Lay a ruler, pionting towards the camera, where the cube should be. Shoot the ruler. That will tell you where your focus is and what your depth of field is. Work from there..
If you'r worried about the camera casting a shadow, move your light. Use ordinary light bulbs if you have to. remember to adjust your White Balance..
If I zoom in to get it larger in frame I can't focus at all, even inmanual. Apparently 20" is below the minimum focal length for thezoom I want..
So if you switch to Macro Mode it still won't focus at this distance?.
'Money doesn't buy happiness, but it makes for an extravagant depression' by golf tournament sportscaster..
You've discovered the number one problem in macro photography - working distance. You can't realistically expect to shoot a 1 1/2" subject from 20" - even with a DSLR and a true macro lens you would be lucky to get more than 6-8"..
Like it or not you have to get closer, and as you have already guessed, the challenge will be lighting...
Maybe I should make a mini-light box..
Okay, how does one get color into a message?.
Stupidity got us into this mess - why can't it get us out?.
- Will Rogers..
The question still remains, Do I need to be close enough that I have to switch to Macro mode?.
Or is it simply a matter of how much of the frame I want to fill? If I need to get within Macro range to fill the frame, then I need to switch to the mode?..