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Working with focal length

From: SketchUp Rendering Using Twilight

Video: Working with focal length

One aspect of the Twilight camera that we do need to give a little bit of an explanation for is its use of this Focal Length value. Now, in photographic terms, the focal length of a lens is defined as the distance in millimeters from the optical center of the lens to the focal point, located on the sensor or film, if the subject at infinity is in focus. The values associated with focal length are based on the 35 millimeter film format. Now this means that choosing the appropriate focal length can get a little tricky in the digital arena, as many of today's cameras, even many SLR models, do not use what are called full-frame sensors-- that is sensors that are equivalent to 35 mm film.

Working with focal length

One aspect of the Twilight camera that we do need to give a little bit of an explanation for is its use of this Focal Length value. Now, in photographic terms, the focal length of a lens is defined as the distance in millimeters from the optical center of the lens to the focal point, located on the sensor or film, if the subject at infinity is in focus. The values associated with focal length are based on the 35 millimeter film format. Now this means that choosing the appropriate focal length can get a little tricky in the digital arena, as many of today's cameras, even many SLR models, do not use what are called full-frame sensors-- that is sensors that are equivalent to 35 mm film.

In such cameras the cropped, or reduced, size of the sensor means that the given size of a lens--for example, a 60 millimeter lens--does not produce the same result as a 60 millimeter lens when mounted on either 35 millimeter film camera or a camera that has a full-frame sensor. In the words, composition, framing, even depth of field will not look the same on two cameras using different sensor sizes, even though we may use the same lens on each of them. Now, of course you're probably wondering why we're throwing all of this information your way.

Well, simply put, Twilight is essentially working as a cropped-sensor render engine. You may already have noticed that the reported focal length of your SketchUp viewport does not match the reported focal length inside the Twilight Render dialog. If we just make certain that we have our Zoom tool selected and then come down to the bottom-right of our SketchUp interface, you can see we have our reported focal length, which is 35 millimeters. This is the setting that was used to render this particular image, but you'll notice that Twilight is reporting a completely different focal length value.

Here, we're getting 24.306. This is happening because Twilight is basing its values on an expected film size of 25, not 35 millimeters. Now again, you may wonder why this is the case. Well, the Twilight engine is built on the Kerkythea Echo 2008 Render Engine. Kerkythea was built on the premise of a 25 millimeter film size, hence the reason that Twilight uses the same camera model. Now, the good news is that all of this doesn't really alter what we will get in our final render.

If we have used Twilight's Scene View tool to setup our SketchUp viewport, then our composition, our framing, will all be preserved in our final Twilight render. We do, however, need to keep in mind that when we are choosing focal lens for our shots, SketchUp will be using established photographic conventions, whereas Twilight will be reporting its focal lengths based on a 25 millimeter film format.

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SketchUp Rendering Using Twilight

33 video lessons · 4338 viewers

Brian Bradley
Author

 
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  1. 4m 1s
    1. Welcome
      1m 5s
    2. What you should know
      2m 10s
    3. Using the exercise files
      46s
  2. 6m 53s
    1. Installing the Twilight renderer
      2m 52s
    2. Locating Twilight tools and features
      4m 1s
  3. 50m 22s
    1. Adding the Physical Sun and Sky
      6m 17s
    2. Employing the Point light type
      6m 35s
    3. Using the Spot and Projector light types
      7m 7s
    4. Adding the IES light type
      3m 48s
    5. Using light-emitting materials
      6m 59s
    6. Creating image-based lighting using High Dynamic Range Images (HDRIs)
      6m 12s
    7. Using Sky Portals for interior global illumination (GI)
      6m 43s
    8. Understanding the importance of reflectance in materials
      6m 41s
  4. 21m 54s
    1. Exploring Light Transport options in Twilight
      9m 18s
    2. Managing the Quality presets
      5m 57s
    3. Editing and saving presets
      6m 39s
  5. 22m 8s
    1. Positioning your scene view
      3m 23s
    2. Altering projection types
      5m 12s
    3. Working with depth of field
      3m 59s
    4. Working with focal length
      2m 44s
    5. Harnessing tone mapping, exposure, and gamma
      3m 59s
    6. Using two-point perspective correction
      2m 51s
  6. 38m 13s
    1. Introduction to Twilight materials
      8m 23s
    2. Creating diffuse surfaces
      6m 53s
    3. Creating reflective surfaces
      6m 53s
    4. Creating glassy refractive surfaces
      9m 28s
    5. Creating watery refractive surfaces
      6m 36s
  7. 31m 28s
    1. Rendering for animation
      8m 55s
    2. Rendering out an alpha mask
      3m 44s
    3. Setting up a depth render
      4m 3s
    4. Creating an RGB mask using the Diffuse Texture Pass preset
      5m 45s
    5. Working with a composite
      9m 1s
  8. 1m 13s
    1. What's next?
      1m 13s

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