Nathan Wajsman wrote:
> In my case, I had visited RG Lewis a few times during the 1990s and
> also bought some Leica stuff there,
I purchased my first two Olympus OM lenses from R.G.Lewis in the 1970s. At
that time, R.G.Lewis had a TRULY unique USP(!) -- they tested all of the SLR
lenses that they sold new. They put each lens on a body and shot several
frames of a lens testing chart, at different apertures. When the film was
developed, it was passed to their lens assessment expert to rate, and those
frames and ratings were provided with each lens sold. This was not without
cost, of course, and R.G.Lewis lenses were about 10% more expensive than
from other retailers in London. Later, they obtained an MTF machine and
provided MTF charts with each lens sold. Later still they discontinued this
practice.
>From my files, here are some test results for actual lenses, garnered from
looking in their shop window every few weeks; figures are "effective" lines
per mm at centre/edge, for apertures: max aperture, f4, f8:
Olympus 50mm f1.4: 112/65, 112/80, 136/104
Pentax 50mm f1.4: 96/92, 112/100, 136/108
Canon 50mm f1.8: 100/65, 112/85, 136/100
Mamiya 50mm f1.8: 88/68, 104/77, 120/92
Olympus 50mm f1.8: 112/74, 112/81, 136/92
Pentax 50mm f1.8: 88/74, 96/88, 112/96
Pentax 50mm f1.8: 96/65, 96/81, 112/100 (another sample)
For comparison, here are the figures for the two lenses that I purchased
(figures for zoom are f4 and f8; figures for 28mm are f3.5, f5.6, f8):
Olympus 75-150mm f4 @75mm: na, 96/62, 96/84
Olympus 75-150mm f4 @150mm: na, 96/62, 96/88
Olympus 28mm f3.5: 104/74, 112/92, 120/96
I still have the zoom, but sadly not the 28mm which got damaged (it was
clearly a cut above the performance of other 28mm lenses that I saw in
R.G.Lewis shop window).
Finally, here is an extract from the "Notes on Lens Testing" leaflet written
by A.L.M.Sowerby (a sometime editor of "Amateur Phhotographer" magazine) and
publishd by R.G.Lewis; it relates to the term "effective lpm" that I used
above:
"One of the greatest difficulties in "reading" negatives lies in the
character of the definition afforded. If it is "clean", one set of lines
may be unmistakably sharp, the next finer group not visible at all. The
verdict as to "lines per millimeter" is then clear cut. But with a soft
lens, it can happen that even fairly coarse lines are not really sharp, but
nevertheless quite fine lines can be seen, perfectly detectably, through a
kind of haze of background fuzz. How many lines per millimeter should one
quote for the performance of that lens? Personally, I take the view that
the figure quoted for lines per millimeter should represent, as fairly as
possible, the practical performace of the lens, so in such cases I report
that the lens will resolve, say 80 lines per mm, even though I can detect
perhaps 100 or even 110 through the foggy background." -- A.L.M.Sowerby
I don't imagine that A.L.M.Sowerby assessed R.G.Lewis test negatives
personally, although he probably did help them develop their lens testing
regime, and provide guidance on the assessment of test negatives.
-- from CyberSimian in the UK
--
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