[PMunks]

I just bought a 1.4x TC expecting to have to short out the data pin to enable focus confirm & CIF, tried it out without modification & found that autofocus works.
It worked quickly even though the light was pretty poor.
Has anyone else found this?

[Lowell Goudge]

I just bought a 1.4x TC expecting to have to short out the data pin to enable focus confirm & CIF, tried it out without modification & found that autofocus works.
It worked quickly even though the light was pretty poor.
Has anyone else found this?

Why wouldn't it work, and why did you think you had to short out pins.

this combo represents F6.3 I believe and is within any camera's ability to auto focus, it is only when you go to combinations f* and slower that you really have trouble.

[PMunks]

Why wouldn't it work, and why did you think you had to short out pins.

this combo represents F6.3 I believe and is within any camera's ability to auto focus, it is only when you go to combinations f* and slower that you really have trouble.

The sigma spec sheet (& web site) says that it is manual focus only plus it has always been given as a disadvantage v Canon 500mm.

The AF limit is F5.6 where I have seen it.

[Biro]

My Pentax 18-250mm f/3.5-6.3 superzoom lens has no problem auto focusing at the long end... f/6.3 is just fine in any kind of halfway-decent light. I've heard that f/5.6 figure in a few places myself. I'm not sure where that comes from. Perhaps, as light begins to fade completely, f/6.3 will run into problems first. That makes sense. But in general use, it's fine.

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Last edited by Biro; 06-10-2010 at 11:14 AM.

[Lowell Goudge]

The sigma spec sheet (& web site) says that it is manual focus only plus it has always been given as a disadvantage v Canon 500mm.

The AF limit is F5.6 where I have seen it.

impossible re AF limit

the bigma would not AF if this was the case.

Not sure where you got your info but there are just too many lenses at F6.3 to 6.7 which are sold by all lens makers for this maximum aperture to be a limit.

If you follow the forum threads frequently you will see a lot of dicsussion about the SMC-F 1.7x AF TC.

This works reliably on any F4 lens and the 1.7x factor translates to 510mm F7.1 I think. It has been reported to work on the SMC 500 F4.5 also, which would take you to F8 although I have no first hand experience of that. I do have first hand experience with the 1.7x TC on AF bodies back as far as the PZ-1 with no issue so the F7 limit for AF working has been around for some 20 years.

Where ever you got it, it is bad information.

[PMunks]

Where ever you got it, it is bad information.

This would be the Sigma web site Tele Converter matching list

I posted my experience with the combination because it seems to contradict the manufacturer's specification & it might be of interest to anyone considering a 500mm lens. This subject has been quite widely discussed. The normal conclusion is that the lens is well capable of AF with a 1.4 tc but is crippled by the manufacturers. This might be true, I don't know.

The Pentax 1.7x (which I also own) is a poor example because it does it's own AF. It does not work with the 500mm F4.5 btw.

[Lowell Goudge]

This would be the Sigma web site Tele Converter matching list

yeah looking at my product sheet for the TC it shows MF also, but since the TC reports the native lens aperture to the camera, the camera does not know it is connected. Based on the performance of pentax cameras, known by all those who push the limits, I am not surprised it works, but more surprised that even sigma won't gaurantee it.

I posted my experience with the combination because it seems to contradict the manufacturer's specification & it might be of interest to anyone considering a 500mm lens. This subject has been quite widely discussed. The normal conclusion is that the lens is well capable of AF with a 1.4 tc but is crippled by the manufacturers. This might be true, I don't know.

perhaps for nikon and canon, but clearly not for pentax.

The Pentax 1.7x (which I also own) is a poor example because it does it's own AF. It does not work with the 500mm F4.5 btw.

Interesting, but note that the pentax TC modifies the native aperture reported to the camera to include that of the TC, so the camera might just figure things out and disable AF. WHat happens if you put the lens out of A and use the aperture ring, does it work then, because in this case the reading of the aperture is disabled?

Also note that pentax cameras can't read what is published. the 1.7x AF TC manual states AF only for lenses faster than F2.8, but every one uses them on F4 lenses. When I bought mine in 1991, pentax canada let me try one out on my F4 because the store wanted a 20% restocking charge if I didn't want it. Pentax was only a few miles from me and I arranged a test through their service group at the time. It worked so I bought it (through a store)

[PMunks]

Interesting, but note that the pentax TC modifies the native aperture reported to the camera to include that of the TC, so the camera might just figure things out and disable AF. WHat happens if you put the lens out of A and use the aperture ring, does it work then, because in this case the reading of the aperture is disabled?

AF hunts all over the place with the 1.7TC. I have put the Sigma out of A before but had trouble getting it back in (the lens was 2nd hand though little used) so I'll leave that experiment for a while.

Sigma say the TC should be mounted on the lens before attaching the combination to the camera & not doing this seems to change behaviour. Since the camera is powered off, do you know why this might be?

[Asahiflex]

I have the same combination (albeit a K-7 and not a K-x) and the AF works great with the Sigma 1.4x TC and the Kenko 1.5x. Of course, the camera will have difficulty focusing when the light level drops. But in my experience it works.

[PMunks]

I have the same combination (albeit a K-7 and not a K-x) and the AF works great with the Sigma 1.4x TC and the Kenko 1.5x. Of course, the camera will have difficulty focusing when the light level drops. But in my experience it works.

Excellent. I've only tried a few test shots & wondered if it was just some kind of fluke.

[Lowell Goudge]

AF hunts all over the place with the 1.7TC. I have put the Sigma out of A before but had trouble getting it back in (the lens was 2nd hand though little used) so I'll leave that experiment for a while.

this will be an issue of available light (hunting that is) remember I said others have posted that it works, but I have no first hand experience with a combo at this speed

Sigma say the TC should be mounted on the lens before attaching the combination to the camera & not doing this seems to change behaviour. Since the camera is powered off, do you know why this might be?

I have never had an issue but I generally mount TCs to the lens first to make sure the aperture linkage is correctly engaged. The sigma TC is a completely passive device, so there should be no impact on operation otherwise, unless there is something with respect to the screw drive linkage that takes longer to engage if mounted in the opposite order, I have had issues with getting screw drive to allign on my PZ-1 and sigma 70-200F2.8

[PMunks]

this will be an issue of available light (hunting that is) remember I said others have posted that it works, but I have no first hand experience with a combo at this speed

If the Pentax TC is known to work I wonder if it would AF stacked on the Sigma TC. I'll give it a try sometime.

The sigma TC is a completely passive device, so there should be no impact on operation otherwise, unless there is something with respect to the screw drive linkage that takes longer to engage if mounted in the opposite order, I have had issues with getting screw drive to allign on my PZ-1 and sigma 70-200F2.8

Yes, the screw drive linkage could well be the issue.

[dadipentak]

The 1.7x worked just fine with my Tak 500mm f/4.5 in good light: ditto my 1000mm f8 (in which case, make that "nuclear light" ;~) I wouldn't expect much in the way of AF from a 500mm & stacked TCs but I'd be delighted if you prove me wrong.

[PMunks]

I wouldn't expect much in the was of AF from a 500mm & stacked TCs but I'd be delighted if you prove me wrong.

Yes, I don't seriously think it would work.

[Asahiflex]

By the way: I also tried the Sigma 500/4.5 with the SMC Pentax-F 1.7x AF adapter and I was really underwhelmed with the results. IMHO this combination is not recommended.