ERF for SCT 250 mm

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Arrakis97
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ERF for SCT 250 mm

Post by Arrakis97 »

Hi everyone
I would like to do an observation test in H alpha with my “old style” Marcon SCT 250 mm. Unfortunately, as the Aries ERF filters were not available for the war in Ukraine at the moment, I contacted the supplier Airylab for an alternative; unfortunately, the company replied that they no longer produce ERF filters.
Since Baader produces ERFs with a maximum diameter of 180 mm, I don't know which alternative is available on the market.
Is anyone able to point me to an alternative solution for a 250 mm ERF ??

However, I take this opportunity to wish Valery to be able to resume production of the ERF as soon as possible :) :) .
Thanks


Carlo Casoli
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Re: ERF for SCT 250 mm

Post by MalVeauX »

You'd have to get it commercially made custom from someone, like Edmund Optics, etc, or any other lab but it will be enormously expensive for a single filter run that is custom (remember, the glass needs to be high quality and optically flat too, this adds to the cost). Baader does 180mm and Altair is doing some (and duo band ones) but nothing bigger either. And BelOptik only has smaller ones, when he's active.

I don't think there is anyone making a D-ERF in the 10~11 inch range at the moment, only Aries was. Hopefully Valery will be able to resume this after the war/politics clears up. We can only hope.

I have a 214mm Aries and it's in use every week to this day.

Very best,


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Re: ERF for SCT 250 mm

Post by marktownley »

Your best chance is the second hand market short of a custom job which is ££££££££££££££££££££££££

Your other solution (assuming your seeing supports this aperture - have you checked this?) - ditch the idea of using the 250mm scope you are talking about and pick up a suitably large refractor and use a smaller (180mm/160mm) DERF sub aperture...


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Re: ERF for SCT 250 mm

Post by MalVeauX »

Altair astro now has 160mm duo band (HA & CaK). They call it tri-band but in reailty CaK & CaH are the same for a DERF's FWHM.

https://www.altairastro.com/d-erf-energ ... s-71-c.asp

So you could do a 150mm full aperture frac, or you could go for a 7 inch frac and mask down to 160mm.

Note, these DERF still pass energy so you could still image with nearly any wavelength just at lower transmission, which is fine for filter systems that are loose FWHM like photosphere imaging filters (like 500~540nm).

Very best,


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Re: ERF for SCT 250 mm

Post by mami813 »

It is said that 240mm erf filter is currently in stock in Altair.uk.
I exchanged mail a few days ago.

This is the contents of the mail I exchanged.

``Hi there, the 240mm Ha only D-ERF would be £2000.00 and the clear aperture would be about 230mm (you would need to hold the edge by 5mm). We have one unit left in stock and they take about 2months to make.``


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Re: ERF for SCT 250 mm

Post by marktownley »

Interesting, good to know thanks.


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