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Aaah yes, amateur Boffinry at its British best.
It's basically a Dialyte, folded. The Dialyte (dating from the era of uncoated optics) was based on the idea of using a whopping positive singlet first element, as big as one could afford, followed by a second negative element well down the optical path of much smaller aperture (and lower cost) to correct the aberrations of that first element. The Dialyte design was a big compromise when it comes to off-axis astigmatism, field curvature, chromatism and lateral colour. Basically its a very big telephoto camera lens, with only 2 elements.
These guys have folded it and modernised it - coated optics suggests a four element second group should be no problem, and modern glass types suggest a significantly better result should be possible than the early Dialytes I have data for.
The snag is, if you're going to shell out for a multi-element sub-aperture second group you may as well shell out for a really decent ED doublet or better, triplet and folde the path of that; it will wind up about the same size, costing much the same, and outperforming it in all aspects. Finding some fool silly enough to make a 30" triplet shouldn't be too hard, in England, methinks...
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