M31 asi120mm rgb

ndb

Hello, M31 with ASI120MM, RGB astronomik filters in a manual filter wheel (and spacer, too), 180mm photolens with a DIY M42/Nikon adapter.

The ASI was attached by a head to a dovetail, on an unguided EQ6 Mount.

Red 188 x 20s

Green 200 x 20s

Blue 200 x 20s

gain 60%, 12-bit mode

darks and flats

I forget to use Firecaptures's dark-on-the-fly.

Humidity level... 2000%. A heating resistor was attached to the lens, but the suburban sky was polluted by light. Sensor temp 19.5 downto 16 °C.

Clear sky.

Nicolas

patthehorse

Lots of detail in there with 20s subs. A top Pic. ;)

sweiller

Hello,

Please

Where to buy an accesory to fix a ZWO ASI Camera to a Nikkor 180 mm lens (and of course get infinite focus) ?

Where to buy an accesory to fix a Nikkor 180 mm on a mount (losmandy or Vixen) ?

Sylvain

riklaunim

Check bigger astro-shop for a Nikon lens mount to T2. You will need that plus some T2 spacers.

ndb

Riklaunim is right. But the spacer depends on your camera. With the ASI120MM, the depth (distance between M42 thread and sensor) is 12.5mm (C/S standard) while more recent cams (e.g. ASI224) have a depth of 17.5mm (C standard). My filter wheel acts as a spacer, but I'm expecting a big problem to adapt my future new ASI in 17.5mm. The back focus of a telelens is about 44mm (for Nikkor, Canon is shorter).

The telelens is attached to a vixen-standard dovetail with the help of two DIY rings (aluminium + threads and screws 120° apart). You can purchase a ring including an nikkor - M42 adaptor like this one:

http://www.teleskop-express.de/shop/product_info.php/info/p2837_Geoptik-Adaptor-for-Nikon-lenses-to-T2-for-CCD-cameras---w--1-4--thread.html

Some telelenses have a Kodak thread; in this case you'll only have to purchase a Nikkor/T2 adapter.

Mine is made out of spare adpaters (a bayonet from a film SLR, out of order) and a T2 spacer ring. I unscrewed the back part of the T2 adapter then I glued it with cyano on the back of the front part of the bayonet. Fortunately you'll easily find all necessary adapters at some dealers.

Nicolas

firstc8

I have been going through several online RGB tutorials in prep of working with a mono cam for the first time.

I noticed your above RGB image although very clean, lacked color. Is it because no lum channel was used? I have not seen too many use narrow band on M31, would a narrow band channel help with M31 imaging?

riklaunim

H-alpha filter can be used on galaxies to bring out H-alpha nebulae in those galaxies. The RGB color depends on processing and color balance.

firstc8

riklaunim wrote:
H-alpha filter can be used on galaxies to bring out H-alpha nebulae in those galaxies. The RGB color depends on processing and color balance.

I was planning on doing just that but on NGC6888. Can I do the regular RGBs, then use the Ha image as lum channel? If not how do I add the Ha channel to the RGB channels? I use Photoshop.

riklaunim

Usually H-alpha in such images is added to red channel (or replaces red channel). For nebulae you don't do RGB unless you want color stars mixed with nebulosity.

firstc8

I want to show off nebulocity and tight stars in their more natural colors. So I could just do HaGB, or HaRGB?

Any of you use Russell Croman's Starshrink and GradientXterminator plugins? They seem to be for high end imaging.

riklaunim

HaRGB or HaGB depends on your capture - you can check what will turn out better. Good color stars are much harder to get than clean H-alpha image ;)

firstc8

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ndb

I reprocessed the image with a monochrome (green layer) image taken with my Celestron 5 and a Canon EOS 350D:

https://www.facebook.com/Nicolas-Dupont-Bloch-193140867687757/timeline

The luminance layer from the DSLR image contains more details because of a better sampling. However, due to differences in field width and orientation, I severely cropped the final image.

Usually the color layer comes from a color imaging device while the luminance layer comes from a monochrome camera ;)

But it was easier to manage the light pollution with the ASI120MM and a filter wheel than with the DSLR.

firstc8

Much more detail, fantastic. I thought red is the most immune to LP or dispersion?

I am getting a mono with FW, hope to combat LP this way.

betacapricorni

I can't see the image.... Why? (Page error)

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ndb

To Betacapricorni: my page is available here:

https://www.facebook.com/Nicolas-Dupont-Bloch-193140867687757/timeline?ref=page_internal

In case of problem, the image is attached.

To FirstC8: you're right, but the DSLR has a better signal/noise ratio in green (twofold green photosites). Dispersion from turbulence happens in shorter wavelengths but refraction acts on all wavelenghts. Nonetheless with such a short focal length none is visible; light pollution is by far the 1st ennemy, especially with galaxies which emit a continuous spectrum. At the exception of HII clouds in the arms (e.g. M33, M51) no narrow-band filter can improve such images. This was confirmed by chairman of "la clef des etoiles" in France, PhD in astrophysics. Only LPR filters can improve the results. Anyway imaging galaxies from country-side is the best solution. I've got better results on M106 with a Celestron 5 f/6.3 from unpolluted sky than with the 10-in Newton f/4.7 from my suburban location, with the same camera, the same acquisition parameters and the same galaxy : Sharper image with the 10-in f/4.7 but better S/N ratio and larger faint extensions with the 5-in f/6.3.

m31_celestron5-f6_eos350d-g+color-asi120mm-rgb.jpg

betacapricorni

Beautiful pic!!!!

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