5 replies to this topic

[gmalin]

I recently imaged the Crescent Nebula with conditions as follows :

 

- RASA8 w/ uncooled ASI183MC

- gain 120
- 75 X 20 s (25 mn total), 11 flats, 50 darks, 50 offsets

- no filter (not even UV/IR cut)
- Moon : 43%

- North of France, Bortle 5
- Processed w/ Siril + Gimp

 

As shown below, the nebula has a very low contrast, so I wonder if the use of a Celestron filter #93619 "Hα-Hβ-OIII Imaging Filter for RASA 8" could improve things ?

This #93619 replaces the RASA 8 optical window, and Celestron says in its manual that this allows to maintain optical performance, as no extra piece of glass is added to the optical system.

Does anybody have some experience with this filter ?

Thanks !

 

 

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[rob1986]

Thsts a really wide fov.

[licho52]

Thsts a really wide fov.

It's a Rasa8, that's how it gets all that "speed" - it's wide and not diffraction limited.

[andysea]

It should increase contrast considerably as it appears to be a tri-band narrowband filter. Assuming that it works as advertised, that is a really good price for such a filter. I wonder what is the bandpass. I had very good results with the 12nm Astronomic filters when I had the rasa but I was using a mono camera, so I had to shoot each channel separately.

[rob1986]

It's a Rasa8, that's how it gets all that "speed" - it's wide and not diffraction limited.

I know, but it would seem to me that this target might benefit from a longer fl.

[gmalin]

It should increase contrast considerably as it appears to be a tri-band narrowband filter. Assuming that it works as advertised, that is a really good price for such a filter. I wonder what is the bandpass. I had very good results with the 12nm Astronomic filters when I had the rasa but I was using a mono camera, so I had to shoot each channel separately.

I was unable to find anyone with first-hand experience with this Celestron filter #93619 "Hα-Hβ-OIII for RASA8, but in the end I bought it anyway.
Here is an image taken with the filter, almost in the same conditions as the one I originally posted (same place, same RASA8, same ASI183MC camera, two months later...)
As you expected, the filter definitely increases the contrast on this nebula, so I'm quite satisfied with it, thank you for your advice.

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