The role of the diagonal mirror in the Coronado BF10 and BF15 filters.

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Valery
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The role of the diagonal mirror in the Coronado BF10 and BF15 filters.

Post by Valery » Wed Dec 06, 2017 9:43 am

Hi all,


Does anybody know the real role of the diagonal mirror in these BF10 and BF15 filters.

It seems for me that the only role it plays is just an image brightness control (decreasing).

However I can be wrong and if so I would like to know does this diagonal plays any specific
filtration role.

Thanks in advance.


Valery
Last edited by Valery on Wed Dec 06, 2017 2:17 pm, edited 1 time in total.
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GUS
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Re: The role of the diagonal mirror is Coronado BF10 and BF15 filters.

Post by GUS » Wed Dec 06, 2017 10:53 am

Hi Valery, Lunt, on their website state that their diagonal mirror is an IR longpass mirror. I have noticed with my two Lunt BFs that there is a difference in reflection between the two as you say, for brightness control. The Coronado mirrors look very similar in size and coating to the Lunt mirrors but not sure if they have similar roles. I have three Coronado BF's, but the reflectivity on all three looks the same.

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Re: The role of the diagonal mirror is Coronado BF10 and BF15 filters.

Post by Valery » Wed Dec 06, 2017 2:22 pm

GUS wrote:
Wed Dec 06, 2017 10:53 am
Hi Valery, Lunt, on their website state that their diagonal mirror is an IR longpass mirror. I have noticed with my two Lunt BFs that there is a difference in reflection between the two as you say, for brightness control. The Coronado mirrors look very similar in size and coating to the Lunt mirrors but not sure if they have similar roles. I have three Coronado BF's, but the reflectivity on all three looks the same.
Thanks a lot, GUS!

So, they blocks something shorter than H-a? Or may be they are IR cut filters?


Valery
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Re: The role of the diagonal mirror in the Coronado BF10 and BF15 filters.

Post by GUS » Wed Dec 06, 2017 8:32 pm

Hi Valery, this diagram might help.Image

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Re: The role of the diagonal mirror in the Coronado BF10 and BF15 filters.

Post by marktownley » Wed Dec 06, 2017 9:57 pm

maybe someone can measure transmission etc?
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Re: The role of the diagonal mirror in the Coronado BF10 and BF15 filters.

Post by Merlin66 » Wed Dec 06, 2017 11:35 pm

I'm sure I've done this before....
I'll separate the filter elements in a Coronado BF15 and test with the spectroscope.
The ITF, the mirror and the final sort filter.
I can only think that the additional elements suppress any minor resonance transmission bandwidths. If the ITF/ sort filter are doing their job there should be nothing else to filter????
(Additional belt and braces??)
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