[runjmb]

So I have about $750 to spend on upgrading my telephoto equipment. Right now I am shooting with a K100D and have a Tamron 70-300mm. Its acceptable, but for wildlife it doesn't give me a lot to work with.

I have thought of a few options:

1. Get the Sigma 120-400mm f/4.5-5.6 DG. That would be about 600mm of reach on my K100D. However it is only 150mm more than what I have now.

2. Get the Pentax DA 55-300mm and slap on a 1.4 or 2.0x teleconverter. That would give me about 750-900mm of reach. The only downside is that I would lose some image quality.

3. Beg my wife to let me get the Sigma and a teleconverter.

Any thoughts?

thanks!

[PePe]

A key question is what reguirements do you set for IQ ?
A teleconverter never improves image quality. With zooms this degradation is more severe as primes in general are optically better.
Personally I only use TC´s with primes.
However, I guess even the longer zoom with TC will be all right if you do not print your images larger than A4

[runjmb]

I probably won't blow any of these up past 8x12. I am also likely to upgrade to the K20D, so I will have a lot better IQ compared to my current K100D.

Are there any decent 300mm primes that would work on the K20D with a TC?

[Lowell Goudge]

there are a couple of issues to look at here.
fiirst, what is the speed of your present lens, f5.6 I bet. This would not be fast enough to use with a teleconverter, and therefore a TC would be of no use.

you also need to consider cost. 750 is kind of between the two options below.

I have 2 options, which I have posted many times.

I have the origonal Sigma APO 70-200 F2.8 EX with 1.4x and 2X TCs. it is a good autofocus solution.
https://www.pentaxforums.com/forums/187646-post19.html

I also have a SMC Pentax 300mm F4 and the 1.7x AF TC.
https://www.pentaxforums.com/forums/106132-post4.html

both are acceptable in my view