Basic question about Coronado Blocking filter

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Basic question about Coronado Blocking filter

Post by rsfoto » Sun Sep 17, 2017 3:02 pm

Hi,

I started about 10 years ago with H-alpha imaging and bought from the first day on a BF30 from Coronado.

Meanwhile I own 3 of them but what annoys me is the lifetime of this BF Filters.

All 3 in this 10 years have been exchanged already because they start to rust from the outside into the inside. Is there no way to avoid rusting ?

Why do I rant about this. I live in Mexico and it is not easy to pass them through customs even if they are a free of cost exchange. I always have to pay duties when getting them back into Mexico.

Can the blocking filter be exchanged by some other type of filter or are they specially made and they have a certain bandpass through characteristics ?

Thanks for any tips and regards Rainer
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Re: Basic question about Coronado Blocking filter

Post by Merlin66 » Mon Sep 18, 2017 1:32 am

Sorry,
No real solution, all the ITF elements in all the blocking filters equally suffer.....for smaller BF's the replacement Maier ITF seems to be a good solution.
There are no altrnatives to the required narrow band transmission required for a good BF.
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Re: Basic question about Coronado Blocking filter

Post by marktownley » Mon Sep 18, 2017 5:40 am

The Maier ITF works up to BF15
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Re: Basic question about Coronado Blocking filter

Post by rsfoto » Mon Sep 18, 2017 9:19 pm

Hi Merlin66 and Mark

Thanks for the info ...

regards Rainer
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Re: Basic question about Coronado Blocking filter

Post by Bob Yoesle » Fri Sep 22, 2017 12:39 am

If you have the Coronado RG630 ERF in palce on the etalon, you can replace the ITF with Oliver Smie's (BelOptik) UV/IR blocked KG3 filter. I have done this very successfully, and the image will be noticeably brighter than with the ITF. Oliver can reduce the diameter of the 2 inch version to 34.5 mm at a modest fee for a direct drop-in replacement of the ITF, and you then also retain the tilt of the original ITF cell:

http://beloptik.de/en/left/if-uv-ir-cut ... ng-filter/

Additional info. here:

https://www.cloudynights.com/topic/4721 ... nom/page-2
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Re: Basic question about Coronado Blocking filter

Post by rsfoto » Fri Sep 22, 2017 5:37 pm

Bob Yoesle wrote:
Fri Sep 22, 2017 12:39 am
If you have the Coronado RG630 ERF in palce on the etalon, you can replace the ITF with Oliver Smie's (BelOptik) UV/IR blocked KG3 filter. I have done this very successfully, and the image will be noticeably brighter than with the ITF. Oliver can reduce the diameter of the 2 inch version to 34.5 mm at a modest fee for a direct drop-in replacement of the ITF, and you then also retain the tilt of the original ITF cell:

http://beloptik.de/en/left/if-uv-ir-cut ... ng-filter/

Additional info. here:

https://www.cloudynights.com/topic/4721 ... nom/page-2
Hi Bob,

Thanks for the interesting info. It would be good not to use so many abbreviations :-) What is an ITF ?

OK, I have the red windows in front of the etalon anad at the rear my BF30. What you just wrote, ¿ does it mean I can replace the BF30 for the filter Oliver is offering in 2" versión ? I can use 2" version in a cell as I using a wide T-Mount adapter from Takahashi and that one accepts the 48mm threaded filters which are normally those 2" filters

Thanks for you comments in advance
regards Rainer
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Re: Basic question about Coronado Blocking filter

Post by Bob Yoesle » Sun Sep 24, 2017 12:22 am

Hi Rainer,

The Coronado blocking filter has two main components. First in the optical path is the ITF - induced transmission filter - which is a filter incorporating silver and dielectric layers (for long wave IR blocking) deposited on a RG630 filter for UV blocking. The filter layers are a sandwich sealed with epoxy around the edge to prevent atmospheric moisture from degrading the silver layers. However, under the intense IR focused through the etalon, thermal cycling and loading can create small expansion cracks in the epoxy through which atmospheric moisture can intrude, causing the well-known "rust" or deterioration encroaching from the perimeter inward. The "cure" for the deterioration is to use IR blocking on the etalon's ERF. Baader and Lunt do this on their BK7 and RG630 ERFs respectively.

The second element is the relatively narrow band (~ 6 angstrom) "trim" or "order selection filter," which isolates the H alpha peak from the etalon and blocks the unwanted side-band harmonic peaks. This filter is again precise dielectric filter coatings deposited on a BG38 (blue glass) filter for brightness control. THIS FILTER IS ESSENTIAL FOR H ALPHA OBSERVATION.

Therefore, you can't use Oliver Smie's KG3 UV/IR filter alone (or his ITF) as a blocking filter - you must retain the order selection filter as well. The KG3 with UV/IR blocking filter acts to block IR out to ~ 5000 nm. The KG3 glass takes the place of the metallic silver of the ITF, while the UV coating acts to block UV instead of the RG630. The KG3 UV/IR filter also requires a RG630 component to be implemented elsewhere, such as the accompanying RG630 ERF of the OEM etalon.
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Re: Basic question about Coronado Blocking filter

Post by Merlin66 » Sun Sep 24, 2017 12:38 am

Bob,
Hmmm,
"""The KG3 UV/IR filter also requires a RG630 component to be implemented elsewhere, such as the accompanying RG630 ERF of the OEM etalon.""
Why do you think an additional RG630 is required???
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Re: Basic question about Coronado Blocking filter

Post by Bob Yoesle » Sun Sep 24, 2017 2:21 pm

Hi Ken,

Oliver's UV/IR block on KG3 has considerable transmission from 380 to 690 nm:
IR_cut_on_KG3_Spektrum.jpg
IR_cut_on_KG3_Spektrum.jpg (120.15 KiB) Viewed 550 times
So if there is no RG630 element in the system, the cumulative transmission results in this:
IMGP3354.JPG
IMGP3354.JPG (201.12 KiB) Viewed 550 times
Baader DERF, Coronado SM90-90, BelOptik UV/IR block KG3, BF30 OSF (trim filter).

Adding one of the original RG630 ERFs to the primary DS etalon removes everything below ~ 620 nm, and resulted in greater transmission than the ITF on a RG630 substrate:
ITF KG3 compare.jpg
ITF KG3 compare.jpg (332.19 KiB) Viewed 550 times
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Re: Basic question about Coronado Blocking filter

Post by marktownley » Sun Sep 24, 2017 2:41 pm

Good discussion chaps!
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Re: Basic question about Coronado Blocking filter

Post by Merlin66 » Sun Sep 24, 2017 10:34 pm

Bob,
My apologies....I got myself confused and was thinking about the Tri-ERF, not the UV-IR/KG3.
Your reply makes sense......
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Re: Basic question about Coronado Blocking filter

Post by rsfoto » Wed Sep 27, 2017 10:37 pm

Hi,

Thanks for the detailed information.

What is the RG630 and who makes it ?

Rainer
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Re: Basic question about Coronado Blocking filter

Post by Bob Yoesle » Thu Sep 28, 2017 10:17 pm

Hi Rainner,

RG630 is a standard "red glass" filter made by many companies. If you have a standard front etalon from Coronado, Lunt, or SolarScope, it is already there in the form of the first element ahead of the etalon itself- the ERF or "energy rejection filter."
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Re: Basic question about Coronado Blocking filter

Post by rsfoto » Tue Oct 03, 2017 6:37 pm

Bob Yoesle wrote:
Thu Sep 28, 2017 10:17 pm
Hi Rainner,

RG630 is a standard "red glass" filter made by many companies. If you have a standard front etalon from Coronado, Lunt, or SolarScope, it is already there in the form of the first element ahead of the etalon itself- the ERF or "energy rejection filter."
Thank you Bob.

I have a double stacked SM60 and I took out the internal RG630 filter because I said " I do not need it if I already have on on the Top Etalon "Q. What I noticed is I got shorter exposure times and perhaps I got a bit more contrast in my images.

regards Rainer
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