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Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Mon Oct 01, 2018 11:16 pm
by Bob Yoesle
Hello all,

Spoke to Dick Stewart at Chroma Technology about the CT 392.37 0.1bp filter's tilt performance, and he provided me the following data:

0.0 degree tilt peaks at 393.999 nm 99.69%
1.0 degree tilt peaks at 393.386 nm 99.69%
1.5 degree tilt peaks at 393.371 nm 99.70%
2.0 degree tilt peaks at 393.350 nm 99.69%
2.5 degree tilt peaks at 393.322 nm 99.69%
3.0 degree tilt peaks at 393.289 nm 99.69%
4.0 degree tilt peaks at 393.203 nm 99.69%

It appears about 1.5 degrees of tilt is the optimum for this filter using the data set provided. The transmission curve at 1.5 degrees looks like this:
CT393.4 1.5 degree.jpg
CT393.4 1.5 degree.jpg (66.92 KiB) Viewed 795 times
Of course, this would be with perfectly collimated light rays. Towards this end, it appears the Baader TZ 3 telecentric might be an ideal component, and is stated to have a strehl "well above 80%" at 396 nm. This can be combined with the matching 0.4 telecompressor to restore the native EFL.

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Wed Oct 03, 2018 7:15 am
by Valery
TheSkyBurner wrote:
Wed Oct 03, 2018 5:33 am


This will be the only time I ask for help, because I need funds for a future development.
Do you mean spinal surgery/probe equipment development you recently announced? I belive this is much more
important than playing with sun imaging.


Valery

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Wed Oct 03, 2018 5:01 pm
by Bob Yoesle
I don't know why there is a discrepancy, all I know is that this is the data Dick Stewart sent me. My filter also appears to need more than 1.5 degrees of tilt, but I have yet to calculate it from what I can measure in the Skybender - going to have to brush up on my trigonometry skills ;-)

Dick did inform me that any future CT 393.37 0.1 filter production would cost ~ $2250+ per filter given the R&D prototypes required even tighter tolerances and complex production methods than they originally anticipated.

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Wed Oct 03, 2018 6:14 pm
by Valery
Bob Yoesle wrote:
Wed Oct 03, 2018 5:01 pm
I don't know why there is a discrepancy, all I know is that this is the data Dick Stewart sent me. My filter also appears to need more than 1.5 degrees of tilt, but I have yet to calculate it from what I can measure in the Skybender - going to have to brush up on my trigonometry skills ;-)

Dick did inform me that any future CT 393.37 0.1 filter production would cost ~ $2250+ per filter given the R&D prototypes required even tighter tolerances and complex production methods than they originally anticipated.

Is this CT 393.37 0.1 a single cavity or a double cavity filter?


Valery

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Wed Oct 03, 2018 7:10 pm
by Bob Yoesle
Single.

Chroma Tech said they could do a double cavity filter, but not a triple. I didn't ask what the price would be.

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Wed Oct 03, 2018 8:36 pm
by Valery
The price for a single cavity is $2250 and for a two cavity filter I'd expect at least $4000. If a two cavity filter will be a stack of two
single cavity filters (each of 1A FWHM) then it should have FWHM about 0,75A - 0,8A with steep sides and well supressed skirt. Still not enough to see dark filaments. But fibrils within bright AR near sun spots should be visible as well at the limb as spiculaes.
May be worth of $4000, may be not. Depends of how much better it will peforms on the sun vs DS of PST CaK.


Valery

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Thu Oct 04, 2018 5:11 am
by Bob Yoesle
I have asked Dick at Chroma Tech about the discrepancy of the data sets. So far, no answer. I did ask about the nomenclature difference; Apollo's files were labeled 393.37 0.1, the data sets Dick sent me were labeled 393.4 0.1. Dick stated it was just a labeling difference and that they indeed were for the same limited (two filter) R&D production run. The data sets he sent me do have a finer resolution.

Here's the 1.5 degree and 4 degree tilt data sets I received. Comparing the two 4 degree data sets (see Apollo's txt file above) indicates a substantial difference - ???
393.4-0.1bp-1.5 deg.txt
(35.46 KiB) Downloaded 16 times
393.4-0.1bp-4 deg.txt
(35.46 KiB) Downloaded 12 times
My findings regarding tilt more closely match Apollo's - the tilt for on band seems much nearer to 3 - 4 degrees.

Despite the now higher price, the filter appears to hold significant promise - when tilted it is quite close to the PST filter in an f9 system, and appears much better when used in a telecentric system. If one could afford it, as Valery references, it could provide pretty outstanding performance when double stacked. I have not used a PST (or Lunt) filter in such a telecentric system, so this comparison must wait.
The price for a single cavity is $2250 and for a two cavity filter I'd expect at least $4000. If a two cavity filter will be a stack of two
single cavity filters (each of 1A FWHM) then it should have FWHM about 0,75A - 0,8A with steep sides and well suppressed skirt. Still not enough to see dark filaments. But fibrils within bright AR near sun spots should be visible as well at the limb as spiculaes.
May be worth of $4000, may be not. Depends of how much better it will performs on the sun vs DS of PST CaK.
I understand how cost can be a deciding factor for purchase. On the other hand, my first DayStar H alpha 0.7 Angstrom ATM filter (circa 1976) was ~ $4000 in today's dollars (and has consistently stayed there: Quantum 0.7 A SE @ $4025). If getting a two cavity CT 393.37 version could provide the performance Valery refers to - 0.7+ A for CaK - it could be worth it for those who desire that level of contrast performance. The problem is finding someone who wants to risk that amount of investment for a new product. I risked $1250, and even with my limited trials so far it seems to have been worth it...

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Thu Oct 04, 2018 7:59 pm
by bart1805
[/quote]
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Your Skybender is on its way to your door!
[/quote]

Thanks Apollo, I received it today. That is an ingenious piece of equipment!! Let's Bend!
And ouch. 4.000 instead of 1.250. That means saving a whole lot longer.....

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Mon Oct 08, 2018 6:01 pm
by krakatoa1883
Looking forward to see the results of the comparison.

I am using a Baader VIP (Zeiss design) for imaging Venus in the UV and it seems very well corrected. I never use it for CaH but I can try comparing it to my Powermates.

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Thu Oct 11, 2018 8:16 pm
by bart1805
Found this information about a UV-Barlow lens.
https://www.astrosystems.nl/uv-barlow-

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Wed Oct 17, 2018 11:49 am
by krakatoa1883
As a starting point it would be enough to use a barlow fully transparent to the UV. At slow focal ratios even a single long focal lens would work fine
20151021.jpg
20151021.jpg (11.89 KiB) Viewed 480 times
while for fast f/ratios a singlet would not be enough due to increasing spherical aberration. Of course if one needs a telecentric system things become more complicated anyway.

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Wed Oct 17, 2018 12:38 pm
by marktownley
Good point Raf. What lens is that one you used?

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Wed Oct 17, 2018 2:30 pm
by krakatoa1883
This one from Edmund Optics

https://www.edmundoptics.eu/p/25mm-dia- ... lens/8568/

it was just an experiment but gone very successful. One can obtain even better results by a plano-concave (instead of a double-concave) lens provided with a UV-AR coating that covers 250 to 425nm, the price difference is small and worth the extra money.

Lenses can then be easily mounted in T threaded barrels

https://www.edmundoptics.eu/p/25254mm-d ... unt/10576/

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Wed Oct 17, 2018 7:18 pm
by marktownley
Very interesting Raf, which is the plano concave lens you tried?

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Thu Oct 18, 2018 7:08 am
by krakatoa1883
This is the page

https://www.edmundoptics.eu/p/250mm-dia ... lens/8557/

look under Technical Images in that same page for further information on how the lens works.

Choose the focal length based on the amplification you wish to obtain, ideal would be a long f.l. lens (say 100 mm) as this helps to contain aberrations, however if you have to amplify much (3x - 4x) a long f.l. would lead to a cumbersome (very long) optical train. The slower the scope the better the performance, no good with my newtonian at f/5, for example, much better at f/10 or slower.

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Mon Oct 29, 2018 3:11 am
by highfnum
very interesting!

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Tue Oct 30, 2018 4:35 pm
by highfnum
i sent email to chroma
no response

Re: Narrowest 393.37 ever by Apollo Lasky

Posted: Sun Nov 04, 2018 7:30 pm
by highfnum
sent e-mail over a week never got an answer back