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11-25-2021, 04:48 PM - 1 Like   #16
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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!

11-28-2021, 02:13 AM   #17
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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.
11-28-2021, 07:08 AM - 2 Likes   #18
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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 itís 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.

11-29-2021, 08:06 PM   #19
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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...


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