Darn, Keith, now everyone will be bidding for it!
Yes, this keeps getting listed periodically and I did speak to the seller about it.
But as a 3rd order lens assembly, this is not the largest! A 1st order lens is seen here
(another of my sites if you were wondering). I think, conventionally, 4-6 panels were required but there are exceptions, such as a land-based lighthouse tower - no point in lighting the land, if the optics were static; earlier ones rotated the entire mechanism floating on a bed of mercury, like the Skerries one on my website.
The 'order' of the lens signifies how far the parallel beam of light could be projected, so a 7th order could be used at sea level within a harbour, whereas a 1st order would often be up a cliff, inside a tower, projecting a beam up to 25 miles (40km) away.
The first photo posted here show René Vas and myself at the Hook of Holland lighthouse in front of a Chance 1st order lens - about 8ft (2.44m) tall?
The second shows us at the top of the Hook tower with René inside the lens assembly. I think this is a 3rd or 4th order lens. As you can see, the rear of the assembly is left open.
The third shows the lighthouse in its entirety. Well worth a visit - René purchased the tower for the price of one guilder, I think, after starting a campaign as a teenager when it was scheduled for demolition. This started a lifetime's commitment and it is now a museum. Put your climbing legs on, though, as there are seven levels...
The fourth photo was on the drive back and shows one of those coincidences you must photo!