Originally posted by Saxtonine As far as my next steps: I am hoping to make my next purchase the HD 1.4 teleconverter to give me a little more reach. The idea being to use that with the 100-300 and then maybe some day my ship will come in and I'll pair it with the DA* 300. I also eye the HD DA 55-300 but really - the only metric I care about is performance at 300mm so unless it is significantly better at 300, I don't really care about the weather sealing and such. The FA 80-320 is also on my radar, as it would give me a little bit more reach.Am I barking up the right tree? What would you do in my shoes?
A 1.4x TC costs 1 stop of light, so used with the zoom at 300mm f5.8 your effective aperture wide open would be upwards of f8. AF is marginal in those circumstances. And with these consumer zooms you usually need to stop down one or two stops for better resolution. I doubt the results with the K-3ii would be better than cropping. TCs are really designed for use with faster sharper lenses like the DA*300 f4 that produce very good resolution wide open.
What's more, the HD 1.4x is not cheap (about $US400 at B&H). You'd be better to put that money towards another lens, whether one of the Sigma zooms like those that Boriscleto mentioned or a 300mm or 400mm prime. Personally, I'd suggest the latter. You might find an F*300 f4.5 or FA*300 f4.5 for around $650 or so. Either of those can be paired with a more affordable but still decent third-party TC like the Kenko or Tamron pz models. And the lens alone will be much better than the zoom. You will get more resolution and better images generally with the prime wide open than with the zoom at f8. The F* and FA* are very fine lenses.
The budget end of the long lens market in K mount is kept artificially high by the paucity of options. For example, a secondhand Bigma (Sigma 50-500) in K mount costs a lot more than its Nikon or Canon counterpart. (Because there are so many other options - such as the Tamron or Sigma 150-600 - that aren't available in K mount.) Even the premium telephotos lenses in Nikon or Canon are a lot more affordable than their Pentax counterparts. Painful as it is to say, to get 400mm+ you might be better off getting something like this:
- Canon EOS 7D (mark 1) $300 + 100-400mm f4.5-5.6 (mark 1) $600
- Nikon D7100 $350 + Nikkor 80-400 f4.5-5.6 (non-VR) $500