Since the lens was wide open it wasn't really focusing at f22, it was
focusing at ~f5.6. Now the relatively slow Pentax FA 28-105 with an
effective aperture wide open of 8.0 with a 1.4x TC is getting to be a
test. There ate two things that effect auto focus, absolute aperture,
and absolute light level. I expect that in bright light that even f8
lenses of a long enough focal length will have no great issue auto
focusing.
On 3/26/2014 8:09 PM, Paul Stenquist wrote:
I shot a frame at f22 last week with the 1.4x and 60-250. It focused quickly.
Paul via phone
On Mar 26, 2014, at 7:01 PM, Stanley Halpin <s...@stans-photography.info> wrote:
I’ll further explore that question tomorrow.
stan
On Mar 26, 2014, at 2:59 PM, Ken Waller <kwal...@peoplepc.com> wrote:
I'm more interested in the smaller aperatures at which it fails to focus. It would
be nice to be able to use it on my 600. I have both the A-1.4X-L & A2.0X-L but
of course I lose AF with those.
Kenneth Waller
http://www.pentaxphotogallery.com/kennethwaller
----- Original Message ----- From: "Rob Studdert" <distudio.p...@gmail.com>
Subject: Re: Because inquiring minds want to know (more on the 1.4x)
Thanks for the report Stan, it does look useful, but I will have to
sell a K5 body to afford it :(
On 21 March 2014 02:38, Stanley Halpin <s...@stans-photography.info> wrote:
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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