Question on Pentax tele-converter and SDM lens.


Teaman

Link Posted 11/06/2017 - 18:43
I have a Pentax K-F2 camera. Lens is a smc DA 18-270mm ED SDM. This is an auto-focus lens with hyper-motor in the lens and no mechanical focus-coupler to the body.
I have seen a tele-extender by Pentax: smc Pentax-F 1.7X AF adapter. it is not clear if it will convey the focusing information from camera to lens or if I will lose the auto-focus feature. Any information is welcome.

bforbes

Link Posted 11/06/2017 - 19:25
The Pentax 1.7X is not designed to transfer the AF from the lens. It was originally designed so you could have Auto focus with a Manual lens.
I think the original instruction was to set the manual focus lens at infinity and let the 1.7x do the focusing for you. In practice I found you were better off getting the focus somewhere near and let the 1.7x do the fine tuning.
Barrie
Too Old To Die Young
.
Pentax K1 K5-IIS K-01 K20D A50/2 A50/1.7 DA10-17 DA18-250 DA18-135 DA18-55 DA300 DA40 DA50-135 DA50-200 DA55-300 DA70 F35-70 DFA150-450 FA20-35 FA100 FA135 FA35 FA28 FA43 FA50 FA77 K55/1.8 M135/3.5 M200/4 M28/3.5 M28/2.8 M40/2.8 Q 01 02 MX-1 I-10 Sigma 15 24 105 180 8-16 10-20 17-35 17-50/2.8 24-70 400/5.6MF Tamron 70-200/2.8 17/3.5MF 24/2.5MF 28/2.5MF 90/2.5MF


http://www.pentaxphotogallery.com/artists/barrieforbes

LennyBloke

Link Posted 11/06/2017 - 21:11
bforbes wrote:
The Pentax 1.7X is not designed to transfer the AF from the lens. It was originally designed so you could have Auto focus with a Manual lens.
I think the original instruction was to set the manual focus lens at infinity and let the 1.7x do the focusing for you. In practice I found you were better off getting the focus somewhere near and let the 1.7x do the fine tuning.

Barrie is spot on. I use mine with MF and AF lenses regularly - you'll have to input the calculated focal length for the Shake Reduction system but once that's done exposure is calculated for you. These were taken with an F 100 Macro and the 1.7x AF converter the other day..







Excellent quality converter, highly recommended.

My spare will be available in a couple of weeks
LennyBloke

JAK

Link Posted 11/06/2017 - 22:24
SDM will work with the HD Pentax-DA AF Rear Converter 1.4x AW and adjust the focal length as reported by the lens.
Alternatively the Kenko (and others) AF/Pz-AF 1.4x will also work with SDM lenses but it doesn't adjust the focal length.
The Pentax 1.7x converter is really an adapter for converting a manual focus lens into an AF lens and does it really well. It's strange mounting an early manual focus K lens and have it respond to a press of the shutter release or AF button. With an A series lens it all works just like having an AF lens attached.
John K
Last Edited by JAK on 11/06/2017 - 22:26

LennyBloke

Link Posted 12/06/2017 - 12:41
JAK wrote:
SDM will work with the HD Pentax-DA AF Rear Converter 1.4x AW and adjust the focal length as reported by the lens.
Alternatively the Kenko (and others) AF/Pz-AF 1.4x will also work with SDM lenses but it doesn't adjust the focal length.
The Pentax 1.7x converter is really an adapter for converting a manual focus lens into an AF lens and does it really well. It's strange mounting an early manual focus K lens and have it respond to a press of the shutter release or AF button. With an A series lens it all works just like having an AF lens attached.

The HD Pentax-DA AF Rear Converter is probably the best converter I've used on APS-C, but the designers weren't on the same page as the Full Frame team when they released it - it vignettes on the K1 with some lenses at least - I know they couldn't be expected to predict significant changes in future Pentax bodies but a FF model has been on the cards for a long time

Some of the Kenko/Teleplus/Tamron PZ versions do work with SDM (depending on the particular type/model) but on the whole tend to be not quite as consistent as the Pentax HD model. There are many reports of focus hunting with some combinations, even when the lens has a relatively fast aperture.
LennyBloke
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