Heya,
I don't do a lot of jewelry, but just trying to replicate a similar shot to see where a problem may exist, here's an example I just threw together with very basic and inexpensive stuff.
Key light is a $49 Flashpoint 120Ws strobe with modeling light, inside a 31" Neewer Brolly Box ($20) on a boom stand.
The backdrop light to force it to be whited out no matter what, is a basic speedlite, a Yongnuo 560 III ($50) on a stand, bare flash against the backdrop.
Yongnuo RF603 transmitter on the camera and strobe (560 III has it built in).
Backdrop is a basic white muslin, cotton basically, over a table and box.
Random kid's earring I found on my floor (2 year olds...).
I used a cheap $40 Canon 10D camera that is only 6.3MP to go with a low quality sensor with low resolution, with a 90mm macro lens.
Camera settings 1/200s, F11, ISO 200. Basic ambient killing settings for macro.
I metered the light at the ring to F11 (see image) based on camera settings.
I metered the light on the backdrop to be +1 stop over exposed to make it all whited out, to F16 (see image), based on camera settings.

IMAGE LINK: https://flic.kr/p/D8t8iX
IMG_0344
by
Martin Wise
, on Flickr
Here's the low resolution JPG result:
IMAGE LINK: https://flic.kr/p/Cif1TE
CRW_0545
by
Martin Wise
, on Flickr
***************
Having done it now, I feel mine is softer than it could be. So having mimiced it, I think the way to fix that is actually just to use depth of field and resolution to your advantage. Basically, don't try to focus at minimum distance, or basically, don't try to go to macro on it. Instead, use depth of field to get the whole thing in focus, and do it from a farther distance. Then crop using the high resolution of your camera. This is what TeamSpeed described in terms of letting your 5D2 do the work for you.
So to test that idea, I re-did it with the same settings. The only difference is, I used a higher resolution camera (650D, so 18MP) and I backed up my distance so that my depth of field at F11 would envelope
most of the object, so that it's mostly in focus which will help with the perception of sharpness (which is really just contrast).
I think I like how that worked out even more, as it puts emphasis on all the jewels and while the band is soft, it's ok that it's only slightly soft.
Again the only difference was I used higher resolution and backed up so that depth of field would include more of the subject, and cropped down (the reason for the higher resolution used).
IMAGE LINK: https://flic.kr/p/D8uLnK
IMG_0348
by
Martin Wise
, on Flickr
Very best,