This picture of an American Treefrog illustrates several points.
The first is to ask permission.

The frog was in a Vivarium in a local garden centre. I could see
that it was well positioned but was behind poor quality and quite
dirty glass. I approached an assistant and asked if the vivarium
door could opened for a few seconds. He was interested in what I
was doing, so the door was duly opened. 



Next is the difficulty of close up exposure. I had my Canon T90
with it's dedicated 300TL flash, so knew that, with a relatively
still subject I could use the spot metering flash mode for spot
on exposure.

It is a real pity more cameras were not fitted with this mode,
and Canon have now dropped it !




How much would be sharp ? I also had a Tamron SP90 macro lens
fitted, so a close shot was going to be quite easy. Choosing a
small aperture, which I knew the flash could easily supply enough
power for, and focusing carefully on the face solved the
sharpness problem.

The result is a strong print which required some extra exposure
round the edges to prevent there being light, distracting
highlights. The picture has appeared in a photographic magazine
illustrating an article on Ilford XP1 film.