Can I have an 2020 update on where we are with Ca-K filter controls.

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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by solarGain »

Valery Hi. PM sent.
All the best
John


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by marktownley »

And, as always, silence was the response... :(


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by marktownley »

I thought I would feedback and share with the group my initial experiences of using a 'new' sub aperture D-ERF for my CaK system. Previously I had been using the Baader Blue CCD filter for this purpose, and while this is fine for shorter focal ratios, as the f ratio goes the light throughput rapidly goes down, never good!

I bought an Astronomik L1 Uv/IR filter whose transmission is high at 393nm:
ak_uv-ir_l_transmission_chart.png
ak_uv-ir_l_transmission_chart.png (1.66 MiB) Viewed 3366 times
Well the graph is right, I have oodles of light at longer focal ratios, that have allowed me to reduce both exposure time and gain which should help freeze the seeing. Yes, it naturally lets more energy through than the Baader Blue, but this will offer about a 60% reduction in thermal load compared to no sub aperture DERF, so, should be safe to use with a Lunt CaK at apertures up to about 150mm.

Just need some decent clear skies to try some imaging with it now.

Mark


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by solarGain »

By my reckoning the comparison between the two is at most 2% is that enough "oodles of light at longer focal ratios".
Indeed I need all of this light but have nothing to compare with the Baader blue filter. More opportunities in front of the scope would be good to hear about this. Many thanks.
All the best
John


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by marktownley »

solarGain wrote: Wed Jul 08, 2020 7:04 am By my reckoning the comparison between the two is at most 2% is that enough "oodles of light at longer focal ratios".
I'm confused? What is the 2% and where have you got it from?


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by solarGain »

This was just a reading of the graphs for Baader Blue and your new Astronomik filter.
Baader looks like say ~95% and the Astronomik ~97%. Or have I misunderstood something.
John


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by Bob Yoesle »

In my home brew CaK module the Badder B CCD filter lets way too much off-band energy trough for my tastes (which seems to be converted to lots of heat), and the Astronomick filter would be worse in that regard. I'm now considering one of these two filters as an CaK module ERF, perhaps combined with a KG for longer IR:

Edmund 390 45 v 394 10.jpg
Edmund 390 45 v 394 10.jpg (160.82 KiB) Viewed 3337 times

https://www.edmundoptics.com/p/390nm-cw ... ter/28795/

https://www.edmundoptics.com/p/394nm-cw ... ter/19839/

The differences come down to substrate - fused silica versus optical glass, OD, FWHM, and wavefront, scratch/dig, etc., and of course price - though both are on the $pendy side! The 394 10 seems to be similar to the Baader K line, and might eliminate the need for that filter in the stew.


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by christian viladrich »

Just for info, we have measured the transmission of a Baader B CCD filter last year with a photometer. We found 18% at 393.3 nm.
The old B Astronomik filter has a transmission of 87% at 393 nm. This is the one as use as a 50 mm sub-apeture filter. Unfortunatly, the new version has a very low transmission at 393.3 nm.
I also use a 25 mm EO 394-10 nm filter. But it can't be used as a 50 mm ERF. The fluorescence filter pointed by Bob has much better optical quality (still L/4 RMS).


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by marktownley »

solarGain wrote: Wed Jul 08, 2020 12:43 pm This was just a reading of the graphs for Baader Blue and your new Astronomik filter.
Baader looks like say ~95% and the Astronomik ~97%. Or have I misunderstood something.
John
Ahh got you. Here is the Baader trsnsmission curve for the blue CCD filter:
BAA-blau-G.gif
BAA-blau-G.gif (34.4 KiB) Viewed 3320 times
I think that graph above is very ambitious, and for me the transmission is in line with what Christian measured, certainly that is reflected in the difference in exposure times with it and the Astronomik L1.

What's the optical train in your filter Bob? I hear what you're saying about more energy coming through the L1.

I've recently reconfigured mine and my first element is the EO 387/11 filter this offers OD6 blocking and is a laser filter hence my choice of it as first element, then it goes CaK PST#1 filter, then EO 394/10 (OD4) then another CaK PST #1 in the tilter of the skybender to tune. I originally tried the setup with only a singular EO filter (for more transmission) but there is quite clearly, in both filters, an out of band leak, but combined it is gone... I replaced the K-line for the EO394/10. I've certainly got more light to play with in CaK than I have in Ha now.


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by christian viladrich »

Here are some measurements we made :
Version of Astronomik B filter previous the current one:
Image
Image

Baader B CCD :
Image
Image
Last edited by christian viladrich on Wed Jul 08, 2020 4:06 pm, edited 1 time in total.


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by christian viladrich »

ZWO B filter. I have no idea of the optical quality in 50 mm diameter :
Image


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by george9 »

The other half of the equation, if you are using a Lunt CaK, is what it the transmission of its ERF? Depending on that profile, there may not be much to gain by adding another ERF in front. If the Lunt is already narrow and sharp, then adding another filter with high transmission in front of it ends up putting the same amount of heat through the Lunt ERF to the filters behind it. So if the 4" aperture limit on the Lunt is due to the heat passed through its ERF, this won't help. You will instead need to attenuate the signal (like the Herschel wedge on Lunt's 6" CaK) or put an even narrower ERF in front of it (like Bob's suggested 10nm).

On the other hand, if the problem is long IR, then yes a KG3 will help. The Lunt looks reflective, not absorbing, so that is not an issue to fix.

I need to double check my Baader blue-CCD. It is just a couple of years old but I think the gain did not change so perhaps I just made it. My Astronomik UV-IR L-2c does cut CaK quite a bit, which is what pointed me to the L1. My no-name UV-IR does pass CaK well (but perhaps it passes all UV well).

George


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by george9 »

I stand corrected. I had a little time before sunset when the clouds cleared. In CaK:

Baader blue-CCD - passed 33%
Astronomik UV-IR cut L-2c - passed 50%
Baader double stack K-line 8nm - passed 66%+

I didn't measure it, but my PST #1 yellow filter passes the least light, but that boosts contrast, so it is worth it. (That is, the light it blocks is preferentially outside the CaK line.)

I forgot to try tilting the blue-CCD, which should shift it bluer and perhaps clearer.

Perhaps the blue-CCD could be helpful for large apertures by removing some of the energy getting into the Lunt CaK, at least on the blue side.

George


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by MalVeauX »

george9 wrote: Thu Jul 09, 2020 12:20 am I forgot to try tilting the blue-CCD, which should shift it bluer and perhaps clearer.

Perhaps the blue-CCD could be helpful for large apertures by removing some of the energy getting into the Lunt CaK, at least on the blue side.

George
Hi George,

That's what I use the Blue CCD-IR Block Filter for, with bigger apertures, 120mm~150mm, with the Lunt CaK B1200 module. I'm not sure what exactly the Lunt's primary D-ERF is, it indeed looks reflective, but not sure how much visible spectrum is passing and how much IR is passing. Since it's only rated per Lunt up to 100mm apertures, I can only imagine what it's doing. That said, I have no issues with transmission with 150mm F16 on 2.9um pixels with my current system, more transmission would be welcome, but I'm not hurting for it at the moment with a single filter; maybe a double stack would cause me to want to increase transmission significantly.

That is an interesting point about tilting the filter. I wonder how it would change the reflection to throw the energy out of the tube and if tilting it does indeed shift it blue enough to increase transmission or not. Would be neat to test it. I have some Skybenders, so I will try this next time my weather allows and just do a few tests (but I can only measure by what exposures are needed, which may not be ideal since transparency fluctuation could throw up some inconsistent numbers).

Very best,


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by marktownley »

Interesting, seems like our respective Baader Blue filters seem to have quite different transmissions...


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by george9 »

I did better measurements today, and I added tilting. Titling 3 degrees did little. But at 25-30 degrees, many of the filters passed a lot more light. At 30 degrees, I assume the image is degraded.

This is all measured with a Lunt CaK B1200 and PST #1 yellow filter double stack on an ASI290, assuming pixel brightness is linear.

Untilted:

35% = 2" Baader blue-CCD
50% = 2" Beloptic UV-IR cut on KG3
55% = 1.25" Baader K-line
60% = 1.25" generic UV-IR cut filter
65% = 2" Astronomik UV-IR cut L-2c

Tilted 25-30 degrees:

80% = 2" Baader blue-CCD
80% = 2" Beloptic UV-IR cut on KG3
90% = 2" Astronomik UV-IR cut L-2c

George


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by marktownley »

Interesting you got something out of the L2 George, I bought one of these initially (over the L1) but found it just wasn't getting any light through for me in CaK despite the transmission graph suggesting it should.


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by george9 »

I wonder if my L-2c is a previous generation before the L-1, L-2, L-3 series. For example, I see no "c" mentioned anywhere any more. I got it about six year ago. It actually says:

L filter
UV IR cut
Type 2c

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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by LTHB »

One more data point for Baader blue CCD filters: about 35% transmission in CaK for my copy (measured by stacking it with a Lunt unit and comparing the exposure times).


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Re: Can I have an 2020 update on where we are with Ca-K filter controls.

Post by Bob Yoesle »

What's the optical train in your filter Bob? I hear what you're saying about more energy coming through the L1.
Hi Mark,

I don't have it all worked out as of yet. I'm working with a double-stacked pair of PST CaK filters, and going from there. My primary goals are to 1 - reduce reflections, and 2 - reduce the heat load at the PST filters:

1. PST CaK
2. PST CaK
3. Edmund 394-10 or Baader K-line or Edmund 400 lo-pass or Apollo L/Chroma 394.01
4. Andover KG3
5. Edmund 390-45 or Edmund 394-10 or Baader B-CCD.

Italicised filters are what I have on hand, bold filters are what I'm considering the best alternatives for the system. Keeping the number of filters as low as possible would seem to mitigate against the Baader K line and in favor or the other single filter alternatives at position 3, but the Edmund 400 nm short pass might not work as a blocking filter, and the Chroma results in a triple stack that has greatly reduced image brightness and necessitates using a Skybender to come on-band. In position 5 I already have experience that a significant amount of heat from the 400 to 500 nm transmission of the Baader B-CCD filter makes it less than ideal for an ERF.

CaK module 2 clr.jpg
CaK module 2 clr.jpg (260.1 KiB) Viewed 3131 times

I've collected a bunch of filter-tilters and tubing inserts to hopefully address the reflection issues for each individual filter, and a Baader TZ3 (suitable for CaK) should I need it, but have yet to assemble an integrated system... lots of projects underway ;-)

CaK components.jpg
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Any insights or suggestions greatly appreciated...


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