Thanks all for replies!
Thanks for advising a technical camera system. Sure, the Arca Swiss is superb.
I owned 2 and for a shorter time ever 3 MF digital systems in the past, and found it a not money wise acquisition.
I sold everything and just use the Hasselblad H as my working horse.
I have the Stackshot long macro rail, and 28mm, 50mm II, 100mm and 120mm II lenses. That's almost all optics I may need for my kind photography.
The Stackshot rail helps to get jewelry rings all sharp from corner to corner. I suppose I don't need the HTC for that work.
The 120mm is a very sharp macro lens with 1:1 magnification, but only at the closest distance.
The problem is that many jewelry rings are too small to fit the whole frame.
I need a magnification solution, preferable without degradation of image quality, to completely fit the frame with a jewelry ring to fully utilize the 40 megapixels sensor.
Have you considered using your Hasselblad Back on a Fuji GX680. There is an 80mm rail extension option and you would have tilt shift ability.
With the 100mm and a full frame digital back the subject area is about 4x2.75cm with a comfortable focusing distance.
The 80mm will get you about 3.2x2.2
The camera also has a moving loup viewfinder option for fine focusing.
Here is the camera with a 40mm rail extension and the moving loup viewfinder
I have not done a side by side test with the Hassy Macro, but here is a 100% magnification
with the 250mm wide open just to give you a very rough idea of image quality.
I have shot jewelry with this, but mainly on models or "artsy fartsy" still lifes with grainy film etc.
Anyway just a suggestion as a nacro tilt shift sidekick for your Hasselblad back.
A fuji gx680 body version I can be bought for a couple of hundred and same goes for the lens.
kapture group makes high precision digital back adapters, but there are some cheap chinese ones available just to give it a try.
There are a couple of other forum members that shoot product with the 680 and digiback. Maybe they can chime in.
Also it is relatiely simple to have a longer extention rail machined to extend the rails at the body end.
The communication cable that goes to the front end of the camera is a flat cable, similar to a floppy dist flat cable and can be crimped by any cable shop.
There is what the rail looks like taken out of the body. Just two large screws to mount it to the body.
Then all you need to do it connect two bellows together,
There is a little about macro with the Fuji here by Danny Burkhttp://www.luminous-landscape.com/reviews/gx680iii.shtml