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04-14-2021, 07:19 AM   #1
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Pentax-DA Rear Converter 1.4x Question

I have a Pentax K70 that I purchased last year from B&H with the standard Pentax DA 18-135 ED AL IF DC WR lens. I have subsequently acquired the HD Pentax DA 55-300mm F4-5.8 ED WR lens (not the PLM version). I'm finding for my nature photography (I have a number of rather reclusive bald eagles living nearby) that I need a little extra distance on my 55-300mm lens. I'm looking into the Pentax 1.4x rear converter as an option for a longer reach with that 55-300 lens. However, I'm confused by Pentax's comments in their lens guide about this combination of the 1.4X converter and the HD DA 55-300 lens. Pentax states the converter may not properly auto focus with a camera that has a "phased matched" AF system.
I have no idea what this means and if my Pentax K70 has this type of system. Can you tell me if the Pentax 1.4x converter will autofocus with my K70 and the two lenses listed above.

Thanks,
Jim Krause

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File Type: pdf Page 21 from Pentax lenses & accessories.pdf (1.79 MB, 18 views)
04-14-2021, 07:48 AM   #2
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I think it would work as expected.
The 55-300 PLM would not have aperture control with that converter, non-PLM will be just fine.
I do have my reservations about using a converter with a variable aperture lens, but for your bright and outdoor bald eagles it may work fine.
04-14-2021, 08:03 AM   #3
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I have a Pentax 1.4x rear converter that I sometimes use on my smc DA-l 55-300 4-5.8 (non plm). It works quite well. The thing with the converter is you lose a stop, so my f5.8 becomes f8. Which means you need Good light for it to focus properly. Even on my K50 it works surprising well, in brite light. I've never used the converter with my 18-135.
04-14-2021, 08:34 AM - 1 Like   #4
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QuoteOriginally posted by FozzFoster Quote
I think it would work as expected.
The 55-300 PLM would not have aperture control with that converter, non-PLM will be just fine.
I do have my reservations about using a converter with a variable aperture lens, but for your bright and outdoor bald eagles it may work fine.
Where do you get the idea that the DA converter won't control the aperture on a KAF4 lens?

04-14-2021, 08:49 AM - 1 Like   #5
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QuoteOriginally posted by FozzFoster Quote
I think it would work as expected.
The 55-300 PLM would not have aperture control with that converter, non-PLM will be just fine.
I do have my reservations about using a converter with a variable aperture lens, but for your bright and outdoor bald eagles it may work fine.
Fozz, here is the list of HD DA 1.4x compatible lenses:
HD PENTAX-DA AF REAR CONVERTER 1.4X AW / Converter / AF Lens Adapter / K-mount Lenses / Lenses / Products | RICOH IMAGING
04-14-2021, 08:50 AM   #6
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The following two images were taken with the K70 with the 55-300 (non PLM) and the 1.4 tc attached, images aren't as sharp as using the 60-250 and tc, but everything works fine.



04-14-2021, 08:53 AM - 1 Like   #7
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QuoteOriginally posted by FozzFoster Quote
I think it would work as expected.
The 55-300 PLM would not have aperture control with that converter, non-PLM will be just fine.
I do have my reservations about using a converter with a variable aperture lens, but for your bright and outdoor bald eagles it may work fine.
Fozz, here is the list of HD DA 1.4x compatible lenses, and as you mentioned there is a note attached to the use of the 55-300PLM version with it:
HD PENTAX-DA AF REAR CONVERTER 1.4X AW / Converter / AF Lens Adapter / K-mount Lenses / Lenses / Products | RICOH IMAGING
04-14-2021, 08:59 AM   #8
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QuoteOriginally posted by boriscleto Quote
Where do you get the idea that the DA converter won't control the aperture on a KAF4 lens?
Although never personally tested, this is what I was informed of...

QuoteOriginally posted by gatorguy Quote
and as you mentioned there is a note attached to the use of the 55-300PLM version with it:

And gatorguy seems to have found your answer!

04-14-2021, 09:05 AM   #9
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QuoteOriginally posted by FozzFoster Quote
Although never personally tested, this is what I was informed of...




And gatorguy seems to have found your answer!
The note attached is
QuoteQuote:
*2 AF support confirmed model: K-1 Mark II/K-1/K-70/KP/K-3 II / K-3 / K-S2 / K-S1 / K-50 / K-30 / K-5II / K-5 IIs / K-5 / K-01 / K-7 / K-r (Update of latest body firmware is needed)
Nothing about aperture control. And I can assure you the aperture works just fine.
04-14-2021, 09:07 AM   #10
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QuoteOriginally posted by boriscleto Quote
Nothing about aperture control. And I can assure you the aperture works just fine.
That is the #2 at the bottom.. look at the legend at the top for the triangle.
"compatible with condition"
The chart is saying AF works fine, but there is a condition. What's the condition? It's the aperture.

---------- Post added 04-14-21 at 10:11 AM ----------

QuoteOriginally posted by boriscleto Quote
And I can assure you the aperture works just fine.
You so sure?

KAF4 - electromagnetic diaphragm:

"This lens can be used on PENTAX K-1, K-3 II, K-S2 and K-S1 by firmware upgrade. If this lens is mounted on a camera without proper firmware upgrade, its diaphragm control mechanism becomes inactive, making it impossible to obtain correct exposure."


Table of Functions by Mount / Lens lineup/ Lenses / Products | RICOH IMAGING
04-14-2021, 09:22 AM   #11
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QuoteOriginally posted by FozzFoster Quote
That is the #2 at the bottom.. look at the legend at the top for the triangle.
"compatible with condition"
The chart is saying AF works fine, but there is a condition. What's the condition? It's the aperture.

---------- Post added 04-14-21 at 10:11 AM ----------



You so sure?

KAF4 - electromagnetic diaphragm:

"This lens can be used on PENTAX K-1, K-3 II, K-S2 and K-S1 by firmware upgrade. If this lens is mounted on a camera without proper firmware upgrade, its diaphragm control mechanism becomes inactive, making it impossible to obtain correct exposure."


Table of Functions by Mount / Lens lineup/ Lenses / Products | RICOH IMAGING
Yes. If you set the aperture and a long exposure and look in the front of the lens you can see it stop down when you open the shutter. The condition is *2...that the AF works with the latest firmware. KAF4 aperture compatibility was added to the K-50 and K-3 some months after release. The K-30 can be made to work with K-50 firmware. The K-5, K-5 II, and other older cameras were left out.

K-3 firmware download...

QuoteQuote:
Changes to V1.30
Corresponded to [KAF4 lens mount] that is equipped with an electromagnetic diaphragm control system.

Enable new lens HD PENTAX-DA 55-300mmF4.5-6.3ED PLM WR RE to shoot stable by updating firmware.
Improved stability for general performance.

*Contents of [Version 1.21] and earlier version will be also updated.
04-14-2021, 09:38 AM   #12
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QuoteOriginally posted by boriscleto Quote
K-3 firmware download...
I had been told it's an issue with the converter, not the camera.
04-14-2021, 09:44 AM - 1 Like   #13
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QuoteOriginally posted by FozzFoster Quote
I had been told it's an issue with the converter, not the camera.
You were told wrong. Amazing how incomplete information can lead to disinformation in the era of instant information access. For years Sigma's US lens information pages said OS doesn't work with Pentax cameras. It was only partial information, Sigma Japan added that OS and HSM didn't work with Pentax film SLRs, the *ist series and the K100D / K110D. But it was said on this site in many posts that the OS wasn't functional on K-mount.

Last edited by boriscleto; 04-14-2021 at 09:53 AM.
04-14-2021, 09:49 AM - 1 Like   #14
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QuoteOriginally posted by boriscleto Quote
You were told wrong.
Well, I guess that's good news then.
04-14-2021, 10:20 AM   #15
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I use the ks2 with 55-300 plm and 1.4x tc all the time. I use it more to get a picture for inaturalist data than to get a nice picture.
The big one that flew away - PentaxForums.com
But it helps as explained some on above link.
If this link works it is eagles from 2 days ago. The first pic was closer and the 1.4x didn't help but the second pic wouldn't happen because af wouldnt focus through the trees and they were too small in the viewfinder for mf. I would need a tripod and zoomed focus.
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