Very large focal distance range

The manual focal distance slider was previously capped at 20 (#91), and with release v0.3.1 was increased to 1000 (#92), which makes it very difficult to fine tune focal distance.

Release notes for v0.3.1 indicate the increased cap should be 100, which sounds a bit more reasonable.

Thoughts?

Thanks!

## Used AI_Graphics Version
v0.3.1 +
