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

Discussion in 'Digital Photography' started by David Kilpatrick, Jul 13, 2004.

  1. 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/
     
    David Kilpatrick, Jul 13, 2004
    #1
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