Quote: Not sure what the Pentax older 250-600 options have to do with anything. They aren't 7000 on eBay. I've been looking. Seem to be between 2500 and 4000.
I've seen pristine copies go as high as $8000 but I haven't looked recently so maybe the prices have fallen, the one I bid on 8 years ago up here went for over $7000, an old RCMP lens. If there was ever a functional one for $2500 5 years ago, I'd own one. The ones you've been looking at must have been in pretty bad shape.
Quote: In neither case did I feel that the results with TC beat cropping. But that's my opinion only. And I don't have a 600 to compare
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Understanding folks saying a TC doesn't ad more detail. - PentaxForums.com
The images are reposted on page 3 of the thread.
My first series of images went as follows... taken at about 40 feet, with not a lot of detail in the test subject.
DA*200
DA*200 plus 1.4
DA*200 plus 1.7
DA*200 by itself enlarged to the same size as the DA*200 2.8 plus 1.7x AF Adapter
Yes you can take images that don't show a difference, but I've posted how you can find out what the difference is. I've never tested a lens where the TC made no difference except for an old bargain basement Vivitar M135 2.8, which is a really bad lens.
My first 55-300 PLM broke in half after a drop. My DA*60-250 was repairable after two such drops. The current cost of my DA 55-300 PLM is about $900. Value priced for some but not for me. One more drop and it will have cost me DA*60-250 money. (But it's worth if for the light weight.)
Pentax recently released a 70-210 that will undoubtedly poach sales form the DA*60-250. So, I'm just not buying it. As for the 600 FL, that is also covered by the DA 560, also a 5.6 lens that can be pushed to almost 800 ƒ8.
That's what's real. Your list of probablies demonstrates your own biases, not much more.
Quote: So while I personally would like a Pentax equivalent to the Tamron or Sigma, I just can't see them doing it.
You want a Pentax equivalent to 3rd party cost cutters? I'm with you on that but it's unreasonable. Pentax is an OEM. Tamron and Sigma can't make money selling to Pentax customers at the same prices they sell other brands too. But for some reason people think Pentax should be able too. An OEM building for 3rd party manufacturer prices when even the third party guys can't survive in the Pentax market.
But the big reason in my mind Pentax won't compete with them.. as I said (and you ignored) Pentax will not build a 6.3 lenses except under dire circumstances where it's mechanically necessary. And there are very sound AF reasons of doing that. That's the most likely reason. Even their old 250-600 was 5.6. You could argue, and I frequently do, there's one reason for using 6.3 lenses, you can't afford better. The physical limitations of such glass make them less than desirable.
At 600mm the Tamron 150-600 MTF is terrible.
Now look at the 150-450 Chart at 450
And the Tamron values
Given the Tamron 150-600 values at 600 and the Pentax TC estimated resolution loss of 3% it is very unlikely the Tamron can mach the DA 150-450 with the TC.
My probabilities have a lot more numbers to support them.
Despite the incessant chatter about why can't Pentax compete, it's quite probable that the simple reason is, they don' want to, they don't want the Pentax name on that quality of lens even in the current market, and they currently have covered the focal length with the 150-450 and the TC, and the DA 560.. Anyone who has followed the DA 55-300 PLM, which was immediately branded "top of class" by several different websites understands that.
Pentax cut off the zoom on this lens while it still had excellent or near excleentvalues in 3 of 5 categories. Tamron extended the front element a little further and tanked their lens performance at the long end. It's just not a Pentax type of choice.
I'm going to pull a trick out of your hat, and throw out a probably.
If Pentax had designed the 150-450 by extending the front element so that they achieved 600mm (and ƒ6.3), it would still have been better than the Tamron, but Pentax gave you the opportunity to use the TC, and do better, for more money. Because it was the better option optically, even though it doesn't have the wow marketing effect that can pry sales away from OEMs, not the 3rd party price reducing (but loss of value option.) Because that's what OEMs do.
The Tamron lenses that Pentax rebrands these days (20 years ago with my rebranded Tamron 28-200 that wasn't the case.) are defined to compete optically. The old style, big range big number lower quality lenses (like the 28-200 was), I think Pentax learned their lesson. Selling low end options (like that Tamron at 600mm) doesn't play well for the brand, and in the end produces dissatisfied customers.