Layout of filters in a CaK PST

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Merlin66
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Layout of filters in a CaK PST

Post by Merlin66 »

Can't seem to find the details I'm looking for...
Can you help with a detailed breakdown of the filters fitted to the CaK PST?
I hear of the #1 PST yellow filter....there may be others internally, and it looks like there is a final small (5mm) filter in the eypiece holder.
Any link/ assistance welcome.
Thanks.
Ken


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Re: Layout of filters in a CaK PST

Post by Merlin66 »

Is the front objective ERF coated, like the original Ha PST ( but with a coating to suit CaK)???
OK.
So in the PST CaK scope we seems to have a front "ITF?" element followed by the "PST Yellow filter" and a smaller "IR?" filter in the eyepiece holder - three filter elements in total.

(I'm hoping to obtain one soon, so will be able to carryout spectrograph appraisal of each filter element......)


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Re: Layout of filters in a CaK PST

Post by Merlin66 »

Thanks guys.
We seem to agree that there's only three internal filter elements to identify and measure.....


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Re: Layout of filters in a CaK PST

Post by Merlin66 »

OK.
I've already built a CaK filter with a Baader Blue-CCD as the front ERF, then a couple of Omega filters...... works OK.
As you know any hope of using a CaK filter visually means you have to be less than 12 years of age ;) won't work for a BoF like me.

I'll test all the elements when the CaK PST arrives.


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Re: Layout of filters in a CaK PST

Post by Merlin66 »

OK, The PST CaK arrived, s/n 50059............
There are five filter elements, including the objective (excluding the pentaprism)....
1. The objective has a light yellow (AR?) coating
2. The first filter in the blue ring has a bright blueish AR(?) coating, otherwise clear
3. The second filter is what I assume we call the #1 yellow filter, bright reflective yellow coating
4. At the bottom of the eyepiece holder, at the black box there's a small (5mm) highly reflective silver filter.
5. In the top section of the eyepiece holder, there's another small (5mm) clear filter with a light yellow (AR?) coating.

Weather and time permitting I'll test and measure transmission of each filter element.


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Re: Layout of filters in a CaK PST

Post by marktownley »

Merlin66 wrote: Mon Sep 09, 2019 1:05 am Weather and time permitting I'll test and measure transmission of each filter element.
Looking forward to the findings Ken :)


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Re: Layout of filters in a CaK PST

Post by bart1805 »

Hi Ken, the filter that is useful is the thin one, diameter about 25 mm, it is the first one after the lens.
The one with the bright reflective coating is the one which is often deteriorated. It is way thicker than the front one.


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Re: Layout of filters in a CaK PST

Post by Merlin66 »

Thanks guys!
May be tomorrow with the spectroscope.
Quick visual test...removed the gold tube and the filter capsule ( i.e. using elements #1 to #3 above), looking at a Quartz halogen (bright!) lamp.
I can see a central bright green(ish) image of the lamp with three secondary images decreasing in brightness towards the edge.
When the gold tube is reassembled to the black box, looking through the eyepiece holder nothing is seen!!!!
I think element #4 must be a "blocking" filter element.......
Onwards and Upwards.
( I did find some interesting references/ messages from back in 2011/2012 on the CaK filters but unfortunately the associated images have been lost to the forum :( )


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