Thursday, January 26, 2012

Step 2

Having got myself a flash brolly kit, I needed to work out how to use it.

The first thing I had to do was to make sure that the flash filled the brolly (not much point having a large brolly and only using part of it).  That meant using the zoom facility on my flashgun to set the widest angle (smallest number) possible.

Since the flashgun was off the camera, I had to set the exposure manually.

Flash on my reflex camera will only work properly if the shutter speed is set at 1/200th of a second or slower so I set it to about 1/150th. Since the duration of the flash is much less than that, the speed set will not affect exposure. The exposre will be determined in this case by setting the aperture and the film speed (ISO).

Apart from controlling exposure, I use the aperture to control depth of field so I will want to set that accordingly. A smaller aperture (higher number) gives greater depth of field i.e. more of the subject will be in focus and a larger aperture (smaller number) will give less. Sometimes I want more and sometimes less. So I set the aperture first.

That leaves the film speed as the means to control exposure. A lower ISO number will give less exposure and a higher number more.  I could calculate the correct ISO number to use by using the guide number of the flashgun and the distance of the flashgun from the subject but to be honest, with a digital camera it is just as easy to use trial and error and examine the results on the screen at the back of the camera. Start with a rough estimate and then fine tune it is the way to go.

Ah but surely, having to use a high ISO will create a lot of horrible digital noise. That is true, anything less than about 1600 ISO is going to be OK on my camera. However, in those cases where I am going to use a small aperture which will mean setting a high ISO to compensate there is another trick I can employ. My flashgun can be set to different power levels ranging from full power to 1/128th power so, when I use a large aperture I can still use a low ISO speed by turning the power down.

You know this all sounds a lot more complicated than it actually is in practice.  As I said, it is all a matter of trial and error.

Step 3 Using the brolly as a reflector or as a diffuser.

No comments: