Used Formatt Hitech Firecrest Ultra 4x4" Neutral Density 5.4 Filter

Firecrest were the first photographic filters to use carbon neutral coatings to bring unprecedented neutrality to the market. To ensure the filters were as durable as possible, Firecrest bonded the coating in the centre of two pieces of optical grade polished glass (using a very precise amount of an equally neutral bonding agent, developed in-house.) This process gave the filters two vital areas of protection:
• The critical part of the filter, the Neutral Density coating, was shielded from wear and tear. Instead of a coated filter where one piece of glass is coated on the outside and protected with an anti-scratch treatment. No matter how good the anti-scratch coating, it's not as tough as glass.
• They have more structural strength than a single piece of glass

Firecrest Ultra filters are the first bonded, then lapped and polished filters available in the photographic market. They have a lower reflectivity than earlier filters and a clarity and sharpness, even at longer focal lengths, unprecedented in photo filters, whilst still delivering the neutrality that made Firecrest so popular.