Answers.Body: <p>There are three ways that film cameras do this:</p>
  
  <ol>
  <li>Using a rangefinder, i.e. a viewfinder that doesn't actually view
  through the lens. Common on cheaper consumer format cameras such as
  super-8 </li>
  <li><p>Using a beam splitter. The ubiquitous Bolex 16mm cameras
  have a prism in the light path that splits the light coming through
  the lens, so that some of it goes to the film gate, and the rest
  goes to the eyepiece. </p>
  
  <p>This has the advantage of being through the
  lens, and continuous, but at the cost of brightness for the viewer
  and a stop or so of exposure for the film. From personal experience,
  in low light it can be really hard to focus a Bolex. </p></li>
  <li><p>Using a rotating mirror. In this setup a reflective mirror interrupts the
  light path to the film, similar to a DSLR, but instead of hinging up it rotates.</p>
  
  <p>When the camera is
  stopped the mirror is parked so that it sends the light to the
  viewer, and when shooting it rotates, acting as the shutter. While
  the mirror is sending light to the viewfinder the film is being
  pulled down to get the next frame in position in the gate. Then the
  frame is exposed, during which time the viewfinder will be black. This cycle is repeated for each frame</p>
  
  <p>This has the advantage that all the light available goes to expose
  the film, but at the cost of some flickering in the viewfinder (I
  found that helpful: it lets you know that the camera is running—on
  silent cameras it can be almost impossible to tell otherwise).</p></li>
  </ol>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-12-06T04:15:42.310Z
Answers.LastActivityDate: 2018-12-06T04:15:42.310Z
Answers.UserDisplayName: stib
Body: <p>As we all know, a DSLR camera works by moving a mirror out the sensors way when taking a picture and then going back to start, not exposing the sendor.
  How does this process work, on an optical motion picture camera, while filming?
  How can the dop/camera operator see what's beeing recorded?</p>
  
Tags: <camera>
Title: How does an optical viewfinder on a film camera work?
UserDisplayName: Frezzley
ThreadText: # How does an optical viewfinder on a film camera work?
  
  (Asked by: username_0 on 2018-12-05)
  
  As we all know, a DSLR camera works by moving a mirror out the sensors way when taking a picture and then going back to start, not exposing the sendor.
  How does this process work, on an optical motion picture camera, while filming?
  How can the dop/camera operator see what's beeing recorded?
  
  **Tags:** camera
  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_1 on 2018-12-06. Score: 3 | Accepted answer
  
  There are three ways that film cameras do this:
  
  1. Using a rangefinder, i.e. a viewfinder that doesn't actually view
     through the lens. Common on cheaper consumer format cameras such as
     super-8
  2. Using a beam splitter. The ubiquitous Bolex 16mm cameras
     have a prism in the light path that splits the light coming through
     the lens, so that some of it goes to the film gate, and the rest
     goes to the eyepiece.
  
     This has the advantage of being through the
     lens, and continuous, but at the cost of brightness for the viewer
     and a stop or so of exposure for the film. From personal experience,
     in low light it can be really hard to focus a Bolex.
  3. Using a rotating mirror. In this setup a reflective mirror interrupts the
     light path to the film, similar to a DSLR, but instead of hinging up it rotates.
  
     When the camera is
     stopped the mirror is parked so that it sends the light to the
     viewer, and when shooting it rotates, acting as the shutter. While
     the mirror is sending light to the viewfinder the film is being
     pulled down to get the next frame in position in the gate. Then the
     frame is exposed, during which time the viewfinder will be black. This cycle is repeated for each frame
  
     This has the advantage that all the light available goes to expose
     the film, but at the cost of some flickering in the viewfinder (I
     found that helpful: it lets you know that the camera is running—on
     silent cameras it can be almost impossible to tell otherwise).
  
  
  ---
  
  