From: Gary Reese <pcacala@xxxxxxxxxxxxx>
Reply-To: olympus@xxxxxxxxxxxxxxx
To: olympus@xxxxxxxxxxxxxxx
Subject: Re: [OM] Depth of field questions
Date: Fri, 05 May 2000 17:38:25 -0700
Re: Garth invited further comments from me on C.H.'s reminder that
Modern Photography found poorer performance in the 90mm at macro range
than at 1:40
Here is the Modern Photography data:
90/2.0 MC (8/87 p. 62):
Actual: 90.44/2.04, Distortion: 0.470incush, Falloff: 0.3 stops at
f/5.6
2 2.8 4 5.6 8 11 16 22
Resolution (lines/mm) at 1:50x
Center: Ex 56 Ex 56 Ex 63 Ex 70 Ex 70 Ex 63 Ex 56 VG 50
Corner: Ex 50 Ex 50 Ex 50 Ex 56 Ex 63 Ex 56 Ex 50 Ex 45
Contrast (%) at 30 lines/mm
Center: Low 30 Med 47 Hi 69 Hi 68 Hi 60 Hi 54 Hi 48 Low 33
Corner: Low 25 Med 30 Med 43 Hi 45 Hi 50 Hi 42 Hi 40 Low 27
Resolution (lines/mm) at 1:4x
Center: Acc 40 Gd 45 Gd 45 VG 51 Gd 45 Acc 40 Acc 40 Acc 40
Corner: VG 32 VG 32 Acc 36 Gd 40 Gd 40 Acc 36 Acc 36 Acc 36
Resolution (lines/mm) at 1:2x
Center: Acc 40 Gd 45 Gd 45 Gd 45 VG 51 Gd 45 Acc 40 Acc 40
Corner: Ex 36 VG 36 VG 36 Gd 40 Gd 40 Gd 40 Acc 36 Acc 36
What it basically reveals is that performance is lower at 1:4 and 1:2
than at 1:50. My test is at 1:40
The floating element design in the Zuiko macros offers a compromise to
an optical limitation. Lenses can only perform their theoretical optimal
at a particular magnification ratio. Olympus designers where first to
market with a combined close and far focus aberration correction system
(using floating elements) in the 50mm f/3.5, then later in the 50mm f/2
and 90mm f/2. In contrast, the f/2 ultra wide angles only offer close
focus aberration correction.
If these data reflect real world results, it says that the floating
element design in the 90mm f/2 isn't as effective as we would hope in
correcting close focus aberrations within the true macro range. The
design actually favors pictures taken in the range of f/4 to f/8 at
magnifications ratios of at least 1:40 to 1:50 (probably wider, but we
don't have data).
I'm not real concerned about this, because floating element design macro
lenses from other manufacturers also show image deterioration in the
macro range. They must all be optimizing performance for the more often
used middle distances.
But this is all consistent with info which Olympus, particularly Maitani,
has revealed already. The 90/2, 50/2, 50/3.5 macros give good performance
up to 1:5 lifesize. Beyond this the user should employ the 80/4 from 0.5 to
1.2 lifesize (2.2 with the 170mm close up diopter). Then onward to the
38/2.8 (1:1.7 to 1:6.7 lifesize) and the 20/2 (about 1:4.2 to 1:16).
Maitani stressed that it was impossible for the designer to produce a lens
capable of providing good performance over a wide macro range. Therefore,
Olympus chose to provide a series of lenses with increasing (or decreasing)
ranges for macro lens excellence.
John
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