I don't recall the teleconverter used, probably the Pentax 2x. I've found the use of converters helpful with this lens.
This first image was taken with the K-5iis across the bay. Google says distance was 3275 feet, almost exactly 1 kilometer. Actual Pixel Crop.
The day was hazy. On the left side of the upper round railing, you can just make out the fine antenna. I've taken sharper, but could not find.
Cana Island Lighthouse crop taken with Pentax-A* 300mm F4 (Crop)
This second image was taken with the K20D. It was around sunset, hazy conditions again. It shows the observation tower.
The image below it is a crop, actual pixels. You can actually make out the 1 inch stabilizing bars. Google places distance at
1.23 miles or almost 2 kilometers.
Observation Tower taken with Pentax-A* 300mm F4
Actual pixel crop of above:
Taken with Pentax-A* 300mm F4 (Crop)
Picture from Google Maps of observation tower, now closed (not mine):
Penninsula Park Observation Tower (Picture from Google)