<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>

CC BY-SA 4.0
2018-12-06T04:15:42.310Z
2018-12-06T04:15:42.310Z
stib
<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>

<camera>
How does an optical viewfinder on a film camera work?
Frezzley
# 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).


---

