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01-14-2010, 12:27 PM   #1
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A-50mm 1.7 + teleconverter?

I acquired a good condition A-50 f/1.7 in a Forum trade, and now I'm wondering if anybody has any experience with the Kenko 1.5x converter on this lens?

It's fast enough that losing a stop isn't an issue for me, but will the excellent center resolution hold up enough to justify the expense?

Brian

01-14-2010, 12:41 PM   #2
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I would say yes, based on this test:

jr-worldwi.de: Photography: Technic

The A50/1.7 is sharper or equal to the A50/1.4. The Kenko is probably equal to or better than the Vivitar MFTC just by being 1.5x instead of 2x. It's going to depend on your definition of "hold up enough".
01-14-2010, 04:58 PM   #3
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QuoteOriginally posted by FHPhotographer Quote
I acquired a good condition A-50 f/1.7 in a Forum trade, and now I'm wondering if anybody has any experience with the Kenko 1.5x converter on this lens?

It's fast enough that losing a stop isn't an issue for me, but will the excellent center resolution hold up enough to justify the expense?
I've got that lens and that TC. Tried to like it for a while, but gave up. I could get decent pictures of my bookshelf sometimes, but in real life, everything just had this soft fuzzy glow when shooting wide open or anywhere close to it. In order to get decent results, I had to stop it down to the point where the 50-200 was faster and had AF - and the 50 + TC still never outperformed the 50-200.
01-15-2010, 11:14 AM   #4
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Marc, so at 75mm the 50+Kenko was equal to the 50-200 @75mm? Across the frame or was the center better than the edges? I ask because I envision using it for specific kinds of shots where I'd only use the center 50% or so, so edge softness wouldn't matter as much, and a friend has a 50-200 I can borrow to try that FL out. Just trying to save $400 or so it would cost for a DA-70,
Brian

01-15-2010, 02:41 PM   #5
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No, even at the equivalent of f/4.5 (the best the 50-200 can actually do at that focal length), the DA50-200 was a better everywhere in the frame by as large a margin as I've seen in any lens comparison I've ever made. The 50+TC combo sort of eventaully caught up by f/8 or so, but I didn't bother doing much in the way of controlled tests at these apertures because I wasn't interested in that combo except for the possibility of getting wider apertures than the 50-200 was capable of. It wasn't sharpness per se that was the problem, but the "soft fuzzy glow" I referred to above (*extreme* CA, I guess) that just totally put that thought out of my mind. With some of my longer focal lengths lenses, the Kenko TC can come close to or slightly exceed the performance I get by simply cropping. With the 50, it just isn't close. Cropping is a *way* better way of getting the 75mm field of view. And if you see yourslef cropping even further, $the same mney as the TC will get you an M100/2.8 that will absolutely *blow away* the 50+TC combo. If you *don't* want to be cropping down from that field of view, I think a better use of the money would be to put it toward an M85/2.

Again, on shots of my bookshelf, it looked like it had potential. I think that's because I wasn't dealing with the sort of lighting in which CA becomes most obvious. It's shots of real world three dimensional subjects - light subjects against dark backgrounds, or vice versa - where there is just no getting around the poor IQ of this combo.
01-15-2010, 08:51 PM   #6
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Marc, thanks, that's what I needed to know. And I'll check out the M100/2.8,
Brian
01-15-2010, 11:17 PM   #7
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I apologize for guessing without owning any of the items mentioned.
01-16-2010, 11:38 AM   #8
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Dave, no harm no foul, most of us are guessing most of the time anyway,
Brian

01-16-2010, 04:31 PM   #9
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Well, I wouldn't completely discount those promising pictures I took of my bookshelf. I'm sure in some conditions, you can get decent images. I just decided it wasn't worth the trouble.
01-17-2010, 01:32 PM   #10
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I've used the SMC-M and -A 50/1.7's and 2.0's with TC's and extension tubes for years and never found them lacking for general purposes although if you're planning on using it for critical, flat-field reproduction you might consider a dedicated macro lens or a lens reversing adapter for that lens. I'd say any degradation in image quality was attributable to the nature of the particular TC being used (with some being better than others as expected).

At the moment, I've got an auto Vivitar 2X Variable macro TC on an A50/1.7 and have also had good results with it using a Tamron 1.4x Pz-AF MC4 for flowers and such.

I'd consider my Tamron SP 90/2.5 macro to be more consistently sharp throughout the full range of apertures but the SMC 50's + TC or rings work just fine for typical close-ups and are more compact, versatile and weigh less. A Tokina EL 2X TC sans optics preserves the A-functions and makes a neat 26mm extension tube.

H2
01-18-2010, 12:18 AM   #11
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Here is an alternative configuration for using the A 50/1.7 for extreme macro - 2.7:1 magnification. A 50/1.7 ($25), Promaster 135/2.8 ($10), Sunpak 411 flash ($16), 49mm to 52mm reverse macro ring ($6.5).

A silverfish taken with flash at 1/32 power and A 50/1.7 reversed mounted on the 135/2.8 (set at f22), front of lens about 40mm from subject - hand held.


The second one is taken with the A 35-70mm/3.5-4.5 (set at 70mm) reversed mounted on the 135/2.8.
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01-18-2010, 05:47 AM   #12
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My experience is not exactly the same lens+teleconveter combo, but I had FA 50mm f/1.4 + Tamron 1.4x Pz-AF MC4 combo producing images with "soft fuzzy glow" as Marc mentioned. I tried to stop down from F/1.4, F/2.8, F/4.5, but the fuzzy glow didn't go away and I stopped trying.

Until yesterday I met one of the Forum users in person, I had thought either 1) a TC in general does not work with wide~normal lenses or 2) my TC is a faulty one. But he said he had the same issue with FA 50mm and the Tamron TC. He also told me that he had a rare Pentax "macro" teleconverter which works wonderfully with his FA 50mm and FA* 24mm. I don't remember what this teleconverter was, but it was for sure not a macro extension tube.

So I assume you can use a teleconverter with A-50 f/1.7 and get decent results as long as you can identify a TC which works fine with it. Sorry, I am not really helping here. But wanted to share this FA 50mm + Tamron 1.4x experience from two users.
01-18-2010, 06:26 AM   #13
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QuoteOriginally posted by PentaJP Quote
So I assume you can use a teleconverter with A-50 f/1.7 and get decent results as long as you can identify a TC which works fine with it. Sorry, I am not really helping here.
Well, that is the general picture anyway. One lens+tc combo may work and another one not.

So, it is of interest but not of relevance to report the experience with one combo, if another one is under discussion. Even slight variations in the lens design (like a couple of millimeters more or less distance of the rear element to the mount) will visibly influence the performance of a tc combination.

In the film days there were several genral rules repeated all over about the use of tcs:
  • never use a tc with a wide angle lens. Firstly, it doesn't make much sense, as one would have usually covered the resulting fl anyway with another lens. Secondly, wide angle lenses often are not telecentric and that's bad for a tc.
  • never use a tc with slow zooms or consumer grade zooms - the image degradation will be too obvious and anyway the resulting combination is too slow to be useful, except in rare circumstances.
  • cheap tcs usually will not provide high IQ.
  • tcs are meant to be combined with the longest lens in your portfolio, to give that extra reach.
  • and then there are some (more or less) dedicated tcs, which work well with one or a few select lenses (like the Sigma tcs, the old Vivitar tc for the 70-210/3.8 zoom or the Pentax L tcs)

In my own experience, I feel, this rules generally true, though some exceptions may apply in real life.

Ben
01-18-2010, 10:10 AM   #14
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QuoteOriginally posted by Marc Sabatella Quote
Well, I wouldn't completely discount those promising pictures I took of my bookshelf. I'm sure in some conditions, you can get decent images. I just decided it wasn't worth the trouble.
Did you take those pictures outside without a hood?

.
01-18-2010, 02:47 PM   #15
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QuoteOriginally posted by Ben_Edict Quote
In the film days there were several genral rules repeated all over about the use of tcs:
  • never use a tc with a wide angle lens. Firstly, it doesn't make much sense, as one would have usually covered the resulting fl anyway with another lens. Secondly, wide angle lenses often are not telecentric and that's bad for a tc.
  • never use a tc with slow zooms or consumer grade zooms - the image degradation will be too obvious and anyway the resulting combination is too slow to be useful, except in rare circumstances.
  • cheap tcs usually will not provide high IQ.
  • tcs are meant to be combined with the longest lens in your portfolio, to give that extra reach.
  • and then there are some (more or less) dedicated tcs, which work well with one or a few select lenses (like the Sigma tcs, the old Vivitar tc for the 70-210/3.8 zoom or the Pentax L tcs)
Thank you, Ben. I am glad to know these tips. I haven't heard about them as I am relatively new to photography and SLR cameras. With a FA 50mm F/1.4 and a Tamron 1.4x TC, I had thought I could get a 70mm F/2 setup so that I could pass FA 77mm and DA 70mm. But certainly did not work that way.
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