Mirror lenses are compact for their focal length. The downside is that they have a fixed aperture - often f8 - and the "doughnut" effect may be good or bad depending on your taste.

Apart from the excellent Pentax mirror lenses, there are plenty of independent 500mm ones. Most of these are of dire quality, but I believe the Tamron is not bad. There are also some 350mm lenses around, but these will be relatively rare.

The doughnut effect is part of the design of the lens and will be the same on film or digital.

Are they worth the money? I think for me the answer would be no, but if you have the application for them then maybe yes. That's hedging my bets, isn't it? But really only you can decide.

And finally, welcome to the forums!

Lens testing is a demanding procedure if it is to be done properly and is well outside the scope of this forum. There are plenty of books on the subject, some old, some new.

I would suggest you make up a still life set of various items with lots of different colours and masses of fine detail and take lots of identical pictures at all apertures and with all the lenses you want to compare. Then have a close look at the results at high magnification. Alternatively, perhaps photograph a sheet of newspaper or a map. The disadvantage of a flat subject is that the lenses might not have a flat field so the results could be misleading.

Use of a tripod for the testing is absolutely essential. It doesn't matter so much if you shoot RAW or JPEG, just that the settings are the same every time. This will give a good idea of the general qualities of the lens, but the best test of all is how it works for the type of pictures you make.

If we are talking Digital-only lenses then the SMC Pentax-DA 50-200mm is a very nice lens.

If you need to use it on film cameras the SMC Pentax-FAJ 75-300mm can turn out some respectable results, although it is not quite as good a lens as the above.

A Takumar in bayonet mount is a lower priced alternative to the SMC Pentax-A version. It has simplified construction (fewer lens elements) and no SMC coating. However, it should still give very good results.

At that price it's difficult to see how you can go wrong. Give it a try, if you like it that's great, if not, it can always go back on eBay!

Not sure about that one - surely it would look very strange to have grain only in, say, the midtones? Certainly it would look nothing like film!

However, maybe worth experimenting as digital offers new effects - for example, you could have digital Infra-Red without the usual grain added - and eventually perhaps we will forget that we have been simulating film effects....

When scanning film it does seem to increase the grain, unless of course it is because the focus of the scanner is much better that the focus of an average enlarger and we are actually just seeing it reproduced properly for the first time.

I've never minded grain in black and white too much as long as that grain is crisp. So it will be no surprise that I like Tri-X best of all, and my current developer would be Paterson FX-39. I say would be because I haven't developed a film for almost two years.

Lovely subtle shots, full of style and grace.

Nothing. I think it might have been exclusive to Jessops in the UK.

The ES and ESII are not the most reliable cameras, and spares could be very difficult to find. If you are in the UK rey AsahiPhoto and Harrow Technical, if you are elsewhere try phoining around the repair houses local to you.

Alternatively, look out for a replacement camera on eBay, which might be a good option.

Two points on that I think. For older photographers familiar with transparencies, in general if you expose as though you were making slides then you won't go far wrong. Overexposure is well understood to kill slides and the same is largely true of digital.

The second point is that the Pentax DSLRs if anything err towards under-exposure, which is a very good thing.

As regards histograms, it's worth adding (this is a third thing after all!) that you need to think what the histogram is representing. A nice even spread is not necessarily right. If you took a picture in a coal cellar you would expect a lot of black and the histogram would be, correctly, very much on the left...that is, if the exposure was correct....A picture of a white subject on a bed of snow would give a histogram very much to the right....and so on.