Filters

Hi,

I have some questions about filters. I am going to Yellowstone National Park in Sept. & am wondering which would be the best & most useful filters to purchase for the trip. On a website about the trip it was suggested to have a polarizer, a neutral density & a gray/split neutral density. Someone else told me she has a variable neutral density filter that she recommends. I do not want to have to buy too many & have 2 lenses of different sizes so would need step up or down rings so I could use them on both. The owner of a local photography store said it would be easier to have a filter for each lens to avoid switching them back & forth with the rings but that will be a lot more costly. With the rings I can use a variety of filters on both lenses.

I received a polarizer filter for my birthday for my 58 mm lens so was going to buy a step down ring so I can use it on my 52 mm lens however am wondering if it is better to have the filter for the smaller lens & buy a step up ring to use it on the larger lens. A book I have on filters says that step up rings can cause vignetting but a site on the internet where I read about them says the opposite, that step down rings can cause vignetting. So I don't know which is the best wasy to go.

If I was only going to buy one other filter which would be the best & is it better to get it for my 58 mm lens which is 75-300 or my 52 mm lens which is 18-55.

Any advice would be greatly appreciated.

Thanks

Janice