I would think about 40 to 60 feet but that is a guess on my part. I may have a small crop on that picture. With the 2x mounted, my 600mm can't go AF, and I was using MF for the shot panning the moment I saw the Pelican coming into view. I hand-hold the shot and I got an off focus on 1st shot and the above shot was the 2nd shot in a series in AF.S. I was not using AF.C at the time.



Pentax F* 300mm f/4.5 + Kenko 2x MC7 AF TC

Here is a shot using the Pentax-F 1.7x AF TC on a Soligor 200mm f/2.8 in M42 mount. Darn it, I sold the Soligor due to too-many lenses.




My biggest problems with TC are usually on heavy CA/purple fringing seen in high contrast area such as the tree branches and bird's white feather

Thanks,
Hin

I am one of the TC junkie's. I have tried various TC to some degree of success. But the lost of light and image quality lead to more bad images than good one. But I still stick to the TC for a few simple reasons -- portability and great bargain for occasional use on that silly birds.

My most favorite TC is the Pentax AFA 1.7x TC as it really work well with MF lenses and turn a MF lens into partial auto focus. I prefer it to use with 'A' capable lens.

There are few other TC's worth noting and I listed here in order of my frequent use
1. Pentax AFA 1.7x TC
- magical in turning MF to partial AF
- I prefer it to work with MF lenses with A setting
- allow you to enter SR focal length
-

2. Tamron Pz-AF 1.4x TC
- this has the least lost of light
- one of the few TC working with SDM lens.
- I see a lot of PF/CA from this TC

3. Promaster 1.7x AF TC
- works with AF, not on DA* 50-135mm f/2.8
- I see some claim it to work with DA* 60-250mm f/4.0
- has less PF/CA when compared to Tamron 1.4x TC


With a 2x AF TC MC7 from Kenko, I can hardly get it to AF with Pentax F* 300mm f/4.5, but the combo is hand-holdable




Thanks,
Hin

Thank you everyone for your warm welcome. I am from California of USA. I think I know Mike-P from PentaxForums.

Yes, Mike. I am still using my Tamron SP 70-210mm f/3.5 adaptall-2 (19AH). It is a fine lens except that I have CA/purple fringing from the zoom. And to add to the poor man's LBA collection, I got Tamron 75-250mm f/3.8-4.5 adaptall-2 (104A) which closely resembles the DA* 60-250mm in focal length. Someday when I get enough funding, I will trade in the MF zooms to the latest Tamron 70-200 f/2.8.

Warmest regards,
Hin

I just join this forum. I want to drop a note to say Hi to Pentax friends in UK.

Warmest regards,
Hin