Minolta CE Rokkor 30/2.8 (as a studio macro lens)

Austrokiwi

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Mar 19, 2016
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This is a very preliminary post. I have a number of good adapted-for-macro lenses. UP until mid last year I would try out different enlarger lenses to see how they would perform. I stopped doing this once I had discovered the lenses that I liked the most. There was one lens I was always intrigued with: the subject of this thread. Last week the Leica shop in Vienna had a boxed example arrive. The price (Euro 80.00) seemed reasonable given the pristine condition of the lens. I couldn't resist the opportunity to find out how it might perform as a macro lens, my hope is that reversed it will perform well in the 4X -8X range.
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Lens data: it is a Gauss design consisting of 6 elements in 5 groups and is for enlarging 16mm negatives. it has 6 aperture stops ranging from 2.8 to 16. An interesting additional factor is it is designed so that if you pull the aperture ring forward the click stops are disabled, so allowing for continuous variation of the aperture.

Initially I have been unable to properly test the lens reversed as it doesn't have a filter thread. I contacted RAF camera and provided them with the outside measurements and they are in the process of producing an adapter that will allow me to use a 52mm reversing ring. In the mean time I had to have a play mounting the lens normally. I initially tried the lens on a bellows but found at minimum extension I was getting 1-1 magnification. That may read well, but as the front element of the lens is deeply recessed the effective working distance at 1-1 means effective lighting is extremely difficult( I would say unworkable). I then switched to a Kiwi M39 - MFT adapter and some M39 extension rings. This dropped the magnification range( with a practical working distance( but still close) to 0.25X to 1-2. On a MFT camera in that magnification range the lens really does perform well. Here is a slightly less than half sized image of a commemorative medal( followed by 100% center crop):
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I also tested the lenses resolution ability by projecting the image of a resolution test target through a 10X microscope objective. This technique enables frequencies beyond the sensors resolution limit to be assessed. The test target was an Edmunds optical 1951 USAF resolution target.The testing technique I use sees a light gap between the rear of the lens being tested and the microscope objective... this always results in poor contrast. So in the following crop from the resolution test shot ignore the low contrast as it is not a problem with the lens just the test rig. The 16mp sensor on my MFT camera stops resolving around group six element 3 (or 4). I have drawn a reddish bracket on the shot to show this sensor limit. I was pleasantly surprised to see the lens easily exceeded the sensors resolution limit. The lens is resolving to Group seven element 2( green arrow) this equates to 143 cycles per mm. A cycle is a black line followed by a white line( the gaps between the targets lines). Both group 6 and 7 can not be seen unaided.

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I didn't test for CA as the test shot above clearly shows that CA is not controlled( but I didn't expect that it would be. As far as resolution goes this lens actually out performs the native oly 60mm macro. I don't think its a field lens. This lens due to the short working distance is probably best for coins and other inanimate objects. For now its going on the shelf once I get the reversing adapter I will test the lens further a share the results here.
 
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