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06-23-2013, 08:49 PM   #1
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Evaluating the Lens Turbo

As many of you are probably aware, there is a new full frame lens to APSC mount adapter called the "Lens Turbo." This was released after the much anticipated Metabones Speed Booster. The main advantages of the Lens Turbo are that it costs under $200 and that it comes in a native K mount. I bought one one ebay and took a few test shots. Below are links to the three shots I took. They are available at full size on flickr. Only post processing was a bit of exposure adjustment, white balance fixing, and watermarking. All shots were taken with a Rokinon 85mm lens at F/1.4.

The first shot is the baseline shot with a standard PK to E-mount adapter. This is a dumb adapter with no glass. It only serves to adapt to the proper flange depth.

Original


The second shot shows the affect on depth of field and field of view when adding the Lens Turbo. For reference, the cards are spaced about 1 inch between them relative to the camera.

Lens Turbo


The final shot is also using the Lens Turbo, but this time the camera is closer to give a similar composition to the first shot.

Lens Turbo Recomposed

My observations:
The Lens Turbo maintains the central sharpness quite well. It will allow you to compose your shot from a closer distance and get a shallower depth of field. So it does what it's intended to.

Using the Lens Turbo will gather more overall light to the sensor.
Adding Lens Turbo caused camera to meter as +0.3EV vs the regular adapter in a similarly composed shot. This of course depends on how much your lens vignettes. But if you were hoping to use this specifically for it's light gathering ability, you will be let down. In other less rigorous testing, I have seen it register as +2/3 EV when adding the lens turbo. But never a full stop.

The same lens has a closer minimum focus distance with the Lens Turbo vs regular adapter.
I focused the lens with the Lens Turbo, then switched to the regular adapter. The image was then back-focused. So with the lens set to the same focus distance, the Lens Turbo actually makes it focus closer than the markings. So you should be able to focus at closer than the minimum focusing distance without the Lens Turbo.

Adding the Lens Turbo causes a shift in the distribution of focus zone in terms of in front vs behind the plane of sharpest focus.
When the Lens Turbo is used, more of the in-focus range is in front of plane of sharpest focus. For my tests, without the Lens Turbo I would estimate that the focus distribution is close to 50/50 in back of versus in front of the plane of sharpest focus. But When using the Lens Turbo, there is a noticable shift of this ratio where there is distinctly more of the acceptable focus range in front of the plane of sharpest focus versus behind it.

06-23-2013, 09:14 PM   #2
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Nice tidy little review thanks !
I had been wondering how it would good.
cheers
Pete
06-23-2013, 09:26 PM   #3
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Thanks for this!

You can definitely see the difference in DOF between the same framed images. At first I thought the Lens Turbo was adding quite a bit of CA but looking closely it might just be exaggerating CA already from the lens because of less DOF. Maybe a little less contrast though.

Overall its pretty interesting. Would be interesting to see what it was like across the frame (with subjects lined up with the focal plane).

P.S. Like your card holders.
06-23-2013, 11:34 PM   #4
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Man, Id love to use my legacy glass with the lens turbo on an APS-C camera. But I really dislike the NEX interface.I am spoiled by the K-5 layout / interface.

Thanks for your findings though. 85/1.4 + turbo lens is a really interesting combination. Some field samples would be really appreciated.

06-23-2013, 11:54 PM   #5
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QuoteOriginally posted by carrrlangas Quote
Man, Id love to use my legacy glass with the lens turbo on an APS-C camera. But I really dislike the NEX interface.I am spoiled by the K-5 layout / interface.

Thanks for your findings though. 85/1.4 + turbo lens is a really interesting combination. Some field samples would be really appreciated.
I haven't used this combination much yet. But I did take this one the other day.

06-24-2013, 12:01 AM   #6
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Perhaps there is some motion blur but it looks really good. Might there be some vignetting?
06-24-2013, 12:09 AM   #7
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QuoteOriginally posted by carrrlangas Quote
Perhaps there is some motion blur but it looks really good. Might there be some vignetting?
I don't think there's any motion blur. I have a 100% crop in my Album here if you are interested.

Link

I did add a slight vignette in post.

06-24-2013, 12:21 AM   #8
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True. Its just the DoF is so thin... The adapter seems to work really good despite the possible difference between f-stop and t-stop you remarked.
06-27-2013, 12:22 PM   #9
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QuoteOriginally posted by devorama Quote
I don't think there's any motion blur. I have a 100% crop in my Album here if you are interested.

Link

I did add a slight vignette in post.


Does this converter change the minimum focus distance or the infinity focus?
06-27-2013, 01:05 PM   #10
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QuoteOriginally posted by konraDarnok Quote
Does this converter change the minimum focus distance or the infinity focus?
Check the second to last paragraph in my first post. I explain how the minimum focus distance is affected. I haven't checked infinity focus. Maybe I can do that later.
06-27-2013, 09:53 PM   #11
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Well I don't have a good infinity focus target handy right now, but I just tested my 70-300mm Tamron lens with it. Both adapters seem to get sharpest focus on my indoor target at the same mark on the lens. This is at about 15 meters. So perhaps the difference in focus distance is more at the close end of the focus range.
06-27-2013, 09:59 PM   #12
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Hmm... This sounds confusing to me.. Are you meaning to state that you are able to focus "closer" due to the wider FOV because to obtain the same framing at x1.1(w/ LT) compared to x1.5(APS-C)?
06-27-2013, 11:07 PM   #13
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QuoteOriginally posted by SyncGuy Quote
Hmm... This sounds confusing to me.. Are you meaning to state that you are able to focus "closer" due to the wider FOV because to obtain the same framing at x1.1(w/ LT) compared to x1.5(APS-C)?
No. I'm not referring to anything to do with crop factor or the field of view. I'm saying that with the Lens Turbo vs. a dumb adapter, you can focus at a closer distance to the subject. Not by a lot, but it's there. So if you turn the lens to the minimum focus distance and your subject is in focus with the dumb adapter, if you then switch the the Lens Turbo it will be out of focus. You'd have to move closer to the subject to get it back in focus.
06-28-2013, 11:20 AM   #14
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QuoteOriginally posted by devorama Quote
No. I'm not referring to anything to do with crop factor or the field of view. I'm saying that with the Lens Turbo vs. a dumb adapter, you can focus at a closer distance to the subject. Not by a lot, but it's there. So if you turn the lens to the minimum focus distance and your subject is in focus with the dumb adapter, if you then switch the the Lens Turbo it will be out of focus. You'd have to move closer to the subject to get it back in focus.
Oh.... That's interesting!
Thanks for the clarification!
07-22-2013, 09:22 PM   #15
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Perhaps Pentax can release one of these to convert Pentax FF lenses to function at their intended FOV on their own APS-C cameras. People might be less interested in a Pentax FF for the moment if that were the case.
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