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Review by Klaus Schroiff, published April 2007
THIS IS A LEGACY TEST REPORT BASED ON THE ALPHA 100. AS SUCH IT IS NOT 100% COMPARABLE TO THE CURRENT TESTS BASED ON THE ALPHA 700!
Introduction
The Minolta AF 50mm f/1.7(N) is one of the old standard fix-focal lenses by
Minolta. Obviously it is a discontinued item now because Sony took over Minolta's
photo department back in early 2006. The lens has no real equivalent in the
current Sony line-up. Sony decided to keep the 50mm f/1.4 only but this lens
is fairly expensive which is why used AF 50mm f/1.7 are fairly popular over
at eBay or 2nd hand dealers. On APS-C DSLRs such as the Sony
Alpha 100 (used for testing) its field of view is equivalent 75mm so it behaves
more like a basic portrait lens here. Not too bad for about a hundred bucks.
The mechanical quality of the AF 50mm f/1.7 is relatively decent. It is a
plastic lens with a metal mount. The focus ring, located at the very front,
is rubberized (in this version) and handles Okayish (a bit sticky at times).
It rotates during AF operations. Surprisingly the lens features a tiny
build-in lens hood. If you bought the item without a manual you may well
overlook it because it is a secondary plastic barrel between the inner lens tube
and the focus ring. You can lift and lock it in position. The hood is not
overly efficient but it is better than nothing. The lens extends slightly
towards closer focus distances. The front element does not rotate so using
a polarizer is no problem.
Like most (though not all) Sony/Minolta lenses the 50mm f/1.7 relies on
the conventional focusing system driven by the camera (via a slotted drive screw).
Consequently the AF produces a moderate degree of noise but the speed is fairly fast.
| Specifications |
|---|
| Equiv. focal length | 75 mm (full format equivalent) |
| Equiv. aperture | f/2.6 (full format equivalent, in terms of depth-of-field) |
| Optical construction | 6 elements in 5 groups |
| Number of aperture blades | 7 |
| min. focus distance | 0.45 m (max. magnification ratio 1:6.7) |
| Dimensions | 38x46 mm |
| Weight | 186 g |
| Filter size | 49 mm (non-rotating) |
| Hood | barrel shaped, build-in |
| Other features | - |
Distortion
The AF 50mm f/1.7 shows very slight barrel distortion (0.4%) which isn't really relevant in field conditions.
The chart above has a real-world size of about 120x80cm.
Vignetting
The AF 50mm f/1.7 is a full-frame lens so it can take advantage of a sweet spot effect
on the Alpha 100. However, at wide-open aperture the vignetting is still quite pronounced
at ~0.9EV but it is negligible from f/2.8 onwards.
MTF (resolution)
50mm lenses are simple beings which were only marginally modified since the late 70s.
Usually there's very little room for improvement left here but the Minolta AF 50mm f/1.7 is
not among the best normal lenses tested to date. The center performance is already
very good at wide-open aperture and stopping down lifts the quality to levels at
or possibly even beyond the sensor resolution of the Sony Alpha 100. However, the
borders are a different story - at f/1.7 they're downright soft and not much better
by f/2.8. It takes f/5.6 to reach very good territories and the peak performance
is not reach prior of f/8 here. The Canon or Nikon counterparts show a much better
border characteristic.
Please note that the MTF results are not directly comparable across the different systems!
Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness.
If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations
Chromatic Aberrations (CAs)
Lateral chromatic aberrations (color shadows at harsh contrast transitions) are relatively
well controlled but not something to rave about for such a lens. With a peak width
approaching 1px on the average at the image borders you may see CA traces at times.
Sample Shots
Here're some sample shots taken with the Sony Alpha 100 and RAW-converted via ACR 3.7.
Click on a thumbnail to view the original file (opens in a separate window). Please note that the originals are FULL SIZE
(=several megabytes) which requires quite some bandwidth for downloading so please don't waste the limited resources here.
| Make |
SONY |
|
| Model |
DSLR-A100 |
| ISO Speed |
100 |
| Focal Length |
50.0mm
|
| Exposure Data: |
f/2.8 @ 1/4000s |
| Size |
2592x3872 |
|
| Make |
SONY |
|
| Model |
DSLR-A100 |
| ISO Speed |
100 |
| Focal Length |
50.0mm
|
| Exposure Data: |
f/11.0 @ 1/320s |
| Size |
2592x3872 |
|
| Make |
SONY |
|
| Model |
DSLR-A100 |
| ISO Speed |
200 |
| Focal Length |
50.0mm
|
| Exposure Data: |
f/8.0 @ 1/250s |
| Size |
2592x3872 |
|
| Make |
SONY |
|
| Model |
DSLR-A100 |
| ISO Speed |
200 |
| Focal Length |
50.0mm
|
| Exposure Data: |
f/3.5 @ 1/1000s |
| Size |
3872x2592 |
|
| Make |
SONY |
|
| Model |
DSLR-A100 |
| ISO Speed |
100 |
| Focal Length |
50.0mm
|
| Exposure Data: |
f/5.6 @ 1/320s |
| Size |
2592x3872 |
|
| Make |
SONY |
|
| Model |
DSLR-A100 |
| ISO Speed |
100 |
| Focal Length |
50.0mm
|
| Exposure Data: |
f/11.0 @ 1/320s |
| Size |
3872x2592 |
|
| Make |
SONY |
|
| Model |
DSLR-A100 |
| ISO Speed |
100 |
| Focal Length |
50.0mm
|
| Exposure Data: |
f/8.0 @ 10.0s |
| Size |
3872x2592 |
|
Verdict
The Minolta AF 50mm f/1.7 is a very good lens but it is slightly inferior
compared to its cousins over at Canon or Nikon. The center resolution is great
but the borders are soft at wide-open aperture and it takes a couple of f-stops
till they reach decent levels. Nonetheless it is an excellent lens for portraits
where the border performance is not really an issue and it can take superb
images around f/8.
As you may have noticed in the sample images above the out-of-focus blur (the
bokeh) is pretty smooth and buttery - a seldom characteristic actually and it
is also very resistant against flare (see the night shot above) so there's also
a truth beyond sheer resolution figures. The Minolta AF 50mm f/1.7 is a cheap
lens on the used market and for about a hundred €/US$ it is easily worth
it - all other 50mm alternatives are a magnitude more expensive.
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