There is the Pentax 17-28 fisheye zoom which appears fairly regularly second hand an may still be available new. The idea of a fisheye zoom seems daft to me.

Otherwise Sigma do a 16mm full frame fisheye and an 8 mm fisheye which gives a circular image about 23mm diameter.

I keep looking for the SMC 17 f4 for sensible money but no luck so far

There is also a SMC A 16 2.8. And there are also hens teeth....

Autofocus on a fisheye is probably unnecessary as the depth of field is huge - just stop down to f8 and go!

There was a head to head review of both lenses in either Practical Photography or Photography Monthly quite recently. From memory there was not much to choose between them but neither of them were all that good.

You might want to compromise to the Sigma 18-125 which has had favourable reviews

Just downloaced CaptureOne1 LE (trial version) and while I'm only at the beginning of the learning curve it looks much better than the Pentax Photo Lab. Notably it seems to do a much better job with noise. I have been disapointed with the 'colour speckle' noise that the Pentax program produces even at 400 ASA. C1 LE does not seem to have that problem.

A question though - I currently use PaintShop Pro as my image editor. However Photo Shop Essentials 3.0 includes RAW support. PSE 3 has good reviews but what is its RAW perfomance like with Pentax files? After all I can buy PSE 3 for only a little more than C1 LE (and don't tell me to buy photoshop CS - I'm not prepared to py that sort of money - I'd rather buy a nice lens)

As one who has for many years used slide film and done slide shows there is a certain satisfaction in producing a well composed image with no cropping. I will still use slide film (at least until you can get a digital projector that can come close to the quality of a slide projector for money I am prepared to pay) and so that urge to compose well in the camera will remain.

However when shooting digitally in a moving environment I am now tending to allow a bit more space around the subject - you can crop in but you cannot crop out. Better a bit to much sky than risking cutting a wing off!

I mostly print to A4 with a border which gives plenty of scope for cropping from a 6MP image

They are all but identical - the ME has exposure compensation but you can acheive the same on the MG by using the film speed setting. The MG is about an ounce lighter.

I'd consider going for the ME super - it has a manual exposure mode as well as the aperture priority of the ME and MG (However they tend to be a bit more expensive second hand)

See http://kmp.bdimitrov.de/ for all things to do with Pentax K mount.

Well, I've given the Sigma 170-500 its first field test at the WWT in Arundel. Quite please with the results, a crop of a swan displaying taken at full stretch at f13 and 1/1000 at 400ASA printed at 200dpi onto A4 looks pretty good to me at least. Not quite 'you can see every feather' but the day was slightly hazy.

The lens handles pretty well, though the zoom is the 'wrong way round'. The tripod mount could be further forward - it is still a bit front heavy (maybe I need a heavier camera body!). Autofocus is pretty good, the internal focus is a boon for this.

Not bad for £279!

My Manfroto MN360 head is good for this sort of work. Set the horizon level and leave the other two dimensions (pan and tilt) slightly loose and I get good support while shooting and yet can still quickly relocate to anoher subject.

Picked up a mint Sigma 170-500 for £279 from Ffordes. Not had chance to try it properly yet but initial tests look promising. I'll take it down to Arundel (wildfowl reserve) in the near future!

Thanks. I intend to use it on a tripod anyway so that is not an issue. The weight of the 50-500 does put me off, and as you say, I'm not likely to use the shorter end of the zoom.

So it is probably between this and the 135-400 (which I can fit my Cokin P filter system on)

Thanks for the help everybody!

Thanks for that

I already have the Sigma 70-300 APO Macro Super which is fine for some purposes (I got some good shots on the Farne Islands handheld but sat down and bracing elbows on knees), but fully extended prone to camera shake even on a tripod. I would like a lens with a tripod mount as that gives much better balance. I do own an older sigma 400 5.6 AF lens which can produce passable results and is nice to use on a tripod, but being the non APO version it is quite soft.

Maybe I should wait for a Pentax 400/5.6 to come up on ebay. Might be waiting quite a long time though. Can you still get it new does anyone know? How much is it??

Hmm. Talking to myself. Always a bad sign!

Perhaps I will make the question more general.

I want to get a long lens (400mm+) for use on my Pentax bodies - primarily the *istDS. I don't want to spend a sackload of cash as I don't have it. However I can probably budget £800 sterling if necessary. I would be happy to pay less! Zoom would be useful. Autofocus is essential. Obviously the faster the better but I won't get a fast long lens for this money. Image quality, especially sharpness, is, of course, the primary consideration.

Principal use will be birds at nature reserves and wetlands.

Any helpful suggestions welcome!