Special Topic: Pentax Rear Converter A 2X-S

on smc Pentax-DA* 1:2.8 200mm Telephoto Lens





The topic "Are Teleconverters any good?" is about as worn-out as "Do you shoot raw?" or "Are filters any good?". I have dealt with that question elsewhere, and this review is rather a specialized one dealing with the specific question:


Is the Pentax Rear Converter A 2X-S any good for my

smc PENTAX-DA* 1:2.8 200mm ED (IF) SDM?



Many DA* 200mm owners have probably experienced that this lens doesn't behave too well with generic teleconverters - in particular 2X converters -designed for use with a bit of "each and everything". So have I.


Of course, any teleconverter will be an add-on to a carefully optimized (one should hope) lens design and introduce some limitations such as lowering the fully open aperture f-ratio,and any (quality) teleconverter will magnify aberrations of the lens that it is sitting upon. But that's not the point. The point is: Does it work as a quality converter should work on a quality lens?


Anyway, detailed information on good teleconverters matching contemporary Pentax telephoto lenses is scarce - in particular when it comes to the FA* 200mm and DA* 200mm lenses. But the A 2X-S (manufactured during 1984-2005) is, according to Pentax themselves, designed to work with (most of) their longer lenses up to 300mm F.L. And the DA* 200mm is, optically speaking, a design from 1993 so, maybe, just maybe......?



Thus - 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 labeling, these images are unprocessed JPEG straight 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).


I have continued testing the A 2X-S extensively on my DA* 200 and I have not been disappointed.


I have a hard time seeing the IQ degradation mentioned by others. What I do find, is that this TC unquestionably does help when a quality lens like the DA* 200 outresolves the sensor (the sensor under-samples the image produced by the lens). Images may sometimes at a casual glance look "sharper" without TC, but I have found that to be a matter of under-sampling and pixelation, as the following 100% comparison crops will hopefully demonstrate:



Downsized (approx. 30%) crops: The softness observed at f/2.8 is no worse that what the lens itself without TC would show.



Test Target: Remote building. I am aiming at the guarding rails in front of the windows.




100% non-resized crops of images with and without Rear Converter A 2X-S. Note the bars of the railings.




Starlings on a powerline. Again 100% non-resized crops. Note the speckles on the birds' chests.



And finally the infinitely remote.100% non-resized crops of single, non-postprocessed images.

Look for the tiniest craters resolved in the two images.




1. Be it tiny craterlets on the Moon, speckle's on the starling's chests, bars in the guarding rails on a remote building: With this TC I can capture detail that lens and sensor alone cannot resolve. Add to that the splendid manufacturing quality and I can only recommend this converter - if used with the right matching lenses and if you know what to expect and not to expect from a quality teleconverter.
2. 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)


Pentax Rear Converter A Operating Manual(1990)


Copyright 2013 - Steen G. Bruun