Re: TC thoughts - YMMV:

[Pacerr]

X-posted from some recent PM's:

Quote from: david
. . . which 2x teleconverter do you have ... does it manual focus only ?   can the A setting be used as in A lenses if it's not autofocus ?

Dave, I've used quite a few of 'em. Most haven't been worth the effort compared to cropping except for these:

The best IME (and I've had two of 'em), is the Tamron Pz-AF 1.4x which has the contacts for SDM. The Tokina EL 2X I just posted about is the best 2X I've used. I wasn't especially impressed with the Pentax AFA 1.7x and quickly sold it. The PK/A Vivitar 2X Variable Macro converter is worth having around for close-up work but not as a FL extender. The Adaptall 140F and 200F flat field converters are very good used with the Adaptall SP lenses they're made for.

Rules for success:
- The better the lens, the better the results -- always.
- Never use a TC unless you can't get to the desired FL any other way.
- Use it ONLY with the longest and BEST lens you have on hand.
- If you DO have one you're happy with, USE it. The picture you got is always better than the one that got away.  That's why you're carrying it around anyway, right?
- Experiment a lot so you'll know what to expect.
- If you see marginal results with a bare lens they'll be even worse with a TC.
- Old M42 screw mount tele-lenses seem to do better with TC's from that era.

- Unless there's good reason (such as a demonstration) don't admit you used it -- it won't make anyone think better of the image and they'll always nit pick it no matter how good it is.


If it's a PK/A converter (it has the data pins) it's capable of acting like any other PK/A lens that it's paired with. It must have a drive screw (or the Pz contacts for SDM) to use with auto focus and they will always be labeled AF, not just Auto -- and are more expensive too.

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Quote from: davidhampshire
 . . . my reason for getting the Q camera was to use it for telephoto,  but never can get good results with it )  this tc stuff would make a good post for others . . . but never can get good results with [a TC ] . . . )

IME, learning to shoot consistently and successfully with telephoto effects and with lenses longer than 150mm, is a lifetime project; and substituting sensor crop for lens focal length doesn't change the challenge in the slightest. Fewer or lower quality pixels simply reduces the potential to crop in PP. Using a high quality lens is important and adding the potential optical issues of a TC  can certainly compound the problems.

- Pairing a lens and a TC is no different than checking out any new lens. Takes time and luck and experience enough to understand what you're lookin' at. If you want to know whether a TC is performing to its potential you have to be comparing it to a reasonable standard. The test is your lens plus the TC versus the longer lens you'd really rather have but can't afford or that is too cumbersome or expensive to risk carrying on the 'mission' (sometimes it's a smart decision to carry a $250 TC rather than a $2500 lens as my son learned in Alaska   ).

- The single most important issue is to appreciate that you're using a LOOONG lens that's subject to all types of degradation from mirror shake to motion blur to atmospheric effects and mirage to . . . Hey, you're doubling the FL!   Some of the bad-mouthing you see about TC's OF GOOD QUALITY may be offered by people that couldn't use a prime lens at the equivalent FL with any better results and/or can't discriminate between operator induced blur and true optical sharpness or aberrations.

-  A long FL lens is simply a shorter optical design with a built-in TC element. Maybe it's actually well matched to the optical formula by the manufacturer -- maybe not. What a TC actually does is SPREAD the light coming out of the rear of the lens so the sensor only 'sees' a narrower part of the image (and less of the light as well which is why it costs you an f-stop or two!). In a way, a TC is a funky kind of wide angle converter in reverse!  

- A shot made with a TC may only APPEAR to be much less sharp in the plane of focus than it really is because the effect on the out-of-focus areas and DoF is exaggerated compared to an equivalent crop. Compare a cropped image with a prime lens and a shorter lens with a TC to see this effect. Other characteristics of distant shots such as mirage, haze and reduced contrast affect the image too and may not be recognized without comparison shots.

If one wants to use an expensive TC, or any long lens, I suggest you get a cheap, used 400mm and use it for "training wheels" first. Shoot it til you understand what must be done to eliminate all operator induced variables (like motion blur) and how to "see" the DoF and to manually focus that sucker. Learn under which conditions it's smarter to crop or to use a TC than a longer lens.

Ultimately, if a TC gets you satisfactory shots you couldn't get any other way, it has served its purpose well. You can always "upgrade" from a TC to a longer lens if desired -- just as soon as you can afford it. THAT'S the real compromise.

I still throw away 95/100 of the shots I make in the field with a TC -- not because the TC is necessarily bad, but because ANY loooong lens is a bitch to use and it takes constant practice to use it consistently well.  Aye, an' that's the rub, eh?

[blackcloudbrew]

No time to really weigh in here but, I will say that several years ago I did a lot of research into these and settled on the Kenko Pz-AF 1.5x Teleplus SHQ Teleconverter, which will work just fine with SDM as long as the aperture is f4 or larger. It's almost as good as the Tamron which review after review is felt to be the best for the money. However, for 2 or 3 times the money Pentax made a 1.7x t/c that can do miracles or so I've been told.

I don't use t/c's very often though and like Hank, I toss a lot of shots with them.