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09-15-2008, 04:36 PM   #1
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Some Kenko 1.5x findings...

Just got the Kenko 1.5x and got some interesting results with it on my 50 f/1.4 and the new 28-105 f/3.2-4.5.

50 f/1.4 vs the 50 f/1.4+Kenko = lens with Kenko is sharper
28-105 @ 50mm vs 28-105 @ 50mm + Kenko = lens with Kenko is sharper
29-105 @ 105mm vs 28-105mm @ 105mm + Kenko = lens without Kekno is sharper

Is this consistent with others' use of teleconverters?
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09-15-2008, 05:42 PM   #2
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is the sharpness due to the increased magnification?
09-15-2008, 06:18 PM   #3
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OP response...maybe, or maybe not

QuoteOriginally posted by k100d Quote
is the sharpness due to the increased magnification?
Don't know, I was hoping somebody could tell me. It usually works the other way, doesn't it? Smaller digital images appear sharper than larger?
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09-15-2008, 06:49 PM   #4
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you gotta show some photos

09-15-2008, 06:55 PM   #5
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QuoteOriginally posted by FHPhotographer Quote
50 f/1.4 vs the 50 f/1.4+Kenko = lens with Kenko is sharper
That's basically impossible. The TC takes the image from the 50 and magnifies it. If it performed absolutely flawlessly, the resulting image would be larger and *exactly* as sharp, but it cannot add sharpness that was not already there. And in the real world, some sharpness is always lost.

Now, with any luck, the lens was producing more resolution than the sensor was capable of recording, and the lost sharpness won't really be noticed. That's part of why it's usually recommended to use a TC with the lens stopped down.
09-15-2008, 07:00 PM   #6
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QuoteOriginally posted by Marc Sabatella Quote
That's basically impossible. The TC takes the image from the 50 and magnifies it. If it performed absolutely flawlessly, the resulting image would be larger and *exactly* as sharp, but it cannot add sharpness that was not already there. And in the real world, some sharpness is always lost.

Now, with any luck, the lens was producing more resolution than the sensor was capable of recording, and the lost sharpness won't really be noticed. That's part of why it's usually recommended to use a TC with the lens stopped down.
unless it is a case of where for whatever reason TC+lens focused better.
09-15-2008, 07:48 PM   #7
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OP response ... Kenko images

QuoteOriginally posted by Marc Sabatella Quote
That's basically impossible. The TC takes the image from the 50 and magnifies it. If it performed absolutely flawlessly, the resulting image would be larger and *exactly* as sharp, but it cannot add sharpness that was not already there. And in the real world, some sharpness is always lost.

Now, with any luck, the lens was producing more resolution than the sensor was capable of recording, and the lost sharpness won't really be noticed. That's part of why it's usually recommended to use a TC with the lens stopped down.
If you say so, and maybe the Kenko'd image isn't really sharper but it certainly is as sharp... but here is the comparison, first the 50 f/1.4 at 100% crop



then the same lens from the same place with the Kenko 1.5 at a 100% crop

09-15-2008, 10:01 PM   #8
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You have any pics where the chair is the same size with teleconverter and without?

09-16-2008, 12:00 AM   #9
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doesn't look any sharper to me, just bigger...
09-16-2008, 03:19 AM   #10
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The example image does not look sharper to me, too. Basically a TC could improve lens performance, if the lens exhibits for example curvatore of field, which is compensated by a TC with curvatore of field of the opposite kind. This is possible, though I have never seen something like this in photographic lenses. Though this is a common concept, when computing lenses for scientific purposes.

Ben

Last edited by Ben_Edict; 09-16-2008 at 04:02 AM.
09-16-2008, 03:39 AM   #11
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Kenko teleconverter definitely makes the image sharper. Thank you for taking your time to show this.
09-16-2008, 05:25 AM   #12
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Maybe it is all about focusing: as camera focuses wide open and the wider it is the less contrast hits AF sensor- and as 1.5TC adds ca. 1 stop thus making Your 50/1.4 an 75/2.0 one- dimmer but more contrast to decide for AF system?
Best and happy shooting, JR

And BTW You cheated a bit: first shot is F4 and another with TC is F8 :-(
And we all know how it improves DOF and other visible (and not only) image parameters :-(

Last edited by Reps; 09-16-2008 at 05:28 AM. Reason: Something overlooked before posting...
09-16-2008, 03:35 PM   #13
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QuoteOriginally posted by FHPhotographer Quote
If you say so, and maybe the Kenko'd image isn't really sharper but it certainly is as sharp...
I'd agree it looks quite good. The 50/1.4 is a very sharp lens stopped down a bit as you have. It's definitely a case where it outresolves the sensor without the TC, meaning adding a TC might cost you *some* resolution, but you weren't getting the full resolution anyhow, so you don't notice much loss. A higher resolution sensor *might* expose more of a difference. But an easier test would be to perform this same test at f/1.4, where the resolution of the lens is nowhere near up to what the sensor can record, and adding a TC definitely makes it noticeably worse.

However, as another poster noted, you shot these at different apertures, which makes a lot of difference. Both because the lens probably is sharper at f/8 than f/4, but also because f/8 provides more DOF, making more of the scene in focus.

I'm a bit confused, though, because the EXIF shows apertures F/4 for the first and F/8 for the second - a two-stop difference - and shutter speeds of 1/750 for the first and 1/80 for the second - again a two-stop difference. The one with the second should really have needed 1/90 to get the same exposure because you lose a stop of light. And yet, the images don't look that different in exposure. They *do* look quite different in color, and this is consistent with my experience - images shot with that TC are less contrasty and have more of a bluish tinge.
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