UV filters.

If the bright sky is in the field of view, then it is very much *not* what the lens hood does.

Cutting out the bright sky, if it's in the field of view, is actually deliberately vignetting the scene, in order to reduce the contribution to the eye's total exposure from the part of the scene you don't want.

Lens hoods should not cause vignetting, so it's really a completely different thing.

It illustrates, yes, but does not help understanding.

I'm not at all disagreeing with using lens hoods, but they do not work by cutting out a bright part of the scene.

I know you know that, and I know that the 'shield your eyes' analogy is seductive, but it's really not going to help people that want to understand lens hoods.

It might help them to remember to use them, of course, but that's a slightly different issue.

after a little testing with my 50mm lens i decided to test a little more last night.

Took each of my lens into testing, camera in the same position i took a picture with the uv filter on, took the filter off without moving the camera at all and the focus was out so hit the AF to refocus. Each lens at different scales all changed focus when removing the uv filter, withought the filter pictures were also very slightly sharper and a little brighter and more vibrant.

So thanks to the many comments made it urged me to do some testing and make my own mind up to the fact that uv filters do affect lenses/pictures and i will only use them when neccesary.

My own opinion that i've come to from this thread:
In general use the filter is not going to protect the lens, i'm carefull anyway and unless its extremely dusty or sandy i cant warrent useing it for protection.

It does affect the focus of the lens.

On a maual focus lens i found it easier to focus without the filter on.

Pictures withought the filters (indoors anyway) seem a little sharper, brighter and more vibrant.

I'm wondering if it was causing/contributing to my tamron lens not being able to focus very well above 200mm with a polarizing filter on.

UV's are off.

Should you not carry out the same tests outdoors, that is where the UV light is. I would have thought that indoors even standard glass in windows would filter out some UV.

That will be next, my main point of this though was to find out wether leaving them on permenantly was a wise choice and if it affected things useing them indoors, which i have found to me they do, and learning form what stefan said that there is uv filter infront of the sensor anyway makes it a pointless piece of glass/plastic on the front of the lens.

Glover also test for flares then, when your outside