Macro with Sigma 70-300

When I use the field macrophotography Nikon D300s with Sigma 70-300 zoom lens along with the Nikon flash SB 600 and a set of extension tubes up to 68 mm.
This is not far from the best team, especially the goal is one of the cheapest on the market.
Basically I use the zoom from 70 mm to 200, over 200 quality low strength. This gives an expansion ratio close to 1 and 0.34 to 70 mm to 200m. Regarding the working distance measured from the tip of the subject in order to photograph varies from about 14 to 85 cm. As we can see with this small team can cover the most common relationships Extension without change of optical zoom and changing the working distance.
In the following table we can see the ratio increase, the working distance and the size of the rectangle photographed according to the selected focal zoom.

f R Distance Width Height
70 0,971 142 24,7 16,5
90 0,756 209 31,8 21,2
110 0,618 288 38,8 25,9
130 0,523 379 45,9 30,6
150 0,453 481 52,9 35,3
170 0,400 595 60,0 40,0
190 0,358 721 67,1 44,7
210 0,324 859 74,1 49,4

I use the flash of the camera with a separate bar and 25 cm shoot with a sync cable. All equipment weighs about 2 kg that can be handled by hand.
It is clear that using a macro lens of 135 mm or 180 would be a better option, but I have and the results are pretty decent. Here I show a series of photos taken with a tripod in the laboratory to see the quality of the set is good enough.

DSC 2328

Focal length 70 mm 

DSC 2328 detall

Focal length 70 mm real pixel

DSC 2341

Focal length 90 mm

DSC 2341 detall

Focal length 90 mm real pixel

DSC 2358

Focal length 102 mm 

DSC 2358 detall

Focal length 102 mm real pixel

DSC 2364

Focal length 112 mm 

DSC 2364 detall

Focal length 112 mm real pixel

DSC 2400

Focal length 155 mm 

DSC 2400 detall

Focal length 155 mm real pixel

DSC 2402

Focal length 195 mm

DSC 2402 detall

Focal length 195 mm real pixel