Monday, September 26, 2011

Tokina 50-135 f/2.8 AT-X Pro DX: Bokeh Comparison

The pace of life has picked up after the summer holidays, which unfortunately has meant less time for shooting and posting. While the full review of the Tokina 50-135 slowly makes its way down the pipeline, we'll do a quick review in the form of the following bokeh comparison.

I've lined up the following, all at 50mm.

  • Nikon 50 f/1.4 AF-D, 
  • Tamron SP AF 17-50 f/2.8 XR Di II, 
  • Tokina, all at 50-135 AT-X

Other than the fact that they cover 50mm, these are three lens with three completely different uses. On a DX camera, the Nikon is the best pure portrait lens, the Tamron is an all-purpose normal-zoom, and the Tokina is a professional-grade portrait zoom. The following test shots are not so much an indication of the quality of the lenses, but an illustration of how differences in intended lens purpose show up in shots. All three shots used the same indicated focal length, same distance to subject and same aperture. Key things to look for are the quality of rendition of the foreground subject verses the texture and appearance of the background subject. (Also try to guess where I went for vacation over the summer...)


Big caveat: Because I am currently using a Nikon D80, I don't have the focus fine-tune function present on newer cameras like the Nikon D7000. Differences in subject sharpness will have more to do with focus calibration than they will with the actual design of the lens. However, for our purposes, the impact that will have on background rendition will be minimal.


Nikon 50mm f/1.4:
ISO 100, f/2.8, 1/1600s, Matrix Meter
This will be a bit familiar if you've read my post comparing the Nikon 50mm versus the Tamron 17-50. The Nikon has the best background rendition out of all three lenses here. It has a reputation for giving busy backgrounds, but that's only true at wider apertures. From f/2.0 to /2.8, the bokeh is fairly smooth and consistent.


Tamron 17-50mm f/2.8:
ISO 100, f/2.8, 1/1250s, Matrix Meter
This part will be a bit unfamiliar.  In the last comparison between the Nikon and the Tamron, I normalized the pictures in order to concentrate solely on bokeh. This time I've left the output as-is. You'll notice by the shutter speed that the clouds rolled by a bit in between shots, but as you can see, my Nikon D80 rendered the pictures a bit darker with this lens than it did with the nifty-fifty. This is fairly normal, as I have yet to see two lenses meter exactly the same way on the same camera body. However, you'll notice also that Hello-Kitty also looks a tad bit smaller in this frame. There are two reasons for this. The first is that the markings on lens are often approximations of the true optical properties... your f/2.8 lens may in fact be f/2.9, your 200m lens may only go to 195mm... yes the manufacturers will round the number in favor of their marketing departments. What did you expect?

However, there is a second and less sinister reason, which is the phenomenon of 'focus breathing'. By convention, a lens' maximum focal length is defined when it is focused at infinity. When focusing on nearer subjects, the effective focal length my not decrease at a linear rate.. more often than not it decreases faster than what you think it would be. The upshot is that the subject looks smaller than what you think it would be at close distances. Some lenses do this more than others. The Nikon 18-200 is especially notorious for this... at close range and maximum zoom, it barely beats the 'shorter' 18-135DX  in magnifying objects. 


Of the three lenses, the bokeh for the Tamron is easily the harshest. I've seen this story enough times to seriously think about avoiding trees in the background when using this lens, but in real world terms, it's also about as sharp as the Nikon at this aperture. Most lenses are at their weakest when shot at their widest aperture, but the Tamron is still very sharp within it's plane of focus.. it's a lens you don't have to think twice about for opening up. Watch out for corner vignetting, though, it s stronger than normal at max aperture.


Tokina 50-135mm f/2.8: 
ISO 100, f/2.8 1/1250s, Matrix Meter
Here the bokeh is in between the Tamon and the Nikon. Not as creamy as the Nikon, but not as harsh and fringe-y as the Tamron. At 50mm and the same distance, you'll notice that the Hello-Kitty is rendered slightly larger than with the Nikon 50mm. The metering and colour rendition are more Nikon-like than the Tamron. However, the Tokina had the longest minimum focus distance out of all three lenses. The Tamron has the closest, at just under a foot. The Tokina has a minimum distance of about a meter, which is moot because it's intended use is for medium distance subjects.

Conclusion

All three of these lens are very sharp and have great image quality for their intended purposes. However, despite being a jack-of-all-trades, the Tamron 17-50 isn't as good at portrait distances as the other two lenses. This comes down to how the lens is designed for a specific purpose... and as a reminder, the Nikon 17-55, costing much much more money, tends to give similar results. The Tamron is still the lens that stays on my camera all of the time, but perhaps you've heard it said that pros tend to not use normal zooms as much as amateurs. This is why. If bokeh were a priority, the 85mmAF lenses are better. If width were important, the current generation of ultrawides are better. Same goes with low-light... primes are better still.

The Nikon 50AF-D still makes a case for itself. Even though it's a lens that doesn't get used often, many people are reluctance to  part with it. My web stats tell me posts related to this lens draw more traffic than any other lens or camera that I've touched upon, which should give you an idea of how popular this venerable lens still is. 

The Tokina also does well. It's fantastically sharp, and as will be demonstrated in the full lens review, the bokeh only gets better as you zoom out. It's a tad bit weak opened up all the way at max zoom, but other than that, it's an optical gem. 50 to 135mm sounds like a limited zoom range, but it's the equivalent of 70-200 on full frame, an equivalent focal length that has been popular with camera makers for some decades now, and because it doesn't try to do to much, the Tokina is very good at what it does. And you'll be reading a lot about me raving about the build quality when the review finally sees the light of day.

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