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10-20-2017, 03:14 AM - 11 Likes   #1
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0.666 Devil's Speed Booster for Pentax Q

The 0.666 Devil's Speed Booster is a focal reducer specially crafted for the Pentax Q series. It has the unique ability to reduce the focal length of any lens mounted by half, and at the same time to increase its aperture by two stops. Other focal reducers for APS-C or M4/3 cameras only go to x0.71 and allow to increase the aperture by 1 stop.

The very short register of the Pentax Q mount allowed Metabones' Brian Caldwell to create this pretty extreme focal reducer. To maintain acceptable image quality, the maximum aperture had to be limited to F/0.666. Therefore, any lens with an aperture brighter than F/1.3 will have its aperture limited to F/0.666 when used with this focal reducer (hence its name).

For the moment, the Devil's Speed Booster (DSB) is only available in Nikon F mount, but a Pentax K version has also been announced.

The question is: does this clever contraption really work and is it any good? To try to answer this, I used a Pentax Q-S1 with my old Nikkor-S 55mm F/1.2 and did two series of test shots of a ColorChecker chart taken from about 3 meters. The first one was made with the lens on a plain Nikon to Pentax Q adapter and the second one with the lens on the DSB. Here are the JPEGs straight from the camera (you can click on the pictures to display them full size).

55mm F/1.2:


At F/1.2 this old lens is not very sharp and exhibits lots of aberrations. The field curvature is very strong.

55mm F/2.0:


It's already much better.

55mm F/2.8:


55mm F/4.0:


55mm F/5.6:


55mm F/8.0:


At F/8.0, the image is good but we begin to see the effects of diffraction on the small sensor of the Q-S1.

Now, let's try the same lens with the DSB, First, wide open, 27.5mm F/0.666:


No miracle here, there are still plenty of aberrations. But I have two remarks: first, image quality wide open is not worse than without the DSB (no added vignetting), it's even a tiny bit better from a sharpness point of view, and secondly, the aperture is really F/0.666. If you look at the EXIF of the picture taken wide open without the DSB, the speed is 1/2500s for an aperture of F/1.2. With the DSB, the speed is 1/8000s (and the picture is a bit overexposed because 1/8000s is the top speed of the Pentax Q-S1), which means there is a gain of almost two stops, as per the specs.

27.5mm F/1.0:


Image quality begins to increase.

27.5mm F/1.4:


F/1.4 is already quite good (even though there is still some chromatism).

27.5mm F/2.0:


27.5mm F/2.8:


27.5mm F/4.0:


At F/4.0 the image is sharp over the whole field and we are still below the diffraction zone of the small sensor. There is added lateral chromatic aberration though.

Here are some pictures taken at F/1.4 with the DSB (F/2.8 on the aperture ring of the lens):



Check the part of the blossom that is in focus and you will see that the sharpness is impressive at F/1.4!







The bokeh is not bad either...













And to conclude, two pictures taken at infinity at F/4.0 (F/8.0 on the aperture ring of the lens); don't forget that these are JPEGs straight from the camera with no post-processing whatsoever:





As a conclusion, I think the DSB is an interesting product. It makes vintage SLR lenses more usable on Q series cameras because it reduces greatly the crop factor (from 5.6 to 2.8 on the Q and Q10; from 4.6 to 2.3 on the Q7 and Q-S1) and also because it helps keeping the aperture below the diffraction zone. The DSB doesn't impact significantly vignetting (which is very low anyway because we only use the center part of the image circle of the lens) or sharpness. It does add a significant amount of lateral chromatic aberration though. As for shooting at F/0.666, it can be done in a pinch, but it will require quite a lot of post processing. One way to avoid having to deal with color shifts and chromatism is to convert your pictures to black and white.

Cheers!

Abbazz

10-20-2017, 03:48 AM   #2
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thanks for the opportunity to see what its like,NOW you can send it back to Hell!
10-20-2017, 04:14 AM   #3
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QuoteOriginally posted by Abbazz Quote
It does add a significant amount of lateral chromatic aberration though.
But this can be easily fixed if you shoot raw, right? So this tool is actually pretty good, since the Q lineup doesn't have any super fast lenses
10-20-2017, 04:25 AM   #4
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QuoteOriginally posted by Na Horuk Quote
But this can be easily fixed if you shoot raw, right? So this tool is actually pretty good, since the Q lineup doesn't have any super fast lenses
Yes, the lateral chromatic aberration can be fixed very easily with most image editors. Even the ugly purple fringing can be fixed on most of the pictures. Converting to black and white is always possible for the desperate cases!

Cheers!

Abbazz

10-20-2017, 06:52 AM   #5
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Thank you Abbazz for a great review. Much more indepth than I was expecting. The DSB looks darn good! I will study your excellent comparison photos in greater detail. This looks like a very useable product on the Q! Appreciate all the work you put into this.
Thanks again,
barondla

This review also needs to be posted on the PentaxForums front page! Maximum exposure for the Q, DSB, and Abbazz!
10-20-2017, 07:13 AM   #6
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Thanks for the quick review. That actually looks pretty good!
10-20-2017, 10:00 AM   #7
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Thanks for the positive write-up. I look forward to the release of the K-mount version!
10-20-2017, 11:13 AM   #8
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Thanks Abbazz, would love to see the opportunities here for portrait work.

If my math is correct shooting the above example at F1.0 (which looks passable with PP work) would be very roughly equivalent to shooting an 85mm@F2.8 on APS-C in terms of FOV/DOF(background obliteration).

10-20-2017, 11:32 AM - 1 Like   #9
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QuoteOriginally posted by barondla Quote
Thank you Abbazz for a great review. Much more indepth than I was expecting. The DSB looks darn good! I will study your excellent comparison photos in greater detail. This looks like a very useable product on the Q! Appreciate all the work you put into this.
Thanks again,
barondla

This review also needs to be posted on the PentaxForums front page! Maximum exposure for the Q, DSB, and Abbazz!
Thank you for the kind words, barondla.

Cheers!

Abbazz

---------- Post added 20th Oct 2017 at 20:46 ----------

QuoteOriginally posted by ruggiex Quote
Thanks for the quick review. That actually looks pretty good!
You're welcome. I must admit that I have been surprised by the image quality of this focal reducer, when I read on another forum that even Brian Caldwell, its creator, seemed to consider it as some kind of weird prototype released mainly for the collectors:

QuoteQuote:
The Q666 was mainly just a fun project meant to explore how far the Speed Booster idea can be pushed. Its really hard to get down to 0.5x combined with faster-than-f/0.7 speed, but the Pentax Q offered a chance to do it. I suspect the Q666 is destined to be mainly a collector's item. Accordingly, you won't get mine until you pry it from my cold dead hands!
Cheers!

Abbazz

---------- Post added 20th Oct 2017 at 20:57 ----------

QuoteOriginally posted by CarlG Quote
Thanks for the positive write-up. I look forward to the release of the K-mount version!
My pleasure! I sure hope the DSB will be released in K-mount soon. It's a shame the K-mount version was not released first, because it is of greater interest for us Pentaxians. And those old Nikkor lenses can be mounted on a Pentax K bayonet without any adapter but the reverse is not true.

Cheers,

Abbazz

---------- Post added 20th Oct 2017 at 21:15 ----------

QuoteOriginally posted by caliscouser Quote
Thanks Abbazz, would love to see the opportunities here for portrait work.
You're welcome. I will try to find a model and shoot a few portraits.

QuoteOriginally posted by caliscouser Quote
If my math is correct shooting the above example at F1.0 (which looks passable with PP work) would be very roughly equivalent to shooting an 85mm@F2.8 on APS-C in terms of FOV/DOF(background obliteration).
I am not very keen on this "equivalence" stuff, which I find very confusing for newbies, but I think a 27.5mm f/1.0 lens on an 1/1.7" sensor would rather be something like a 127mm f/2.3 on a 24x36 sensor and an 84mm f/1.5 lens on an APS-C sensor.

Cheers!

Abbazz

Last edited by Abbazz; 10-20-2017 at 12:17 PM.
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