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Hello all, I've been seeing some amazing images taken with the Askar Color Magic Duo Super-Narrowband H-a/O-III & S-II/O-III (D1 + D2) Imaging Filter Set and OSC's. I'm considering purchasing a set. Some filter manufacturers have filters optimized for fast focal ratio scopes (usually f/3.6 and faster) to take account of the centerline shift at fast focal ratios. I'm using a SharpStar 150/2.8 HNT. Does anyone know if these filters will perform well at f/2.8? Thanks so much, Arnie |
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Arnie: I am following you....same OTA and same question....! |
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Arnie: If it is the 6nm (which is wrongly quote as the typical passband) Duos you are referring I'm not too pleased with their efficiency, especially in the OIII band. I'd consider it a pass. No halos that I can see at f/4 and at f/2.8 but the test at f/2.8 wasn't very extensive to rule out halos with different star spectra. |
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For what it's worth, love these filters. I don't, however, use them at F2.8. I recall, however, in another forum post another user was using them at this focal length and reported no problems. To Andrea's comment on quoted band width, this is correct. Testing that I've seen, and the way Agena advertises these, suggests the bandwidth is actually 8 to 9 nm... |
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Unfortunately for you I use them until f/3,8 with my FSQ106ED and it’s focal reducer. I haven’t noticed any problems with such a focal ratio. |
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| Thanks everybody for the input! I will continue my research and report about what I find. Since these are going to be installed in a remote observatory about 1700 miles away, returning them if they don't perform well at f/2.8 is not an attractive option. |
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Arnie: I'm looking forward to seeing how those work out Arnie. I was thinking of using fhose filters for my 135mm Rokinon and ASI2600MC. I'll be stopping down to roughly f/3.0 to f/3.5. |
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Daniel Carter:Arnie: I'll let you know! |
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For what it's worth, I have a good experience with these filters (HaOiii and SiiOiii) on a Takahashi E180 with f/2.8 (FL=500mm). A couple of examples: HaOiii filter on the Heart nebula. A) HaOiii filter on the Heart nebula. Raw integration 50x120s exposures (60):  OK Halos that can be rather easily dealt with in post-processing:   B) SiiOiii filter on the Heart nebula. Raw integration 50x120s exposures (60):  Again, halos that are bearable   CS Manuel |
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Manuel Peitsch: Thanks, Manuel! Nice images! I'm so glad to see how good they look at f/2.8. I'm going to order a set. |
