[axl]

I remmember, just can't find it anymore.

yes, unfortunately the search engine of our page is not the best one...
though it improved dramaticaly since I started frquenting these forums.

BR &
Good luck

[netuser]

If it is the Px-AF version it should work with SDM/HSM otherwise the contacts are not active.

It's the Pz-AF

[netuser]

.....

Bear in mind that even if you do get AF working, it might not actually work because the resulting f/8 aperture might not be bright enough for the AF sensor to lock focus. In this case what would happen is that the lens motor would whir back and forth but never achieve focus. But you'll never know unless you get the AF working.

I'm aware of that but I want to use it only for surf images at mid of the day so no problem

How did you mask the contacts? I assume you used think electrical tape.

I didn't have any so I use three layers of normal tape.
Will buy some tomorrow and also try it.

Thanks

[netuser]

Just found my "problem"...

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/38514-converti...erter-sdm.html

Will read it

[Pål Jensen]

Hi

Seems this is the right place

I would like to know if this specific teleconverter
(https://www.pentaxforums.com/forums/sold-items/56201-sale-sold-tamron-2x-mc7-af-tc.html) is supposed to work with the DA*300/4. (or other 2x teleconverter)

I mean, (not with SDM but) with screw.

I'm asking because this teleconverter with tamron 70-200 2.8 works perfectly (screw drive of course) but with my DA*300 (arrived today) only works on MF no SDM and no screw drive.

Any ideas ?

Thanks in advance

A 2X converter make your 300 F:4 lens into an F:8 lens. No camera will AF at a max aperture of F:8 (some camera/lens combination will attempt it but it won't be reliable or within the manufacturers specification). Thats why there are no AF lenses with a max aperture of F:8.
A 2X converter need a lens of max aperture of F:2.8 or faster to AF reliably...

[netuser]

A 2X converter make your 300 F:4 lens into an F:8 lens. No camera will AF at a max aperture of F:8 (some camera/lens combination will attempt it but it won't be reliable or within the manufacturers specification). Thats why there are no AF lenses with a max aperture of F:8.
A 2X converter need a lens of max aperture of F:2.8 or faster to AF reliably...

Not even at 1 pm full sun for surf images ?
(Azores Islands sun )

[netuser]

Pål Jensen, this means there is no way to have a 2x teleconverter to work screw AF with DA*300 ?

[Miserere]

Not even at 1 pm full sun for surf images ?
(Azores Islands sun )

Pal is quoting manufactuer's specs. The truth is quite different. You can achieve autofocus with an aperture of f/8 in good light, and even in decent light with certain lens combinations. For example, I have managed correct AF with the following lens + TC combinations:

• Sigma APO 70-300mm @300mm + Tamron 1.4x = 420mm f/8
• Tokina AT-X 400mm f/5.6 + Tamron 1.4x = 560mm f/8
• Tokina SD 400mm f/5.6 + Pentax FA 1.7x = 680mm f/9.4

That last combo only autofocuses in bright light, but the other two work fine in the shade during a sunny day.

All these combos worked with screwdrive AF. SDM, however, is a different beast. I tried the Tamron TC on the DA* 50-135mm f/2.8 and it wouldn't lock focus. It would hunt back and forth between close and infinity but only lock focus in really bright light with a very high contrast subject.

I don't know why SDM makes a difference, but it does.

Bottom line: If you manage to disable the SDM and get the screwdrive working, it's possible that you will get AF on the beach. If you do, the next question will be whether the IQ is any good.

[netuser]

For what I have been reading on the last couple of days in the forum it seems so far there isn't any way to get a 2x teleconverter to work with SDM lenses.... damn

Now I understand why is "everyone" waiting for a Pentax teleconverter.

[snostorm]

Pal is quoting manufactuer's specs. The truth is quite different. You can achieve autofocus with an aperture of f/8 in good light, and even in decent light with certain lens combinations. For example, I have managed correct AF with the following lens + TC combinations:

• Sigma APO 70-300mm @300mm + Tamron 1.4x = 420mm f/8
• Tokina AT-X 400mm f/5.6 + Tamron 1.4x = 560mm f/8
• Tokina SD 400mm f/5.6 + Pentax FA 1.7x = 680mm f/9.4

That last combo only autofocuses in bright light, but the other two work fine in the shade during a sunny day.

Actually, the improved low light AF capabilities of the K7 allow a lot more latitude in max aperture for AF. I've achieved reliable AF lock (slow but accurate) with an FA* 300/4.5 + Sigma EX 1.4x APO TC + P F 1.7x AFA (714mm, f10.7) and an FA*300/2.8 +Sigma 1.4x + Tamron 1.4x + 1.7x AFA (1000mm, f9.3) both on an overcast day with no shadows. Not my everyday setup, I was just playing around. . . the images were surprisingly good IMO.

I also tried the 1.7x AFA with the Tamron SP500/8 mirror, and it locks focus reliably (also slow), so I now have a 850/13.6 AF mirror lens if I want it for use on anthing brighter than a moderately overcast day.

Good low light AF sensitivity works for more than taking pics in the dark. . .

Scott

[netuser]

Yes, I see, but none of the lens with SDM

[shane33]

what would be the best brand TC to get to work with my sigma 70-300 f4-5-6 DG either 1.4x or 1.7x

[snostorm]

Yes, I see, but none of the lens with SDM

Hi netuser,

Sorry I cot carried away and went OT, but it's worth noting that the improved sensitivity of the K7's AF system allows for something of a change of the paradigm that AF won't work with slower lense/lens-TC combos.

I have a Tamron AF PZ 1.4 MC4 TC, and it doesn't work even close to acceptibly with my DA*50-135 -- hunts terribly, even in bright light. The only AF TC that does work well (both optically and mechanically) in AF with this lens is the P F 1.7x AFA, but it's the TC doing the focusing, not the lens.

Scott

[wtlwdwgn]

Netuser, I'm in the same boat. I have the DA*300 also and I have an F 1.7X Adapter. There is an extra contact on the adapter that is not on the lens and that's the one that reports the focal length. The screw drive works on the adapter but not on the lens. IIRC, the K10 or K20 firmware doesn't allow the DA* lenses to revert to the screw drive. I had an SDM failure on a DA*16-50 and it would not revert to the screw drive and would only MF. For the SDM to work the adapter has to have the SDM contacts on both the male and female mounts. I've looked for the Tamron adapters but have had no luck finding one and Tamron doesn't list one on their website now. I guess we'll have to wait for Pentax to bring out DA* adapters.

[Miserere]

Actually, the improved low light AF capabilities of the K7 allow a lot more latitude in max aperture for AF. I've achieved reliable AF lock (slow but accurate) with an FA* 300/4.5 + Sigma EX 1.4x APO TC + P F 1.7x AFA (714mm, f10.7) and an FA*300/2.8 +Sigma 1.4x + Tamron 1.4x + 1.7x AFA (1000mm, f9.3) both on an overcast day with no shadows. Not my everyday setup, I was just playing around. . . the images were surprisingly good IMO.

I also tried the 1.7x AFA with the Tamron SP500/8 mirror, and it locks focus reliably (also slow), so I now have a 850/13.6 AF mirror lens if I want it for use on anthing brighter than a moderately overcast day.

Good low light AF sensitivity works for more than taking pics in the dark. . .

Scott

Cool! I was using a K10D (I don't think I mentioned that). Good to know I can look forward to an improved TC experience when I get the K-7.

FA* 300/4.5 + Sigma EX 1.4x APO TC + P F 1.7x AFA

Holy crap