Grabbed my *ist D, 300mm F4, 2X TC, a tripod, then went for a walk in my backyard today. Been sifting through my shots, here's one of a little black-capped chickadee. I do think he/she needs a napkin...

Attachment 63925
Code:
Camera/lens: PENTAX *ist D with PENTAX SMC PENTAX-A* 300mm F4 lens. (MF-only).
Other equipment used: TAMRON 2X tele-converter, Velbon CX-540 tripod, PENTAX AF-330FTZ external flash unit (did not fire).

1/200 second @ F1.7
ISO 800
900mm (35mm equivalent)
Spot-metering mode
Aperture priority
Contrast: Hard
Saturation: Normal
Sharpness: Hard

Above data is according to EXIF*, which should still be intact.

*Except focal length (recorded as "0.0mm") and other equipment used.
Another chickadee.

Attachment 63952
Code:
Camera/lens: PENTAX *ist D with PENTAX SMC PENTAX-A* 300mm F4 lens. (MF-only).
Other equipment used: TAMRON 2X tele-converter, Velbon CX-540 tripod, PENTAX AF-330FTZ external flash unit (did not fire).

1/200 second @ F1.8
ISO 800
900mm (35mm equivalent)
Spot-metering mode
Aperture priority
Contrast: Hard
Saturation: Normal
Sharpness: Hard

Above data is according to EXIF*, which should still be intact.

*Except focal length (recorded as "0.0mm") and other equipment used.

Now, I am aware that the super-fast apertures have to be bogus – maximum with this setup would be F8.0, so I guess that's what it is. But this is still a very "fishy" issue for me, I'm not completely sure what the *real* aperture value is, only I do know that F1.7 is the largest the camera allows me to dial in, and only when using the 300mm F4/2X TC combo. Also, the focal length reads as "0.0mm" in the EXIF data, lens/camera probably aren't communicating like they should.

However, I really do like my TC, it provides plenty of reach, making MF easier because you can see the subject's details larger in the frame. And the *ist D's 6 megapixels don't leave much cropping flexibility, so every extra mm of focal length is most welcome. Bokeh seems to improve with the TC.

The only disadvantages in my opinion are a very noticeable loss of light, and very ugly chromatic aberration problems (see below).

Attachment 63926
Code:
Camera/lens: PENTAX *ist D with PENTAX SMC PENTAX-A* 300mm F4 lens. (MF-only).
Other equipment used: TAMRON 2X tele-converter, PENTAX AF-330FTZ external flash unit (did not fire).

1/400 second @ F2.0
ISO 1600
900mm (35mm equivalent)
Spot-metering mode
Aperture priority
Aperture priority
Contrast: Hard
Saturation: Normal
Sharpness: Hard

Above data is according to EXIF*, which should still be intact.

*Except focal length (recorded as "0.0mm") and other equipment used.