[clackers]

When you narrow the aperture down, it gets to be difficult to get light from both ends of a line to converge on separated AF rows of pixels.

f5.6 is the traditionally accepted limit - after this, there are no guarantees.

In sports and wildlife shooting, you can see the lens and TCs acknowledge this ... you'd conventionally only use a 1.4xTC with an f4 lens, but could put a 2x on an f2.8.

In those disciplines, high performance AF is desired, compromises can hurt you!

[Rider0974]

A further test outside, 100% cloud cover,
K1 ii, FA 80-320mm, Kenko MC7 2x converter,
Shutter speeds varied from 1/13 at ISO 100 f5.6, to 1/100 at F10 ISO1600
AE works at 320mm F5.6 & F10. Single point (centre) af
on brickwork & some distant trees. There was a little hunting
on the trees, but I have had worse while tracking birds, in
good light against a clear sky, without a converter fitted.

[ramseybuckeye]

I use the DA 1.4 with the 55-300PLM at the beach or on water, places wher you also get a lot of reflected light. It works fine there, but it’s not going to find focus in a wooded setting, I include a couple examples here, I included the second to show it was able to focus on the shaded side of the willet, but most likely because of the light reflected off of the sand, I doubt it would have been possible had the willet been walking on grass.

[cdd29]

Awhile back I thought I do something stupid (mainly because I was bored) and see how many teleconverters I could stack and still get some kind of image. Well, I was up to three and the camera had no idea what f/stop it was on (said f/1.7 which is impossible as it's an f/4.5. AF didn't work but I could get a workable image in daylight. That was with 2 2x and a 1.4 I believe. I have since acquired another 2x I might try and see if I can make the camera go into a fetal position...

[PentaxScott]

This is what interests me a lot, too (not quite yet being able to try myself...). Depending mostly on the amount of light, I guess?

I have been using this combo on my K-5 for the last couple months learning to shoot birds in flight, and its been nothing but amazing. Ive really snagged some great pics learning, and find that I have no issue with AF save for my own faults (some of those birds move quick!)

[normhead]

In good light I regularly use the HD DA 1.4 TC with the DA 55-300 PLM 6.3.



There's absolutely no issue.

[bobore]

I started using the first generation autofocus Tamron AF 70-300 (f5.6) coupled to a 5-element Sigma 1.4x Teleconverter back in the fllm days with a PZ-1p. It would not autofocus when fully extended to 300mm, but when I finally converted to digital with the K-100d, I was amazed when it rather easily locked on birds at full extension (with center-point focus).

I continued to use that setup with a K-200d, which provided superb ergonomic balance - and as of last year, the same set up with a K-5IIs, which feels almost identical ergonomically to the K-200d. The film-era Sigma 1.4x is a real winner, and predates a number of APO versions that came later. I’ve recently aquired a second copy of the Sigma converter, and mated it to Tamron’s initial long AF tele effort, a 90-300mm, with very satisfying results. Both of these early Tamrons take 58mm filters and were made in Japan.

Additionally, I have a number of other lenses and teleconverters purchased within the last few years that also do quite well in getting you out to the same tele length while maintaining autofocus. Just stick with f5.6 at the 300mm tele end, and it should work quite well with a 1.4x converter.

[mlag]

What is the experience with the DFA 150-450 and the 1.4 DA TC? I guess it would work with the K3iii in decent light.

Just tested it a few days ago in winter daylight : it focused as normal on my K3II.
Post your HD PENTAX-D FA 150-450mm F4.5-5.6 ED DC AW pictures! - Page 197 - PentaxForums.com

And this evening , indoors in low light (1/10 s and f8 = f5.6 with tc loss), it still works on both K70 and K3II, but there is occasional hunting (I switched between close and far objects to test autofocus).

[swanlefitte]

My ks-2 1.4x and 55-300 is great even in low light with any contrast as an f/8 combo but can have trouble at the f/9.5 extreme. So f/5.6 is great and f/6.3 needs some light.