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12-17-2010, 08:07 AM   #1
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TC Advice

Almost put this in the beginner's threads, because I know almost nothing about TCs.
I'm thinking specifically of getting a TC to use with my DA*200mm f-2.8.
I use MF most of the time anyway, so don't need AF capability, which I presume means I don't have to buy the "best," and can save some money.
What do the numbers (such as 1.7) mean according to increased focal length?
I understand the common trade-off is one stop. Right?
But what about IQ? I expect some degredation simply because of the increased focal length (atmosphere and all that), but does the extra piece of glass have a noticable effect? Is it a little like adding filters: more degredation with cheap ones?
Finally, presuming I have equally sharp focus on the same shot (same physical distance) with and without the TC, do you think the TC image would be sharper than a normal 200mm shot cropped to the same FOV?
Of course, I welcome purchase suggestions.

12-17-2010, 08:45 AM   #2
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I can't answer all of your questions because I only recently bought my first TC, a Kenko 1.5 with PZ contacts. I've found degradation in the form of reduced contrast and sharpness on my D FA 100mm. I would say buy a high quality TC or don't bother. The only use I can see for a TC is for very, very long distance shots. If you can get by with your longest lens and a crop, do that. If you use your longest lens and crop and you don't have enough pixels left, then use a TC.

The numbers are pretty straightforward. For a 1.4X TC, multiply focal length and aperture by 1.4. Your 200mm f/2.8 would become a 280mm f4. With a 2x TC, your lens would be a 400mm f5.6.

Last edited by audiobomber; 12-17-2010 at 08:59 AM.
12-17-2010, 11:50 AM   #3
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Coupl'a thoughts, Ron.

As you noted, using a TC to reach out an' touch something at long range exacerbates the issues associated with any long lens -- contrast, haze, heat shimmer, camera motion, etc. I suspect that some of the dissatisfaction with good quality TC's lies in the fact that many casual users simply aren't familiar with really long FLs.

Those that actually have knowledgeable, practical experience with them can produce respectable results that couldn't be attained in other ways under reasonable conditions. (Search DPR for threads by "Brandrx" -- Ron's posted some credible, real-world results with many lens/TC combinations with actual images to support his conclusions.)

My own experience with TCs is limited to older, manual focus glass of the SMC-M and M42 variety. I've found some things to be generally true there: 1) TC's of the same era as the lenses seem to produce subjectively better results, 2) there's a lot of variance in results from one TC to another of the same type and brand when paired with a particular lens and 3) many older TCs (and lenses) can be tweaked for noticeably better performance by ensuring the lens mounting rings are snug and any internal reflections are eliminated with paint or markers.

I suspect that with your experience with outdoor photography and available long lenses that you wouldn't see much value except to extend your longest lenses which also puts the TC in its worst situation. However, one often overlooked use of TCs is to extend the close-up capability of otherwise excellent prime lenses and that's where I find them most useful. The SMC 50mm's and the Tamron SP 90 and 180mm lenses have performed well with selected TCs in the close-up role.

With the price of older 2X TCs as low as they are today, I'd suggest you find one to play with to see if it actually solves any situational problems -- if that works, then you could consider IQ and high end glass.

I recently broke down and acquired the AFA 1.7 AF converter to explore auto focus with my Tamron Adaptall SP primes and was pleasantly surprised with the IQ results using the SP 80-200, 180 and 300mm lenses.

H2
12-17-2010, 12:03 PM   #4
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I've got a DA* 300mm f/4 and a Kenko 1.5x TC. Overall, I've been disappointed with the TC. Unlike you, I just can't get by without AF. The AF is rather aggravating to use and MF ends up being easier for me. I don't have side by side comparison shots for you, but the TC shots did seem to lose sharpness and contrast. Perhaps I could get better results if I worked at learning how to best use the TC, but for now it's mostly stayed at home and I've opted to crop my 300mm shots.

You might have better luck with AF with a 2.8 lens compared to my one stop slower f/4, but if you already prefer MF that may not matter much to you.

What applications are you considering for the TC?

12-17-2010, 01:20 PM   #5
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The only TC I've ever used with the DA* lenses that came close to being worthwhile, was not really a TC but the Pentax 1.7x AF Converter. It acts as a TC however and will take your 200 to 340. I use it on my 300 to get the range of the Bigma I use to have..

Pentax DA*300mm SDM - a set on Flickr

I'll let you be the judge. The photos that the TC was used with are noted in the titles of the photos with 17xAFTC on the end. One thing I know from reading other's comments on teleconverters, is that the Sigma TCs don't play will with the SDM lenses (in case you were considering one).

Good luck.

12-17-2010, 01:29 PM   #6
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I'll echo the above comments, and add: I have more than a few TC's, which I don't use here, but who knows? Maybe someday I will have a NEED to put my Spiratone 400/5.6 on two each 2x and 3x TC's for a 4000mm f/56 lens experience. Sure, that could happen. Most of those TC's came in batch-lots amidst more desirable glass. I've sold a few for around US$6 each, both M42 and simple PK. I recently got a PK-M Panagor 1x-10x variable macro TC (CHEAP!) to play with. It hopefully won't perform any worse than +dioptre closeup meniscus glass.

A TC matched to a specific lens is one thing -- all telephoto lenses have built-in TCs, and all wide-angles have built-in reverse TC's. A TC unmatched to specific lenses, designed to work somewhat adequately with any lens, is an entirely other thing.

Bottom line: Some TC's (especially high-end), matched with specific lenses, do quite well, or so I hear. I would use an average (cheap) TC on a long tele in circumstances where the image content is more important than its quality: surveillance, blackmail, target-marking, etc. Any captured image is better than any missed image. Many TC's are now cheap enough that they can be experimented with, tried on different lenses, without too much financial pain. Or just buy a cheap mirror for that extra reach.
12-17-2010, 02:00 PM   #7
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Excellent, intelligent replies. Thanks all. It all adds up to pretty much what I expected. Guess I'll continue to wish and save for a DA 300 f-4 or a Bigma. Image IQ probably is more important to me than the average shooter, and although I think I have enough long range experience to get the most from a TC, I strongly suspect it won't be good enough.
But one response did bring another question to mind.
RioRico: how would you (or anyone else) compare the IQ between using a TC and a mirror lens of equal FLs? Most mirror lenses are actually cheaper than a good TC.
12-17-2010, 03:53 PM   #8
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Ron
TCs can work wonderfully. Depends on your subject, the reproduction requirements, and of course the quality of glass. The better the glass the better a high quality TC will work. Zooms are less satisfying than primes that way in my experience.

I've used a Kenko 1.5x TC with an A*200 mm f2.8 happily. On the DA * 50-135mm it was OK. The AF worked well though.

The larger issue is the lack of Pentax-quality TCs as well as long fast high quality glass--which helped spur me to go Canon. Look at the collections of the best shots from the winter Olympics and you will see a fair number of Canon TCs being used. My neighbor used to shoot sports for the Seattle daily paper and his best shots on his wall were done with a TC. Go to the Nature Photographers avian gallery and about 30% of those great ones are with a TC. But the main lenses are 4-500mm f4 and $6K.

Re: your question I'd go with a Sigma 100-300 f4 +TC over a Bigma if optical quality was key. The Bigma is amazingly convenient and cheap, but not a professional lens at all. One can get good shots with it but I found the focus to be inconsistent and very slow.

M

12-17-2010, 06:42 PM   #9
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Thanks Miguel. I wasn't thinking of using the DA 300 f-4 or the Bigma with a TC. The longest lens I own is the DA*200mm f-2.8, and if you will check out the wildlife shots on my website, you'll see I've done pretty well at getting close with it. But lately I've been considering if a TC to make this lens into a 300mm or so would work.
Optic quality of this lens is good, and it is fast for a 200. My reproduction requirements are for covers and insides on mags, plus prints up to 30X40. I've found the 200 more than meets these requirements. In fact, an outfitter once enlarged a shot from it to a 4-foot by 8-foot banner, and I was surprised how good it looked from a dozen feet away. So, considering I probably have some IQ to spare with it, I started thinking about a cheaper way to extend the range.
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