Three steps to heaven – and a few pitfalls along the way…
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Over the past few weeks, I took an in-depth look at the various Metabones lens adapters for Nikon lenses, and at their remarkable Speed Booster model in particular. What started as a simple evaluation – do these lens adapters live up to their claims and to my expectations? – ended up with a comprehensive series of test shootings.
More details can be found in the following earlier blog posts:
- Introduction to lens adapters
- Metabones Nikon F to Fuji X adapters
- The Metabones Speed Booster
- The Metabones approach to aperture control
- Speed Booster image sharpness evaluation
- More Speed Booster sharpness tests
- Other Speed Booster image quality tests
My experiments are limited to the combination of Nikon (and a few third-party) F-mount lenses and a Fujifilm X-mount camera. Note however that the Speed Booster optics tested here are identical to the Sony NEX version, as both cameras use APS-C sized sensors.
What did I learn from my test images?
To start, a number of positive conclusions that confirm the manufacturer’s claims:
1. Using a full-frame lens on a Fuji X (APS-C) camera, the Metabones Speed Booster nearly restores the “original” field-of-view and depth-of-field experience of working with a full-frame camera
The final overall crop factor is reduced from 1.5x to 1.07x (rounded), meaning a 50mm lens on a Speed Booster will deliver the field-of-view equivalent to a 53mm lens. The corresponding shallower depth-of-field and bokeh rendering are available again as well.
2. The Metabones Speed Booster adds one full f-stop in light capturing performance
A 50mm f/1.4 lens becomes a 36mm f/1.0; an 85mm f/1.8 turns into a 60mm f/1.3, a 180mm f/2.8 acts like a 128mm f/2.0… Great news for low-light shooters!
A discussed later however, with some lenses the available f-stop range may end up slightly reduced.
3. The Metabones Speed Booster delivers excellent image quality
A large selection of lenses likely to be combined with a compact system camera shows a similar to slightly better optical performance in the center of the frame. The corner performance turns out to be similar to slightly lower (especially at wider apertures), and varies more with the specific lens itself.
All things considered, I can only conclude and confirm that the Speed Booster does not significantly degrade the performance of the attached lens (as some forum and blog posts sometimes suggest). This holds true for sharpness, vignetting, bokeh rendering, color fringing…
The characteristics of the lens attached of course play a big role, and so does its condition when it’s an older, well-used copy. Furthermore, you need to compare apples to apples: it makes little sense to put side-by-side images shot using the full-frame area with others from a crop sensor using only the center area of the lens, or with pictures made on a full-frame camera with its built-in image correction features enabled.
There are also a few minor negative remarks, all related to the operation of the aperture control ring shared by the Speed Booster and the Nikon-G-to-Fuji-X adapters:
4. The aperture ring scale is neither linear nor uniform with respect to actual f-stop settings
The Metabones website claims: “Industry's best aperture ring covers an 8-stop range with half-stop markings, clearly indicating actual number of f-stops. No more guesswork!”
In reality, you do get 15 clicking positions, but not 15 half f-stop settings as the wording may suggest. The aperture increments are not equally spaced across the available f-stop range of the lens: the step values are bigger at the open aperture end and decrease towards the smaller apertures.
You can use my “magic numbers” scale to perform the translation:
5. You may not be able to use the full aperture range originally offered by the lens
The aperture ring design limits the control span to about 6 f-stops only (starting from fully open). If your lens offers more, the smallest f-stop(s) will no longer be available.
In addition, with some lenses (or lens/adapter combinations?) the fully open iris position may not be reached, losing ⅓ to ½ stop at the wide open end. That takes back a little from the one f-stop gain, at least for who is looking to shoot with a minimal DOF. Note that this is often also the case with other adapters equipped with a different form of aperture control mechanism.
If – like myself – you mostly have F-mount lenses that do have an aperture ring, you might have preferred a Speed Booster version without aperture control on the adapter…
Both “negatives” will likely not have a major impact on real-life use, as the smallest aperture settings are generally avoided, in light of diffraction effects.
Are the Metabones lens adapters worth the investment?
The manufacturing quality of the Metabones adapters is simply best-in-class. Each adapter is precise, well-finished, robust, and a pleasure to operate. The Arca-compatible tripod mount is a nice feature, certainly with heavier or longer lenses.
Looking at the Speed Booster, the resulting images come very close to the “experience” obtained with a full-frame camera, and the image quality of the attached lens is largely preserved. The extra f-stop is a welcome addition to that. The Speed Booster helps to fill gaps in Fujifilm’s current XF lens line-up, at least until new lenses are added to the roadmap and become available (and the extra cash is spent).
In the end, the added value of a Speed Booster will vary from user to user. How extensive is your Fujifilm XF/XC lens collection, and how wide and fast will you let it grow in the future? How many Nikon F-compatible lenses do you already own, or do you plan to acquire some mint used copies to extend your lens line-up? Questions only you can answer for yourself…
The three Metabones lens adapters have found a warm place within my X-camera system. I use them on a regular basis with primes between 17mm and 180mm. The Speed Booster has opened up interesting opportunities, especially with fast lenses in the normal to short-telephoto focal range. Some of that may change when Fujifilm releases new XF lenses – the XF 56mm f/1.2 comes to mind immediately. But I guess all three adapters I acquired – and the Speed Booster in particular – will see plenty of action in the coming months.
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