CaK blocking filter question

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Brett
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CaK blocking filter question

Post by Brett » Sat Dec 20, 2014 11:18 pm

Hello Everyone,

Firstly, this is my first post here on the forum. By way of introduction, my name is Brett, I live in South Africa and have just recently completed my own white light newtonian with a herschel wedge.

I have been reading and have gained a lot of information on this forum. I am hoping that there will be much more to come. On to my question then:

I am building a CaK telescope for myself for photography use. I am noticing that everyone uses the basic train of filters: ERF, narrowband CaK, broadband normally around 394nm (like Baader k line). If an ERF is used, what is the reason for the extra broadband filter? The narrowband filter already rejects these wave lengths? What am I missing?

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GUS
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Re: CaK blocking filter question

Post by GUS » Sun Dec 21, 2014 6:06 am

Hi, and welcome to the site Brett.

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swisswalter
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Re: CaK blocking filter question

Post by swisswalter » Sun Dec 21, 2014 7:33 am

Hi Brett

welcome to that wonderful site. Have fun in the sun.

In my setup using an additional K-line filter gives a tad more contrast
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

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Re: CaK blocking filter question

Post by marktownley » Sun Dec 21, 2014 8:17 am

Brett wrote:What am I missing?
By using additional filters, you get greater out of band blocking, which, like Walter says, gives extra contrast.

Welcome to the forum btw :)
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Re: CaK blocking filter question

Post by Brett » Sun Dec 21, 2014 2:34 pm

Thank you Mark, Gus and Walter.

So it is then my understanding that the narrower the band width of the blocking filter, the more contrast one will have when combined with a good narrow band CaK filter?

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Re: CaK blocking filter question

Post by swisswalter » Mon Dec 22, 2014 5:15 am

Hi Brett

yes exactly. I hope to post today some pics with double stacked CaK filters taken yesterday at less than optimal conditions
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

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Re: CaK blocking filter question

Post by Valery » Tue Dec 23, 2014 2:50 am

swisswalter wrote:Hi Brett

yes exactly. I hope to post today some pics with double stacked CaK filters taken yesterday at less than optimal conditions
Hi Walter!

Where you will post them? Here on in imagining forum?

Valery.
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Re: CaK blocking filter question

Post by swisswalter » Tue Dec 23, 2014 5:20 am

Hi Valery

yes here . Where else ;)
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

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Re: CaK blocking filter question

Post by Brett » Sat Jan 03, 2015 11:31 am

I am also wondering if it would not be better to use a second CaK narrow band filter in stead of a blocking filter. By going for the Baader as a CaK, on could just pay a liitle more and rather get Bob's CaK as a blocker.

I am waiting for my first Bob CaK, but am now wondering if I would be better off by just. Double stacking and leaving the blocker out.

Of course the appropriate ERF will be used to protect the filters.

What do you guys think?

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Re: CaK blocking filter question

Post by marktownley » Sat Jan 03, 2015 11:59 am

I think I would see how you get on with just the one filter from Bob at the moment.

What ERF were you thinking of using?
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Re: CaK blocking filter question

Post by Brett » Sat Jan 03, 2015 6:46 pm

Mark, I was thinking of using a 45 degree dichroic mirror as a diagonal. The mirror would block out everything above 405nm.

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Re: CaK blocking filter question

Post by swisswalter » Sat Jan 03, 2015 6:52 pm

Hi Brett

it is better to have the blocking filter even narrower, that's what practise is telling me.
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

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Re: CaK blocking filter question

Post by Brett » Sat Jan 03, 2015 9:23 pm

Walter, do you mean that the blocking filter should be even narrower than the Baader CaK filter or narrower than Bob's new Omega CaK filter?

Mark, why do you suggest staying with one filter from Omega Bob? At this stage my concern is to get the best blocking filter for the job. What would you suggest?

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Re: CaK blocking filter question

Post by swisswalter » Sun Jan 04, 2015 7:28 am

Hi Brett

I can only speak about the configurations I used so far. The blocking filter as such is important but the preblocking is at least as important. I use the LUNT hot mirror and the K-Line as prefilters followed by CAK PST #1 and LUNT CaK stack. Me too I just can't wait to see how the new Bob CaK stack performs without the CaK PST #1 and LUNT CaK stack. Finally I will stack up to five filters to see what we get.But for that I need sunshine ;)
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

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Re: CaK blocking filter question

Post by marktownley » Sun Jan 04, 2015 1:26 pm

Brett wrote:Mark, why do you suggest staying with one filter from Omega Bob? At this stage my concern is to get the best blocking filter for the job. What would you suggest?
At the moment we only have seen pictures from from highfnum using the omegabob filter, personally, I would like to see more images from more people to see how it performs.
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Re: CaK blocking filter question

Post by swisswalter » Mon Jan 05, 2015 5:31 am

Hi Mark

maybe today is the day ;)
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

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Re: CaK blocking filter question

Post by marktownley » Mon Jan 05, 2015 7:09 am

Hope so! :)
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