2x KAX Teleplus with K3

**longbo** · 05-03-2018, 01:26 AM

I'm trying to use a KAX Teleplus with my Pentax 55-300 DA 4.5-5.8 version on a K3. I know the KAX is manual focus, but I had thought it would be able to detect the focal length of the lens - albeit not the correct figure allowing for the doubling effect. However, when I switch on my K3, it asks for the lens focal length - is this expected. I can then control the aperture of the lens from the camera OK, but the indicated value is not correct. Again, I don't expect it to allow for the 2 stop change from the converter, but I had expected the displayed figure to be correct otherwise? I have "Aperture Ring Permitted" set on the camera, so it fires OK.

When I open the lens at maximum zoom, the indicated aperture is 4.5, when it should be 5.8 - I presume this may be because the camera doesn't know the focal length that's been set?

Is this behaviour correct, or do I have a faulty KAX Teleplus?

Apart from this focal length / aperture issue, the converter appears to work well, so I don't have the problem reported by galegg in 2015

Any help appreciated!

Ole · 05-03-2018, 04:21 AM

Originally posted by longbo

I'm trying to use a KAX Teleplus with my Pentax 55-300 DA 4.5-5.8 version on a K3. I know the KAX is manual focus, but I had thought it would be able to detect the focal length of the lens - albeit not the correct figure allowing for the doubling effect. However, when I switch on my K3, it asks for the lens focal length - is this expected.

Yes, that is expected. The KAX teleconverter does not transmit the focal length to the camera. It lacks the digital information contact with which to do so.

Originally posted by longbo

I can then control the aperture of the lens from the camera OK, but the indicated value is not correct. Again, I don't expect it to allow for the 2 stop change from the converter, but I had expected the displayed figure to be correct otherwise? I have "Aperture Ring Permitted" set on the camera, so it fires OK.

When I open the lens at maximum zoom, the indicated aperture is 4.5, when it should be 5.8 - I presume this may be because the camera doesn't know the focal length that's been set?

Is this behaviour correct, or do I have a faulty KAX Teleplus?

Since the focal length is not known by the camera the F-stop values displayed are assuming that the zoom is at its shortest focal length. Therefore it shows F4.5 when the aperture is fully open regardless of focal length. Also, if zoomed in, any displayed value will be off. This behavior is expected.

**longbo** · 05-03-2018, 06:36 AM

Thanks for the info, which is disappointing.

Why does the Teleplus have all those 7 contacts then? It would seem that not too many of 'em work!

Ole · 05-03-2018, 08:25 AM

If the converter in this link is the one you have, it just has six contacts.

The only teleconverter on the market with full functionality is the Pentax-DA 1.4x converter. As you can see on the image in the link it has seven lens information contacts (plus two power contacts inside the mount).

You can read all about the various K-mount variants and their electrical contacts in this article.

**longbo** · 05-03-2018, 09:19 AM

Thanks again Ole. I do have the converter you illustrate, except mine's the MC7 version. There are 7 contacts, but having inspected my camera, the seventh doesn't connect to anything on the camera!, so just the 6 you mention can be used.

As I said, it's disappointing - the Pentax converter is rather too expensive.

Cardinal15 · 05-03-2018, 11:04 AM

longbo, sadly you are correct the Pentax 1.4 is too expensive, however there are alternatives. I have both the Quantaray 2XAF, and Tamron F 1.4X Pz-AF MC4. They look virtually identical so Quantaray (the old 'house brand' of Ritz & Wolf camera stores) likely sourced Tamron as the manufacturer. Each have the old Power Zoom contacts so they work with all the modern SDM lenses and the other contacts pass along all the EXIF data including focal length. As far as using them I greatly prefer the Tamron 1.4.it does not reach as far but the results are excellent the Quant 2X clearly has image degradation as most 2X teleconverters suffer.Both of these are available across the web at much better prices than the Pentax 1.4.I highly recommend the Tamron 1.4 it gives you AF and makes your 55-300 an 80-420 and very usable.

**longbo** · 05-06-2018, 01:46 AM

I've not managed to find a Tamron or Quantaray converter here in the UK, but I have found a Sigma model. However, this model appears to be designed to work with specific Pentax-fit Sigma lenses - there may be a physical issue with the position of the rear optic on the lens and the mounting into the converter?. Has anyone tried the Sigma converter with Pentax lenses?

There is also apparently a Kenko converter that does provide full AF and focal length communication, but the MC7 version is discontinued and I've not found a used one as yet.

05-03-2018, 01:26 AM	#1
longbo Loyal Site Supporter Join Date: Apr 2018 Posts: 98	2x KAX Teleplus with K3 I'm trying to use a KAX Teleplus with my Pentax 55-300 DA 4.5-5.8 version on a K3. I know the KAX is manual focus, but I had thought it would be able to detect the focal length of the lens - albeit not the correct figure allowing for the doubling effect. However, when I switch on my K3, it asks for the lens focal length - is this expected. I can then control the aperture of the lens from the camera OK, but the indicated value is not correct. Again, I don't expect it to allow for the 2 stop change from the converter, but I had expected the displayed figure to be correct otherwise? I have "Aperture Ring Permitted" set on the camera, so it fires OK. When I open the lens at maximum zoom, the indicated aperture is 4.5, when it should be 5.8 - I presume this may be because the camera doesn't know the focal length that's been set? Is this behaviour correct, or do I have a faulty KAX Teleplus? Apart from this focal length / aperture issue, the converter appears to work well, so I don't have the problem reported by galegg in 2015 Any help appreciated!

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05-03-2018, 04:21 AM	#2
Ole Administrator Join Date: Sep 2006 Location: Copenhagen, Denmark Photos: Gallery \| Albums Posts: 4,409	Originally posted by longbo I'm trying to use a KAX Teleplus with my Pentax 55-300 DA 4.5-5.8 version on a K3. I know the KAX is manual focus, but I had thought it would be able to detect the focal length of the lens - albeit not the correct figure allowing for the doubling effect. However, when I switch on my K3, it asks for the lens focal length - is this expected. Yes, that is expected. The KAX teleconverter does not transmit the focal length to the camera. It lacks the digital information contact with which to do so. Originally posted by longbo I can then control the aperture of the lens from the camera OK, but the indicated value is not correct. Again, I don't expect it to allow for the 2 stop change from the converter, but I had expected the displayed figure to be correct otherwise? I have "Aperture Ring Permitted" set on the camera, so it fires OK. When I open the lens at maximum zoom, the indicated aperture is 4.5, when it should be 5.8 - I presume this may be because the camera doesn't know the focal length that's been set? Is this behaviour correct, or do I have a faulty KAX Teleplus? Since the focal length is not known by the camera the F-stop values displayed are assuming that the zoom is at its shortest focal length. Therefore it shows F4.5 when the aperture is fully open regardless of focal length. Also, if zoomed in, any displayed value will be off. This behavior is expected.

05-03-2018, 06:36 AM	#3
longbo Loyal Site Supporter Join Date: Apr 2018 Posts: 98 Original Poster	Thanks for the info, which is disappointing. Why does the Teleplus have all those 7 contacts then? It would seem that not too many of 'em work!

05-03-2018, 08:25 AM	#4
Ole Administrator Join Date: Sep 2006 Location: Copenhagen, Denmark Photos: Gallery \| Albums Posts: 4,409	If the converter in this link is the one you have, it just has six contacts. The only teleconverter on the market with full functionality is the Pentax-DA 1.4x converter. As you can see on the image in the link it has seven lens information contacts (plus two power contacts inside the mount). You can read all about the various K-mount variants and their electrical contacts in this article.

05-03-2018, 09:19 AM	#5
longbo Loyal Site Supporter Join Date: Apr 2018 Posts: 98 Original Poster	Thanks again Ole. I do have the converter you illustrate, except mine's the MC7 version. There are 7 contacts, but having inspected my camera, the seventh doesn't connect to anything on the camera!, so just the 6 you mention can be used. As I said, it's disappointing - the Pentax converter is rather too expensive.

05-03-2018, 11:04 AM	#6
Cardinal15 Junior Member Join Date: Aug 2015 Location: Massachusetts Posts: 31	longbo, sadly you are correct the Pentax 1.4 is too expensive, however there are alternatives. I have both the Quantaray 2XAF, and Tamron F 1.4X Pz-AF MC4. They look virtually identical so Quantaray (the old 'house brand' of Ritz & Wolf camera stores) likely sourced Tamron as the manufacturer. Each have the old Power Zoom contacts so they work with all the modern SDM lenses and the other contacts pass along all the EXIF data including focal length. As far as using them I greatly prefer the Tamron 1.4.it does not reach as far but the results are excellent the Quant 2X clearly has image degradation as most 2X teleconverters suffer.Both of these are available across the web at much better prices than the Pentax 1.4.I highly recommend the Tamron 1.4 it gives you AF and makes your 55-300 an 80-420 and very usable.

05-06-2018, 01:46 AM	#7
longbo Loyal Site Supporter Join Date: Apr 2018 Posts: 98 Original Poster	I've not managed to find a Tamron or Quantaray converter here in the UK, but I have found a Sigma model. However, this model appears to be designed to work with specific Pentax-fit Sigma lenses - there may be a physical issue with the position of the rear optic on the lens and the mounting into the converter?. Has anyone tried the Sigma converter with Pentax lenses? There is also apparently a Kenko converter that does provide full AF and focal length communication, but the MC7 version is discontinued and I've not found a used one as yet.