In normal photos, that isn’t much of an issue. Let’s face it, in the grand scheme of things - with
normal photography - a bug that takes one step forward won’t even be visible, much less noticed.
But, in macro work your depth of field is so narrow that even a millimeter of movement can
destroy your whole image.
So, while using a longer shutter speed is an option for more light, it should only be selected with
scenes where there is no possible movement. And even then, you absolutely must use a tripod.
In scenes where there is a possibility for movement – one of the other methods for introducing
more light may work better...
Increase Your ISO
The concept of ISO (ISO stands for International Organization for Standardization), was born
back in ancient times when we shot film. Sometimes you’ll see it referred to as ASA which is
what it was called before the ISO designation came along.
ISO/ASA is a rating scale for a films’ sensitivity to light. Film comes in various light sensitive
“speeds” such as an ISO rating of 25, 100, 200, 400 and so on.