500 Telephoto advice for K100d.

Hi,
my first post to the forum so I hope I dont sound a bit clueless! I've not long upgraded from a Fuji 5600 to a K100d as my photography interests have moved on to bird photography. I want a 500mm telephoto for this as the Pentax FAJ 75-300 is often not big enough and also I think the image quality is not quite good enough at the 300 end. I am on a constrained budget and dont mind using older equipment if the quality is there albeit if things are not as automatic as the newest lenses. The manual is written in a slightly confusing manor on the subject, so using my past knowledge I thought a quality lens of some vintage would be a cheaper way to go and if it didnt automatically do things I would be able to by running the K100d in its various manual modes. (As I used to with my old Zenith E). Camera shops and Ebay have various makes of lenses but I dont know which are good and which to avoid.

All makes can have outstanding, good and less good lenses in their range, either because theye were more or less successful with that model or because they were built to different price points so there is no global answer, you will have to research the quality of the particular lens you are interested in.

To perhaps give you a start - how much do you want to spend on the lens?

There aren't any affordable autofocus lenses significantly longer than the 75-300 you already have. There are a few options for around £700-1000, but many if not all use in lens motors that the k100d can't operate.

Even with older 'legacy' lenses the decent options are generally expensive, but mirror lenses do give you a possibilty. I've used both 500mm & 600mm mirror lenses with my k100d and got some good results for motorsport with both. Most lenses of this type go for £50-150.
DOF is very limited with such long lenses, and mirrors don't give an aperture control to help.

Another option is to link your camera to a telescope. Spotting scopes are the most portable option, but good ones are also expensive! I tried a cheap Tasco 'world class' which gives an effective 1000mm f16 zooming to 4000mm f64. Again no aperture control, and it is usable at the short end, but not worth zooming.

If you can stretch to about £350 then an older version of the Sigma 150-500 would be a safe choice. You may find the earlier Sigma 170-500 for a little less but I'm not sure how the IQ compares. Even if you do not mind manual focus I cannot think of a quality 500mm that you will find for less. Perhaps some other members will know of something.
(sorry, cross posted with Mike)

Well it does very much depend on the budget, with lenses available from £50 to £5000 its kinda hard otherwise

But a quality 500 for less than £350? The Tamron 31A 200-500 is undoubtedly a quality lens and probably available a bit cheaper - but there are good reasons both for and against that sort of lens. A Tamron 500mm mirror could be considered a quality lens for £70 or so - depending on your definition of quality and budget of course. And a 300/f4 of some sort with the 1.7x AF converter is a viable but possibly no cheaper option depending on how you count these things and if you are spreading the converter cost across multiple lenses.

I do agree the 150-500 is certainly a safer and generally all round easier option both to find and use though - if the budget is right.

Thank you all above for your helpful comments.I have a sort of top spend of about £500. Taking that a bit loosely I have seen Sigma 120-400 & 150-500. I believe in both cases the K100d would not run the Auto focus, and why pay for a bit I cant use? I want the quality of image that will make a Sparrow look like it has feathers not fluff at postcard size of print with the bird being Sparrow size type of image. I have looked into using a scope but its not the way I want to go. Similarly from my reading I dont think mirror lenses are for me. There is quite a lot of info on the Pentax User on this subject and as pointed out above and in the Forums it is a bit of get some idea of shots from various lenses, find one at the right price and try it out and post some results here to help others.

You're not going to like this but I'm going to suggest a body upgrade to go with one of these lenses. I've got a Sigma 150-500, really nice for the type of shots you're looking to take, it's a big old lump and you'll want some OS and, for me some help with the focusing, especially with the smaller and faster garden birds. It might stretch your budget a tad but I'd seriously consider a K20d and a 150-500, I think you might be able to secure both for around £600 used, maybe a little more, and sell the k100d. Not only will the functionality be better but you'll have room to crop with the increase in resolution on the k20d.
Whichever way you go happy snapping.
Chris