Forget the cling film, IMO anyway.

My Grandmother bought a three piece suite and immediately covered it with chair covers. She never saw the colour of the suite she had so carefully chosen up to her dying day.

You might as well enjoy the clear, uncovered screen.

I hope that isn't your current Broadband Wireless key that you've put on here for all to see....

Your first paragraph correctly identifies that for the same magnification the DOF is the same at a given aperture regardless of the lens. This is why it doesn't matter from a purely DOF point of view whether we use a 50mm or 100mm Macro lens. There are other factors of course, such as working distance and the change in perspective that causes.

You've also correctly identified that the circle of confusion is more demanding for smaller formats and less demanding for larger ones. This relates to the amount of enlargement needed.

If you carry on your logic you will arrive at conclusions regarding the resolution needed for a sharp print and how this varies also with print size because of changing viewing distance.

There are entire books about all of this, so you might like to look one up as I'm sure you'd find it interesting.

What you need in smaller formats is not more sharpness but more resolution. Also a higher degree of manufacturing accuracy.

You also define a smaller circle of confusion, which takes care of your increased magnification requirement.

In the case of digital there will be no loss in theoretical quality using a smaller
format because you will be using the same number of pixels. That is, supposing 10MP on a full frame sensor using a 75mm lens and 10MP on APS-C using a 50mm lens. The "sensor factor" will be the same number of pixels in the image. Obviously there are tother factors, such as noise, crosstalk between photosites.....

The answer to the second paragraph is a simple yes. A 55mm lens remains such in every respect. It has to because it's still a 55mm lens.

However, what happens when we compare it to the same lens on 35mm film. Let's assume for a moment that it covers both formats. On 35mm film it's a standard lens with a "normal" perspective. Put a small CCD behind it and it's only seeing part of the frame. It's cropped the image. To fit all the image in you would have to walk backwards. In other words, it's now a telephoto lens. With the DOF of a standard lens on 35mm.

This has been covered before both on here and in a recent article on lenses I did for Pentax User Magazine. Have a search on the forum. Order a back issue.....

I always have a Pentax compact digital in my pocket and use it quite a lot for recording items of interest, a visual memo device if you like.

At the moment it's a T30. It's not bad and can produce some nice results, but none of them are up to DSLR standards.

As a consequence of quality issues, these sort of cameras rarely produce competition winning shots.

Everyone is entitled to bid and to bid right up to the deadline. If you put in a suitable maximum bid you will win the item, regardless of any software employed by other bidders. They will have set their limit too, and if it's higher than yours....

As regards the *istD this is getting quite old now and I would expect the newer models to give superior image quality and faster response time. SD card slots are now even appearing on TV sets, so they are more or less universal over a wide range of electronic products.

New DSLRs are now very well priced, until all the price rises start to hit!

Selling the A3 with its standard lens will not raise much money at all. It might fetch £10 for the body and a bit more than that for the lens depending on which one it is.

A JPEG file is compressed, so when recorded on the card might be 3MB or whatever, but when opened into Photoshop(or another imaging program) will open up to 18MB or more.

A 10 MP (megapixel) camera will have smaller JPEGs than say a 14MP one and will fit more images on a card.

For best results, the K10D should be set to 10MP and *** quality (the lest amount of compression) if you are using JPEG. The K20D has an even higher level of JPEG file described as **** Premium.

RAW files have some compression but are lossless, that is, they do not lose any information. These files are much larger and fewer will fit onot a card.

Hope that helps!

Maybe so, iceblinker, but it's no way to test a lens. It ends up telling us nothing.