Review: Zhongyi Lens Turbo II with Minolta MC 58 mm & MD 50 mm lenses


The Lens Turbo II is a focal reducer available for E mount, Micro FourThirds and Fuji X cameras, produced by the Chinese company Zhongyi. It was originally ‘inspired’ by the Metabones Speedbooster and reduces the focal length of any attached lens by a factor of 0.726. For E mount cameras, this results in a proportional reduction of the crop factor to 1.11, giving you a nearly full frame equivalent lens characteristic on the NEX. Because you are shortening the focal length of the attached lens while keeping the aperture opening constant, you gain one full f-stop (+1 EV) of light – in theory.

Review_LensTurbo_II_mount-detailThe Lens Turbo itself is light and a little shorter than the usual glassless adapters. Build quality isn’t perfect, but still very good. My copy had a tight fit on the camera and a very tight one on the lens. Attaching it to the camera is a little tricky, because the optics protrude into the housing and the adapter can therefore not be turned to lock like you usually would with a lens. Instead, you align a small bore in the adapter (see orange marking in the image on the right) with the locking pin on the NEX and then rotate the corrugated ring on the Lens Turbo. There is no distinct clicking noise when everything is mounted correctly. One small flaw with this system is that the bore on the Lens Turbo is chamfered. While it looks nicely machined at first, this also tends to push the locking pin on the NEX back into the body, leaving the adapter free to turn. It’s a little annoying to look out for this, but you get used to it quickly and it doesn’t affect optical performance at all.

You should be aware that the Lens Turbo cannot be combined with every Minolta lens. Lenses where the back element protrudes more than 3 mm from the back of the mount when focused to infinity can collide with the Lens Turbo optics and shouldn’t be used. Further, there are reports that the aperture lever can jam on some lenses while mounting – I can confirm this for the MC Rokkor-PG 50 mm f/1.4. Details on compatibility and how to overcome some small quirks of the LT can be found in a seperate Lens Turbo tips & tricks article.

 

Condition of my copy

Optics: Excellent. No scratches, no dust – new.

Mechanics: Very good. Smooth locking mechanism for camera mount, a little too tight on the lens mount.

Exterior: Excellent. Like new.

 

Optical performance on NEX-5N / 5T

Notice: The quality of images taken with a focal reducer is limited by the converter as well as by the lens it is attached to. The following review is therefore only valid for the combination of the Zhongyi Lens Turbo II with the lenses tested here. As one lens alone wouldn’t be all that interesting to see, this review is a little different from my usual ones. It’s a competition of three loveable Minolta 50s: the MC Rokkor-PF 58 mm f/1.4 (MC-II), the MD Rokkor 50 mm f/1.4 (MD-I) and the MD Rokkor 50 mm f/1.2 (MD-II). Judging the quality of the converter is best made by comparing the shots of the lens with and without it.

(-> jump directly to test charts)

 

MC Rokkor-PF 58 mm f/1.4 (MC-II) with Lens Turbo II

The lens is soft, shows hazing and very little contrast at f/1.4. Stopping down to f/2 bumps contrast and reduces the haze to an acceptable level. Resolution and sharpness do not increase, yet. Up to this point, performance is very close to the lens without the LT. When stopping down to f/2.8, the haze fully disappears and the image shows a huge gain in central sharpness. Ironically, corner sharpness drops when pretty much stays at the same level till f/16. This is very different from the performance of the lens alone and possibly attributable to an increased field curvature. Stopping down to f/4 increases sharpness in the central region a little further, close to a very good rating. And while f/8 may even be very good, the overall impression is that the lens performs identical from f/4 up to f/16. The center is nice, the corners stay soft – again, very different from the lenses performance without the LT, where the 58 mm reaches excellent sharpness at f/5.6 and the corners are top notch from f/5.6 until f/11. Diffraction should be apparent at f/16, but a difference to f/11 is hardly visible because sharpness with the Turbo isn’t high enough at the lower apertures.

As far as CAs go, a minimal red glow is visible at f/1.4 and f/2 in the corners. From f/2.8 on, the lens shows very small red/cyan CAs – a little worse than without the LT, but still very good.

Vignetting is about 2/3 of a stop at f/1.4 and disappears by f/2. Barrel distortion is -0.7% and the effective T-stop at f/1.4 is approximately T1.55 (-0.3 EV) – better than the T1.7 without Lens Turbo II, but certainly not one full stop better.

 

MD Rokkor 50 mm f/1.4 (MD-I) with Lens Turbo II

Review_LensTurbo-II_MD_50_1.4_defocusedThe lens is soft and shows an extreme glow in the center at f/1.4 with acceptable contrast. If you think that this may just be misfocused: It’s not. On the right is a direct comparison. The left shot of the lens at f/1.4 has been focused for resolution, the right is the same shot taken seconds later but focused for contrast (click to enlarge). It’s easy to see that the shot focused for contrast looks better at first, but is clearly out of focus and softer than the shot focused for resolution. The same effect is still visible at f/2, but contrast in the center is greatly improved. At both apertures, the lens performs worse than without the Turbo. At f/2.8, the sharpness increases radically to good levels, the haze / glow is finally gone and the corners do profit from stopping down, too. In the central region, the result is nearly identical to a shot without the LT. When stopping down to f/4, the sharpness increases to very good and close to excellent at f5.6 and f/8. The corners pretty much stay at the same level as f/2.8, though. Diffraction becomes visible at f/16. All things considered, central sharpness from f/5.6 to f/11 is very, very close to the capabilities of the lens – maybe even equal. It truly is splitting hairs. Only the corner regions suffer from f/2.8 on, which is understandable since you are now using the more problematic, outer part of the image circle that is out of frame without the Lens Turbo.

Looking at the CAs, a light green/magenta glow is visible at f/1.4, which transforms into red/cyan glow at f/2 in haze-affected areas. From f/2.8 to f/16, the lens shows small to medium red/cyan CAs when used on the Lens Turbo II. This is certainly worse than what the lens is capable without the Turbo, but nothing to worry about, either.

Vignetting is about 1 stop at f/1.4, improves to half a stop at f/2 and is gone by f/2.8. The lens also exhibits a medium barrel distortion of -1.2%. Both values are slightly worse than without the Turbo. The effective T-stop at f/1.4 is approximately T1.55 (-0.3 EV) – better than the T1.8 without Lens Turbo II, but certainly not one full stop better.

 

MD Rokkor 50 mm f/1.2 (MD-II) with Lens Turbo II

The lens is soft and shows an extreme glow in the center at f/1.2 in combination with low contrast. The glow is still visible at f/2, but contrast is greatly improved. At both apertures, the lens performs worse than without the Turbo. At f/2.8, the sharpness increases and reaches close to good levels, the haze / glow is finally gone and the corners do profit from stopping down, too. In the central region, the result is nearly identical to a shot without the LT. When stopping down to f/4, the sharpness increases to close to very good and finally to a solid very good at f5.6 and f/8. The corners only increase up to f/5.6 and stay at this level until f/max. Diffraction becomes visible at f/16. All things considered, central sharpness from f/5.6 (maybe even f/4) to f/11 is very close to the capabilities of the lens. Only the corner regions suffer a little, as they did with the MD 50 mm f/1.4.

Looking at the CAs, a dark cyan/red glow is visible at f/1.2, which becomes more prominent at f/2 and sharpens up at f/2.8 to form medium CAs. They grow minimally up to f/16. The CAs are a bit larger than without the Turbo, but the 50 mm f/1.2 is no great performer in this category anyway.

Vignetting is about 1 stop at f/1.2, improves to 2/3 of a stop at f/2 and 1/3 of a stop at f/2.8. It is finally gone at f/4. The lens also exhibits a medium barrel distortion of -1.6%. Vignetting and distortion are slightly worse than without the Turbo. The effective T-stop at f/1.2 is approximately T1.4 (-0.4 EV) – better than the T1.6 without Lens Turbo II, but – again – not one full stop better.

 

Conclusion

The Zhongyi Lens Turbo II is a very interesting piece of equipment for NEX users. It allows you to use your vintage lenses on a compact APS-C body with a field of view very close to a full frame camera. The LT is even a little bit thinner than conventional “dumb” adapters. It’s mounting system is a bit quirky, but that’s something that you get used to within a week or so.

It’s optical performance with the normal lenses used in this shootout is a bit mixed: While the MC Rokkor-PF 58 mm delivers good but not outstanding results throughout the aperture range, the MD Rokkor 50 mm f/1.4 and 50 mm f/1.2 really shine – after you stop them down twice. If you do, results are outstanding –  especially considering that the 50’s attached to the Lens Turbo result in 36 mm f/1.0 and f/0.9 lenses. That also explains why they lack a bit of punch and show a strong glow at f/1.4 / 1.2 and f/2 – you are really pushing beyond the physical limits of these vintage lenses with such large apertures. They are still usable, but will look very “dreamy” in real life shots.

One of the major arguments to use the Lens Turbo besides the change in focal length certainly is the effective light gain in T-stops. My measurements wide open indicate, that you can expect about +0.3 EV with these lenses. That may seem small, but f/1.0 and below certainly hit the limits of the LT’s design specs. At smaller apertures, the effective gain is much larger: 0.6 to 0.8 EV, to be precise. This is close to a full stop and more within the expected range.

In conclusion, I can recommend the Lens Turbo II to anybody wanting to keep their compact APS-C camera while moving closer to the full frame look. You gain close to a full f-stop of light, a much wider field of view and it is by far cheaper than buying a full frame body. But it is wise to combine the LT with lenses that perform well on full frame cameras: The outer parts of the image circle you normally wouldn’t see in an APS-C image will of course become visible with the LT. And if the lens offers mediocre corner performance on full frame, it will do the same on the Lens Turbo.

 

Test charts

The following images are pixel-level crops from the test chart. They may appear scaled in your browser window. Click on them to view the crops in full size and cycle through them easily. For more info on the test setup, visit the details page.

 

Overview

Test chart overview

(Cropped areas marked in orange)

 

f/1.4 & f/1.2 (effective f/1.0 & f/0.9)

Three Rokkors with Zhongyi Lens Turbo II @ f/1.4

 

f/2.0 (effective f/1.4)

Three Rokkors with Zhongyi Lens Turbo II @ f/2.0

 

f/2.8 (effective f/2)

Three Rokkors with Zhongyi Lens Turbo II @ f/2.8

 

f/4.0 (effective f/2.8)

Three Rokkors with Zhongyi Lens Turbo II @ f/4.0

 

f/5.6 (effective f/4)

Three Rokkors with Zhongyi Lens Turbo II @ f/5.6

 

f/8.0 (effective f/5.6)

Three Rokkors with Zhongyi Lens Turbo II @ f/8.0

 

f/11 (effective f/8)

Three Rokkors with Zhongyi Lens Turbo II @ f/11

 

f/16 (effective f/11)

Three Rokkors with Zhongyi Lens Turbo II @ f/16

 


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2 thoughts on “Review: Zhongyi Lens Turbo II with Minolta MC 58 mm & MD 50 mm lenses

  • Antoine

    There are 2 further comparisons which would be good to help make a decision:
    1 – versus FF camera
    – How does the lens with turbo on APS-c performs versus the same lens on a Full frame body (circa same focal length +7%)
    2 – APS-c versus wider angle lens without turbo
    Biggest drawback for APS-c use of Vintage wide angle lenses: a 17mm gives you a 25.5mm eq FF with limited light (f 3.5 or f 4.0), a 20 mm gives you a 30 mm (f 2.8)… The lens turbo gives you real wide angle (17mm gives you 18mm eq FF 20mm gives you 21.5…). related question is
    – How does the 50mm lens Plus turbo perform against a 35mm without turbo (both giving circa 53 mm eq FF focal length). One can note already that, in terms of light the 50 mm 1.4 +turbo (real aperture 1.55) is lighter than say the MD 35mm 1.8 (real aperture 2.2 ), e.g a full stop (2 full stops versus the 35mm2.8)
    – How does a 35mm f 1.8 (or 2.8) with turbo performs against a 24mm f 2.8 without turbo
    etc…