Narrowest 393.37 ever by Apollo Lasky

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Re: Narrowest 393.37 ever by Apollo Lasky

Post by krakatoa1883 » Wed Sep 12, 2018 5:16 pm

Nice to see these results. How does it perform behind a ND 3.8 astrosolar foil or a Herschel wedge ? Thanks.
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by marktownley » Wed Sep 12, 2018 7:30 pm

Good results Apollo!
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by Bob Yoesle » Fri Sep 14, 2018 10:30 pm

Had another chance to try some imaging before the weather deteriorated. The imaging train consisted of a Orion ED100/900, Baader Blue CCD and KG3 for ERF duties, Baader K line used as a blocker, a ND 0.6 for image brightness control, and finally either the PST CaK or CT 393.37 0.1 filter. All images taken with a PGR Chameleon with FireCapture at zero gain ("160"), gamma set at 1000, and Histogram min ~ 5 and max ~ 175. Aligned, stacked, and wavelet processed identically with RegiStax 6.

PST @ 1.258 ms:
140918 PST no tilt.jpg
140918 PST no tilt.jpg (471.97 KiB) Viewed 947 times
CT 393.37 w no tilt @ 0.871 ms:
140918 CT393 no tilt.jpg
140918 CT393 no tilt.jpg (396.63 KiB) Viewed 947 times
CT 393.37 with tilting that seemed to balance highlight detail with good contrast @ 1.037 ms:
140918 CT393 tilted.jpg
140918 CT393 tilted.jpg (447.81 KiB) Viewed 947 times
Not sure the exact amount of tilt which was applied, but this is what it looked like with the Skybender opened after the exposure:
20180914 Skybender.jpg
20180914 Skybender.jpg (216.77 KiB) Viewed 947 times
As Apollo has noted, tilt is required for this filter, and it seems to be approaching a performance level similar the the PST CaK filter. I will be doing some more imaging and evaluation of tilt angle performance changes as soon as the weather improves.
Last edited by Bob Yoesle on Fri Sep 14, 2018 10:42 pm, edited 1 time in total.
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by marktownley » Sat Sep 15, 2018 5:39 pm

Very good bob and apollo, glad this is working out!
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by Bob Yoesle » Wed Sep 19, 2018 3:58 am

A little better seeing today, so here are my latest test images for the CT 393.37 (used in Skybender tilt unit) - ED100/900, FireCapture set at minimum gain (160), gamma 700, histogram max ~ 190 +/- 10. All used a Baader B CCD and KG3 sub-aperture ERF's. All are 30 sec. captures @ 18 fps, aligned and stacked in Registax 6, best 10%, identical wavelet processing.

CT 393.37 single stack: Baader K line, CT CaK, 0.6 ND, exposure 0.982 ms.
CT.jpg
CT.jpg (449.32 KiB) Viewed 799 times
PST single stack: Baader K line, PST CaK, 0.6 ND, exposure 1.037 ms.
PST.jpg
PST.jpg (452.02 KiB) Viewed 799 times
The PST CaK seems to have a slight amount of more detail, but this could be seeing dependent for the particular capture run. Note I used a ND0.6 filter to keep the exposures reasonable for the single stack images, and removed it for the multiple stack images the follow. Once the CT393.37 was tilted for what I felt was the best overall contrast and detail single stacked, it was left that way for subsequent stacking images.

CT/PST double stack: Baader K line, CT/PST CaK, exposure 0.572 ms.
CT PST.jpg
CT PST.jpg (409.57 KiB) Viewed 792 times
PST double stack: Baader K line, PST/PST CaK, exposure 0.605 ms.
PST PST.jpg
PST PST.jpg (524.25 KiB) Viewed 799 times
There is considerable improvement of image contrast with double stacking, and more detail manifests itself near the solar limb.

CT/PST/PST triple stack: Baader K line, CT PST/PST CaK, exposure 2.217 ms.
CT PST PST.jpg
CT PST PST.jpg (534.23 KiB) Viewed 799 times
A subtle improvement to my eye, and again most visible near the limb...

Apollo recommended trying no Baader K line, PST/CT/PST CaK; the resulting exposure was 1.701 ms. No real change in detail level. The law of diminishing returns appears to be set in for these filters. Double stacking makes an obvious improvement, triple stacking is more subtle, but there.

My overall conclusion from the above is that the CT393.37 is almost identical in contrast performance to the PST CaK filter, and slightly superior for transmission and shortening of exposure times when double and triple stacking (tilting the filter apparently reduced peak transmission). While triple stacking two PST CaK filters with a CT393.37 increases exposure time significantly over double stacking, it does appear to have a subtle increase in contrast. Removing the Baader K line improved (shortened) the triple stacking exposure. Whether or not triple stacking is worth the overall increase in exposure is up to the individual and their local seeing conditions. From Peter's very fine spectroheliograph images it seems it won't be until a narrower profile 0.3 A FWHM filter becomes available that these results might be improved upon.
Last edited by Bob Yoesle on Wed Sep 19, 2018 6:06 pm, edited 3 times in total.
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by marktownley » Wed Sep 19, 2018 6:35 am

Brilliant!
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by Carbon60 » Wed Sep 19, 2018 11:33 am

Nice work, Bob. Was the seeing fairly consistent throughout the experiment? If at the end of the run you'd have gone back to the 'Lasky' filter as we could call it, would you have seen any difference between the first run with this filter and the last run with this same filter in the same configuration?

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Re: Narrowest 393.37 ever by Apollo Lasky

Post by Bob Yoesle » Wed Sep 19, 2018 5:30 pm

Hi Apollo,

Hoping to get out for another run for prominence imaging this coming Monday the 24th... hoping some prominences will cooperate !-)

Hi Mark,

Brilliant no - just results of being a bit obsessive compulsive ;-) As you know, one must reduce the variables as much as possible, and it's impossible to compare random images taken by others. You have to control for using the same equipment and processes in order to do valid and reliable comparisons and evaluations.

Hi Stu,

The seeing was pretty consistent, and I don't think another run would change the overall results. These results are also pretty consistent with my previous runs with the filters. Of course following double-blind testing methods and more data points - and others doing the evaluations - would help make it most definitive, but so far the direction is pretty clear.

As with any narrow band filter, the CT393.37 would likely do better with a longer f-ratio light cone, or in a collimated or optimized telecentric configuration. I tried ~ f25 with my Klee 2.8 x barlow, but couldn't get the system I kludged together to come to focus. That being said, my intention was to see what it would do in comparison to the PST filter(s) I use in the same configuration I usually employ (ED100 at f9), and how well a triple stack configuration would perform. As the PST filters are no longer available, it would be nice to do a comparison with the Lunt CaK filters instead.

From these results I now know that triple stacking filters - at least for me - offers some additional improvement for CaK, and if all can be optimized through tilt, spacing, ancillary filters, and exposure - may become my new standard for CaK imaging. Whether or not the CT 393.37 can hold its own with a Lunt CaK filter (or how well Lunt CaK filters perform in double or triple stacking) is going to be a question someone else may have to evaluate.

Yet to be evaluated is quad stacking (I may have an answer to this relatively soon), and if anyone would be able to do similar comparisons and stacking with the Lunt CaK filter(s).

Again, thanks to Apollo for making this filter available to the solar community for evaluation.
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by bart1805 » Wed Sep 19, 2018 8:54 pm

Thanks Bob and Apollo!
So the Lasky CaK seems to behave almost the same as a PST CaK. With indeed the big difference that if I wanted to buy a PST CaK I would have to be very lucky to be really able to buy one. The Lasky CaK costs about 1.300 dollar and requires tilt. So a Skybender would be necessary. Are they for sale Apollo?
A Baader Blue and KG3 can be used instead of the 1NM Chroma filter as Erf. Or as Apollo pointed out you could use a 402 NM filter.
Am I correct?

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Re: Narrowest 393.37 ever by Apollo Lasky

Post by marktownley » Sat Sep 22, 2018 6:08 am

Enjoy Colorado!
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by christian viladrich » Wed Sep 26, 2018 8:08 pm

Hi Bob,
Thanks for your test. The incraese of contrast from the Chroma filtre, PST single stacked, PST double stacked and triple stack is clearly appearant.
BTW, I have probably overlooked the information ... what F/D ratio did you used with the Chroma filter in this test ?
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by bart1805 » Thu Sep 27, 2018 10:15 pm

That looks cool and very promising! Congrats!

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Re: Narrowest 393.37 ever by Apollo Lasky

Post by bart1805 » Thu Sep 27, 2018 10:31 pm

Thanks, will first try it out with what I have already. But the things you and Bob showed with the Chroma filter are very tempting.... Curious how the images compare to yours and those of Bob when the Chroma is stacked with a Lunt BF. It is a shame the filters are so expensive. (-;

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Re: Narrowest 393.37 ever by Apollo Lasky

Post by bart1805 » Thu Sep 27, 2018 10:50 pm

Yes, but I happen to have a LuntCakB600, I am not planning to buy one. Solar season is almost over for me, so have a few months to gather the funds.

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Re: Narrowest 393.37 ever by Apollo Lasky

Post by marktownley » Fri Sep 28, 2018 5:09 am

Quite a difference! Came out well. That telecentric is going to narrow the bandpass down from what is achievable in a converging beam I guess.
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by MalVeauX » Fri Sep 28, 2018 12:19 pm

Interesting stuff, can't wait to see how it handles a huge prom group!

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Re: Narrowest 393.37 ever by Apollo Lasky

Post by krakatoa1883 » Fri Sep 28, 2018 4:04 pm

A giant step forward, Apollo, congratulations. Does a telecentric beam make some difference ?
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by Bob Yoesle » Sat Sep 29, 2018 3:57 am

Hi Bob,
Thanks for your test. The incraese of contrast from the Chroma filtre, PST single stacked, PST double stacked and triple stack is clearly appearant.
BTW, I have probably overlooked the information ... what F/D ratio did you used with the Chroma filter in this test ?
Best regards
Hi Christian,

That series was taken through an ED100 at the prime focus FL of 900 mm: F/D = 9

As informed by Dick at Chroma Tech, the CT 393.37 0.1 will perform much better in a collimated (or telecentric) configuration, as would any very narrow band filter. Since it is a single cavity filter I would expect it to provide even better performance when implemented in a collimated or telecentric system. But for my tests I wanted to see how it performed directly head to head against what I have readily available in the same f9 system, and if it would make an efficacious stacking filter. It seems the answer is indeed yes.

Per Apollo's latest images, a collimator or telecentric implementation would be even more desirable, and appears to put the single CT 393.37 0.1 filter into the same league as the results I obtained with double and/or triple stacking with the PST CaK filters I have ;-) Not sure how the PST/Lunt filters would perform in a similar implementation.
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by christian viladrich » Sat Sep 29, 2018 7:50 am

Thanks Bob,
F/9 is definetly too slow. I use at least F/15 with my Cak 0.24 nm filter.
BTW, if you have the average index (n) of the Chroma filter, I can try a simulation of the impact of the F/D on the effective FHWM.
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by mdwmark » Sun Sep 30, 2018 6:03 am

Hi Group,
OK Christian, I modeled an filter similar to the Chroma. My design came out 1.2Ang which I though was close enough.

CW Ang HW Ang %of original transmission
at zero deg 3934 1.2 100
At F/30 3933.79 1.23 96
at F/20 3933.54 1.28 86
at F/15 3933.30 1.7 70
at F/10 3932,3 3.2 40
at F/8 3931.7 4.7 28
at F/6 3930 8.3 16
so you still need to worry about the F/# just like any other filter to keep the Hw narrow.
Mark W.

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Re: Narrowest 393.37 ever by Apollo Lasky

Post by christian viladrich » Sun Sep 30, 2018 8:28 am

Hi Mark,
Very interesting, thanks for the simulations.
That would explain why the contrast at F/9 is lower than with the PST (= etalon in a collimated beam) : about 4 A resulting FWHM vs 2.2 A for the PST.
F/15-20 seems to be the minimum ratio to make good use of the filter.

Bob, if you have a TZ-2, you might give it a try. They are designed for Ha but, by chance, they might do well for Ca K too. I remember having played with a Ha telecentric design for my 300mm. It was not too bad in Ca K too.
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by marktownley » Sun Sep 30, 2018 11:35 am

christian viladrich wrote:
Sun Sep 30, 2018 8:28 am
That would explain why the contrast at F/9 is lower than with the PST (= etalon in a collimated beam) : about 4 A resulting FWHM vs 2.2 A for the PST.
CaK PST does not use collimating / refocusing lens either side of the all important filter, it sits in a converging f/10 beam. Maybe the PST filter is natively narrower and the quoted 2.2a is the bandpass in the f/10 beam?
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by Bob Yoesle » Sun Sep 30, 2018 2:41 pm

Maybe the PST filter is natively narrower and the quoted 2.2a is the bandpass in the f/10 beam?
Perhaps a multiple cavity filter with steeper transmission sides, which may make it less susceptible to light ray incident angle effects(?)
Bob, if you have a TZ-2, you might give it a try. They are designed for Ha but, by chance, they might do well for Ca K too. I remember having played with a Ha telecentric design for my 300mm. It was not too bad in Ca K too.
Thanks for that information Christian. May have to contact Baader to see if they have any info on their TZ''s and their performance at 394 nm.

The Baader TZ3 looks to be the ideal telecentric, and is specifically stated to be "diffraction limited at 396 nm (CaK)"

https://www.baader-planetarium.com/en/r ... ngth).html

Then would have to find a suitable focal reduction lens ;-)

Looks like Apollo is working on a COTS (commercial off the shelf) lens solution as well...
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by christian viladrich » Sun Sep 30, 2018 3:03 pm

Thanks for the clarification Mark.
Does anybody have a drawing of the optical design of the Ca K PST ?

Bob, interesting what they say about the correction of the TZ-3 at 393 nm.
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Re: Narrowest 393.37 ever by Apollo Lasky

Post by Valery » Sun Sep 30, 2018 5:29 pm

The corrective optics I do use with my C11 works also as barlow lens. It makes all my SCTs - C8, C11 and C14 diffraction limited at 393nm. Unfortunately, the market for this optics is too small to justify all the troubles, hairs and money loss making this optics.
There are plenty of other much more appeling and cost effective projects with a small optics.
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