Panorama, Canon glass, and an extender

Hi, I am trying to capture high resolution panoramas of petroglyphs in Mongolia. I am currently using a T3i with a 70-300 IS USM lens on a Gigapan Epic Pro.

I looked through the Tcon FAQ, and some other pages on the web, which seem to suggest that the 2x canon extender II is not compatible with my lens. Do you all have a different 2x teleconverter recommendation for my lens? Or a different lens altogether? I am open to all of these possibilities, although I think I may need around 600mm (plus my sensor crop factor) to achieve what I want (I have about $1200 to work with)

To get a feel for what I'm trying to do, here is an example of a panorama I stitched together from this past field season at 300mm/f8 (click on the snapshot below the image to zoom into the petroglyphs) - http://gigapan.com/gig​apans/110574. I'm looking to get a closer, sharper image of the petroglyph panel when zoomed in. Having AF is not critical. The terrain simply restricts where I can take the panoramas from, putting me at such a distance that I'm not getting the close, sharp image I'd like.

Any other suggestions or advice are very welcome. Thanks!

Most lenses don't do well with a 2x tcon, you're going to be better off sticking with a 1.4. I'd look at one of the Canon primes such as the 300mm f4L, or 400mm f5.6L, paired with a 1.4 tcon. You'll retain AF with the 300 but not have AF with the 400.

Ok thanks for the feedback. So you think buying a 300mm L + a 1.4 canon tcon is really worth the money over using the lens I have with a tamron or kenko 1.4? I am skeptical that my lens + a 1.4 is going to give me the reach I'm looking for, but maybe with the added IQ of an L lens I'd be in good shape . . .

Your 70-300 is very soft at 300mm. Have a look here for a comparison. A TC is only going to make this even worse! I think you will get much better results with a long prime (300 or 400) or the 70-300L which is close to prime sharp at 300mm.

i think a 400mmL with a 1.4 TC would be the best option for your budget...you should be able to get close to it for $1200, you don't need IS on the tripod, and it'll be sharper and longer than the 70-300IS

Hmm... This probably isn't helpful but I would snag a 17 tse or stick with what everyone else is suggested. Slapping a tele converter on anything less for landscape will be soft. There are a lot of extra complications on the long end with landscape..... Especially with tele converters....

Just curious but why do you need extra pixels and opposed to using a few stitched wide angle shots?

Oops sorry. Terrain restrictions..

Wow, thanks for the comparison chart! I've been to that site before but had completely forgotten about it. Definitely a stark difference between the two. I had been considering the Sigma 150-500, but it too falls significantly short of that 400 prime. In light of this I think I'll try to get that 400mm 5.6 L with a canon 1.4x, unless there are other recommended combos in this range.

With respect to wide angles, I'm just not sure this is feasible. I'll be taking gigapans of a wide variety of petroglyph panels, and getting the height and angle to match seems like a monumental task, though I've never tried stitching images that way. If you know of any tutorials or explanations I'd definitely be willing to check them out. Here's another example of a gigapan I did with a ton of petroglyph panels (though it admittedly has some very bad vignetting issues) - http://www.gigapan.com​/gigapans/110568

Thanks so much for the help!