On rereading what I wrote, I think it could be misunderstood.

There are two types of blur. Motion blur occurs because the camera moved
(shake from not being on a tripod with too long an exposure) or the
subject moved.  That type does not happen with flash, because the
duration of the light is so short, and it overwhelms any ambient light
source.

The second kind of blur is depth of field. This is a result of the fact
that your camera cannot focus on both the flower you hold in your hand
and the mountain behind it.  Your eye has the same issue, but it has a
much deeper depth of field, and you tend not to notice it because your
eye can refocus so quickly when your mind says to look elsewhere.  In
the photo, the focus is frozen and when your mind says to look at the
mountain, the focus cannot change (in the print).

Depth of field is controlled by the f-stop of the lens at the time the
picture was taken.  The smaller the f-stop number, the wider open the
aperture is, and the shallower the depth of field.  Most lenses can open
as far as f4, or maybe f2.8 for bigger (heavier) and better lenses.
Crank open as wide as you can if you want a really shallow depth of
field -- so the bee is in focus and the flower he sits on is not.

Conversely, the higher the f-stop number, the smaller the aperture, and
the deeper the depth of field. Most lenses go down to f22, though some
go even smaller.  Crank it down as small as it will go if you want to
have the bee and the flower both in focus.

Mind you, in macro photography, depth of field is always very shallow.
You can increase it a bit with smaller aperture, but you will never have
the bee and the flower pot both in focus (assuming the bee is on the
flower, and not the pot).

Hope that is clearer...

    Well, I don't real all messages of this thread, but just few responses and
I can see few things ain't exactly macro-photography, even the lens is a
real macro-lens.  Lets just look at the whole thing.

- Canon 100mm macro-lens is a real macro lens for sure.

- But using macro lens to photograph a large and fast flying butterfly or
fast moving object isn't true macro photography.  Or macro photography
usually on small none (still object) or very slow moving object, because
it's pretty hard to focus (and many people even use tripod on these tiny
still object)

- Flash, 1/250 is the fastest the normal flash can offer or the camera can
operate.  And with newer digital camera, it should report if the camera
setting meets the requirement's or not.  Or the status will report the flash
isn't correct if Flash is ON and set faster than 1/250's (s = second), or
the camera should have the Warning LED ON

    Also, there is some difference between 1/250's using regular flash and
studio strobe, because they work differently.  As well as macro flash, ring
flash for macro photography etc..

P.S.  I don't mean to quote or try to correct anyone.

I thought 'bokeh' was a typo for something else... :-)

I have never heard that term before.  How would you define it?  (Yeah, I
could Google, but it is 3AM XMas Morning and I am heading for bed...)

Type A

Yes, I've been saying that all along. FEC is controlled by the camera. At
this stage I have it set to +2..i.e. full power

True. I'm considering then Canon 580EX or even the MR-14EX ringlite.

A simple way to check this is to set up the same but in low light, so a
slow shutter won't produce adequate exposure from the ambient light.  
Shoot with both fast and slow shutter and compare the results.  I
suspect that even at 1/60 the flash won't provide enough light.

Ahh! remember the days when we could check this by a test shot with the back
of the box open? If we saw the flash through the lens, we were in sync.