Controlling Ambient With Shutter Speed
Tuesday, September 29th, 2009, 17:53
When shooting Monika at the weekend, I was very kindly assisted by Lola Gavin, a member of my camera club. Lola was also one of the participants at the most recent workshop I gave on flash photography. During the shoot I wanted to demonstrate the effect that shutter speed had on exposure when mixing flash with ambient light. I know I’ve covered this many times before in my various tutorials and workshops on flash (flash 101, mixing flash with ambient etc.), but with that said, now that I have some images to back up the theory I thought it was worth posting them here.
First of all let me acknowledge that these aren’t the strongest images in themselves, but for demonstration purposes I think they serve the purpose very well. When dealing with a pure flash exposure, where there is no ambient light at all, we have various methods of controlling the exposure:
- ISO
- Aperture
- Flash power/duration
- Distance of flash to subject
NOTE: Shutter speed has no effect on the exposure when using flash
When we’re using ambient light, we have the traditional methods of exposing an image:
- ISO
- Aperture
- Shutter speed
If we’re in a situation where we have both ambient light and flash, we’re now mixing flash with ambient and all 5 controls come into play (as shown below).
Shutter speed is the most interesting factor because it is by controlling the shutter speed, that we can mix in more or indeed less ambient light into the shot. Changing any other variable will either effect both the flash exposure and the ambient or change the exposure for the subject.
The three shots above were all taken such that the aperture, ISO, flash power and distance between the subject and model are all constant. For each shot I simply changed the shutter speed. Decreasing it, allowed more light into the shot, brightening the sky (ambient part of the exposure) as is shown on the left image, which is taken @ 1/60. Increasing the shutter speed, to 1/125 for the middle image, I decrease the amount of ambient in the shot, turning an other wise bright evening, that little bit darker. Finally increasing the shutter speed by another stop to 1/250 I can kill most of the ambient light in the shot. However in all 3 cases, the subject is exposed the same as it is the flash that is lighting the subject. Click here to see a larger resolution version of the image.
This technique can be a very creative tool for the photographer. Indeed given a powerful enough shot you can make the brightest day look like night. A system which allows you avail of high speed sync is also advantageous, because it allows you increase your shutter speed to levels which cut out virtually all ambient light, but still allow you expose the subject with flash.
Tags: ambient, colour, dublin, flash, model, monika, strobist, work shop
