Bring on the magnifying glass…
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Time to share my findings on optical performance and image quality.
I told you before that I am not at all into pixel peeping, but rather want to find out where and how I can make best use of my lens collection. Even so, I slowly slid into the trap of chasing details and worrying about test outcomes that did not always match up well with other results… So here comes a load of test results and sample images, collected during a few weeks of image quality evaluation.
One more time: caveat emptor!
- I am not equipped, qualified nor experienced for in-depth image quality testing. So take my attempts for what they are worth: a good swing at discovering whether the Metabones Speed Booster lives up to its manufacturer’s claims;
- Lacking the tools and skills for real optical measurements, I focus on comparisons between different camera/lens setups under similar conditions. That means however that each of the alternatives compared may suffer from its own inaccuracies and so lead to conclusions that may be influenced by less-than-ideal test conditions;
- Everything is based on sample-of-one testing: one camera, one lens adapter, each lens… only.
So I urge you to look at my test results NOT as an absolute measurement of the Metabones Speed Booster’s capabilities, but rather as an indication of what it CERTAINLY CAN achieve!
I include some information on the test setups and on the processing of the results, so that you can make your own judgment on the outcomes as presented.
Common test conditions
- Test scenes were built inside my familiar light tent, with continuous fluorescent bulb lighting providing a (verified) stable light intensity and color temperature over time;
- “Best efforts” were used to maintain proper alignment between camera and subject;
- The cameras (X-Pro1, D700, occasionally X-E1) were mounted on a sturdy Manfrotto 190PROB tripod with 3-way head;
- The X-cameras were triggered by a cable or remote , with additionally a 2 sec self-timer setting;
- Focus was always done manually at maximum lens/adapter aperture, using the back LCD with 10x magnification; focus peaking was on or off dependent on the subject (whatever felt more reliable);
- For the D700, Live View was used at maximum magnification, triggering by MC-30 release;
- Exposure in aperture priority mode, matrix metering with exposure compensation added for an optimal histogram;
- F-mount lenses were mounted on the X-cameras using either the Speed Booster, or via a Metabones G- or F-adapter (depending on lens type);
- Aperture setting was done on the lens if an aperture ring was available; with G-lenses I set the aperture via the adapter ring following my “magic number” scale described earlier;
- Vignette Control set OFF on the D700 (it does affect NEF files!);
- When a 12Mpix D700 image is compared to a 16Mpix X-Pro1 image, the latter image is scaled down to the smaller pixel dimensions before extracting 100% crops, to keep the represented image areas alike;
- All images were shot in RAW using AdobeRGB space and a fixed custom white balance setting;
- Post-processing in Adobe Lightroom 5.2RC using 2012 (Current) process, Adobe Standard profile, all settings on default, no image adjustments other than specifically noted with each test.
TEST ONE: image sharpness
I assembled a small colorful scene in my familiar light tent. The center resp. (lower right) corner focus areas are indicated by the white center mark symbols. The grey card in the background was used to “equalize” the individual shots with respect to exposure and white balance (the D700 images have a different color rendering, due to in-camera processing or post-processing?).
A series of lenses was tested across a range of apertures (typically fully open through f/5.6). The camera was repositioned between shooting with and without the Speed Booster, to obtain a comparable reproduction size (no excessive effort was applied beyond being reasonable...).
The size of the scene was relatively small and the shooting distance (with 50mm lens on Speed Booster) around 50cm only. Shallow DOF, imperfect alignment, field curvature etc. all make this test rather difficult to execute well, and thus more subject to human error.
Because of the shallow DOF and the possible field curvature, the lenses were focused separately for the center and for the corner targets. Focus was left untouched when changing aperture. In some cases, multiple series were captured to select the images with the best focus.
Metabones and Brian Caldwell claim equal to better image sharpness in the center, and a slight degradation in the corners. Roger Cicala’s measurements largely confirm this. Both sources remark that the results may vary with individual lenses. Let’s find out for ourselves.
Testing the Nikon AF-D 50mm f/1.4
It might be more relevant to compare using 100% crops:
(The different size of the 100% crop area is a result from the downscaling of the 16Mpix X-Pro1 image, to end up with the same pixel dimensions as the crop from the 12Mpix D700 image)
The result fully open is not worse with the Speed Booster compared to without, and seems slightly worse compared with the D700 shot (manual focus error?).
Nikon’s 50mm f/1.4 lenses are not exactly known for their corner sharpness wide open; we see the predicted minor degradation when looking at the corner crops, though the result is certainly not bad at all! (remember that a separate series of images was shot, with adjusted focus, for center and for corner sharpness )
The relative differences still hold at f/5.6:
Note how using the Speed Booster – as expected! – reduces the DOF.
Testing the Nikon AF-S 50mm f/1.4G
This more recent 50mm lens is generally said to be slightly better than the AF-D 50mm f/1.4 in both center and corners, but still far from perfect. This lens reaches its maximum performance only around f/5.6.
For some reason I kept having problems to achieve acceptable focus in the corners, and I did not bother to completely redo the test for that. So center crop comparisons only…
Similar observations as before, also at f/5.6:
Slight advantage to the Speed Booster image for center sharpness.
Testing the AF 50mm f/1.8
A Nikon classic, and usually a solid performer.
Similar behavior in the center, slight degradation in the corner, almost gone by f/5.6:
Testing the Nikkor H·C 50mm f/2.0
How will this pre-AI fully manual lens from the early 70s hold its ground with the Speed Booster?
Again the same conclusion: slight improvement of the center sharpness with the Speed Booster.
Testing the Nikon AF-D 35mm f/2.0
Another classic, in the ‘conventional’ wide angle range.
Testing the Nikon AF-D 85mm f/1.8
One of my favorite AF-D lenses, currently filling a hole in the Fujifilm XF lens line-up.
The 85/1.8D shows itself as a strong performer fully open, taking good advantage of the Speed Booster in the center, and not losing much in the corner.
NEXT: More grueling image sharpness tests…
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