Originally posted by patrick9 The only one I have is an ND8 You might also consider getting one that fits your largest lens filter size the getting step down rings. they are fairly inexpensive.
This is what I did. I grabbed two for my two most common lenses (DA*50-135, FA 43/77) and then just stepping rims from there.
The other thing I did was get promaster variable ND filters. Not too much cash ($80 for the DA*50-135 mount one, and $60 for the smaller one) and have been more than happy with them. They give fantastic control over how much light you want to stop, and the image quality is still pretty solid. I really like the Promaster filters, great value for the money, metal rings, and if you go for the "pro" series there is no flex and they feel really solid...almost like B&W filters...but for a fraction of the cost. The pro line also includes a lifetime unlimited warranty. Seriously... I dropped my K5/DA*55 and shattered the filter (lens was AOK, probably the only thing that saved the lens to be honest. camera had a broken LCD screen) and they replaced the filter no charge.
I'd say if you can find a Promaster variable ND, get it.