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M27 Hubble Palette


daneel
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Tried my first Hubble palette image of the Dumbbell. Clouds and short nights limited the exposure time, but managed these over two nights:

10 x 300s Ha = green

4 x 300s OIII = blue

4 x 300s SII = red

post-1233-0-06196800-1340295337_thumb.jp

There's a sort of diagonal grain across the image. I'm not sure if this is because my flats weren't right - I did flats for each filter. The image was taken at a set point of -10 C, and so were the darks.

It's interesting that a lot of stars don't show up in OIII but they do in Ha (not surprising!) and SII (more surprising). The background OIII looks like more than half the stars have been extinguished. All the fine structure's in Ha, OIII is more diffuse and SII is very faint, but you can see the apple-core structure clearly.

I'll add more light when the skies clear, but would appreciate help with removing the diagonal graininess, and any other tips of course!

Thanks,

Ramin.

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Added some more data from last night and annotated the image in PixInsight. Managed another 7 x 5 minute subs in each band but have to admit that I nodded off at 2. Woke up to find the guide star had disappeared at 4:30 as it had clouded over. Dashed out to shut the obsie worried that it might be raining but fortunately it wasn't.

post-1233-0-60492700-1340986310_thumb.jp

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Pretty good signal but I reckon 5 minute subs are very short for narrowband. This might contribute to the background sky noise, I don't know. I generally go for 15 minutes at F3.9 through to 30 minutes at F7.

You'd get a lot more outer halo that way, though you have some already.

Olly

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With emission line imaging there is no specific convention for assigning which filter to each channel so this leaves quite a bit of latitude for experimentation. The two most common palettes are:-

  • HST (Hubble Space Telescope) - SII,Ha,OIII = R,G,B
  • CFHT (Canada France Hawaii Telescope) - Ha,OIII,SII = R,G,B

There are other variations such as the reverse Hubble palette which swaps the SII and OIII around so OIII,Ha,SII = R,G,B

It is possible to use just two filters and create a synthetic channel, e.g. Ha = red, OIII = green and Ha and OIII combined = blue. I have manged this successfully with some images in my gallery, the veil nebula and the crescent nebula being two examples. Below are examples of the same subject with the same data, but just assigning the filters differently when combining

roseSIIHaOIII.JPGroseHaOIIISII.JPG
roseOIIIHaSII.JPGroseHaHaOIIIOIII.JPG
  • Top left - HST palette SII,Ha,OIII = RGB
  • Top right - CFHT palette Ha,OIII,SII = RGB
  • Bottom left - "Reverse" HST palette - OIII,Ha,SII = RGB
  • Bottom right - Two colour Ha,OIII,OIII = RGB

As can be seen from the above images there are some distinct colour variations and in some .

So basically mapping these Narrowband images to RGB channels.

The Hubble,as you can see uses S11/Ha/O111 To RGB.

Very nice image by the way.

Mick.

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Thanks Mick for the beautiful sample images and concise explanation - just the tutorial I needed. They remind me of the early false colour pro pics, then as now, to presumably highlight certain features not apparent in 'true' colour imaging - the latter is a debate in itself :rolleyes: For me the most pleasing pic of the series in the last one eg via 2 filters into RGB :cool:

Edited by nytecam
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Must hasten to add,these are,nt my images,i.m just using them to try and answer your question.

Yes i think both you and Gina are right,its all a matter preference.Although these filters do bring out their individual wavelengths.

Mick.

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Thanks for your suggestion Olly I loved the M27 image you posted recently. Ten minutes seems like a bit of a gamble here. Clouds, satellites, and aeroplanes (we're under one of the Heathrow stacks in Amersham) are another kind of noise that increases linearly with exposure time. But I'll have a go when it clears.

Also do you have equal exposure time for each wavelength, or give, say H alpha a bit longer because it has more of the structure in the case of M27?

Le Grange is on my list of things to do before I pop my clogs, so hopefully I'll get to learn from you first hand.

Those images were useful Mick, thanks for showing some of the combinations. I suppose the palette for narrowband is really just a matter of taste.

Ramin

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