[golfcoachnoel]

Hello folks! Just got this teleconverter and was told that it would work just fine with all my pentad lens and K20. Well...I'm having a hard time making it autofocus with my lenses..Any help / advice would be greatly appreciated.

Thanks very much!

[dantuyhoa]

What lens do you use ? I don't have this TC but do have some other TCs . Generally, faster lenses ( f.28 or so ) will work better . Slower lenses will have focus hunt .

[snostorm]

Hi golfcoachnoel,

I use TCs pretty extensively. I don't have the Promaster, but have heard good things about it. From my experience with the Pentax F 1.7x AFA, I've had good AF performance with lenses with max apertures of f4.5 and faster in anything brighter than about Ev 12 (heavy overcast) with any of the Pentax DSLR bodies.

The problem with TCs is that you lose maximum Aperture value in direct proportion to the magnification factor (so you need to multiply your lens' max Av by the x factor of your TC to get the effective max Av with the TC). Pentax DSLR bodies will usually AF reasonably with effective max Av of about f8 or faster. There are other factors involved like lens contrast and sharpness wide open, and the particular body (the newer Kx and K-7 have more sensitive AF sensors).

Scott

[golfcoachnoel]

What lens do you use ? I don't have this TC but do have some other TCs . Generally, faster lenses ( f.28 or so ) will work better . Slower lenses will have focus hunt .

Hi! I use a DA* 16-50 f/2.8, DA* 300 f/4 and a DFA 100macro f/2.8.

Thanks

[golfcoachnoel]

What lens do you use ? I don't have this TC but do have some other TCs . Generally, faster lenses ( f.28 or so ) will work better . Slower lenses will have focus hunt .

Hi golfcoachnoel,

I use TCs pretty extensively. I don't have the Promaster, but have heard good things about it. From my experience with the Pentax F 1.7x AFA, I've had good AF performance with lenses with max apertures of f4.5 and faster in anything brighter than about Ev 12 (heavy overcast) with any of the Pentax DSLR bodies.

The problem with TCs is that you lose maximum Aperture value in direct proportion to the magnification factor (so you need to multiply your lens' max Av by the x factor of your TC to get the effective max Av with the TC). Pentax DSLR bodies will usually AF reasonably with effective max Av of about f8 or faster. There are other factors involved like lens contrast and sharpness wide open, and the particular body (the newer Kx and K-7 have more sensitive AF sensors).

Scott

Thanks...not sure what your saying but...I should use aperture 8 or smaller for it to focus better? I thought it was broken or something hehehe! I guess when it comes to teleconverting I would just use manual focus ?

Thanks

[ivoire]

The Pentax 1.7 AF TC and the Kenko 1.5x SHQ TC are the only 2 that I know of that work on SDM lenses. Some say the Promaster will not auto focus with SDM, others say it will.

[pcarfan]

Hello folks! Just got this teleconverter and was told that it would work just fine with all my pentad lens and K20. Well...I'm having a hard time making it autofocus with my lenses..Any help / advice would be greatly appreciated.

Thanks very much!

According to this post, it works with SDM lenses in the K-x and K-7 but not the older models.

A Pronghorn antelope sequence...: Pentax SLR Talk Forum: Digital Photography Review

[nater]

According to this post, it works with SDM lenses in the K-x and K-7 but not the older models.

A Pronghorn antelope sequence...: Pentax SLR Talk Forum: Digital Photography Review

I think you are confusing the Pentax-F 1.7x AF teleconverter with the Promaster 1.7x teleconverter. They operate very differently:

1) The Pentax-F 1.7x does not allow a lens to do autofocussing itself because the Pentax-F 1.7x does the autofocussing. The screw drive AF from the camera body drives the Pentax-F 1.7 teleconverter's AF system, moving the teleconverter lens elements. Typically a photographer using this teleconverter will operate the lens in manual focus mode to get an approximate focus, followed by having the camera body/teleconverter perform the fine focus automatically before the shot is taken. The AF screw drive does not extend beyond the Pentax-F 1.7x teleconverter, and the Pentax-F 1.7 teleconverter does not pass the power through the PZ (PowerZoom) contacts that SDM (Supersonic Drive Motor) lenses need to AF themselves. In the EXIF data, the teleconverter identifies itself (and I think it reports the adjusted f-stop for loss of light due to it's presence, but someone who has this teleconverter may have to correct me on this last point).

2) The Promaster 1.7x teleconverter does not itself have any AF motor and it's elements do not move. It passes the AF drive screw for standard AF lenses and has PZ contacts on both sides so power from the camera body reaches SDM lenses (whether they can focus correctly or not seems to vary depending on lens/body combinations however). There is no modification of any data communicated between the lens and the body, so the lens and body do not realize there is a teleconverter present. The EXIF data doesn't record any presence of the teleconverter since all data is simply passed, making the recorded focal length and f-stop incorrect for shots taken with the teleconverter in place. Shake reduction also can't work optimally in this scenario, as it is not operating with entirely correct data regarding focal length with the teleconverter in place (but since Pentax shake reduction is reported to make the least different with extreme telephoto lenses, and teleconverters work best with telephoto lenses, this may not be a significant issue).

[pcarfan]

Nater, I have used the Pentax 1.7 X AFA before, and currently have the Promaster for sale at the marketplace.

The thread I had quoted was discussing mosltly the Promaster TC, and I am fairly certain Ron was referring to the Promaster. Whether SDM will work or not work is irrelevant for the Pentax AFA exactly because of the way it works, and therefore if he was referring to the Pentax 1.7 AFA why would he say it wouldn't work with the K20D and the K10D ?

[nater]

Nater, I have used the Pentax 1.7 X AFA before, and currently have the Promaster for sale at the marketplace.

The thread I had quoted was discussing mosltly the Promaster TC, and I am fairly certain Ron was referring to the Promaster. Whether SDM will work or not work is irrelevant for the Pentax AFA exactly because of the way it works, and therefore if he was referring to the Pentax 1.7 AFA why would he say it wouldn't work with the K20D and the K10D ?

'brandrx' (Ron) started the thread by comparing the Tamron 1.4X Pz_AF and Promaster 1.7X Pz_AF. Then 'Nicols' posted about the Kenko Teleplus 1,5 SHQ. 'Radam FG' made a comment about the Pentax 1.7 autofocus adapter.

'brandrx' wrote on Jan 6, "Also, this morning I tried the DA*200mm f2.8 on the K-x and the K-7 using the Promaster 1.7X then the Tamron 1.4X. Both failed to focus, the same as I wrote in the leink [sic] above about the DA*300mm f4." (Note that the DA* 300mm f4 is an SDM lens!)

If you follow his link, in that post he says, "This DA*300/4 really sucks when trying to use it with the Tamron 1.4X, Kenko 1.5X, or Promaster 1.7X teleconverters. Jerky focusing and takes forever to get it into focus. These are not good combinations at all. However, the Pentax-F 1.7X AF Adapter + DA*300mm f4 is very, very good IMO." So therefore we know that brandrx has (or has used) a Pentax-F 1.7X AF Adapter, as well as the other teleconverters.

It's not clear what's going on with the testing 'brandrx' is doing with teleconverters and SDM lenses, and he doesn't seem to offer any theories either, saying things such as "After going through all of this again, it seems strange to me that the DA*200mm f2.8 does not work with the K-7 either, in my tests that is."

Meanwhile, it is 'tcom' who posts, "So far, I took for the wildlife the 50-135, the DA*200 and the DA*300, and the Pentax F 1.7x AF converter for the extra reach... But does the 1.7x AF converter perform good enough on the 60-250 to leave the 300 at home?" Then 'brandrx' responds with the post about the "Pronghorn antelope sequence" which you link to, and unless 'brandrx' is really confused both in his response and what he had posted back in July of last year, he is now talking about the Pentax-F 1.7 AF teleconverter (and is what you originally linked to).

I can't explain why 'brandrx' said the Pentax 1.7 AFA wouldn't work with the K20D and the K10D... I've never heard anyone make any claims like that here.

What I have read here about the Promaster is that SDM performance is not consistent with SDM lenses, but that it does typically work, at least to some extent. There have been different theories for why it doesn't work as well as people think it should, but nothing conclusive.

My personal guess is that since the PZ letters in the teleconverter model name refer to PowerZoom, it all predates SDM, which has re-used the PowerZoom contacts, and since all teleconverters with PZ contacts are third party, I'd say Pentax has done very little if any compatibility testing or tweaking with their SDM lenses and firmware when a PZ teleconverter is present.

In the meantime, if I were you, I would stop quoting people like 'brandrx' who don't seem to have a clear idea of what exactly is going on (and/or can't keep track of what teleconverter he's writing about), and not make any guarantees about the Promaster being compatible with particular SDM lenses and/or bodies, since I don't think there's any conclusive information on that, just anecdotal. Instead just mention the PZ contacts are there on both sides of the teleconverter, so people might get some SDM functionality with certain lens/body combinations. Good luck with your sale.

[golfcoachnoel]

Holy cow! I should scream at the store that sold this thing to me..I mainly got this for my DA*300 for additional reach but I haven't had autofocusing work for me yet. I guess it will have to be manual for now till i replace get the real stuff (Pentax TC). Oh well...!!!

Thanks guys for all the technical info you shared!

Anyone wanna buy a Promaster TC ? lol

[pcarfan]

'brandrx' (Ron) started the thread by comparing the Tamron 1.4X Pz_AF and Promaster 1.7X Pz_AF. Then 'Nicols' posted about the Kenko Teleplus 1,5 SHQ. 'Radam FG' made a comment about the Pentax 1.7 autofocus adapter.

'brandrx' wrote on Jan 6, "Also, this morning I tried the DA*200mm f2.8 on the K-x and the K-7 using the Promaster 1.7X then the Tamron 1.4X. Both failed to focus, the same as I wrote in the leink [sic] above about the DA*300mm f4." (Note that the DA* 300mm f4 is an SDM lens!)

If you follow his link, in that post he says, "This DA*300/4 really sucks when trying to use it with the Tamron 1.4X, Kenko 1.5X, or Promaster 1.7X teleconverters. Jerky focusing and takes forever to get it into focus. These are not good combinations at all. However, the Pentax-F 1.7X AF Adapter + DA*300mm f4 is very, very good IMO." So therefore we know that brandrx has (or has used) a Pentax-F 1.7X AF Adapter, as well as the other teleconverters.

It's not clear what's going on with the testing 'brandrx' is doing with teleconverters and SDM lenses, and he doesn't seem to offer any theories either, saying things such as "After going through all of this again, it seems strange to me that the DA*200mm f2.8 does not work with the K-7 either, in my tests that is."

Meanwhile, it is 'tcom' who posts, "So far, I took for the wildlife the 50-135, the DA*200 and the DA*300, and the Pentax F 1.7x AF converter for the extra reach... But does the 1.7x AF converter perform good enough on the 60-250 to leave the 300 at home?" Then 'brandrx' responds with the post about the "Pronghorn antelope sequence" which you link to, and unless 'brandrx' is really confused both in his response and what he had posted back in July of last year, he is now talking about the Pentax-F 1.7 AF teleconverter (and is what you originally linked to).

I can't explain why 'brandrx' said the Pentax 1.7 AFA wouldn't work with the K20D and the K10D... I've never heard anyone make any claims like that here.

What I have read here about the Promaster is that SDM performance is not consistent with SDM lenses, but that it does typically work, at least to some extent. There have been different theories for why it doesn't work as well as people think it should, but nothing conclusive.

My personal guess is that since the PZ letters in the teleconverter model name refer to PowerZoom, it all predates SDM, which has re-used the PowerZoom contacts, and since all teleconverters with PZ contacts are third party, I'd say Pentax has done very little if any compatibility testing or tweaking with their SDM lenses and firmware when a PZ teleconverter is present.

In the meantime, if I were you, I would stop quoting people like 'brandrx' who don't seem to have a clear idea of what exactly is going on (and/or can't keep track of what teleconverter he's writing about), and not make any guarantees about the Promaster being compatible with particular SDM lenses and/or bodies, since I don't think there's any conclusive information on that, just anecdotal. Instead just mention the PZ contacts are there on both sides of the teleconverter, so people might get some SDM functionality with certain lens/body combinations. Good luck with your sale.

Thank you very much for the explanation, it makes sense now. Ron's assertion that the 1.7 TC wouldn't work on K-10D and K20D is what threw me off. Appreciate your help.

[Russell-Evans]

Holy cow! I should scream at the store that sold this thing to me..I mainly got this for my DA*300 for additional reach but I haven't had autofocusing work for me yet. I guess it will have to be manual for now till i replace get the real stuff (Pentax TC). Oh well...!!!

Thanks guys for all the technical info you shared!

Anyone wanna buy a Promaster TC ? lol

The ProMaster 1.7x seems to not be able to work with the AF and SDM to correct in small enough steps on the K20D and K10D with the DA 50-135mm. The AF bounced between two points in my testing and would never lock. The TC works very well it with my screw driven lenses. If Pentax would just release a firmware that allowed for the choice of SDM or screw driven AF, we wouldn't be scrounging for TC that might or might not work with SDM. A happy customer base, imagine that?

Thank you
Russell

[nater]

The ProMaster 1.7x seems to not be able to work with the AF and SDM to correct in small enough steps on the K20D and K10D with the DA 50-135mm. The AF bounced between two points in my testing and would never lock.

I wonder... does SDM perhaps 'step' the focus in discrete increments based off of focal length data it's receiving from the lens? focal length data which isn't being modified (and therefore off by a factor of 1.7x in the case of the Promaster teleconverter)? If so, another way that Pentax could address this in firmware is if they enabling the ability for the user to manually specify that a teleconverter was in use, letting the body multiply the focal length data and modify the f-stop data, which besides resulting in more correct EXIF information might also result in better SDM operation, if it does somehow work in concert with the reported focal lengths.

[Russell-Evans]

I wonder... does SDM perhaps 'step' the focus in discrete increments based off of focal length data it's receiving from the lens? focal length data which isn't being modified (and therefore off by a factor of 1.7x in the case of the Promaster teleconverter)?

Why would the Tamron 1.4x or the Kenko 1.5x work if this was the case?

Thank you
Russell