Flash, aperture and shutter speed - some examples

[stevoarnold]

Hey there, I just finished writing a blog post about some experimentation i was doing with my new flashes, but thought I would share the same stuff here on a forum that actually has people reading it lol!

I just wanted to share some examples of how shutter speed, aperture and flash power all work together... here are the guts of what I posted having tried a few self portrait shots overlooking the sydney city skyline last night:

I’m still very much learning all this stuff so I may seem a little naive still, but I just wanted to excercise a couple of main principles of flash photography in this post. The first point of which being that the shutter speed is the key in determining your ambient exposure.

The flow I have been using since trying out the strobist techniques has been to manually dial in my exposure a couple of stops below the “correct” exposure. Starting with the shutter speed at 1/200 sec (my camera can synch with the off-camera flashes at 1/250 max, so I’m giving myself some room) I then set my ISO to around 400 to let me go up or down later if needs be. Then finally I place my aperture at around f5.6 to again give myself room to move up or down. If those settings give me a scene which is too light, I start moving my aperture towards the higher numbers to darken it to my liking. Alternatively if it is too dark, I go the other way.



The above shot is an example of getting to my starting point before introducing the flash.

Next, it’s just a matter of placing my off-camera flash in a position that gives depth and dimension to the subject (me!). Generally for this kind of shot high and to one side will fit the bill nicely. I don’t bother with light meters or working this stuff all out properly, it took me a grand total of two test shots to dial in the flash to a brightness that gave me the result I was looking for. In this case, 1/16th power was all it needed.



As you can see, the background stays pretty much identical as I have not changed any settings in camera but the introduction of the flash has brought me up to a good exposure nicely. As mentioned above, the shadows aren’t being cast in as flattering a way as the first shot in this post – with me being turned slightly more towards the flash I am adding more light to the left side of my face and giving it a more fuller appearance. However, we’ll brush over the inadequacies of the model for the sake of a good technical example…

Now that I have got my flash set at 1/16th power and my aperture in this case, fixed at f9.0, I know that whatever I do to the shutter speed (to adjust the ambient background exposure) I will always remain at the same exposure myself. Shooting at twilight this becomes a very important thing to know as the light changes very quickly as the sun disappears off below the horizon. By the time I took the next shot, I was shooting with a shutter speed of 1.3 seconds to achieve a similarly exposed background…



The settings for this shot were: F9.0, ISO400, 1.3 secs – flash on 1/16th power from top left. As mentioned, the difference being the shutter speed. Because the aperture and flash were still set the same as before, I knew I would be exposed exactly as before.

For a bit of a test I decided to really push the example and change my shutter to 6 seconds. This I hoped would bring the background up a couple of stops but keep me looking the same…

Here is the result…



And hey presto! Arguably I do appear ever so slightly brighter in this longer exposure and I did say that my exposure would stay the same, but I put this down to there being a wee bit of ambient light coming into play as there are street lamps lined up along the path which I will suppose cast enough light on me to lighten some of the shadows over the 6 second exposure, but hopefully you get the point.


---- Only being allowed to post 4 images here I didnt get to show you my favourite shot from last lights little session. I think the forum rules let me add it after 24 hours or after at least two more people have replied... In the meantime, its on my blog if you want to see it (linky below)

I'd love to know what you think and if you have any suggestions/corrections!

[RichardTaylor]

Thanks for the tute. Much appreciated.

[zona5101]

Oustanding work and a nice write up. Thanks for sharing this.

[wishvam]

that's great fine result lastly.. and a good guide for a understanding basic shutter speeds and flash lighting..

[Digidave]

Nicely done. Keep up the good work.