I know.
This topic is about as worn-out as
"Do you shoot raw?" or
"Are filters any good?". Still, I want to share the following with you:
Many DA* 200mm owners have probably experienced that this lens doesn't behave too well with generic teconverters - in particular 2X converters -designed for use with a bit of "each and everything". So have I.
But the A 2X-S (manufactured during 1984-2005) is, according to Pentax designed to work with (most of) their longer lenses up to 300mm F.L. And the DA* 200mm is, optically speaking, a desing from 1993 so, maybe, just maybe......?
So, admittedly somewhat gambling, I ordered one of these rear converters to find out myself, and here are a few, first samples.
My target is a powerline a few scores of meters away:
(DA 18-135 mm lens)
and a 100% crop shot with the DA* 200 looks like this:
(DA* 200 mm f/2.8 lens)
and now to a similar crop with this lens plus rear converter:
(DA* 200 mm f/2.8 lens plus Rear Converter A 2X-S)
Apart from cropping or resizing and labelling, these images are unprocessed JPEG straigt out of the camera and the images were shot handheld on a cloudy day with light showers. Still, there is no doubt in my mind that the image taken with teleconverter reveals fine detail that you cannot reach merely by cropping, (and no - I don't mean the bird).
It is unquestionably true that teleconverters MAY degrade image quality in certain situations. But, to me, it is unquestionably equally incorrect to state that this will ALWAYS be the case. There are teleconverters and then there are matching teleconverters.
(DA* 200 mm f/2.8 lens plus Rear Converter A 2X-S)