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Using Minolta's wide adaptor on DX/DC type lenses

 
 
David Kilpatrick
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      07-13-2004
Today, from idle curiosity, I dug out a 58>49mm lens to filter adaptor,
and fitted the 0.8X wide angle converter made for the Dimage 7/A series
by Minolta, on to the Sigma SD10 with 18-50mm Sigma lens.

The Sigma finder shows you the full 35mm field outside the frame, so it
is possible to see how the attachment vignettes, or doesn't; it would
certainly be OK with Canon's 18-55mm at 18mm on a 1.6X sensor, and
almost definitely with the Sigma lens fitted to Nikon on their 1.5X
sensor. There is loads of spare image circle on the Sigma with 1.7X sensor.

Brass tacks: distortion - it added no perceptible distortion at all.
Zero. I was unsure whether it might even be IMPROVING the distortion of
the Sigma 18-50mm at 18mm. It also added no flare and could be aimed
right into the sun without throwing up the lightstorm I fully expected.
Focus: it had an afocal error when mounted on this lens, so that a
distant subject actually required the lens to be focused around 3.5ft,
but the error is progressively less when focusing closer. Using AF,
focus was accurate and sharpness was excellent across the frame.

I don't think this adaptor could be fitted to an 18-70mm DX Nikon zoom,
or anything with longer range like Sigma's new 18-125mm, but for DC/DX
type 18-50ish lenses, it seems like an excellent secondary use. It also
seems to work (not tested on film) with a 28mm lens on full frame
conventional cameras.

The effect on the Sigma was to make the effective 30mm wide-angle given
by the 18mm setting into a 24mm (0.8x 30mm) - it actually turns the lens
into a 14.4-40mm, presumably about at least as wide as buying the Sigma
15-30mm, or any 15mm lens - maybe as wide as many 14mms, given the way
that makers are allowed to quote on the short side when stating focal
lengths.

I did not try the 1.5X Minolta tele adaptor on the 55-200mm Sigma,
because it's four times the weight of the lens and would probably snap
it in half

So, anyway - if you own a Dimage 7/A, and wonder whether it's worth
getting the 0.8X converter because a DSLR beckons, don't fret - it is
optically good enough, and large enough, to function on a DSLR 18mm and
turn it into a 15mm.

Second part of experiment - fitted an ISCORAMA 1.5X-36 anamorphic
adaptor to the front of the same lens! Can be used at the 28mm setting
(just) which is almost equal to 50mm on the Sigma body, as expected. I
reckon the best way to treat the resulting files will be: export at 2X
size from the RAW file, then change dimensions x0.66 times for the
stretched axis. The result will either be square pictures, or panoramics
with a 2.25:1 aspect ratio, depending on how the anamorphot is orientated.

In the past a special anamorphic projection lens or special enlarger
adaptor (for the camera unit) was needed to recover the 1.5X compressed
'squeezed' ratio of Iscorama pictures. Of course with digital, no such
messing is needed.

All experiments destined for next issue of f2 magazine.

David
http://www.f2photo.co.uk/

 
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