Archive for November, 2008

What to do when it’s dark?

Posted in Equipment with tags , , , , on November 30, 2008 by projectxo

Ginny asked me what to do with her camera when the environment is dark.  Point-and-shoot cameras nowadays are very smart; so most likely, it will turn on the flash and try to light up the subject.  This works just fine for an indoor dinner.  But, it will not work well for outdoor night scene cause the background will not be lit by the tiny flash.

First of all, a little camera basics.  The camera takes a picture by opening a hole, and let the light “expose” the sensor (or film).  There are 3 things that affect a picture’s exposure:

Aperture –  Usually called the “A” or “F” number in the lens.  This determines how big the “hole” opens.  The bigger the hole, the more light hits the sensor for the same amount of time.    The smaller the “F” number, the bigger the “hole”.

Here is a lens set to 2 different apertures.





Aperture affects background sharpness.  The bigger the hole, the more blurry background becomes.  This is known as Depth Of Field (DOF).  We will talk about it some other day.

Shutter speed – This is the amount of time the “hole” is opened.  For example, 1/250 means the sensor is exposed for 1/250 seconds.  The more time it is open, the more light hits the sensor.

ISO Sensitivity – the 3rd variable is how sensitive the sensor is.  The higher the ISO, the more sensitive the sensor (film) is.  For example, when sensor is programmed to ISO 400, it will take 1/4 less time to get the same exposure as ISO 100.  i.e., at ISO 400, it will take 1/4 of one second, while it will need 1 full second to get the same exposure at ISO 100.  There is a catch, higher ISO usually increase noise; so your picture will start to look grainy, or even spotty.  Yuk!

So… what to do when it’s dark?  The easiest thing to do is increase ISO.  If that’s not good enough, then open up your aperture (say from F/8 to F2.8).  If that does not work still, then increase exposure time (slow down shutter speed).  Say from 1/60 to 1/15.  There is a catch on shutter speed.  Usually the hand movement (shake) will become noticeable from 1/30.  So if you are shooting 1/15 or slower, then you will need a tri-pod.

Case Study A – portrait in a fancy dimly-lit restaurant.  The ambient is not bright, so you are going to increase the ISO high enough to capture some ambient light at 1/30 exposure (why? cause slower than that will cause camera shake, remember?)  Then, turn on the flash so it will light up the person.  Now, you will have a properly lit portrait with some ambient light in the background.

Case Study B – city lights in Monte Carlo.   There are actually two sub-cases.  1) if you want a person in the picture, you can do the same as in case A.  However, if you just want to capture the scenery, then you need to increase ISO even higher.  If you have tripod, use it so you can increase shutter speed to more than 1/15 of a second.  If you don’t, then try opening the aperture to maximum (smallest number).

Assignment – Yes, you’ve got homework.  Take a self-portrait next to a candle.  The room should have no other light except candle.  Here is the recipe – Shutter speed 1/30.  Aperture widest allowed by the camera.  Flash on.  Experiment with different ISO setting until you get a good “moody” picture where only you and the candle are lit.

Tomorrow, we will use camera’s special modes “sports, portrait, night scene, etc” to explain how the camera use these 3 variables to get better pictures,