I have an old Lunt LS60T telescope (tilt-tuned) and also two 5Omm Lunt aperture filters (tilt-tuned). These come from before 2010, the early days of Lunt.
The LS60T came with the B600 blocking filter and the 50mm filters with the B1200 filter.
I also was very concerned about the highly uneven illumination the Lunt 60mm gave both visually and in images, and did extensive tests, including pulling the filter units apart and using the blockers separately from the diagonals, in a straight-through configuration using an adaptor I made on my lathe (invalidating all warranties obviously).
My conclusions were:
1) The B1200 gave very much better results than the B600, with all other components being the same. It was chalk and cheese, the B600 just seemed to be a low-quality item.
2) The straight-through configuration was better than using a Lunt diagonal, and substituting a 2″ mirror diagonal from another manufacturer was better as well, though not as good as straight-through. When I pulled the Lunt diagonals apart I noticed how crudely and inaccurately made they were, components just glued with a rubbery substance to rough aluminium castings, the inside a total contrast to the polished outside finish!
Since then I have taken all my images with the straight-through system I made incorporating the B1200 and a replacement IR block filter (the original Lunt IR block filters all crazed over after a few years; this is likely due to the dampness in my observatory). That said there is still an unevenness in my images from the Lunt that cannot be completely removed by any adjustment of components. Here’s a typical example. Not flat frames have been used.
Flat frames will (or should) correct Newton’s rings (which I get with certain cameras), but will not make the uneven filtration of Lunt systems even. In other words, even if you flattened the illumination, you would still see the uneven detail. The only H alpha telescopes I have experienced personally that do not suffer from such unevenness at all are the Solarscopes made in the Isle of Man (3 times the price of Lunt). However, I’ve been very impressed by images from users of the new Sky-Watcher Heliostar and Acuter scopes.
