Originally posted by Sean Nelson Besides working distance, another factor to consider is field of view. Macro photogaphers often neglect field of view because they simply move closer or further from the subject in order to make the subject fill the frame. But it makes a difference in terms of the background of the shot.
A shorter lens has a wider field of view, and while this can be a good thing if you want to put your subject into context (ie, see this pretty flower which is one of very many pretty flowers), it's often a problem if what you're trying to do is isolate your subject. I find that a wide lens can make it difficult to find a shooting angle that eliminates distractions from the background.
I've had both a 50 and 100 macro from theh film days.
I use the 50 on flowers because of the depth of field issues.
the other issue has to do with whether and how you use a flash.
If you are going to use a ring light the 100 can be a problem. If you are using other light sources, the longer lens may be easier to work with as options to get light on the subject are greater
with more standoff distance.
If you want to see what a bunch of native flowers look like
done with mostly an F series 50mm macro and a ring flash
feel free to review what I have p osted at
VanNatta Northwest Oregon Native Plant identification guide
Although I haven't documented the precise equipment used,
many of these native flower photos involve thte use of my
F 50 macro, with an AF080C ring light. Generally to get the necessary depth of field the aperture is set at f/16 or smaller (I recall the lens go to f32) The ringlight is set to manual
as it doesn't support P-ttl, I then use an ND filter pack to get the right exposure.
Needless to say I'll be an early adopter when/if pentax produces a P-ttl ringlight, but even with manual exposure, life is much easier that it was with the film bodies. when I first got my ringlight,
i owned a venerable K2 (of the film era) and it was too old to support the TTL automated flash so it had to be used in manual much as I am now, except you had to wait for the film to be processed in order to adjust the exposure.