[garyk]

Will my sigma 1.4 apo teleconverter work with the pentax 300mm da* lens.
Thanks

[dgaies]

Will my sigma 1.4 apo teleconverter work with the pentax 300mm da* lens.
Thanks

There are two issues.

As I recall, the Sigma 1.4x has a somewhat protruding front element which may or may not interfere with the rear element of the DA*300. That said, there is a fair amount of space between the mount and the rear element on the DA*300 (around 1.5-2cm if I recall correctly), so it may physically fit.

The second issue is that you would lose autofocus on the DA*300, regardless of whether or not you can physically mount the 1.4x.

[Eruditass]

Even though the DA* has both focus capabilities? that sucks.

Are the Sigma TC's notably better than other brands optic wise (despite their incompatibilities)?

[dgaies]

Maybe someone else can chime in and correct me if I'm wrong, but I'm pretty sure that on an SDM ready body the camera won't revert to screw-drive with the TC on.

On an older body (pre-SDM) I'm not sure what would happen.

I haven't actually used the Sigma 1.4x TC so I can't comment directly on the IQ. I have used the Tamron 1.4x Pz-AF on several different lenses (including the DA*300) and I feel the IQ is pretty good. The SDM focus is retained when using the Tamron, although the AF tends to hunt a little more and doesn't always lock on the first try.

Even though the DA* has both focus capabilities? that sucks.

Are the Sigma TC's notably better than other brands optic wise (despite their incompatibilities)?

[allart]

The Sigma teleconverter works fine with the latest Pentax 300mm telephoto in terms of fit and optics. I just received both but am having a problem with the converter mounting pin not snapping into place on the lens side. I don't yet know if this is an isolated issue. The pin and hole have very narrow tolerance.

I have only one lens that I can place over the teleconverter besides the 300mm and that is a Sigma lens, which clicks into place over the converter. Filing the pin down might work, but i need to keep my exchange options open while I investigate the matter...

For the record, I do want to boot Hoya in its posterior for not selling their teleconverter in the US. Perhaps Pentax's announcement in 2008 was based on that possibility, but Pentax's parent company chooses to sell the teleconverter only in Japan. Hence, given that Tamron and Hoya have both walked away, I am loathe to bash Sigma for at least supporting us.