The (3+) Sigma  achromat close up

 Here I show what are the results  with this very good +3 achromat.

I found this little thing in a second hand photo market (as usual...):

It is a 3+ achromat two elements diopter which was sold in bundle with the Sigma 90mm macro, the predecessor of the 105 Ex. This close up lens has a good reputation (David Ruether reviewed it in his site)  and its price was about ten times lower than an used Nikon 6T, so I bought it.

I tried it on the Nikon 50 1.8 Af and the results are good even if the reproduction ratio on a 50 mm is obviously not exceptional:

The smaller shell has a maximum diameter of 1cm

The photo of the fishes has been postprocessed with Photoshop (USM 0/18/64) giving very good final result, see the 100%crop below

Then I decided to see what could have happened  by stacking this close up device on my Nikkor 70-210 f 4.5-5.6 Af

Since the filter size of the close up is 52 mm, with two adapter rings and some strong glue I built this home made 62-52 step down ring:

Then I put it on the zoom at 210 mm to avoid vignetting and took some test photos with the combo on a Nikon D70 and compared the results with the pictures taken with a Sigma 105 f 2.8 EX which is a very good lens. The zoom, set at 210 and minumum focusing distance, has a greater working distance, a slightly  larger reproduction ratio and surprisngly slightly softer image rendition. Here below the results: All photos are unprocessed just-out-of-the-camera jpegs.

here is the subject of the test:

the book is 18 cm (ca 7 inches) high

the rectangle shows the photographed area

Here is the maximum RR obtained with the 105 Sigma on the D70

and a 100% crop

And here is the area covered by the Nikon 70 210 + the Sigma 3+ Achromat :

and a 100 % crop:

It is obviously a bit less sharp than the photo taken with the  Sigma, but the magnification is greater and after all not too bad, especially if you think that I paid next to nothing for the close up.

Obviously, It is not advisable to do that with full frame camera, because the corners may vignette and in any case, would be softer than in the smaller format.