I am not one for filters but sometimes think that the haze in some negative images might be reduced by a UV or skylight filter. Pentax SMC lenses, according to the makers, are "opaque to UV radiation". I have just bought a Pentax MX plus 50mm SMC to have a go with but how do other makes fair with UV? The only times I use a filter normally is a skylight for slide film or a yellow filter for black and white. I don't use filters to protect the lens. I also read that modern films are not particularly sensitive to UV.