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Author Topic: The tilt of the BF element  (Read 1471 times)

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Offline JohnM

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The tilt of the BF element
« on: 16:55:03, 07 March, 2011 »
I was looking around in the cabinet in the observatory and found an old no longer used barlow.
It turned out the cavity in the end was a perfect size to accept the 10mm BF cell from my Denk built unit and the bezel screws in perfectly to hold it in place.
Voila' , a Bf that will drop into a standard 1.25" bore!
However it sits perfectly at right angles to the tube.
Do you guys think I should try to add a tilt?
Perhaps with some brass shim stock.
I think I recall Russ told me he built them with about a 2° tilt.

Offline Merlin66

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Re: The tilt of the BF element
« Reply #1 on: 20:56:29, 07 March, 2011 »
In the current Coronado BF there's no tilt.
The original Isle of Man (IoM) filters produced before production was transferred to the US did infact have a tilting/ tuning screw ( Simon has one of these.) All the tilting does is move the centre of the bandwidth towards the blue end of the spectrum... so if the centre of the bandwidth was "out" relative to the Ha and the finesse of the etalon there MAY be some benefit in moving the central point....
C11, C9.25 SCT, 4" Genesis, NEQ6pro, modded 1000D,  ATik314L+, DMK41AF04, SM60DS/BF15, and Spectroscopes (many!).
"Astronomical Spectroscopy for Amateurs", "Grating Spectroscopes-How to Use them" -Springer

Offline JohnM

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Re: The tilt of the BF element
« Reply #2 on: 21:39:33, 07 March, 2011 »
Thanks Ken,
That's good to know.
My 40mm PST has the seat for the 5mm BF milled at an angle too.
I had always been told it was to counteract internal reflections.
A friend of mines CaK PST had a tilted element too.
When I took the tilt out and tried it, the scope performed much better.


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