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HTG Explains: Cameras, Lenses, and How Photography Works

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Confused by that digital SLR you have, and all the photography jargon that goes along with it? Take a look at some photography basics, learn how your camera works, and how that can help you take better pictures.

Photography has everything to do with the science of optics—how light reacts when it is refracted, bent, and captured by photosensitive materials, like photographic film or photosensors in modern digital cameras. Learn these basics of how a camera—practically any camera—works, so you can improve your photography, whether you’re using an SLR, or a cellphone camera to get the job done.

Just What is a Camera?

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Around 400BC to 300BC, ancient philosophers of more scientifically advanced cultures (such as China and Greece) were some of the first peoples to experiment with the camera obscura design for creating images. The idea is simple enough—set up a sufficiently dark room with only a tiny bit of light entering through a pinhole opposite a flat plane. The light travels in straight lines (this experiment was used to prove this), crosses at the pinhole, and create an image on the flat plane on the other side. The result is an upside-down version of the objects being beamed in from the opposite side of the pinhole—an incredible miracle, and an amazing scientific discovery for people that lived more than a millennium before the “middle ages.”

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To understand modern cameras, we can start with the camera obscura, leap forward a few thousand years, and begin talking about the first pinhole cameras. These use this same simple “pinprick” of light concept, and create an image on a plane of photosensitive material—an emulsified surface that reacts chemically when struck by light. Therefore the basic idea of any camera is to gather light, and record it on some kind of photosensitive object—film, in the case of older cameras, and photo sensors, in the case of digital ones.

Does Anything Go Faster Than the Speed of Light?

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The question posed above is sort of a trick. We know from physics that the speed of light in a vacuum is a constant, a speed limit that is impossible to pass. However, light has a funny property, compared to other particles, like neutrinos that travel at such quick speeds—it doesn’t go the same speed through every material. It slows, bends, or refracts, changing properties as it goes. The “speed of light” escaping from the center of a dense sun is agonizingly slow compared to the neutrinos that escape from them. Light may take millennia to escape a star’s core, while neutrinos created by a star react with nearly nothing, and fly through the densest matter at 186,282 miles/sec, as if it was barely even there. “That’s all well and good,” you might ask, “but what does this have to do with my camera?”

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It is this same property of light to react with matter that allows us to bend, refract, and focus it using modern photographic lenses. The same basic design hasn’t changed in several years, and the same basic principles from when the first lenses were created apply now, as well.

 

Focal Length and Staying in Focus

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While they have become more advanced throughout the years, lenses are basically simple objects—pieces of glass that refract light and direct it toward an image plane toward the back of the camera. Depending on how the glass in the lens is shaped, the amount of distance the crisscrossing light needs to converge properly on the image plane varies. Modern lenses are measured in milimeters and refer to this amount of distance between the lens and the convergence point on the image plane.

Focal length also affects the kind of image your camera captures, as well. A very short focal length will allow a photographer to capture a wider field of view, while a very long focal length (say, a telephoto lens) will cut the area you’re imaging down to a much smaller window.

There are three basic types of lenses for standard SLR images. They are Normal lenses, Wide-angle lenses, and Telephoto lenses. Each of these, beyond what has already been discussed here, have some other caveats that come along with their use.

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  • Wide-angle lenses have huge, 60+ degree angles of view, and are usually used for focusing on object closer to the photographer. Objects in wide angle lenses may appear distorted, as well as misrepresenting the distances between distance objects and skewing perspective at closer distances.
  • Normal lenses are those that most closely represent the “natural” imaging similar to what the human eye captures. Angle of view is smaller than Wide-angle lenses, without distortion of objects, distances between objects, and perspective.
  • Long-focus lenses are the huge lenses you see photography aficionados lugging around, and are used to magnify objects at great distances. They have the most narrow angle of view, and are often used to create depth of field shots and shots where background images are blurred, leaving foreground objects are left sharp.

Depending on the format used for photography, focal lengths for Normal, Wide-Angle, and Long-Focus lenses changes. Most ordinary digital cameras use a format similar to the 35mm film cameras, so the focal lengths of modern DSLRs are very similar to the film cameras of yesteryear (and today, for the film photography buffs).

Aperture and Shutter Speeds

Since we know that light has a definite speed, only a finite amount of it is present when you take a photo, and only a fraction of that makes it through the lens to the photosensitive materials within. That amount of light is controlled by two of the major tools a photographer can adjust—the aperture and shutter speed.

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The aperture of a camera is similar to the pupil of your eye. It is more or less a simple hole, that opens wide or closes down tightly to allow more or less light through the lens to the photo receptors. Bright, well-lit scenes need minimal light, so the aperture can be set to a larger number to allow less light through. Dimmer scenes require more light to strike the photo sensors in the camera, so the smaller number setting will allow more light through. Each setting, often referred to as f-number,  f-stop, or stop, typically allows half the amount of light as the setting before it. Depth of field also changes with the f-number settings, increasing the smaller the aperture used in the photograph.

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In addition to the aperture setting, the amount of time the shutter stays open (aka, shutter speed) to allow light to strike photosensitive materials can also be adjusted. Longer exposures allow in more light, particularly useful in dim lighting situations, but leaving the shutter open for extended periods of time can make huge differences in your photography. Movements as small as involuntary hand tremors can dramatically blur your images at slower shutter speeds, necessitating the use of a tripod or sturdy plane to place the camera on.

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Used in tandem, slow shutter speeds can compensate for smaller settings in aperture, as well as large aperture openings compensating for very fast shutter speeds. Each combination can give a very different result—allowing lots of light in over time can create a very different image, compared to allowing lots of light in through a larger opening. The resulting combination of shutter speed and aperture creates an “exposure,” or the total amount of light that strikes the photosensitive materials, be they sensors or film.


Have questions or comments concerning Graphics, Photos, Filetypes, or Photoshop? Send your questions to ericgoodnight@howtogeek.com, and they may be featured in a future How-To Geek Graphics article.

Image Credits: Photographing the Photographer, by naixn, available under Creative Commons. Camera Obscura, in public domain. Pinhole Camera (English) by Trassiorf, in public domain. Diagram of a Solar Type Star by NASA, assumed Public Domain and Fair Use. Galileo’s Teliscope by Tamasflex, available under Creative Commons. Focal Length by Henrik, available under GNU License. Konica FT-1 by Morven, avaiable under Creative Commons. Apeture diagram by Cbuckley and Dicklyon, available under Creative Commons. Ghost Bumpercar by Baccharus, available under Creative Commons. Windflower by Nevit Dilmen, available under Creative Commons.

Eric Z Goodnight is an Illustrator and Graphics Geek who hopes to make Photoshop more accessible to How-To Geek readers. When he’s not headbanging to heavy metal or geeking out over manga, he’s often off screen printing T-Shirts.

  • Published 05/16/11

Comments (10)

  1. Hatryst

    There is a valuable resource for those who are interested in DSLR photography, but don’t have a DSLR right now. Or those who just want to practically FEEL how a DSLR is used to take excellent photos.
    Checkout:
    http://camerasim.com/camera-simulator.html
    via Lifehacker (http://lifehac.kr/jLWyen)

    And this is an excellent article, very easy to understand. I hope this Photography series continues to go on and on :)

  2. Harold

    Good article, for novice DSLR people, like me!

    I think there are a couple of typos…
    First, I think the second ‘slow shutter speeds in the quote
    “Used in tandem, slow shutter speeds can compensate for smaller settings in aperture, as well as large aperture openings compensating for very slow shutter speeds.”
    should read ‘fast shutter speeds’. This typo changes the meaning of the sentence.

    Second, there are minor typos in both the “Wide-angle lenses” and “Long-focus lenses” descriptions. Neither changes the meaning, but you might wish to correct those.

    Suggestions for future articles:

    How about teaching how to take photos under various conditions? It could be a series of articles. Describe the conditions (e.g. an indoor violin recital, taking pictures from the back of the hall, no flash) and the equipment needed (e.g. recommended lens(es), filters, camera sensitivity) and the techniques/settings (e.g. flash forced off, auto vs manual, tripod vs handheld, aperture, f-stop, and shutter speed settings) and anything else useful. Other scenarios could include: 1) indoor sporting events, 2) indoor portraits, 3) outdoor sporting events, 4) scenery on a bright/cloudy day, 5) sunsets/sunrises, 6) macro or close-up shots, 7) taking photos from a moving vehicle (e.g. from a boat of a skier or wakeboarder), and 7) “artsy” shots (depth-of-field, starbust filters, over- & under-exposed, etc).

    How about an article on various filters and their proper use?

    How about an article on flash photography? When are flahes useful? When are they inappropriate? Types of flash units and when & how to use them?

    Thanks for the good and useful articles. Please keep them coming!

  3. Eric Z Goodnight

    Thanks for the encouragement and ideas, guys. Hopefully lots of photo articles coming soon. This one was a fun one to write.

    @Harold: Having a little issue making my edits right now, working with the Geek to resolve it. I’ll make those edits as soon as we can.

  4. Alex

    Thanks for the great article. Comes at a great time. I’ve been thinking about getting an entry level dslr and toying with it just to learn.

  5. Alex

    I would also like to see some more photography related articles as well.

  6. cvframer

    I think your article was fine with or without the edit. I took 6 years classroom/lab photo and I dont think you could get any more of a concise nutshell than this without tackling depth of field(idea for future post?) or intentional blur/stop-action theory.
    But it’s probably all changed since I learned it :- ]
    articles Always appreciated.

  7. Jerry aka The Kiltman

    Beautiful Article. I have been taking pictures for years. Thousands already taken and archived. I have used a shoebox, a Brownie, a Black and White Polaroid, a 35mm Pentax, and now mostly Digital.
    This article was beautifully written. I also liked the Chrome OS Article and spend 2 hours yesterday exploring Google Chrome.

    Thanks,

    The Kiltman

  8. Keith Tomlinson

    Hi, although the article is mainly correct I think some of it needs a little more clarity, mostly in the Focal length section. One part of which this to suggest that a wide angle lens is only focussable at close distances or infinity, whilst this may be true of some if not all Autofocus systems which I believe focus in steps, on a camera where manual focussing is an option the focussing is continuous from minimum distance to infinity.
    Second point is Focal Length and perspective I think the writer should have a look at Advanced Photography by Michael Langford which I believe is still in print and in its 8th edition. It has been a standard for at least 40 years and would probably help the writer clarify his remarks in this area.

  9. Keith Tomlinson

    Sorry to post twice but I pressed send before I meant with the first one:
    Hi, although the article is mainly correct I think some of it needs a little more clarity, mostly in the Focal length section. One part of which seems to suggest that a wide angle lens is only focussable at close distances or infinity, whilst this may be true of some if not all Autofocus systems which I believe focus in steps, on a camera where manual focussing is an option the focussing is continuous from minimum distance to infinity.
    Second point is Focal Length and perspective I think the writer should have a look at Advanced Photography by Michael Langford which I believe is still in print and in its 8th edition. It has been a standard for at least 40 years and would probably help the writer clarify his remarks in this area.

  10. Julesagain

    I’ve worked as a sports and studio photographer for years, and this was an excellent, very clear article. I too would love another one covering depth of field more, as that is tricky for me to figure out. The f-stop explanation was great.

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