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Adam Dargan

Correct exposure for Bolex Rex 5 - Color Reversal

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Hi guys,

I know this topic has probably been talked about many times here and other places but I am still confused about the correct process for getting the correct exposure on a Bolex (or analog film in general). I have shot 35mm still photography and I'm familiar with light, shutter speed, fStop, etc.. But I am totally new to shooting on 16mm film and setting the correct exposure for it. I haven't been able to find great resources about this process if you know of any please share. I'm definitely a beginner but I'm willing to put the time and effort in to learn the proper procedures. 

I'm using a Bolex Rex 5, with a 25mm RX lens, and shooting on Kodak's new color reversal Ektachrome 100 ISO.

I am having a hard time wrapping my head around a couple of things:

  1. When exposing for cinema film how does the shutter angle relate to frame rate?
  2. I'm currently borrowing a friend's light meter- Sekonic L308-B. Not ideal for cine but it's all I have right now. How do I correctly set it up to take a proper reading?
    • Specifically, do I set the light meter to calculate for a 24fps frame rate OR am I setting it to one of the classic Bolex exposure tables? 1/65 @ 24fps (page 2)
    • I don't have the fine control of setting the shutter angle on this model so I believe it's using a 180 degree shutter angle. 
    • As an aside, what light meter would you recommend? I was looking at the L398A.
  3. I've read conflicting things on these forums and others about RX lenses. Some say the RX lenses DO correct for the 25% prism light loss, while others do not.
    • What is the correct answer? If I am using RX lenses do I need to account for the extra light loss?
  4. Any other advice on shooting with a reflex Bolex? Or analog film in general? 


I know this is a lot of questions but I appreciate anyone taking the time to help point me in the right direction. 

Thank you for your time,




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There are so many cinematography.com threads on this topic, but some diverge into abstraction.. we should have a sticky post that succinctly answers these questions.

This recent one is worth a look:

As simply as possible:

1. The shutter angle divided by 360 times the reciprocal of the frame rate gives you the exposure time. So for 24fps:

133/360 x 1/24 = 0.0154 or 1/65 sec.

2. You need to adjust the exposure reading by about a third of a stop to compensate for the light lost to the reflex prism. If using a meter in cine mode that assumes a 180 degree shutter you need to adjust a further third of a stop for the 133 degree shutter. There are several ways of doing this but probably the simplest way is to rate the film stock 2/3 stop slower, so for 100 ISO film set the meter to 64.

3. RX lenses do not compensate for the prism light loss, they only correct the optical aberrations that the prism introduces. 

4. Plenty of good threads on this site about using a Bolex and shooting film in general.



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Thank you Dom.

This is very good information and I appreciate the breakdown you gave as well as the provided resources. 

I will set my light meter's ISO at 64 with a frame rate of 24 to compensate for the 2/3 light loss.  

Thank you for clearing up the misconception about RX lenses. 




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