Archive for March, 2009

LightRails – Dynamic External Exposure Control

Projects | Robots | Time-lapse Video 16 16 Comments

I’ve been sitting on this a little while, and I feel a bit remiss in not sharing it sooner.  I had intended to make it “perfect” before sharing, but feel I’ve reached a point where I’m not ready to spend all of my effort on this project, and instead wish to work more on OpenMoco (but we’ll talk more about that soon!).  So, I’ll share this as a more “rough” project.

Some time ago, I started out with the TSL230R chip from Taos with the intent of producing a (a) my own digital light meter and (b) a dynamic external control system for time-lapse photography.  Certainly, the act of creating my own digital light meter was a smashing success, also having it control my dSLR via a remote cable in bulb mode was also a great success.  Enough so that it should prove an invaluable tool to the DIY pinhole photographer.  (How do you time that 2:35:20 exposure manually?)

The problem I wanted to solve was a difficult, but common one: how do you effectively manage exposure changes across sunrise and sunset time-lapses with a dSLR?  It sounds very easy, just go into Av or Tv mode!  Of course, life isn’t that easy.  The standard dSLRs generally only meter and adjust exposure in the very rough terms of 1/6, 1/4, 1/3, or even 1/2 EV steps!  This means it has a sledge hammer where the problem calls for a gentle tapping of a finger.  I set out to create a system that would control the camera externally, metering and adjusting exposure in 1/100 EV steps…

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