Recently been interested in landscape photography and about to go on a trip with plenty of opportunities to get some good shots. I really want to get some nd filters but cant afford to get the more well known makes and was wondering if the kits on ebay for $30 are good enough to get started or are they a complete waste of time?
Price differences between ND filters are often attributed to differences in quality, as with most other consumer products.
Pricier ND filters tend to have glass optics while their cheaper counterparts would use plastic instead. Glass would more often that not give you images with fewer aberrations as compared to plastic due to the nature of the material, and is also naturally more costly to produce as glass optical glass is an inherently pricey material.
Another obvious reason would be differences in filter size - Bigger filters would require more material to produce and thus be more expensive. Variable ND filters would also naturally be more expensive due to their more complex construction.
Bearing that in mind, seeing as how you're planning to purchase your first ND filter, it may be wiser to invest in a cheap one until you are sure of your need for one. It might be a good idea to invest in a larger filter and several step up rings which would allow you to use a single ND filter on a range of lenses with different filter sizes, thus eliminating the need to purchase ND filters in many different sizes. Do keep in mind though, that ND filters work better when closes to the front element of your lens, and adding step up rings would naturally add to the distance between the two.
A high-priced neutral-density filter will have optical-grade glass in a metal frame, with a multi-layer anti-reflective coating. At the cheap end, you'll have a plastic filter in a plastic frame, with no anti-reflective coating. In between, you'll have various combinations of the above, plus variations such as cheap glass or single-layer AR coatings.
It depends... What is your final intended use for your images? If you're just going to share them on the web, then the quality of the filter is less important. If you're going to blow them up to mural size and paste them on your wall (or a billboard), then quality really matters. That said, I would recommend going for the best filter you can possibly afford. For one thing, you might only be sharing those images on the web, but you may change your mind at a later date, and you'll regret having bought cheap quality filters.