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03-15-2013, 12:44 PM   #1
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Pentax F 100-300/4.5-5.6 vs Pentax 50-135/2.8 with a teleconverter

I have a Pentax 50-135/2.8 lens. It's the best lens I have ever owned and I like it a lot! However I always wanted to have a longer telephoto lens.
Reading some threads on teleconverters I came to a conclusion that it's better to buy a budget telephoto lens than to shoot with a zoom lens+teleconverter kit.
So I bought a used Pentax F 100-300/4.5-5.6 lens. Looking at its rather solid build quality I had been thinking that the lens is underestimated. Well, I guess I had been wrong. Or maybe I got not a good copy of it.
I compared an upscaled image shot by 50-135/2.8 at 135mm and f5.6 to the image shot by 100-300/4.5-5.6 at 300mm and f5.6. I found almost no difference at all! Actually, I consider the upscaled image from the DA* lens even better (it has better colour rendition)! Stopping down the 100-300 lens almost doesn't make any better. Only after stopping to f14-16 there comes a visible improvement.
Here is a proof.
At first, there is a photograph shot by 50-135/2.8 - http://club.foto.ru/gallery/images/photo/2013/03/15/2125888.jpg
Then goes a comparison of the upscaled photograph shot by 50-135/2.8 and crops from 100-300/4.5-5.6 at different f-stops - http://club.foto.ru/gallery/images/photo/2013/03/15/2125898.jpg

I would like to ask, whether a cheap 1.4x-2.0x teleconverter with a 50-135/2.8 really won't be any better than a 100-300/4.5-5.6?
And a question to 55-300 owners: does the perfomance of your lens at 300 mm look similar to 100-300 when wide open?

P.S. Here is also the original image from 50-135/2.8 that I tweaked a little in Lightroom - http://club.foto.ru/gallery/images/photo/2013/03/15/2125899.jpg


Last edited by skyer; 03-15-2013 at 12:51 PM.
03-15-2013, 12:56 PM   #2
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Are you absolutely sure that the 300mm picture is focused correctly? A picture at f/16 shouldn't look better than one at f/9 unless stopping down further has expanded the in-focus area to include your subject.

I don't have the Pentax, but I do have two Tamron tele-zooms, the most recent 70-300 and an older 90-300. They both look pretty bleary at 300mm. If they're not quite in focus, it looks pretty much like what you've posted.

Concerning teleconverters, I've only ever used one once, and I was really disappointed, but you might as well try one and make your own opinion. People are practically giving those things away all over the internet.
03-15-2013, 09:23 PM   #3
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Because the DA* 50-135/2.8 has SDM, a teleconverter is either costly/rare or forces you to manual focus. You would at least need one with contacts so the aperture functions. I think it would be better to get a DA 55-300mm instead, which ought to be better than the F100-300 and a better package.
03-16-2013, 03:45 AM   #4
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I was also surprised when I found out that the image at f16 looks much sharper than at f8 or f9. I made numerous images focusing in contrast, phase and manual modes. It was all the same. It's really strange to me...
As for Pentax 55-300 lens, how do you think, will it perform better at 300mm than my 50-135 + one of these teleconverters:
2X Tamron AF 7 Element MC7 Teleconverter Lens for Pentax Film Digital | eBay
Bower AF SDM Compatible 4 Element 2X Teleconverter Lens Pentax K5 KX | eBay
Kenko 2X AF Teleconverter Pentax Kenko 2X MC4 DG 4961607622384 | eBay
2X Teleconverter X2 Tele Lens AF for Pentax SLR DSLR K 5 K10D K100D K110D Japan | eBay
I do know that the AF almost surely won't be working with them. I also know that even good teleconverters don't work good with budget lenses like Pentax 50-200mm. However, 50-135/2.8 is a rather good lens... So maybe it's a different story with that kind of lens. What are your thoughts?

03-16-2013, 09:46 AM   #5
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I've owned and compared multiple 55-300DAs to (one copy of) the 4.5-5.6 100-300F. Your answer depends on which 55-300. Generally, the coating on all the 55-300 seem superior and the contrast under most practical circumstances is better - often much better. But resolution is all over the map. Some corners are better on some 55-300s, some glaringly worse. Honestly even the 100-300 isn't perfectly consistent between corners - and those "corners" aren't even corners in its full-frame world. And some of the 55-300s really started losing it halfway across the frame. Summary: resolution varies from copy to copy, and not just with this lens.

Multiply that testing requirement when you factor in a lens/converter combination. Since there is no matched converter, you'll be trying maybe a couple brands of converters, maybe a half-dozen copied of each, maybe few 50-135s. And remember, you may have to test at varying distances - I've had lenses where the performance varied corner-to-corner based on focusing distance, not just focal length setting. Good luck with that.

In any event, testing at 300mm is challenging. When I tested outdoors, even my relatively heavy 3036 wasn't solid enough to stand up to a breeze, and barely settles after the 2-second timer delay. And of course you have to either focus manually (almost impossible if your body doesn't have live view, which is the case with at least one of mine) or hope that lens/converter combination autofocuses perfectly.

There is also the issue of physical convenience. The 55-300 is in a completely different league than the 100-300, for example. And autofocus is a huge factor, if you're considering a manual-focus converter vs. the auto-focus in the either of the 300mm zooms. The 100-300 autofocuses better, on my bodies, than the 55-300. It's not even close. They're both accurate, no ff/bf, it just takes the 100-300 much less time to stop hunting on difficult subjects.

Paul
03-17-2013, 11:38 PM   #6
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Wow, the 100-300 focuses much faster than the 55-300?! This is news to me. I've heard that the 50-135 isn't fast enough, but my 100-300 is much slower in comparison. As for focusing speed, however, it may be very fast (judging on the noise the lens produces) but as for locking the focus it is behind (I compared at 300mm though).
Now I am inclined to think that the 50-135 with a decent teleconverter (Tamron 1.4x, Kenko 1.5x) will permorm much better than any budget AF-telezoom (~300mm) at f-stops up to f8. But that Tamron and Kenko teleconverters are rare and very pricy. So now I am leaning towards to not very expensive but decent teleconverters or some old MF-telezooms/primes that may be also not very expensive because of the AF lacking.
As for the teleconverters, what do you think about the Vivitar Series1 1.4x AF teleconverter? Some say its optical quality is close to the Tamron's/Kenko's but it won't autofocus in spite of pz-contacts.
Any recommendations are welcome!
03-23-2013, 12:27 PM   #7
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QuoteOriginally posted by skyer Quote
Wow, the 100-300 focuses much faster than the 55-300?! This is news to me. I've heard that the 50-135 isn't fast enough, but my 100-300 is much slower in comparison.
Yes. I don't know about pure speed (rotating the components), but the 55-300DA hunts dramatically more under identical conditions and takes much, much longer to lock on.

Paul
03-23-2013, 05:39 PM   #8
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QuoteOriginally posted by tibbitts Quote
Yes. I don't know about pure speed (rotating the components), but the 55-300DA hunts dramatically more under identical conditions and takes much, much longer to lock on.

Paul
I will second the idea that the F 100-300 beats the DA 55-300 as far as AF speed. I owned both those lenses at the same time, so I had a good chance to play around with them and compare (they have both since been sold off). The F 100 is really quite fast.

I think it may have to do with the added quick shift ability of the 55-300. But I can't say for sure.

03-24-2013, 06:11 AM   #9
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Thank you all!
I guess, I'd better keep the F100-300 in that case
However, any comparisons of 50-135 + teleconverter vs 100-300/55-300 are still welcome! Comparisons of 100-300 vs 55-300 at 300mm are welcome as well.
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