Camera Parameter: Focal Length

Author:robert952

Tools Needed

* DAZ Studio

You need just a bit of theory on lenses. Don't worry, nothing heavy like refraction properties, diopter measures, and calculated light loss; just some definitions.

Focal point: When you set a photographic lens' focus ring to infinity, the place behind the lens (inside the camera) where light rays converge to a point is the focal point. This point of light touches the film plane to expose the image to the film.

Focal Length: The distance from the center of the lens to the focal point is the focal length of the lens. This means a 50mm lens (considered a normal lens) is 50 mm long. A 200 mm lens is (you guessed it) 200 mm long. Mirrors, refraction properties of glass and modern technology change the real length of some lens, but this is the background to help understand how a lens is measured. Focal length is the parameter that you can adjust in DAZ Studio.

Field of view: The area viewed through a lens is the field of view. A short lens has a wide field of view and, conversely, a long lens has a narrow field of view. Your eyes are considered to be about 35 mm and you see a more or less panoramic view as you look around. When you look through a tube (such as a paper towel roll), you'reduce your field of view to some small portion of your surroundings. Long lenses 80 mm and longer, do the same thing: reduce your field of view.

The magic comes into play since the long lens magnifies the image you see in the narrow field of view, and fills up the view finder, and, of course, the image onto the film. You see the object or scene as a close up (telephoto) view.

The previously defined three factors when combined give the photographer a choice in tools he needs for different situations. When you want to take a picture of your Cousin Ned, you would probably use a normal 50 mm lens and be within a few feet of him when you take his picture. But in order to get the picture of the blue bird perched on the bird bath, you have to keep your distance (so you don't scare the subject away) and need a long lens (100 to 400 mm). Both subjects will fill the image area to produce a normal size picture.

To see how this works in Studio, we'll set up a scene with one or two objects.

Create a new file and add a fairly large object such as a wall or building. (I used DM's Garden Corner. I added Emotiguy and a resized ground plane for interest).

From a top view with your object(s) selected, zoom out so that you can see the whole grid. Next, adjust only the Z-axis of your main object. Move (translate) the object to the top of the grid. (If you want to type in the parameter, set the Z-axis translate to around -1874. Be sure to note the negative sign.)

Still in the top view, select the Default camera from Scene Tab and translate it along the Z-axis down to the bottom of the grid (translate factors X=0, Y=105, Z=2001). You might want to save this scene so that you have a 'playground' for further experimentation on your own with other settings and positions.

Use the Default Camera in the view port and look at the scene. Emotiguy (and wall) is a bit far away and should look a lot like this:

Now, be sure you have the Default Camera selected in the Scene Tab. Change only the Focal Length parameter to 400 (for a 400 mm lens).

IN your view through the Default Camera in the viewport, you should see Emotiguy (or subject you selected) much larger in the image as in the second render below. Note that your field of view is reduced to smaller area around the wall.

Well, you could since Emotiguy isn't camera shy. But, there's another phenomena that occurs in telephoto (long) lenses.

It's called by some, foreshortening, others say compression. In essence, the foreground and the distance between the objects appear compressed. This comes from the fact that you'reduce the field of view as the image is magnified.

Here are two screen shots, not renders, so you can see the grid.

If you want to recreate the scene, pick an object with a strong vertical structure (I used pedestals) and put three of them in the scene. You may find it useful to name them Object 1, Object 2 and Object 3. The Move to Floor' level option proves useful to make sure the objects are all on the floor plane.

Keep the objects the same size either with no scaling factor or the same scaling factor applied to all three objects.

Locate the objects as follows:

Object 1 at X= -72, Y= 86, Z= -42;

Object 2 at X= 29, Y= 86, Z= -744;

Object 3 at X= 130, Y= 86, Z= 1443.

As before you may want to save this scene as a different file. Then you can change various settings and move the camera around to experiment with different viewpoints and focal lengths.

When you look through the Default Camera (in its Default position), you see a normal perspective view as in the picture below.

Note the grid compresses as it disappears towards the horizon and the apparent size of the objects diminishes normal perspective view.

Now, by typing in the parameters, change the position of the camera by setting the Translation factors to X= 19, Y= 105 and Z= 9600. Your objects will seem far way. To correct the situation, change the Focal Length parameter to 1000. The image should appear as below.

The objects appear to be about the same size and the grid is almost non-existent (highly compressed). That's the compression factor illustrated. Even though the items are separated in our virtual space, they appear close together in the image. And all you changed in the image was the Focal Length parameter.

You can use this compression to your advantage and compose a scene without having to move the camera a lot. And without having to rescale the objects. And still make the scene look dramatic. The effect is called 'forced perspective' - a photographic technique that makes objects appear farther or closer, larger or smaller, than they really are.

For this exercise, I recommend you type in the parameters' values as it is quicker than moving the objects and camera with the mouse. Also, using the top view and looking down on the scene will let you build the scene without seeing what it really looks like until the scene is completely built. Looking through the camera and discovering your scene is part of the fun of this exercise. You also get a sense of the distance between objects from the top view.

Create a new file (this will also reset the Default Camera to its default settings and position). Since we are only using two objects, add both to your scene. You will place them in the scene using the parameter sliders.

Add to the scene your favorite large creature (I used Allosaurus). Add in Emotiguy (or other figure). Select each item from the Scene tab, including the Default camera, and type in their respective Translation and Rotation parameters as follows.

Allosaurus/Creature: X= 0, Y= 0 and Z= -1997 (No change to rotation)

Emotiguy: X= 0, Y= 0 and Z=1250 (No change to rotation)

Camera: X= 111, Y=147, and Z= 2048 (and for a good angle: Rotation parameters of X= -1.0, Y= -4.0 and Z= 0. Be sure the Focal Length is at the default 50 mm setting.

Save the scene again for future experimentation.

Look through the default camera in the viewport. Emotiguy isn't too worried. Allosaurus is 'way back there'.

Now, switch back to the top view. Trust me; working from this view and then looking through the camera is worth the effort. Do not change anything with the characters' positions. Change only the Camera parameters as follows:

Translate parameters: X= 55, Y= 175 and Z= 13057

Rotation parameters: X= 0, Y=.23 and Z= 0 (Note that this is very close to the Default parameters.)

Focal Length: 1000mm

Now, look through the camera and see how poor old Emotiguy appears to be in mortal danger.

You have just used forced perspective. All we did was use a trick of photography with our virtual lens to change the perspective to the scene. Ok, so I changed the poses. But Emotiguy is the same size; the Allosaurus is still huge. With the forced perspective, Dino appears to be very close to putting a bite on our hero.

You should now have an understanding on how the Focal Length parameter of a camera lens can be used. By moving the camera away from the scene and applying a long lens, you can foreshorten the distance between objects (forced perspective) and add a dramatic flair to your composition.

Use the scenes you created in this tutorial and experiment with different focal lengths and view points to see how they affect the scenes.

Positioning of objects away from each other also allows more specific lighting of each object. This can help you add even more drama.

Good Luck with your new found knowledge.