[swanlefitte]

For small birds in the field at 420mm I just get the bird the size of that central circle in my viewfinder. 420 is barely enoungh. If you can swing a longer lens, ( literally and finacialy) do it.
The tc and plm work fine up to 270mm where you can keep f8 in low light and 300mm in good light but the main advantage is a more precise focus in branches or for close ups.
It wont help get a great picture from too far away but it helps get a picture and when things are soo small they are less than 300 pixels wide you are glad they aren't 214 pixels like this pike would be in this herons mouth.
The big one that flew away - PentaxForums.com

[dirwood]

I think I got it narrowed down now. I am going with a zoom lens for now so the DA* 300 is out. The TC options are the 1.4x and 1.7x. Is there any difference between the 2 or are they equally as good and one just has longer reach?.. Will Sigma zoom lenses work as good as the PLM lens with the TC's.

This is pretty much what I'm down too without trying to spend more than 1k.

[kypfer]

I think I got it narrowed down now. I am going with a zoom lens for now so the DA* 300 is out. The TC options are the 1.4x and 1.7x. Is there any difference between the 2 or are they equally as good and one just has longer reach?.. Will Sigma zoom lenses work as good as the PLM lens with the TC's.
This is pretty much what I'm down too without trying to spend more than 1k.

I've no experience with either of those two tele-converters, but I do use a Kenko 1.5x as needed. I also use a Sigma 150-500mm almost exclusively for birding. So, in that context, the KP can start to struggle with the tele-converter fitted to the Sigma. It's fine in good light on a static subject … AF/S and go for it … it'll probably take a moment or two to "lock on" but it'll work. Tracking a moving subject, except against a clear sky, is a bit more of a struggle, though the latest firmware does seem to improve things in this respect. This is all (probably) due to the Sigma's maximum f/6.3 aperture effectively becoming around f/9.5 with the converter fitted, well outside of the recommended (if conservative) f/5.6 minimum for reliable autofocus.
Extrapolate from these experiences what you will … a 500mm (with a useful "trombone" zoom action, great for initially finding your subject in the viewfinder) which isn't totally reliable with a converter fitted, or a shorter, wider aperture lens, which is likely to work better with a converter, but doesn't have the initial reach
The other factor to consider when using a converter is that, with the Kenko at least, the camera isn't aware of the converter, so continues to generate EXIF and configure the Shake Reduction for the native length of the lens … just when you need all the help you can get
Good luck and enjoy

[boriscleto]

I think I got it narrowed down now. I am going with a zoom lens for now so the DA* 300 is out. The TC options are the 1.4x and 1.7x. Is there any difference between the 2 or are they equally as good and one just has longer reach?.. Will Sigma zoom lenses work as good as the PLM lens with the TC's.

This is pretty much what I'm down too without trying to spend more than 1k.

The 1.4 and 1.7 are completely different. The 1.7 is an auto-focusing adapter, you manually focus the lens to close to sharp, then the adapter finishes focusing. It was originally intended to be used with A* 200/2.8, 300/2.8, & 400/2.8. It won't really work with a lens slower than f4.

[MikeNArk]

Thanks guys. It almost looks as if I should get the TC and both those lenses. I think a good starting point will be the PLM because I don't always shoot at 300mm. I like the ability to make adjustments at home when I'm shooting the dogs playing frisbee. The TC will make it good for when we head out and go for walks. The issue is I want to find a used PLM but not pay over 400 for a used one...I am trying to be patient.

If you have not found the 55-300 PLM, I purchased one new off Amazon at 399.95 about 10 days ago.