[johnmb]

Well we were told that the DA 1.4 converter was not full-frame compatible. Sure enough it does cause quite a big of vignetting on the Pentax DA 300mm f4 lens. But the news is not all negative.

As far as I can see, the Pentax DA 100mm Macro works fine with the converter attached, with practically no discernible vignetting. Need to check the image quality of course, but previous reports suggest that it should be good. Will be interesting to hear the results from other users. Having an additional working distance would be a big plus for this superb macro lens, which is light an easy to hand-hold.

But perhaps the biggest surprise was with the Pentax DA 55-300 mm zoom. As expected, it had quite a lot of vignetting when used on its own with the K-1, but practically no vignetting at all focal lengths when used with the converter. Hopefully, other users can check this out and confirm with real-life results. (I have not had time to do this yet as the camera has only just arrived.)

Conclusion: with the K-1, the DA 1.4 converter might be quite a useful tool to have in the camera bag, especially if we wish to travel light.

Used with the 150-450 it introduces vignetting. Removes almost all vignetting on the 16-50 and all on the 10-17. IQ vice... It feels like it is not adding any value, no more detail when used with the 150-450, no matter the aperture used.

[ybo1]

Used with the 150-450 it introduces vignetting. Removes almost all vignetting on the 16-50 and all on the 10-17. IQ vice... It feels like it is not adding any value, no more detail when used with the 150-450, no matter the aperture used.

To my knowledge, a TC never adds detail, just increases FL.

[Quartermaster James]

So, with the K-3, the advice regarding the TC with the 55-300 has been to forgo the converter and to crop instead. Does this change with the K-1?

[RockvilleBob]

With a little luck we can hope for a Pentax 1.4 TC for the K-1......in less time than it took for the DA 1.4

To my knowledge, a TC never adds detail, just increases FL.

In that case, why use them? Easier just interpolate in photoshop instead?

Please clarify.

[BigMackCam]

So, with the K-3, the advice regarding the TC with the 55-300 has been to forgo the converter and to crop instead. Does this change with the K-1?

This is a long-debated topic... I wonder if anyone has done any resolution tests on cropped images vs those with the TC? And, potentially, other TCs?

[UncleVanya]

This is a long-debated topic... I wonder if anyone has done any resolution tests on cropped images vs those with the TC? And, potentially, other TCs?

Not a formal test but you can see the FA* 300 on my K-3 with and without the AF 1.7x TC in this thread I posted:
https://www.pentaxforums.com/forums/12-post-your-photos/321782-night-moon.html

The two were not identically processed to the nth degree so that could be a minor factor also. However they were taken in the same night minutes apart and with the same body/lens at the same effective F/stop - not the same amount stopped down. (as far as I recall).
They were taken with 2 second self timer on a carbon fiber tripod and autofocused with manual tests to confirm that this was working well prior to allowing it to be done. (PDAF not CDAF).

I realize this may be a bit off the full topic but it should be a bit helpful.

[BigMackCam]

That's interesting, @UncleVanya - I missed that Moon post of yours originally. Thanks for the links

[Na Horuk]

This is a long-debated topic... I wonder if anyone has done any resolution tests on cropped images vs those with the TC? And, potentially, other TCs?

I think there were some threads about this with certain lenses. I think with a good quality TC, the TC was slightly, but not by a lot, better than just cropping in PP. With those no-brand cheap TC, the difference was not apparent by eye, at least not to most people.

Similarly, APSC cameras were slightly better than taking a FF shot and cropping it, at least in regards with super telephoto (the test subjects were birds, if i remember right)

Edit: that said, yes, TC does not technically add detail. It only magnifies the lens in front of it. This also means that the lens you use is very important, specifically the amount of detail it can render

[UncleVanya]

On the plus side you are magnifying the best (central) part of the image and spraying it over a larger number of pixels than you would have put it over had you simply cropped. However that also means that if the detail was never captured then it has less data to work when when interpolating the image so it may end up being moot or not any sharper. To my eye the FA* 300 with the f/1.7 might be a SLIGHT bit sharper but then I look again and reverse myself. I think it's a toss up at least on the K-3.

[normhead]

To my knowledge, a TC never adds detail, just increases FL.

That isn't knowledge. That is a wives tale concocted by people who should know better. A very simple easy test deproves it. Honestly, there is no excuse for posting this kind of info without supporting images. If you'd taken a half hour of your life to find out if it was true, you'd know better. Detail is determined by focal length and lens quality, not by whether or not a TC is used. The TC makes practically no difference. A simple test would show this.

Mind you, it could be true, if you shoot with really cheap lenses, like something that was a cheap 3rd party product from 30 years ago. But any modern lens is sharp enough to benefit from a TC.

And even old consumer glass, like my A-400 benefits from a TC.

[gatorguy]

As the Pentax 1.7x was made for full-frame wouldn't it be expected to improve compatibility of attached lenses? I'd expect the Tamron-F 1.4X Pz-AF MC4 is also full-frame but not 100% certain.

[Wild Mark]

I did a little testing in this thread (and didn't get too many trolling comments - which often happens when you touch on the TC issue).

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/309566-tele...on-x1-4-a.html

[Shanti]

The Pentax 1.4 TC works fine on the DA70,on DA*300 vignettes a bit,On DFA150-450 not so good,at least for BIF..must check with the 1.7 AFTC later