Sourcing Out Lumicon UHC & OIII 1.25" Filters

[j.gardavsky]

Hello Gib,

I have somehow lost the trace.
How did you manage it with the filters? Any first light report?

Wishing you clear skies,

JG

[cookie223]

Hello Gib007,

congratulations. The DGM filters are an excellent choice.

As others may also read this thread, below find the transmission curves of the very narrow-band OIII filters, including the DGM


http://www.karmalimbo.com/aro/pics/filters/o3b.jpg

Clearly, the DGM OIII will beat the Lumicon OIII on the fast scopes (like f/5), due to the so called blue shift of the narrow pass-bands. The reason is, the Lumicon OIII is too close to the main OIII line at 500.7nm, and the long wavelength cutting edege of the Lumicon may easily touch the emission line, or even intersect it. The difference between the both filters will be less on the slow scopes (f/8 and larger).

The DGM NPB vs Lumicon UHC is here,

http://www.karmalimbo.com/aro/pics/filters/narrow.jpg

The both UHC filters are not CCD filters, and they may transmit some unwanted light in red and in UV, and as it used to have been with Lumicon, one production batch may considerably differ from the other. However besides the perfectionists, hardly anybody will worry about it.

Looking forward to your observational reports on the DGM filters,

JG

Since this is well over anything I know, what is a "Fast" scope and how does one determine how fast their scope is? I hope I haven't purchased any EP that won't perform well. Obviously I am mistaken to think that an any EP will work with any scope.
As always thanks

[j.gardavsky]

Hello Cookie,

'fast' or 'slow' scope is the same notion as used with the camera optics - simply the f- or F- number. It is calculated by dividing the focal length (F) with the aperture diameter (D). Historically it comes from the fact, that highly opened short focus lenses have allowed for a fast shutter speed in the classical photography.

The fast astronomy scopes find their use in astrophotography of th DSOs, and in the richiest field visual observing of the deep sky objects, like the large open clusters and large diffuse emission nebulae.
The slow scopes offer as a rule a very good views of the planets, small planetary nebulae, and they easily resolve the binary stars. But there is still a mass of the DSOs which can be comfortably seen even with the slow scopes.

There is not a fixed line dividing the scopes into the fast and into the slow ones. The F/5 scopes and the F/4 astrographs are considered as fast, the F/8, F/11, etc., are considered as slow.

Some of the nebular filters for imaging have the so called offset of their passband, designed for the fast scopes. these filters are preferable also for the visual observations with the fast scopes. Don Goldman offers a very detailed info here, Astrodon Astronomy Filters - Astrodon Narrowband FAQ .

Best,

JG

[cookie223]

Thanks guys,
I just downloaded the FAQ JG suggested and will go over it.

[cookie223]

Thanks guys,
I just downloaded the FAQ JG suggested and will go over it.