I just did a couple of focus “tests” with my two slowest lenses. I won’t post
any results - I was just handholding on random twigs, turkeys, lawn sculptures,
trees, etc. The images would tell you nothing about sharpness. All of the
following using center-point focus, K-3.
1. Sigma DG 150-500mm f5-6.3 APO HSM + Pentax 1.4x TC
With the Sigma at 150mm zoom (presumably f/5.0)
- Sigma AF OFF: nothing happens - no AF.
- Sigma AF ON: snappy AF, no searching or other bad behaviors
With the Sigma at 500mm zoom (presumably f/6.3)
- Sigma AF ON: Quite a bit of searching on low contrast targets
(e.g., tree trunks.) Fairly quick “snap” to focus on a weed seed head 20 feet
away against a backdrop of the river ice 150 feet away. Quick “snap” to focus
on tree trunks across the river.
- Probably usable at 500mm/6.3 when tripod mounted, looking at
a stationary target with reasonably high contrast. Not sure I would try to
handhold this combination to pick out flying birds above. If nothing else, the
motor noise as it searched would get on my nerves.
2. Pentax FA 28-105/4-5.6 PZ (the original model of this lens)
With the lens at 28mm (presumably f/4.0)
- Quick albeit noisy focus on pretty much everything I looked
at.
(I had forgotten how noisy the AF is on non-SDM lenses!
It has been awhile.)
With the lens at 105mm (presumably f/5.6) [AV, dialed to “wide open”,
f/8.0 indicated on the display]
- Same results. Quick lock in on whatever targets.
If anyone wants to try this on a different lens, let me know and I’ll send you
my shipping address and return the results to you soonest. Or stop by and play
with it yourself.
I will have this with me on an upcoming trip to Sweden/Norway/Denmark and any
Pentaxians I encounter along the way are welcome to do a try out of the 1.4x.
stan
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