Diving in the heart of a CaK PST

[sullij1]

Lanleif,

Thank you for your important contribution and WELCOME! Glad you decided to pitch in!

1 Welcome Karma Point for your contribution!

[marktownley]

Welcome to the forum Lanleif!

Great opening thread, I dismantled my CaK PST like this when made the mod for it, however never disassembled it again, so great to see your pics, brings back fond memories!

I'm working myself on a 'recipe' for a narrowband CaK filter using 'off the shelf' filters, i'm hoping in the new year when the sun is higher and can resume proper testing to get it up and running. CaK imaging for a fraction of the price, even if the filter front element has a finite lifetime and needs replacing is the way forward

Do you have any images you've took Lanleif you can share?

[robert]

Very good images, however you got them!
Robert

[swisswalter]

Hi Leif

welcome to that wonderful TOS free site, have sun have fun. Thanks for all that information. Beautiful shots

[marktownley]

Hey there Langeif!

I was thinking about CaK over the Christmas / New year holiday period and today decided to dismantle my CaK module for an explore inside. Now I don't have a spectrometer so can only pass visual comment on what I saw, but I think there are a few things to add.

The front filter (one closest to the objective)as you say has a yellowish tinge to it and is also very thin - 1.5mm.

The second filter (one closest to the black box originally) when I look through it visually is that deep violet blue colour (same colour as the Baader K-Line looks when you look through it) - however, it is much brighter view than the K-Line. Now, given the K-Line already has high transmission in its working range I would suggest that the silvered filter in the CaK PST has a much wider bandpass - pure speculation as i dont have access to a spectrograph. This filter is also made of 2 peices joined (cemented?) together - the same type as the mini-erf in a coronado Ha blocking filter.

When you look through both of these two filters from the CaK ST together visually there is a very dark green view - I think this is some infra red leak...

Now, lets speculate on how all this works: well, let's start off with the transmission curve from a baader K-Line



If you haven't taken one apart (I have :whistle: ) it is two seperate filters with a wedge shaped ring sat between them to angle one with respect to the other. Look through the individual elements of the K-Line and the view is that really dark green (Infra red leak) with no violet colour visible - I think it is being drowned out - however look through them as a pair and the dark green view goes and the purple/violet view appears.

Now, i'm going to hazard a guess that the front filter from the CaK PST is a 390/395/400(?)ALP (long pass) filter. These are readily available from a wide range of suppliers. If we look at it's transmission curve for the 390ALP we see this:



You can see how that sharp edge at the left could be used to shave off the bandpass from the K-Line.

However, by the power of photoshop trickery, if we superimpose the k-line curve on the 390 curve at the same scale we can see that the 390 encompasses it - hmmm, not this one then...



But if we take the 400ALP transmission curve then this would appear to be out of range - hmmm :dry:

400alp.tif

Maybe if we tilted the 400ALP we could blueshift it to the response we need? However I don't see any tilted filters in the CaK PST... or maybe it is a filter somewhere in between the 2? I've been looking around online but nothing is jumping out at me...

Next steps then - well, when the sun returns i;m going to run my CaK pst mod without the silvered filter - just the ALP filter and the Baader K-Line and see what my results are like. Also, i'm going to search hard for this elusive ALP filter online...

Will keep you updated.

Mark

[swisswalter]

Hi Mark

that is reading a "crimi", great informations :

[marktownley]

Thanks Walter

Maybe it is some Schott GG-395 that we need http://www.uqgoptics.com/_materials_fil ... GG395.aspx

[marktownley]

The front filter (nearest to objective) is the one that do the magic together with the Baader as a blocker of course. It does not reveil much in my visual spectroscope other than showing the solar continuum.

But what is really a mystery for me is the front filter. Coronado did a good job there not showing us the secret!!

Hi Langleif, happy new year to you too

Yes, this front filter is the one we need to work out the transmission of. My money is on it being GG400 or GG395, these filters have the 'visual appearance' the same as the one in the CaK PST, and also have the steep sloped transmission curve we need to 'trim' the bandpass of the Baader K-Line down. The GG395/400 are actually quite cheap to buy, so intend to get some to give it a try.

I've seen all the stuff on the Apollo/Sergio stack on CN, however have not been able to see these stacks first hand or really find out much more information on them. Interesting though.

I think 2013 could be a bumper year for the CaK modders

[swisswalter]

Hi Life

thank you very much for the informations. Can somedy show good pics taken with the reported combination?