I am contemplating buying a long telephoto zoom to g with my *ist DS, mainly for wildlife purposes, especially birds at wetland reserves. Curently I have a Sigma 70-300 APO Macro Super which is pretty good but fully extended is prone to camera shake even tripod mounted because it has no tripod mount on the lens (hardly expected on such a lens). I also have an older sigma 400/5.6 AF which does have a tripod mount. However it is not very sharp. I would like the extra reach of 400 or 500

Pentax do not do anything that fits the bill (except perhaps the 500 4.5 preset which ocasionally crops up for sensible money, but I would like autofocus really. The Pentax 400 5.6 F would be nice but is very rare on the second hand market) The choice thus seems to be
Sigma: 135-400, 170-500, 50-500
Tokina: 80-400

I'm most tempted by the Sigma 50-500 and that would be within budget. I know it has had very good reviews and is due in the lates DG version for Pentax pretty soon. It also means I can cover the full range with two lenses, as I have the 16-45.

However the Tokina 80-400 is half the price, half the weight, has good reviews, and its latest incarnation has a tripod mount. Given the Sigma has been measured at around 460 (rather than 500) the difference at the long end is relatively small. Furthermore it has a 72mm filter diameter, which is the same as my old Sigma 400 - so less filters/adaptors to buy.

Anybody any experience with either of these, especially the Tokina? I'm fairly sure the Sigma would perform well but I don't want to spend more than I need.

I'd look at the Pentax 24-90 - equivalent angle of view to to a 36-135 when mounted on a digital body.

A bit cheaper but also very good is the latest Pentax 28-105 - small light and at f3.2-4.5 a bit faster than your average zoom. I like it on my DS when doing informal family shots

If you want speed (for low light) you will have to go to 3rd party for your budget. Sigma do a 24-60 2.8 EX DG. The 24mm starting point is useful -giving a '35mm eqivalent' of 36mm. Tamron do their 28-75 XR 2.8 which is quite light for a 2.8

Going down the 'digital only' route:

The Pentax DAF 16-45 1nd 18-55 are both a bit short at the long end (I have the former - great for landscape work but not so hot for portraits)

Again looking at 3rd party the sigma 18-125 gives a very useful range and has had pretty good reviews.

True - but that can't be more than a few kilobytes, which is a drop in the bucket compared to 9 megabytes.

in fact Raw files are only 12 bits per pixel - each of the pixels is one of red green or blue. The raw conversion software then 'guesses' what the other two colours would be based on the adjacent pixels of those colours. In theory then the files should be about 9 megabytes. However I think Pentax must use 2 bytes per pixel and then have some modest compression - that seems the only explanation for the variable file sizes (unless someone knows better....)

I've just dug out my Speed Graphic catalogue - they do the "Kaiser Autofocus SLR adaptor" for £7.95 - basically a screw thread with a velcro strap - you position the thread over your shutter release button. Obviously it would work with manual focus SLRs without a standard CR thread

Jessops list a 'Kaiser AF adapter' under cable releases so that is probably the same thing

Jessops used to do a strap on velcro thing that took a standard cable release - but I don't have a current Jessops catalogue at present and the website is not very helpful.

Not quite true - the SMC A 50/2.8 is 1:2

My experience is that high speed cards are significantly quicker. I've just done a quick test using my standard speed Kingston card and my high speed Bytestore card (a cheapie from Amazon) and the write speed for a RAW fle was roughly 9 seconds for the former and 5 seconds for the latter

BTW I wouldn't buy cards from Jessops - they are much cheaper online

The shutter release lock using manual focus lens in autofocus mode occurs with all manual focus lenses (K M or A - and indeed I guess even with screwmount lenses and adaptor). It is a feature of the autofocus film cameras as well. It can be used to acheive a 'semiauto' focus mode. Point camra at sbject. Hold down shutter release. Slowly turn focus ring and when the subject is in focus bingo! the shuter fires. (never bothered doing it this way myself though).

I tried it and the answer is 'sort of'. You can fire the camera with it, and some of the functions work, but the button layout in the program window reflects the *istD and only where the two cameras are the same does it make sense. Also the automatic transfer of the picture to the computer seems not to work. Download it and see!