# Blender 3D: Noob to Pro/Understanding the Camera

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## Real-World Cameras

Before discussing the camera in Blender, it helps to understand
something about how cameras work in real life. We have become accustomed
to so many of their quirks and limitations when looking at real
photographs, that 3D software like Blender often expends a lot of effort
to mimic those quirks.

When taking a photo with a real camera, a number of important factors
come into play:

-   the *focus* --- because of the way lenses work, only objects within
    a certain distance range from the camera (the *depth of field*) will
    appear sharp in the image. Objects outside this range will begin to
    appear noticeably blurred, the blur getting worse the farther they
    are outside the focus range. The narrower the range of in-focus
    distances (the shallower the depth of field), the more quickly this
    blurring happens with objects outside it.
-   the *exposure time* --- how long the shutter remains open. The
    longer this is, the more light is captured, but also the more likely
    the image is to pick up *motion blur* from moving objects.
-   the *aperture* --- how wide the iris opening is. This is expressed,
    not as an actual distance measurement, but as a fraction of the
    *focal length* of the lens (loosely, distance between the lens and
    the image-capturing surface when the image is properly focused),
    written as *f*: thus, say, *f*/2.8 ("*f* over 2.8", not "*f* 2.8")
    is a larger number, hence representing a wider aperture, than *f*/8.
    A wider aperture increases the amount of light being captured
    *without* contributing to motion blur, but it reduces the depth of
    field. The extreme case of a *pinhole camera* has a very tiny
    aperture with infinite depth of field (no need to focus at all), but
    captures very little light, so it needs a very well-lit scene, a
    long exposure, or a very sensitive image-capturing surface.
-   the *sensitivity* of the image-capturing surface to light. In the
    days of film cameras, we talked about film sensitivity ("fast" film
    being more sensitive to light than "slow" film). Nowadays, with
    digital cameras we talk about the *gain* of the light-amplification
    system. High-sensitivity film was more likely to produce a grainy
    image. In a somewhat similar manner, high light-amplification in a
    digital camera is more likely to produce a noisy-looking image under
    low-light conditions.
-   the *field of view* --- how much of the scene the camera can see at
    once. A *wide-angle* lens gives a wider field of view, but you have
    to be closer to objects to be able to see them, and there is greater
    perspective distortion. At the other extreme, a *telephoto* lens
    gives a very narrow field of view, but can take pictures of things
    from much further away. A wide-angle lens also has a shorter focal
    length than a narrow-angle one (remember that aperture is expressed
    as a ratio of the focal length *f*), therefore the telephoto lens is
    going to capture *less* light than the wide-angle one with the
    *same* aperture width. You may also have heard of the *zoom lens*,
    i.e. one with a variable focal length. It can be adjusted from a
    wide-angle mode to a telephoto mode.

As you can see, many of these different factors interact with each
other. The brightness of the image can be affected by the exposure time,
the aperture, the gain sensitivity and the focal length of the lens.
Each of these have side-effects on the image in other ways.

Blender and other computer graphics software are, in principle, free of
the problems of focus, exposure time, aperture, sensitivity and focal
length. Nevertheless, it is common to want to introduce deliberate
motion blur into an image, to give the impression of movement. Sometimes
it is useful to introduce a deliberately shallow depth of field,
blurring objects in the background in order to draw emphasis to the
important part of the image, i.e that which is in focus.

Exposure (the total amount of light captured in the image) is also less
of a problem in computer graphics than in real-world photography,
because in computer graphics you always have total control over the
amount and placement of lighting in the scene. Nevertheless, if you're
not careful, you can produce overexposed (bright parts losing detail by
saturating to a solid, featureless white) or underexposed images (dark
parts losing detail by becoming solid black).

The field of view issue arises from basic principles of geometry, and
Blender's camera is just as much subject to that as real cameras.

## The Camera In Blender

Here we are going to concentrate on the important issue of *field of
view*.

You can change the field of view in two ways - move the camera closer to
or farther from the scene (called *dollying* in film/TV production
parlance), or change the angle of the lens (*zooming*). You do the
latter in the Object Data
![](Blender267CameraDataContextButton.png "Blender267CameraDataContextButton.png")
tab in the Properties window (the Camera has to be selected by
 in Object Mode, or the required tab
will not be visible).

*Perspective* is the phenomenon
where objects that are farther away from the viewer look smaller than
those nearby. More than that, different parts of the *same* object may
be at different distances from the eye, leading to a change in the
apparent shape of the object called *perspective distortion*. The
mathematical theory of perspective was worked out by
Alhazen in the 11th century, and famously
adopted by the Italian Renaissance painters four hundred years later.

Here are two renders of the same scene with two different cameras, to
illustrate the difference.

This one moves the camera closer but gives it a wider field of view:
![](BlenderPerspWidepng.png "BlenderPerspWidepng.png")

This one moves the camera back, while narrowing its field of view, to
try to give the scene the same overall size.
![](BlenderPerspNarrow.png "BlenderPerspNarrow.png")

The latter is like using a "telephoto" lens with a real camera. Notice
how the wider field of view gives you a greater perspective effect. The
boxes are all *cuboids*, with parallel pairs of opposite faces joined by
parallel edges, yet there is a noticeable angle between
notionally-parallel edges in both images, which is more pronounced in
the upper image. *That* is what perspective distortion is all about.

### Specifying the Field of View

![](Blender267CameraDataContext.png "Blender267CameraDataContext.png")

When you select a camera object, its settings become visible in the
Camera Context
![](Blender267CameraDataContextButton.png "Blender267CameraDataContextButton.png")
in the Properties window, which should initially look something like at
right.

Photographers are accustomed to working in terms of the focal length of
the lens - longer means narrower field of view, shorter means wider
field of view. But the field of view also depends on the size of the
sensor (image capture area). Modern digital cameras typically have a
smaller sensor size than the exposed film area in older 35mm film
cameras. Thus, the focal length measurements have to be adjusted
accordingly, in order to give the same field of view.

Blender allows you to work this way, by specifying the focal length in
the "Lens" panel, and the sensor size in the "Camera" panel. It even
offers a "Camera Presets" menu, which sets the sensor size for any of a
range of well-known cameras.

Also, you might be doing compositing of your computer-generated imagery
on top of an actual photograph. In which case, to make the results look
realistic, you need to closely match the characteristics of the camera
and lens that were used to take the photo. If you know the lens focal
length and camera sensor size, it makes sense to be able to plug those
values in directly.

![](Blender267CameraLensAngle.png "Blender267CameraLensAngle.png") But
if you're *not* doing photo compositing, but generating completely
synthetic imagery, you might consider this a somewhat roundabout way of
working. Why not specify the field of view directly as an angle?

Blender allows for this as well. From the popup menu in the Lens panel
that says "Millimeters", select "Field of View" instead, and the Focal
Length field will turn into a Field of View field, showing the angle in
degrees directly. This is *much* easier to relate to the geometry of the
scene!

## See Also

-   Improving Blender Renders with Photography
    Techniques
    --- another explanation covering similar ground.

es:Entendiendo la cámara
