One of the problems with lenses is getting the right information and knowing what they are designed for. Your requirements might be quite different to my requirements, your standards might be much higher than mine, and so on.

There is no substitute for examining a lens before purchase and, if possible, shooting a few frames for assessment. Retailers like Jessops who have a return period after purchase are dieal in this respect.

I have found the 16-45mm to be avery fine lens, but as with all modern zooms, or perhaps I should say most, accurate drawing (freedom from distortion) is often allowed to drift in favour of sharp, crisp, contrasty images.

For better distortion control a prime lens may be the answer. If the 20-35mm was good in this respect that's fine, but who could have told us that? I don't know the answer to the problem you've highlighted, unless it is better and more honest information from all lens manufacturers.

We have two diametrically opposed viewpoints on this forum, the RAW users and the JPEG users, and there are good arguments for each opinion.

My feeling is that as you are having to ask so much that is basic, you really do need to get a suitable book or article to start you off. You might be better just taking some fantastic JPEG images and forgetting about RAW, which will have its own very steep learning curve.

Don't forget that some very high profile professionals use JPEG, although it is true that many use RAW.

The difference in number of images per card will be found in your camera's Manual, and if you do decide to shoot RAW you will need large cards. You will then need to convert your RAW images to JPEG or TIFF (preferably TIFF) to use them in Photoshop. The golden rule is, once you have opened the file whenever you save it after that, always use a "lossless" file type, such as PSD or TIFF. Definitely do not re-save a JPEG as a JPEG.

There's too much to cover in this reply, but hopefully it will be of some help.

A sharp grainy image is usually preferable to a fine grained one that suffers from camera shake. So no need to be shy about using high ISO settings when needed!

The 50mm f1.7 will be the best choice of standard lens to use with extension tubes as it will maintain good performance close up. It will be much better than a zoom at these distances.

This particular macro lens is a low cost one, and it seems to be the same as the Cosina. However, despite the low cost and rather rudimentary barrel contruction it is actually a good performer.

There are better Pentax macro lenses. The SMC Pentax-M 100mm f4 is superb and quite often found on eBay. I have recently purchased a SMC Pentax-FA 100mm f2.8 which is a beast of a lens but looks very promising. One advantage will be its 1:1 magnification.

For serious macro photography, I would choose a proper macro lens every time, but don't forget that even close up lenses (filters) will produce very good results very cheaply.

As far as I know you will lose all electronic connections with any Pentax tubes. There are some other makes that have contacts, but someone else will have to tell us what they are...

The 18-55 is a very respectable lens, but it doesn't have the crispness that the 16-45 does, especially at wider apertures. I tested both lenses and some tiny lettering in my shots was perfectly readable with both lenses, but was very crisp with the 16-45 and quite softly rendered by the 18-55. This difference can be clearly seen on an A3 print, but not from a normal viewing distance say on a gallery wall.

The real adavantage is the 35mm-equivalent of 24mm as opposed to 28mm, which is a significantly wider angle. As I tend to like wide angles, this makes my choice very clear. If you like close-ups, the 18-55 focuses slightly closer.

For general shooting, the 18-55 and 50-200 combination makes a lot of sense.

Only if you're selling it for a fiver. We already have two of them, and a 16-45mm, and an assortment of others too long to mention......

Nice pictures. The 18-55mm is a useful and versatile lens, and for many could be the only lens they ever need.

That's a lot of questions! There is actually a very useful booklet that explains all the Cokin filters very well. It is often included with Cokin adapters so that you get off to a good start. Perhaps eBay could be a place to find one.

The A series is the original, the P series are larger to make them useable on medium format lenses.

Personally, I prefer to use screw-in filters, but I'm not talking about all the special effect ones, just the black and white filters already mentioned, and perhaps the 81A (Cloudy) filter that warms up the image. With digital, I don't use filters but apply all the effects in Photoshop as required.

You can fit close-up filters to the front of your 28-90mm zoom, and although critical sharpness may suffer results can be very good when small apertures are used. f11 or f16 might be a good choice.

As regards recomended filters, that depends on what you want to achieve. I think it is a personal choice.