front of the sensor. When you press the trigger, the curtain opens, exposes the sensor to light from the lens, then closes again after a very precise amount of time, often a tiny fraction of a second. Most shutters operate between 30 seconds and 1/4000s of a second. That duration (the shutter speed) is one of the three very important exposure factors, along with aperture and ISO.
  • A light meter. As the name suggests, it measures the quantity of light and sets the exposure accordingly. How much manual control you keep at this stage is one of the most important questions in photography. There are different metering modes, but except in very specific cases, using the most advanced, most automated one (matrix metering on Nikon cameras) will provide the best results.
  • A focus detector, used to drive the autofocus motor in the lens. There are two competing technologies, contrast detection and phase detection, with at the moment an edge for the latter, which explains why DSLRs tend to focus faster than compact cameras. These systems tend to vary greatly between basic and advanced bodies, but it should be noted that they all need reasonable amounts of light to work properly.
  • A way to store the image just created. Back in the days of film, this was just a lever to advance the roll to the next unexposed frame. Now, it is a pipeline which ends up in the memory card that the camera is using. If you are shooting jpg instead of raw (more on this in another lesson), there is an additional stage where the internal computer performs all sort of black magic on the image to output a ready-to-view jpg file.
  • A way to frame. It can be a multitude of things, optical or electronic viewfinder, LCD screen or even ground glass. Here too, DSLRs have an edge as an optical viewfinder allows “through-the-lens” viewing and immediate feedback, while electronic viewfinders (really, a LCD screen inside a viewfinder) and LCDs often have limited resolution and slight updating delays.



Take a good look at your camera, whatever its type, and try to identify each component we have discussed here. It might be a good opportunity to dig out the manual or to look up its exact specifications online. Now look up a different camera online (for instance at dpreview) and compare their specifications. Try doing this for both a less advanced and a more advanced body, and for different lenses. Report here if you find any interesting difference, or if some parts of the specifications are unclear.

Previous Lesson: On Photography (it’s not rocket science)
Next lesson: Different Types of Cameras


  • I just found this link via Reddit and started reading through. It reminds me of my college course and so far I love how you lay everything out. I’m definitely brushing up on a lot. Thank you for taking the time to write this all out for everyone! You’re appreciated. =D

  • I’ve compared my Canon EOS 400D to the new Canon EOS 650D. One thing noted it the much higher sensitivity (ISO) for the 650D. Also the sensor for the the 650D seems to have greatly improved, supporting higher image resolutions.

  • I have a nikon D3100 with a 18-55 lens

    I love how you go through everything in laymen’s terms without being slow or patronising!

  • I have a Nikon D3200 with an 18-55mm lens, I also have a 55-200mm lens. It has 24.2mp and an ISO from 100 up to 6,400 for extreme low light settings. It captures up to 4 frames per sec. The Nikon D3100 is similar but with 14.2mp & 3fps, same ISO. The Nikon D600 has same mp, but 5.5fps, ISO sensitivity can be expanded from 50 to 52,600.

  • I just picked up a Canon Rebel T3i w/a 18-55mm IS II lens. Pretty entry level, but enough of a camera for my puposes; photographing artwork and making time-lapse, art-creation videos.

  • I have a Canon Rebel T3 DSLR with an 18-55mm focal length. The ISO is 100-6400. The shutter speed is .5-1/4000. Aperture goes from f/4-f/45.

    I’ll compare to my Canon Powershot SX30 point-and-shoot which has a 24-840mm focal length (35x optical zoom). The ISO is 80-1600. The shutter speed is 1 to 1/3200 per second. Maximum aperture is f/2.7.

  • I am learning to shoot with a Canon EOS Rebel t3, with a shutter speed of 1/4000 to 1/60 seconds and a maximum pixel of about 12 megapixels. I have two lenses, one of 75-300mm zoom and an f/4.5-5.6 aperture, the other an 18-55mm zoom and an f/3.5-5.6 aperture.

    For comparison, the Canon EOS Rebel T5 offers a shutter speed of 1/4000 to 30 seconds, and a maximum pixel of about 18 megapixels.

    For a lens comparison, the EF 70-300 lens F/4-5.6L is similar to the long range lens i have, but gives a greater aperture distance as well as image stabilization. (along with the other nifty things i don’t grasp yet.

    Thanks for the lessons, they are great so far

    • I am learning to shoot with a Canon EOS Rebel t3 as well! I have found this site to be immensely helpful in teaching myself more about such a fun hobby I love to do and hope to get better at.

      I have the same specs (sensor being around 12mp, shutter speeds from “bulb” to 1/4000, and ISO range from 100-6400). For lenses I have the same 18-55mm at f/3.5 -5.6 and a EF 75-300mm at f/4 – 5.6.

      Comparing to: Canon 70D – sensor size around 20mp, shutter speeds from “bulb to 1/8000, ISO 100-12800 (but expandable to 25600?)

      • Have you ever thought about adding a little bit more than just your articles? I mean, what you say is important and everything. However think of if you added some great images or videos to give your posts more, “pop”! Your content is excellent but with images and videos, this blog could definitely be one of the greatest in its field. Excellent blog!

  • My camera of choice today is an Olympus OM-D EM-1 with an Olympus 17mm f1/8 lens. The camera is a micro four thirds design so has a crop factor of 2.

    Sensor: 4/3 Live MOS Sensor
    Resolution: 16 megapixels

    The lens is an Olympus 17mm f1.8 fast wide angle prime.

    Focal length is 17 mm or 34 mm 35mm equivalent
    Aperture is f/1.8 so it is considered a fast lens. The aperture range is f/22 to f/1.8
    Focusing: Is autofocus and manual focus
    Image stabilisation: None. The camera has built in image stabilisation.
    Lens construction: 9 elements in 6 Groups (DSA lens, 2 Aspherical lenses, HR lens)

    The alternative camera I considered at the time of purchase was a Sony A6000.

    Sensor: Mirroless BIONZ X™ image processor with a focal length crop factor of 1.5
    Resolution: 24.7 megapixels

    I didn’t really investigate lens options at the time as I was looking only at bodies.

  • I have recently acquired a D800 and would like to make a note on the difference in image quality compared to my previous camera, a D5100. An overview of spec differences can be seen at (http://snapsort.com/compare/Nikon-D5100-vs-Nikon-D800). I think the most noticeable to me are the noise levels at higher ISOs (opening a whole world of night photography) and how much the extra detail the 1.4 stops of dynamic range really allow you to pull out of the shadows and highlights.

  • Just wanted to say I really appreciate your class room here online.
    I’ve been meaning to learn photography but have always fell short because of other priorities. Today is a snow day and i’m stuck home so I’m sitting in front of the computer with a perfected cup of coffee and already learning so much. I do not have a camera but I’m thinking of purchasing a point and shoot. Maybe the Sony RX100MIII or Lumix LX100 either or..

    Gonna read the next chapter now!

  • Recently got my mom the Fujifilm X-E2 for Christmas (but of course I’m the one learning to use it!)

    Sensor: X-Trans CMOS II – 23.6 mm x 15.6 mm
    Resolution: 16 megapixels

    The lens is an Fujinon XF.

    Focal length is 18-55mm.
    Aperture is f/2.8-4
    Focusing: Is autofocus and manual focus
    Image stabilisation: Yes

    Still not exactly sure that all these mean but I am looking forward to further my understanding in the next lesson.

  • My camera (that I just bought a few weeks ago) is the Pentax K-50. I have the 18-55 and 50-200mm kit lenses as well as a handful of manual focus lenses from my dad’s old Pentax film camera. My camera has a 16MP APS-C sensor.

    It’s been pretty great but it’s not full frame and coming from film, that has a pretty big impact. If I were to go to full frame (when I become rich) I’d buy the Canon 6D. Unlike my camera, it has a 20MP full frame sensor.

  • Compared my Panasonic DMC GF3 to the Nikon J1. The Panasonic has 2 more MP on the sensor than the Nikon however, it does lack some of the shutter speed (1/4000 vs 1/16000). The Panasonic also has more light sensitivity with 6400 ISO compared to the Nikon at 3200 ISO.

    I have two lenses right now. The Lumix 14-42 and Lumix 45-200. The 14-42 has an aperture of f/3.5-5.6 and the 45-200 has an aperture of /4-5.6.

  • am now learning photography & videography.

  • I kinda feel that my little compact isn’t going to hold up to some of the questions asked. However, I have a Canon powershot sx280hs that takes fairly decent photos (from previous history). I was interested to see however that the manual settings seem to be able to adjust this quite nicely with an ISO up to 6400 (I’ve used auto in the past and haven’t looked before). It seems like it has a decent range of zoom, but I was unable to find some of the topics discussed above like the aperture.

  • For this course I hoped to use my new camera – its a Sony RX10 and its no DSLR but its close so I hope I wont run into problems later on in this course. ( if so I have a back up I can loan from a friend ) it does has RAW both as JPG options.
    The Lens is Carl Zeiss diameter62 , 2,8/8,8 -73,3 Lens
    24-200mm equivalent stabilized F2.8 lens
    Its a 20MP Camera
    ISO 125 – 12800 (expandable down to ISO 80)
    I compared it with a Nikon 5200 ( the one I can borrow in case I have to )
    And noticed that the nikon5200 has a bigger pixelrange with 6000 x 4000 – and the sony rx10 has 5472 x 3648 as max.
    The max shutterspeed is also in advance of the nikon5200 with 1/4000 sec compared to the 1/3200 for the sony rx10

  • I own a Nikon D3300 DSLR.
    resolution: 24 megapixels
    sensor size: 23.5 X 15.6 mm
    ISO: 100, 200, 400, 800, 1600, 3200, 6400, 12800
    max shutter speed: 1/4000 sec.

    The lens currently attached is the Nikon DX NIKKOR 35mm f/1.8G
    focal length: 35mm. no zoom and relatively short focal length. must use your feet with this one.
    aperture: f/1.8. very helpful in low light.

  • Between the Canon EOS Rebel T6 and Nikon D3300 18, which one is better? I’m still planning on buying my first camera yet. For what I read here and the specs of each camera, the D3300 is better because it has higher ( I don’t know if I’m using the term “higher” correctly here, probably not) ISO.

  • I own the entry level Olympus mirrorless and comparing it to the high end Sony mirrorless.

    OM-D EM10: 1/4000 – 60s
    Sony a7R II: 1/8000 – 30s

    Light Meter:
    OM-D EM10: ISO 100-25600
    Sony a7R II: ISO 100-102400

    Focus detector:
    OM-D EM10: High-speed imager AF with automatic, single, continuous Autofucs, Manual Focus
    Sony a7R II: Fast Hybrid AF with automatic, single, continuous Autofocus, Manual Focus

    OM-D EM10: SD Memory card
    Sony a7R II: Memory Stick Pro Duo, SD Memory card

    OM-D EM10: KCD viewfinder, 1.44M dots
    Sony a7R II: XGA OLED, 0.5 in electronic color viewfinder, 2.36M dots

  • So, I have a Nikon D3300 which has the following specs:
    Shutter speed:1/4000 – 30 s
    Megapixels: 24.2 MP
    Lens Size: 18-55 mm
    Aperture on the lens:f/3.5-5.6
    ISO Sensitivity: 100-12800
    Up to 5fps

    And I was looking online at a Canon EOS 77D with the following specs:
    Megapixels: 24.2 MP
    Lens Size: 18-55 mm
    Aperture on the lens:f/3.5-5.6
    ISO Sensitivity: 100-25600 (still not sure what this is)
    Has an autofocus speed of 0.03 s (not sure how fast mine is)
    Has built in wifi/bluetooth
    Up to 6.0 fps

    My camera was $350, the Canon is $1049. To me at this point, I don’t see a huge difference or an upgrade in the Canon. Hmmmm.

  • I have a Nikon D5100 with the following specs (was good to get the user manual out again and learn more about my camera!)

    Megapixels: 16,2
    Sensor size: 23,6 x 15,6 mm
    Shutterspeed: 1/4000 – 30 sec
    Focal length of lens 1: 18-55 mm
    Focal length of lens 2: 55-200 mm
    Aperture range of lens 1: f/3.5 – f/5.6
    Aperture range of lens 2: f/4 – f/5.6

    I compared it with a similar camera from Canon I looked into at the time: the Canon t3i Rebel. What I noticed is that they’re very similar. Canon has slightly more MP (18) but a smaller sensor.

  • I have a Canon 60D, I’d have to say the most interesting piece of information I learned is that the sensor size will impact multiple things and that I must take it into account, constantly.

  • I have a Canon Powershot SD750 Digital ELPH
    framing- LCD monter
    Sensor-1/2.5in, total pixels 7.4 million
    Lens focal length 5.8(W)-17.4(T) mm, f/2.8(w)-f/4.9(t) zoom 4x
    focus range(settings); Normal= 12in.-infinity Macro= 1.2in-1.6ft (W)/12in.-1.6ft (T), Infinity=9.8ft-infinity
    Shutter- speed 15-1/1500 sec.
    AF system: TTL autofocus &AiAF face detect
    light metering= evaluative, centre weighted average or spot

  • I use digital cameras as well analog ones. One that are 100 years old ( german made camera that was passed down from my grandfather to my father and me eventually. That was my first camera all manual) as well the new ones. Different companies makes settings in different way so need time to get used to for example most common nikon and cannon. Lets not forget about lenses, you can’t just fit ones company lense to different company camera without adapter. And than the lense parameters change a little. I found that choosing which camera Ill be using depends on the effect I want to get or conditions or just if I want to have fun with it.

  • A very informative lesson!

    Have the Canon 60D.

    It is a Canon DSLR with an APS crop sensor (22.3 x 14.9 mm, focal length multiplier 1.6x).
    Has a built in flash. Shoots photos of up to 18 megapixels with an ISO range of 100-6400.
    Has a 9 point autofocus system and an optical viewfinder.
    Shutter speed range – 30 – 1/8000.

    Compared to Canon 5D Mkiii, the biggest difference is the sensor size. The interesting thing discovered is that a full frame sensor (36 x 24 mm) has over 2.5x surface area than a APS-C sensor.
    Some differences are also – 22MP vs 18MP. More autofocus points (61 vs 9 – useful for studio scenarios?) and a higher max ISO (25600 vs 6400). Basically, 5D would capture images easier in low light conditions.
    This would prove useful of taking photos of Brazilian Jiu Jitsu. Gyms often have low lighting, can’t use flash and need to use a quick shutter speed (1/250th and up because of motion).

    Lens comparison is the kit lens Canon EF-S 18-135mm f/3.5-5.6 IS vs Canon EF 50mm f/1.4 USM Lens.
    Kit lens focal length is between 18-135mm (1.6x on crop sensor) versus the non-zoomable prime lens 50mm (field of view 80mm on crop sensor). Aperture of kit lens is 3.5-5.6 versus a maximum of 1.4 (and down to 22) on the prime lens. Have been enjoying the 50mm!

  • I’m getting a used (but great condition) Canon Rebel T2i DSLR. I’m a relatively new photographer and my camera phone just doesn’t cut it. I think the biggest challenge is going to be finding the right balance of aperture, shutter speed and ISO to take the most optimal pictures. I’m already confused, but i’m taking it on as a challenge! I’m looking forward to learning as much as I can.

  • The is exactly what i was looking for. It took a week of searching but finally i have found the right course. thank you very much for taking your time to lay this course for us. God Bless You.

  • I’ve compared my Sony a6000 and the sony a7rii my sony a6000 has a 24.3 megapixel APS-C CMOS sensor and the sony a7rii has a 42MP Full Frame BSI CMOS sensor, one of the main differences is that the a7rii has a 5-axis image stabilization and that allows it to have a high-speed AF with non-native lenses, wich is really cool.

  • This is a superb course as I have been taking photographs for decades without proper understanding of the nuts ancbokts. Finally a proper course to equip me with all the info and great community to discuss too!

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