What do people use for mounting the subject in a setup like this?
Jim
I use different mounting systems for different subjects: Beetles and butterflies are either pinned or glued to pins - the pins are then either stuck into some kneaded eraser or clamped using alligator clips. Then it's placed on a stack of various trimming platforms and linear stages (X/Y/Z/R).
Larger specimens can simply be put on these platforms/stages directly.
For flat subjects (paper, stamps, coins,...) I use the rig in a vertical orientation with plexiglass plates as holders. Additionally I also have mounting methods for microscope slides and a solution for slightly larger/heavier stuff like medium-sized stones/minerals,..they all require a slightly different approach.
however I would definitely not put the subject on a motorized rail, for the following reasons:
1. You introduce vibrations directly onto the subject. It's "bad" enough to do it on the camera side, but the subject may be mounted on a long, thin pin or it may have fine hair etc - all of which would react to even minute vibrations and movements and even more so when it comes to larger step sizes in quick succession. A large, heavy camera would dampen vibrations in a short amount of time, a long thin pin will keep vibrating for quite some time even when one side is stuck in kneading eraser.
2. unless you put the lights onto the rail as well, they are going to remain in place while the subject moves. That may cause changes in shadows, reflections, light falloff and intensity, especially with deep stacks, which will be a problem later on.
3. The alignment has to be very precise, especially at higher magnifications, otherwise it'll introduce a problematic drift, even with a minor misalignment. In your case it's even more difficult because the rail is mounted on a tripod head where minor deviations could occur on all axes (and also potential shifts in gravity combined with the rather soft rubber surface of the horrible Manfrotto tripod plates).
4. it gets in the way when you want to use different backgrounds or use some light from behind /below the subjects.
You may also want to re-think the sideways (perpendicular) swebo rail for the same reason, it'll probably get in the way more often than you'd think. Better to use a small linear stage for macro stuff.