Hoya nx400 for solar imaging?
I would not recommend any sort of ND filter unless it is capable of blocking infra red radiation, which is the real danger with solar imaging.
I would suggest getting hold of Baader film and making your own. See
I used to use Baader Film until I obtained more specialised equipment and found it to be very good, and a lot better than previous types of filter material.
|Umbrellas by pleytime|
from An A to Z of Subjects- Week 21, U
|Glass ball on a perforated metal plate _2 by harubux|