Personally I would leave well alone. The alignment and positioning of the screen is critical for correct focus and the screen itself is very soft and can be easily rendered useless. I don't think this is something anyone should consider as a normal part of user camera maintenance.

Marks on the focusing screen will have no effect on the image anyway.

It makes me wonder if I should ever enter the bathroom again!

Sue and i have had our Pentax *istDs cameras for almost a year now, with no signs that any cleaning is needed.

What sort of time scale are we talking about before cleaning could become an issue? :

There are, I think, two factors here.

Firstly, there is a new batch of digital-only photographers up and coming, and they are graduating from compact digital cameras to DSLRs for the first time. They don't know they are missing an aperture ring, so it's not an issue.

Secondly, no-one else is using aperture rings now, so if Pentax continued to support them the added cost would probably put them at a competitive disadvantage. No point is creating costs for things that few people now actually want.

Personally, I have always liked aperture rings, but I've soon become used to a new way of working, and it doesn't really bother me either way.

Excellent. There are some very exciting independent lenses out there, it's just knowing which ones are worthwhile that's the trick.

It looks like you're going to enjoy using your Vivitar!

Classically, the best macro results will be obtained when using a wide angle lens reversed, or a wide angle reversed on a medium telephoto. You will get much better sharpness this way.

Zooms have very poor close up correction in general, and don't follow the normal optical expectations when reversed either.

If you refocus then you will change the magnification of each individual shot, so I would imagine you need to be a bit selective regarding subject matter and composition.

There's a certain ironic element to this, which is nothing to do with your idea, which is excellent.

I was doing my talk "The Way We Were" which is a light hearted and affectionate look at the way photographer's behaved in the first half of the 20th Century; and indeed a more serious look at some of the very fine work they produced.

One quirky aspect of photography way back then was the way people found such ingenious DIY things to do. Such as "Things You Can Do With Cigar Boxes" (lovely little article from AP) or "How to Build an Acetylene Generator" and "Adventures with Magnesium Ribbon"........

So it's great that the tradition is resurrected, albeit it a relatively harmless way!

So what on earth would we do with an Acetylene Generator?

Fortunately, most modern centrally heated homes have very low relative humidity. Excellent for lrnses, but of debateable value to human lungs....

If you are keeping lenses or any other photographic gear for a very long time, then a bit of care is needed.

Good, dry air circulation is a good idea. Beware cupboards and drawers because of the chemicals in paint and varnish....

I have taken to leaving my lenses that are not in use on a bookshelf in my nice warm centrally heated computer room. The ones in regular use are with their respective cameras in the appropriate Billingham bag. A kit for every occasion!