*
The image [right] shows "sunny side up" as indicated by a penciled arrow
on the edge. The arrow must point towards the sun to
reflect the sun's heat away. This side of the filter appears slightly
more reflective than the rear. Note the multiple reflections on the far edge
of the blank which can be seen descending deep into the glass.A complex layering system is deposited on each surface. This was an indoor, flash image. At different angles and lighting conditions the glass appears partially mirrored. Note that the Baader D-ERF acts only as a pre-filter for H-alpha etalons and matching, full filtration UV/IR rejection systems. The D-ERF must never be used as the sole means of energy rejection for visual or even imaging use.
The T-S , full aperture, objective mounted filter cell, is made to measure. It is flawlessly machined and of excellent design. Providing secure clamping of the heavy glass filter to the nose of the objective cell. With felt to protect the precision polished glass against marking, expansion or shock.
Available in many sizes the cell can be made to order to fit any lens or dewshield. Airies makes much larger ERFs for SCTs and these too can be catered for by TS. Reflective glass, white light, solar filters can also be mounted by this system.
This second image is of the T-S filter cell from the rear. Where it clamps onto the objective cell nose. The clamping screws are of adequate size and of Nylon, or similar. To avoid cosmetic damage to the objective cell finish. A locking ring screws into the front of the cell to secure the filter glass safely in place. It would be a disaster if the costly D-ERF fell off the front of the telescope if it it was accidentally pointed nose downwards! As has happened regularly when I sent my telescopes back to their usual parking position, horizontally, to the east.
The expense of the cell had to be balanced against my serious doubts as to the safety of the filter [and my eyes] had I made myself a similar cell. I have never attempted such a large diameter thread in any pitch on my old lathe. Spread across years of satisfactory use the cost of the cell becomes relatively meaningless. Besides, it makes quite a change for any of my telescopes to look remotely as smart as this unit. I will really have to make an effort to try and match it with the rest of the telescope.
There is a problem! The D-ERF glass will not fit into the T-E made-to-measure filter holder. Both glass and holder recess are of exactly the same diameter at 160mm. Without any allowance for fitting clearance. Nor for thermal contraction of the aluminium cell onto the unchanging glass in a hard, overnight frost. I had lowered the cell onto the glass in expectation of easy insertion. It didn't happen. So now my fingerprints are all around the edge of the glass filter. Should I use a lens wipe? Or leave them? Had I known they wouldn't fit each other and easily, I'd have worn disposable gloves. The wisdom of perfect hindsight. They want me to return both items to see where the error lies. Postage prepaid with a printed PDF label.
*
No comments:
Post a Comment