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PostPosted: Wed Aug 13, 2008 8:25 pm 
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I finally decided to take the plunge and get myself a teleconverter. My choice went to the Kenko as this is the cheapest quality converter and one that can drive Nikon AF-lenses without built-in motor as it puts the slotted screw-drive from the body through to the lens. With the current Nikon converters you can only AF when the lens is of the AF-S/HSM type :cry:

It is a 4 lens/4groups design of 18mm length and 110g weight, so it's small and light enough to have it always with you. It comes with a small pouch and a front- and back-end cap.
It has a 1.5x magnification which is sort of funny, as most other manufacturers make a 1.4x variant. Now, what does this mean: Well, the Kenko gives you just a little more magnification but also a little more loss of light, as a 1.4x converter losses effectively 1 stop and a 1.5x converter is around 1,2 stops.

Initial impressions and results:
- the thing seems sturdy, although many people complain about the plastic body. But it has metal mounts.
- It focusses totally ok with my Sigma 400/5.6 which is quite astonishing as everybody was expecting the Nikon AF-system to fail at an effective aperture of below f/8.0 :D
- so this gives me a 600mm f/8.5 lens which is the equivalent of a 900mm lens on a film body. Whoohoo!
- initial sharpness with my Nikon 180/2.8 seems very good, with the SIgma 400/5.6 slightly unsatisfactory, but I have to eliminate shake from the comparison, which is not easy when handholding.
- contrast and color seems to be unperturbed, but I didn't shoot in very challenging contra-light conditions.

So far so good. Expect more insights to come from my extensive testing of this device. What I'm specifically after is an answer to the following qestion:
Is it better to blow up the magnification with a converter than with postprocessing?

So watch this space for the definitive answer to this decisive question!

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Last edited by Thomas on Fri Sep 19, 2008 9:49 pm, edited 2 times in total.

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PostPosted: Wed Aug 13, 2008 8:59 pm 
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Ah, I forgot. The following is also clear:
The Kenko teleconverter does not change the EXIF data and I assume it is totally transparent to the camera body too!
That means: The lens is still recorded at it's original values. The 180/2.8 is still a 180/2.8* for the camera and software although it effectively behaves like a 270/4.2.
So there is NO WAY for me to find out from the EXIF data whether I had the teleconverter on or not :( Not even CaptureNX or KUSO EXIF viewer can find out.
I briefly wondered if this has some consequences somewhere, but I couldn't think of any :?

-----------
Btw.: You know that every teleconverter will blow up any optical error of the lens in front of it by the exact same amount as it increases the magnification? It's just like you're looking with a loupe at/through the main lens

-----------
* I had just one strange occurrence of a total black-out of the EXIF-communication where the 180+converter combo was registered as a 500mm f/8.0 (!) lens :?
Still the image was perfectly exposed :)
I will watch-out whether these strange things happens more often.

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Last edited by Thomas on Fri Sep 19, 2008 9:48 pm, edited 2 times in total.

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PostPosted: Sat Aug 16, 2008 3:04 pm 
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Back from the testing-front I can report that the total black-out of the EXIF-communication was due to less than shiny contacts on my (t)rusty old 180/2.8 Nikkor. I had a lot of black-outs today, then cleaned the contacts and everything was a-ok :D
As to the EXIF-data being recorded I found out that my micro-Nikkor 105/2.8 reported as 150mm focal length and f/4.2! So in this case either the lens, the teleconverter, or the body calculated the right data. I wonder which link in the chain it was :?: But with my other lenses I had no luck: They are reported with their original values. Even the Nikon 18-200 VR which is a "G"-lens just like the micro-Nikkor.
I just mounted about any of my lenses on the teleconverter. Really, I mean it: even the 10.5/2.8 fisheye or the 14-24/2.8 :shock:
I only found one lens not auto-focusing: The Sigma 100-300/4.0. The AF/HSM was oscillating around the point of sharpest focus but almost never stopped :( This was quite a surprise, as the aperture of said lens is large enough. Remember: the Sigma 400/5.6 worked ok?! Some oscillating ocurred also with the 14-24mm but that lens mostly found focus. I assume that the AS-F/HSM of both the 14-24 and 100-300 were optimized for their respective focal range and the TC just made the lens focus 1.5 times faster and thus made the control-loop over-react.

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Last edited by Thomas on Mon Aug 25, 2008 9:29 pm, edited 1 time in total.

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PostPosted: Sat Aug 16, 2008 3:52 pm 
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Next up are some test shots first with the Sigma 400/5.6 followed by the micro-Nikkor 105/2.8 VR. Both attached to the Kenko 1.5x teleconverter:

Sigma 400/5.6 at f/5.6 1/250sec x 1.5 = 600mm f/8.5 effectively, full frame:
Image
100% crop:
Image

micro-Nikkor 105/2.8 VR at f/3.0 1/250 sec x 1.5 = 157mm f/4.5 effectively, full frame:
Image
100% crop:
Image

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PostPosted: Sun Aug 17, 2008 1:01 pm 
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You can view my ever growing collection of shots with the Kenko TC here.
And some nice macro-shots behind the Sigma 300/4.0 APO macro there.

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PostPosted: Mon Aug 18, 2008 9:23 am 
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Warning: The Tamron 500mm f/8.0 mirror lens with Nikon-adaptall adapter does not mount on the Kenko TC for Nikon! Don't try it, there is some mechanical incompatibility.
So no cheapo 750mm f/12 lens for me :cry:

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PostPosted: Tue Aug 19, 2008 7:22 pm 
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This is an update from today's testing with the brand-new Sigma 150/2.8 EX APO macro HSM.
Same prob as with the Sigma 100-300 HSM: AF oscillates around the sharpest focus, but never stops :cry:
MF is totally ok with this combination.

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PostPosted: Sun Aug 24, 2008 9:56 am 
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Now here's some nice comparison of the micro-Nikkor 105/2.8 with and without converter. The test was done in conjunction with my review of the Sigma 150/2.8 macro here where the micro-Nikkor turned out to have excellent sharpness (just a tad less than the Sigma though). But the Sigma won't AF with the TC while the Nikkor does. So here are the results:

Center performance
105mm w/o TC......f/11.....................................f/8.0.....................................f/5.6.....................................f/4.0.....................................f/2.8:
Image Image Image Image Image
105mm with 1.5x TC:
Image Image Image Image

Corner performance
105mm w/o TC......f/11.....................................f/8.0.....................................f/5.6.....................................f/4.0.....................................f/2.8:
Image Image Image Image Image
105mm with 1.5x TC:
Image Image Image Image

Remember, there can be no f/2.8 shot with TC as the TC reduces the aperture of the combo by a little over one stop!

Now you can clearly see that even stoping the original lens down to f/8.0 (which results in an effective aperture of a little less than f/11 in combination with the TC) the IQ can never quite reach the IQ of the original lens at f/2.8. This is quite astonishing but is also testament to the fact that the micro-Nikkor is really sharp even wide open.

Still: IQ of the combo at f/11 center and corner is quite good ! And esp. in macro photography you often have to stop down even further to get enough dof with your subject. So if you need the longer reach, larger camera to subject distance, or the larger magnification (up to 1.5:1) you may well use the TC. But make sure AF works with your lens :!:

But the final question is as yet unanswered: How does the IQ compare between digitally zooming in 1.5x versus the results from using the 1.5x TC? I'll come back with an answer after the break :wink:

So stay tuned...

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Last edited by Thomas on Mon Aug 25, 2008 9:31 pm, edited 1 time in total.

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PostPosted: Sun Aug 24, 2008 12:15 pm 
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Hello, back again with the results from the "electronic tele-converter" (aka. post-processing).
To simplify my life I just did f/2.8, f/5.6 and f/11 shots and present 100%-crops from the center and the corner as with the other shots before. The rows marked "1.5x pp" were generated in post-processing, the rows marked "1.5x TC" were shot with the tele-converter.

Center performance
105mm with 1.5x pp......f/11.....................................f/5.6.....................................f/2.8:
Image Image Image
105mm with 1.5x TC:
Image.....Image

Corner performance
105mm with 1.5x pp......f/11.....................................f/5.6.....................................f/2.8:
Image Image Image
105mm with 1.5x TC:
Image.....Image

Well, that's really a surprise for me: The electronically magnified images are sharper than the image obtained with the TC! They look a little harsher too. But as you can see even the f/2.8 image magnified 1.5x in post-processing looks sharper than the f/5.6 image from the TC :shock:

This is a nice side-effect of electronic magnification (vs. TCs): It gives you effectively a 1 stop larger aperture (f/2.8 vs. f/4.0) and thus the ability to use a shorter shutter time, which reduces shake and motion-blur :)

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Last edited by Thomas on Sun Aug 24, 2008 7:38 pm, edited 1 time in total.

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PostPosted: Sun Aug 24, 2008 7:34 pm 
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I made a quick check to see whether the results also hold true for the Sigma 400/5.6. With this lens in front both ways to 1.5x magnification (with a TC or with p-p) seem to result in equal IQ. But you lose on stop and the ability to crop/re-frame your shot from a much larger base-image when using the TC. So my preferred way will be to use the p-p instead of a TC when I need even more magnification than the 400/5.6 originally can give.

So: With these results I've decided to give the TC back :cry:
Following are the "parting shots", a view from the front and one from the back showing the electrical contacts and the slotted AF drive-screw.

Image Image

Funny that the mounts are secured by 3 screws on the back (like all the Sigma lenses I know) and 4 screws on the front (like many larger Nikon lenses I know).

The "knob" on the right side is the lens release lever. It can be pulled back to dismount the lens from the TC. Oh and btw: The back-cap of the Kenko TC is just like every Nikon back-cap and mounts easily. The front-cap of the TC unfortunately needs to be mounted in one exact position (just like any cr*ppy Sigma cap) :?

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