Excellent thanks, that's very useful. I'll re-do the tests based on that info.

How do you folks go about lens testing?

I've commented on here before about the 18-55 kit lens being poor so I did a quick test at home, taking shots of a bookcase in my study from a couple of metres away. I did the following tests:

1) At 19mm against a cheap 19-35mm Pheonix AF zoom (same as the Vivitar and Cosina one).
I tested wide open (f3.5) and at F5.6, F8, F11, F16 & F22 looking at the centre and corners of the frame. At all apertures the 18-55 was noticeably sharper that the Pheonix in the centre of the frame but it was a different story at the corners where the Pheonix was a lot sharper. On both lenses the sweet spot seemed to be F8-F11 (f22 was quite bad with both). The colour rendition looked better with the kit lens.

2) At 28mm against the Pheonix again and also against a SMC-FA 28-200.
Again the kit lens gave the best centre sharpness of the the three but the worst corner sharpness. The SMC-FA 28-200 was the best of the three in my opinion, and also had the best colour rendition and contrast.

3) At 50mm against the 28-200 and a SMC-M 50mm F1.7
The difference in sharpness across the frame between the old manual focus prime and the two zooms was remarkable. There wasn't much in it between the zooms at this focal length.

Overall the kit lens delivers reasonable centre sharpness but is very soft in the corners, especially when outwith the F8-F11 aperture range. It reminds me quite a lot of my very first Pentax lens in fact - the old powerzoom FA 28-80. I think the reason I've been more dissapointed with these lenses than others using them might be because I often shoot outdoor wide angles from low down with an object of interest near to the camera in the foreground. The lack of corner sharpness means that the foreground object is quite soft, however if you were placing your main point of interest in the centre of the frame then you'd probably be a lot happier - for example I've found the kit lens gives decent portrait results.

Brian,

Those results look pretty good and certainly I'd expect a 70-200 F2.8 with a good 1.4x or 2x to outperform a consumer zoom which goes to 300 or 400mm. I've seen the 1.4x Sigma on sale in the States but it only seems to list as being compatible with certain lenses, probably because there is a forward projection of the tc's elements. My Tokina 80-200 F2.8 isn't listed as compatible although I think it should probably work.

My son and I did go for a walk in the Pentlands despite the weather - it was mostly dry but overcast and quite windy so we only went up one of the smaller hills (Hare Hill). Because of the overcast I was shooting with a ND grad most of the time and the results weren't much to right home about in composition terms, however I'm very impressed with the Sigma 10-20's optical performance although even with my cut-down Cokin P holder you have to take care to avoid vignetting at the wide end.

I also took the Tokina mirror lens and got a few useful shots of a swan on one of the lochs. I blew what would have been the best shot though as I didn't have the focus spot on. The composition was pretty good as the swan had just dipped its head under the water and I caught it as it came back up with water dripping from the beak, water droplets on the feathers and the curve of the neck and head filling the frame. Some manual focus practice with the lens is clearly required...

Regards
Steve

I hope it is sunny tomorrow as I was planning a walk in the Pentlands with my son and my 10-20mm in tow!

This morning I've been playing around with 2x + 2x + 500mm! None of my tripod heads are really up to holding it steady enough though...

To partially answer my own question - I've not got one of the 7 element 2x Teleplus convertors and it seems considerably better than the 4 element one I was using before.

I had one of the Pentax AF 1.7x adaptors but sold it as I'd switched mostly to AF lenses. I did try it with the 80-200 F2.8 and it did work however the focussing performance was slow.

Any suggestions about decent teleconvertors in Pentax AF fit (including UK online suppliers if possible)? Primarily for use with a Tokina ATX-Pro 80-200 F2.8.

I've got a cheap 2x one I picked up years back but it's not very good.

The lens arrived today and seems a real bargain. I've done some brief tests and it seems even sharper than the SMC-M 50mm F1.7 and that's a pretty good lens.

Seems well made too - shame Vivitar don't make stuff of this quality now.

I've been looking for a cheap macro lens to play with for a while and just won one of these on Ebay for £26. Anyone had one and know if they're any good?

Regards
Steve