Large D-ERF "tri-band"

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Ronnie_Clayton
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Large D-ERF "tri-band"

Post by Ronnie_Clayton »

Hello friends.

I would like to buy a large DERF ("tri-band") for a C9,25 Edge. Do you know some vendor or company to provide this size of D-ERF?

BR

Ronnie


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Re: Large D-ERF "tri-band"

Post by DavidP »

Ronnie.
I could be wrong, but I don’t believe believe that anyone is currently making anything larger than 180mm.
Valery of Aries Instruments was producing some, but the war in Ukraine has stopped that. (I had an order for exactly what you are wanting).
A couple of other companies have made them in the past, but I don’t believe anyone is currently doing so.
It could be that your only option at this point is to sell your current 9.25” and buy a tri-band 9.25” from Baader. I currently have one on order.


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Re: Large D-ERF "tri-band"

Post by Ronnie_Clayton »

Thanks DavidP!

I was checking and now Altair Astro is providing large ERF :).

https://www.altairastro.com/altair-240m ... 2760-p.asp

But I didn´t find any reviews about this D-Erf...

BR


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Re: Large D-ERF "tri-band"

Post by Dennis »

Ronnie_Clayton wrote: Wed Feb 22, 2023 1:42 pm Thanks DavidP!

I was checking and now Altair Astro is providing large ERF :).

https://www.altairastro.com/altair-240m ... 2760-p.asp

But I didn´t find any reviews about this D-Erf...

BR

Interesting stuff.
30mm thickness.. holy moly. I wonder how much it weights with cell. If you come by a filter curve of it pls post it here.


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Re: Large D-ERF "tri-band"

Post by DavidP »

Well, that’s new. Exciting that there’s someone making them now. It offers pre-order, so I don’t think anyone has bought one yet.


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Re: Large D-ERF "tri-band"

Post by marktownley »

Hi Ronnie.

Why does it have to be tri-band? CaK i'm presuming? You're going to get better results in CaK with your 6" APM than you ever will with a C9... Just my 2 cents...


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Re: Large D-ERF "tri-band"

Post by Ronnie_Clayton »

marktownley wrote: Thu Feb 23, 2023 7:42 am Hi Ronnie.

Why does it have to be tri-band? CaK i'm presuming? You're going to get better results in CaK with your 6" APM than you ever will with a C9... Just my 2 cents...
Many thanks for your 2 cents Mark :).

I agreed with you about Cak! I´m thinking to buy a tri-band to use in both telescopes, to get more resolution in h-alpha and "continuum" with C9 and use with my APM to get Cak images.

Ronnie


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Re: Large D-ERF "tri-band"

Post by DavidP »

marktownley wrote: Thu Feb 23, 2023 7:42 am Hi Ronnie.

Why does it have to be tri-band? CaK i'm presuming? You're going to get better results in CaK with your 6" APM than you ever will with a C9... Just my 2 cents...
Agreed. I don’t get the SCT tri-band thing, and while it’s difficult to imagine seeing conditions that would allow for. Ca imaging at 9” of aperture, I remember Christian saying that the 9.25“ can handle the blue end better than other SCTs. I don’t know if the difference is marginal or substantial.
Last edited by DavidP on Thu Feb 23, 2023 11:05 pm, edited 1 time in total.


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Re: Large D-ERF "tri-band"

Post by marktownley »

Ronnie_Clayton wrote: Thu Feb 23, 2023 11:59 am I agreed with you about Cak! I´m thinking to buy a tri-band to use in both telescopes, to get more resolution in h-alpha and "continuum" with C9 and use with my APM to get Cak images.
Sensible!


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Re: Large D-ERF "tri-band"

Post by Dennis »

DavidP wrote: Thu Feb 23, 2023 2:50 pm
marktownley wrote: Thu Feb 23, 2023 7:42 am Hi Ronnie.

Why does it have to be tri-band? CaK i'm presuming? You're going to get better results in CaK with your 6" APM than you ever will with a C9... Just my 2 cents...
Agreed. I don’t get the SCT tri-band thing, and while it’s difficult to imagine seeing conditions that would allow for. Ca imaging at 9” of aperture, I remember Christian want to say that the 9.25“ can handle the blue end better than other SCTs. I don’t know if the difference is marginal or substantial.
I would say it depends on each C9 sample, and many scts have their optimum towards the red for whatever reasons. I doubt that those would give decent results @393nm for WL or Ca k imaging. On the other hand im quite satisfied with the results i got with my sample of C9 and the antlia 393nm filter. Therefore i dont see a reason why it would be much worse with the lunt cak module im going to try soon. If it doesnt i will use a small and slow refractor for it.


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Re: Large D-ERF "tri-band"

Post by mdwmark »

Hi Group,
My concern is that these filters are ion assisted e beam . Which is really not that much different then e beam. Which come down to the coating. I don't think you can get a 1/4 wave on transmission with this coating method. So the filter will work for heat, but it will not be diffraction limited. Sputtering coating is the only way to get there. So being in front of the objective it may soften the image. Now if you go with the idea that the seeing during the day is never diffraction limited. Then it will be fine for you.
The coating of a soft coated filter is never diffraction limited. It doesn't matter how the good of windows you mount it in.
Mark W.


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Re: Large D-ERF "tri-band"

Post by marktownley »

Mark, your insights are always helpful.

Thanks


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Re: Large D-ERF "tri-band"

Post by Dennis »

mdwmark wrote: Fri Feb 24, 2023 8:41 pm Hi Group,
My concern is that these filters are ion assisted e beam . Which is really not that much different then e beam. Which come down to the coating. I don't think you can get a 1/4 wave on transmission with this coating method. So the filter will work for heat, but it will not be diffraction limited. Sputtering coating is the only way to get there. So being in front of the objective it may soften the image. Now if you go with the idea that the seeing during the day is never diffraction limited. Then it will be fine for you.
The coating of a soft coated filter is never diffraction limited. It doesn't matter how the good of windows you mount it in.
Mark W.

Hi, thank you for your insights.
Baader states on their website that their D-ERFs are made with ion assisted beam tech, they claim they reach up to l/10 surfaces. So i think i dont understand.


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Re: Large D-ERF "tri-band"

Post by marktownley »

I see Altair says their filters are L/8.


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Re: Large D-ERF "tri-band"

Post by christian viladrich »

For the record, here the test of my 160 mm Baader D-ERF with a Schack-Hartmann wavefront analyzer (Imaging Optics HASO) :
mesure-DERF160mm.png
mesure-DERF160mm.png (71.5 KiB) Viewed 2036 times
http://astrosurf.com/viladrich/astro/in ... /tests.htm

It is lambda/9.6 P-V wavefront in Ha and lambda/41 rms. So quite within Baader spec.

When specifying quality of an optical window, it is important to know whether it is about :
- transmitted wavefront or surface (and remember there are two surfaces ...),
- peak-to valley (P-V) or rms,
- what is the lambda used (red, gree, , etc..).


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Re: Large D-ERF "tri-band"

Post by Valery »

mdwmark wrote: Fri Feb 24, 2023 8:41 pm Hi Group,
My concern is that these filters are ion assisted e beam . Which is really not that much different then e beam. Which come down to the coating. I don't think you can get a 1/4 wave on transmission with this coating method. So the filter will work for heat, but it will not be diffraction limited. Sputtering coating is the only way to get there. So being in front of the objective it may soften the image. Now if you go with the idea that the seeing during the day is never diffraction limited. Then it will be fine for you.
The coating of a soft coated filter is never diffraction limited. It doesn't matter how the good of windows you mount it in.
Mark W.
Here is the image taken with full size 280mm DERF and additional 7nm Ha filter.
This is a SINGLE frame shot. So, no lucky imaging and deep deconvolution were applied. Just a little noise reduction after a bit of sharpening.

Right click on the image and open it in a separate window to see it in a full resolution. Look at the details inside the larger spot and bridges there.

So, here is the image forming train: atmosphere + DERF + telescope optics + small 50mm H-a filter + Barlow lens.

Does anybody think that diffraction limit was not reached in this image? What is the part of the image destruction was introduced by the coating layers of the DERF?

The world changes. And what were not possible yesterday is possible today.


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_05h 40m fr#1061 C11 DERF 290mm + Ha 7nm.png
_05h 40m fr#1061 C11 DERF 290mm + Ha 7nm.png (1019.98 KiB) Viewed 1980 times


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Re: Large D-ERF "tri-band"

Post by DavidP »

That is phenomenal.


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Re: Large D-ERF "tri-band"

Post by OlegLviv »

Altair best of the best for big aperture!


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Re: Large D-ERF "tri-band"

Post by mdwmark »

HI group
So ion assist is used with e- beam and also sputtering. The idea is that helps with the stress of the coating and reduces the substrate temperature. With e-beam the crystal formation will be larger. This is what degrades the transmission wavefront . While with sputtering the crystal should be smaller and less degrade of the wavefront on transmission. If you want to get fancy . Then Plasma-assisted sputtering deposition if done right, would give us the best wavefront error on transmission. But this would cost much more then the others.
I talked to my friend that has machines that use a planetary to keep uniformity. They can do 4 -24" at one time ( that would be 4 -24" uniform filters narrow enough for an ERF). He didn't think with that many layers for an ERF design that the crystal formation with ion assisted e- beam could get you to diffraction limited on transmission.
But there are companies out there that can coat any size you would want for a price. ( Barr has a machine to make large narrow custom filters for the telescopes in Hawaii and Chile. I was told that $50,000 each would be a good starting price)
Mark W.


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Re: Large D-ERF "tri-band"

Post by marktownley »

Thanks for the information Mark


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