Long Exposure - A Beginner's Guide - Using ISO To Help Calculate Exposure
In our previous blog we did mention that for long exposure the choice of camera is less important than lens. That said one of the advantages of the full-frame camera is that the ISO range drops down to ISO 50, which as you’ll see later allows for more control over long exposure times.
Along with aperture and shutter speed, ISO can also be used to control the length of exposure. The image quality on your camera is determined by what ISO you have selected. The higher the ISO the less colour saturation and sharpness. The advantage of a higher ISO then is to increase the shutter speed to be very fast, which is in the opposite direction for where we want to be.
Important: ISO 50 is actually ISO 100 pulled down - it’s not a native ISO. Although we haven’t noticed any highlight headroom difference between the two, it’s preferable to stay at ISO 100 that way you have the ability to increase exposure simply by dropping the ISO if you like.
By Graham Clark
60s • F8 • ISO 100 • 24mmCANON 6D • CANON 24mm L • X4 ND 6-STOP
On this exposure the correct exposure time was calculated to be 60 seconds by using the cameras metering system, even though it has a 30 second limit. This trick is very useful. Here’s how it works:
Setup camera with composition ready, in this case F8 and ISO 100 set, but we don't know what duration it should be because the camera’s meter just blinks with’30”’, meaning it’s unable to meter the scene. As the ISO is increase up one notch at a time (enable ISO increments in your custom functions menu) , wait until the camera is able to meter again. It locks onto metering at ISO 200, so double 30 seconds to 60 seconds.
ND 3-Stop - By Graham Clark
112s • F13 • ISO 50 • 24mmCANON 6D • CANON 17-40mm • X4 ND 6-STOP
F13 - The small and sharp ice patterns in the centre area, and the saturated sunset red against the sky had to be sharp for the end result to look right, so for this image focusing was done manually in live view on the ice patterns.
ISO 50 - Everything the same except for ISO 100 at 35s (almost within range of metering), then dropped ISO to 50 and triple exposure. As light rises and falls fast at sunset, especially in the mountains, tripling exposure time is always necessary during sunset when shooting with a 6-stop ND. About20 - 30 minutes after the sun sets the 6-stop ND was immediately changed for a 3-stop.
Next week - 'Indirect And Direct Light'
- Long Exposure - A Beginner's Guide
- Anamorphic Lenses
- Circular ND Versus Square ND Filters
- Why Use A UV Filter On Your Lenses
- De-mystifying Infra-red Photography