Key Hole Nebula (Eta Carina) in Ha Light

[Brad Moore]

Hi All,

Here is the first light picture using my new RCOS 12.5" and the Paramount ME.

I will be adding the RGB (colour) and SII:OIII (hubble pallet) frames to it over the coming weeks.

Ha - 16 hours with 1 hour sub exposures.
DDP Stretched and Layered 5 times to bring out all the detail.

Homunculus Region
20 x 1 sec
20 x 10 secs
6 Layers

Small Version
http://www.southern-astro.com.au/gallery.php?PhotoID=11

Larger Version
http://www.southern-astro.com.au/imgs/gallery/nebulas/keyhole/attempt1/keyhole-large.jpg

CCDStack - Darks and Flats
Registar - Registration
Maxim DL - DDP and Sigma Reject Combine
Photoshop - Layering, Curves, Unsharpen Mask, Smoothing, Shadow/Highlights, etc

Cheers,
Brad Moore

[ving]

hey thats great brad!
lovely and clear :)

man are those difraction spikes long!!!

[h0ughy]

Wow, I have a headache trying to take in all that detail. Lovely image, I can't wait until you add the other light sources to this it will be a winner!

[Striker]

Awesome stuff Brad.

Keep them coming.

[avandonk]

That is a very detailed beautiful image. What spectral width is your H alpha filter? I assume the smaller the spectral width is, the signal to noise improves.
How wide is the good field on the RCOS. I would really like to try my Hutech modified Canon 5D on this optic. Is this even possible hardware wise with your current setup.

Bert

[Brad Moore]

Thanks Bert,

It’s a astrodon-schuler 9nm filter.

Bert your right, a narrowband filter will assist in providing better S/N under light pollution conditions *only* if your sub exposure length is sufficient to overcome the readout noise of your camera.

However, generally speaking S/N is mainly controlled by exposure times. The rule of thumb is that noise is the sqrt of signal. You can also reduce your noise by getting a camera with low readout noise, camera with higher QE, a dark site etc. Noise is a complex beast and comes from a large variety of sources.

So in short a 20 min exposure has double the signal of a 5 min exposure etc.
In other words a 16 hour exposure has 9.8 times more signal then a 10 min exposure.

The biggest noise challenge we face is overcoming readout noise. Otherwise you just end up stacking noise into your images. Very generally speaking for astro imaging you will need a 2-3min sub exposure to overcome readout noise with single shot or mono with RGB filters, with narrowband it gets a lot worse. :scared2:
<o:p> </o:p>
In my case it takes me 45min to overcome readout noise when using a narrowband filter. :scared2: Hence the 1 hour sub exposures.
<o:p> </o:p>
The RCOS 12.5 will take about 6MP CCD before it really starts to show field curvature, I also have a field corrector which will take it well beyond a 35mm frame, I think the limit is about a 6cmx7cm medium format frame. The larger the RC mirror the larger the frame you can take, I know a 20” can take a full frame without any field corrector.

Your 5D would be a good match providing a FOV of 29.4 x 44.1 arc-mins at a pixel scale of around .5 arc-secs.

Fitting your camera wouldn’t be a problem I have a t-thread to 2.7" adaptor. I would most likely get a custom adaptor made up as the t-thread is a bit too small for the full frame CCD. Matter of fact I can take 2.7" thread, 2" nose piece, 1.25 nose piece and SCT thread.

Cheers,
Brad

[avandonk]

Thanks for the info Brad. I have Hutech components for fitting the 5DH to various scopes. See pics below. I also have a range of other compatible fittings. The common thread is 57mm metric or 60mm metric (0.7 pitch). There are Hutech adapters to fit to 68mm (2.7inch)The Hutech EOS adapter has a clear aperture of 46mm, more than adequate for a full frame sensor. I have checked out your site and look foward to arranging something in the near future.

Bert

[Brad Moore]

Hi Bert,

Would be more than delighted to have you and your camera over. :welcome:

I would be very intrested to see how it handles the full frame.

Please contact me offline brad.moore@southern-astro.com.au to arrange a time etc.

All the best,
Brad Moore

[Itchy]

Hey Brad,

When are you turning Pro ?????

Great image!

Cheers

[tornado33]

Lovely image there. I take it you were using the SBIG Adaptive Optics system, they are a great idia, especially on lesser quality mounts, I believe they can easily account for a few mins of periodic error with pin sharp images.
What focal ratio was that image shot at? Its amazing that it requires 1 hour sub exposures to get through the H alpha filter.?
Heres a 2x 20 minute shot I took with an unmodified Canon 300D , 10 inch F5,6 newtonian and a 7 nm Ha filter of Eta carina
http://www.users.on.net/~josiah/baader/eta%20carina%207%20Nm%20H%20alpha%2 0small.jpg
Now if I can just get a hold of a narrowband SII and OIII filter.... :)
Scott

[Octane]

Brad,

That is a mindblowing image. Amazing contrast.

I only hope to be able to take images like that one day.

Well done.

Regards,
Humayun

[Brad Moore]

Hi Tony,

I wish! If I could figure out a way to get paid for this stuff, I would give up my day job. :help: Any offers?

Cheers,
Brad

[Brad Moore]

Hi Scott,

No I didn't use a AO-7 for this image. I do own one tho. I would use it if it worked with my AP x.67 FR. They will account for mounts with large amounts of PE. +/-120 with ease. :)

Readout noise is a pain in the rear end. :mad2:<!--[if gte vml 1]><v:shapetype id="_x0000_t75" coordsize="21600,21600" o:spt="75" o:preferrelative="t" path="m@4@5l@4@11@9@11@9@5xe" filled="f" stroked="f"> <v:stroke joinstyle="miter"/> <v:formulas> <v:f eqn="if lineDrawn pixelLineWidth 0"/> <v:f eqn="sum @0 1 0"/> <v:f eqn="sum 0 0 @1"/> <v:f eqn="prod @2 1 2"/> <v:f eqn="prod @3 21600 pixelWidth"/> <v:f eqn="prod @3 21600 pixelHeight"/> <v:f eqn="sum @0 0 1"/> <v:f eqn="prod @6 1 2"/> <v:f eqn="prod @7 21600 pixelWidth"/> <v:f eqn="sum @8 21600 0"/> <v:f eqn="prod @7 21600 pixelHeight"/> <v:f eqn="sum @10 21600 0"/> </v:formulas> <v:path o:extrusionok="f" gradientshapeok="t" o:connecttype="rect"/> <o:lock v:ext="edit" aspectratio="t"/> </v:shapetype><v:shape id="_x0000_i1025" type="#_x0000_t75" alt="" style='width:12pt; height:12pt'> <v:imagedata src="file:///C:\DOCUME~1\BRADMO~1\LOCALS~1\Temp\ msohtml1\01\clip_image001.gif" o:href="http://www.iceinspace.com.au/forum/images/smilies/mad.gif"/> </v:shape><![endif]--><!--[endif]-->

The darker the site the longer it takes to overcome. Basically you want the background of your image to exceed your readout noise.

All the faint good stuff shares almost the same space in the histogram as the noise:

Example Only

20 min HA exposure
Readout Noise - 500 ADU (Analog to Digital Units) - 12bit CCD have 4096
Shot Noise - 250 ADU
Faint Part of Nebula - 400 to 600 ADU (50% of faint part of the nebula is readout noise)

45 min HA exposure
Readout Noise - 500 ADU
Shot Noise - 500 ADU
Faint Part of Nebula - 500 to 800 ADU (much better outcome)

Hope this helps.

That’s a really nice image. What mount are u using?

Yes, these filters are very expensive. Someone really should start a library. :shrug:<!--[if gte vml 1]><v:shape id="_x0000_i1026" type="#_x0000_t75" alt="" style='width:28.5pt;height:13.5pt'> <v:imagedata src="file:///C:\DOCUME~1\BRADMO~1\LOCALS~1\Temp\ msohtml1\01\clip_image002.gif" o:href="http://www.iceinspace.com.au/forum/images/smilies/shrugging.gif"/> </v:shape><![endif]--><!--[if !vml]-->:shrug:<!--[endif]-->

Cheers,
Brad

[Brad Moore]

Thanks for your kind words. You should see some of my early images, I was happy to just capture a smudge! :) :scared:

Cheers,
Brad

[tornado33]

Thanks Brad
I used a 1986 vintage Astro Optical Supplies made "Sampson" German equatorial mount, with brass worm and plastic worm wheel RA drive, manual DEC hand adjustment. I manually guide using a purpose built off axis guider/focusser here http://www.users.on.net/~josiah/focuser/IMG_9934.jpg
I used to use a guidescope but was getting flexure errors.

I guess with your SBIG its a self guided camera with the 2nd guide chip, so is pretty much like an off axis guider, with no flexure errors to worry about :)

Youre dead right about the need to get the background to be brighter then any image noise. With mine the 300D camera can show a histogram, I try to get the peak about 1/2 the way along (easy to do from light polluted Newcastle, but only if not using the Ha filter) I imaging it would be harder to reach the sky background well clear of noise from a very dark site.

If I had the money Id love to get a SBIG camera with the AO sytem for my scope, accurate guiding would no longer be necessary.

My mount has considerable PEC, but thankfully its a gradual error, I can keep up with it without too much hassle and its quite regular so a PEC training drive corrector would probably work well with it too. It does not tolerate wind buffet though.
Scott