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04-04-2011, 08:18 AM   #16
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As someone else said: there is no free lunch. I've been testing some TCs off and on for the past few months. Took one or two shots to throw most of them aside, but I've been keeping the Pentax 1.7 attached to my DA* 200 F-2.8. At mid ranges, it seems to do a great job, with little or no noticable loss in IQ. AF seems to be faster and more accurate than the 200 alone--sometimes.
Set up tests, especially on a tripod with mirror-up function, don't have any practical applications to the field. The idea is to achieve the FL of a 300mm (a little more actually) at a fraction of the price, but there are considerable problems I've encountered.
The first is that for AF to work at all, the focus needs to be somewhere near the distance to begin. This means that some combination of MF and AF needs to be used, which takes time. For real wildlife photography, time to get a shot is often measured in seconds.
Another is that I've found the TC functions a little like an extender. Close focus and infinity become out of range or soft. Now this is not much problem with close focus, because the idea is to extend the distance from the subject, but having a soft infinity with a TC means the effective range is limited to less than the 1.7 multiplication would indicate. Still, at mid ranges, there does seem to be some advantage with acceptable IQ. So, for all practical purposes, the 1.7 on my 200mm does function comparably to a 300mm, but the actual distance one gains is less than might be imagined.
For example, if I must be about 40 yards from a deer to fill frame with my 200mm, I can gain about 1/2 that distance to fill frame with the TC and 200mm. But, from a practical standpoint, there isn't much difference in the spook factor between 40 yards and 60 yards, so being able to get close is still more important that FL. For something smaller, like a duck, the fill-frame distances are even less, about 20 yards for 200mm and 30 yards for TC. With wildlife, that's really no advantage.
The f-stop loss on the f-2.8 turns it into about a 4.5, which is about equal to the expensive 300mm. So, as long as one has enough light for 4.5, one is on a relatively level playing field of light. However, for real wildlife, a great portion of opportunities come durng low light conditions where f-2.8 becomes very valuable. Further, while the 200/TC does seem to match the IQ of the 200 at f-2.8, it doesn't match the IQ of the 200 stopped down the f-4.5. It's close, but I can see a difference.
Along with the loss of light, you do have a bit of a loss in shutter speed because of the increased FL, and for hand-holding that is very important. At f-4.5, I can hand-hold my 200 with reliable results at about 250th sec. With the TC, I need at least 350th sec., making the practical difference in the filed another stop.
So, from a practical standpoint, the distance advantages of the TC are not nearly as great as the math would indicate, and the infinity limitation is considerable. I still think the most important part of wildlife photography is learning to be a good hunter and practicing a lot of patience. The truth is, you need these hunting skills equally for a 200 or a 300.
I plan to return the TC and stick with my bare 200 F-2.8, and the 300 remains not worth the extra bucks, simply because it is f-4.5. If Pentax makes a 300 F-2.8, I'll be saving my pennies.
Having said all that, understand that my judgement is based on shooting for publication and large prints. I'm pretty picky. If your wildlife photography is in parks and zoos, where captive, semi-domesticated animals have to choice but to pose in full sunlight, a good TC might make sense, but there is no free lunch n TCs either. Cheap TCs, from my experience, are just relatively expensive paper weights.

Last edited by Ron Kruger; 04-04-2011 at 08:23 AM. Reason: adding info
04-04-2011, 08:24 AM   #17
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"usually"? How about "always" (although I guess you could get really lucky at a yard sale ;~)
Well, you know I usually don't like to speak in absolute terms. I like to leave a little wiggle room in case I'm wrong. (Which I frequently am.)


Some pretty nice lenses in that list. Guess the Tamron's a good 'un...
04-04-2011, 08:25 AM   #18
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QuoteOriginally posted by reeftool Quote
Some converter/lens combinations work very well and others don't.
Right. I use Pentax (AF 1.7x, 2x-S & 2x-L) TCs and Pentax lenses. One of these days I may get a Sigma 1.4x to use with my Sigma zooms (primarily for travel.)

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