Both well known. I have bought from ffordes and they were fine.

If you were drinking the coffee I make, something to distract you from it would indeed be an essential.....I mix better developer.

As most will realise, it was an example, so feel free to substitute any item you like in the sentence!

I suspect the iPad is not aimed at the sectors we belong to, but perhaps is looking to appeal to new markets. While the existing computer users may well be right that this particular product does not appeal, there will be new, heavily researched, markets just waiting for this exciting new technology.

It's not necessary that we should like every product that a company produces. After all, we're not annoyed because Pentax produces a 300mm lens and we don't want one are we? :

I would suggest cut off filters for infra-red and ultra-viol;et photography repectively. That is, both would remove all visible light leaving one or the other extreme to pass.

Indeed, that is rare!

With respect, I think we should like that comcept because it means security is not compromised on our iPhones. Where people have used non-approved apps and cracked their phones to do so there have been security breaches already.

Sometimes there is a good reason for things to be the way they are.

Interesting, that's what people say about Microsoft and use as an argument to fragment the business. Apple is tiny by comparison - what is it they stop you from doing?

A simple one element lens is easy - it's the diameter that counts. So a 100mm lens 50mm across would be f2. End of story.

With a complex lens it's the effective size of the lens, which is very different from the front element diameter in most cases.

Now glass reflects light as well as transmitting it, so an uncoated four element lens, for example, loses about 35% of the light as it reflects around the lens. Single coating reduces this loss considerably, multicoating to around 1.4% loss. So the actual transmission is different to the f number and is called the T number.

These days f numbers are pretty much the same as T numbers, so the difference is ignored. As well as coating, lens design will also change the actual dimensions.

The Takumar and SMC Pentax 50mm lenses were offered as follows;

The original Spotmatic lenses were either the 50mm f1.4 or the 55mm f1.8 and these were also available in bayonet versions for the K series cameras.

The 55mm f2 was a screw thread lens for the budget SP1000 but it was actually an f1.8 with a baffle inside to reduce the aperture. Obviously a different aperture ring would also be needed.

There was also a 55mm f2 for the K1000, the bayonet version.