Coronado BF30

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Fenrir
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Coronado BF30

Post by Fenrir » Fri Sep 25, 2015 1:52 pm

Hello all,

I have the opportunity to buy a second hand 2" Coronado BF30 filter.
I am working on a PST mod with a 150mm f/8 skywatcher refractor,the intention
is to use a 110mm Baader erf filter in the middle of the scope and a pst etalon.
The scope would be used mainly for imaging.

I was still looking for a recent model BF10 or BF15 filter.
How does this first generation BF30 filter compare with respect to above 2?
What do I need to watch out for? The original itf is corroded, but will
be replaced with a 35nm h-alpha filter.
Can the BF element itself also degrade over time? The owner commented
the view through the filter was fairly bright and required an extra grey filter (ND filter?)
to use visually.

I don't have actual pics of the BF30 yet, but this is the model.
It has a ring on the outside to slightly tilt the blocking element.

Image

Thanks!

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Bob Yoesle
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Re: Coronado BF30

Post by Bob Yoesle » Fri Oct 02, 2015 5:08 am

Even though you say you will use mainly for imaging, I wouldn't be comfortable without some longer IR blocking than the DERF alone can provide. Consider using a KG filter in addition to the 35 nm filter... http://beloptik.de/en/left/if-uv-ir-cut ... ng-filter/

The Baader 35 nm filter is on a RG610 substrate. It would be better to use a filter with RG630 as a substrate (I believe the 7 nm is on RG630).

Lastly, be sure that you can return the filter if it doesn't work well. If the blocking filter was designed for an etalon with a greater distance between the harmonic side-band peaks than the PST, the blocking filter won't block out-of band continuum, and you will have poor contrast from this "parasitic" light which will "leak" through.
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