Pleiades Cluster

[S_J_P]

Well I finally got outside a few evenings ago with my homemade Barndoor Tracker with the intention of trying to capture NGC281, The Pacman nebula, which I think was a little optimistic of me as I didn't get anything of any merit, but I did turn my camera onto The Pleiades before retiring indoors to warm up and came up with this image which I'm quite pleased with There's some nice nebulosity around the stars.

The image is a stack of 95 two and four-second images taken at ISO 1,600 and ISO 3,200 using a 6D with EF 100 f/2.8 IS Macro at f/2.8. I found that the Barndoor Tracker was jogging the image significantly during exposure so for these shots I took the images static and then tracked between exposures to keep the cluster in the same area of each subsequent frame.

I used the EOS Remote app on my iPhone to focus manually which was much simpler than laying upside down below the camera to view the LCD - oh how I miss the 60D's articulated screen on the 6D!


Pleiades by S.J.P, on Flickr

[Hereford_EOS]

Re: Pleiades Cluster

Nicely done Steve
I have had an interest in astronomy for many years so enjoy seeing this and other images. Thanks

[Columbarius]

Re: Pleiades Cluster

retiring indoors to warm up

It does get a bit chilly on winter nights when there's no cloud to hide the stars. But it looks like it was worth it this time

You're lucky to be able to find a bit of dark sky. In this part of Hampshire what with street lighting, security lighting, and people who for some unknown reason feel the need to light their gardens we enjoy(!) permanent twilight once the sun sets.

What software did you use to stack the images?

[S_J_P]

Re: Pleiades Cluster

Thanks for looking Stephen and Russell!

I used DeepSkyStacker run on the Mac using Wineskin, using recommended settings as I'm no expert on how to extract the most from the software! The registering and stacking too around 16hrs in all and the resulting image in DeepSkyStacker did look better than the one I saved into Lightroom, so I then had to play around the the sliders in LR to bring-out the nebulosity again.

The light pollution was a real pain, on my longer exposures (15-30sec) the whole sky turned reddish-brown, which was another reason I dropped back to 2-4 sec exposures.

[Dave_S]

Re: Pleiades Cluster

Hi Steve, I hope you don't mind, but I've taken the liberty of some re-processing on your image.

The overall colour cast of the sky, and the colour noise I have removed in Pixinsight. This has made for a more natural looking sky background.

I have also adjusted the colour balance so that the nebulosity around the stars in the cluster is the correct blue colour. This was done in CS.

Finally, I applied a small amount of star reduction to the main stars in the cluster, so they are a little less bloated. This was done in CS, using 'Modify', 'Expand' (5 pixels), 'Feather' (3 pixels), and the 'Minimum Filter', faded to 80%.

That apart, the Pleiades (M45) is nicely framed, and the Barn Door Tracker has worked well, as there is no star trailing, which also means that your Polar Alignment was good.

Dave

[tesarver]

Re: Pleiades Cluster



Tom

[DeeGee]

Re: Pleiades Cluster

[S_J_P]

Re: Pleiades Cluster

Thanks Dave, I fettled the processed image but your version is so much better. I'll make a note of the bloat-reducing settings in PS for future processing of bloated stars (great term!). Processing astro-images is a whole new area for me to learn.

I wasn't sure of the WB setting to use, and adjusted it in post but next to you version mine was still too red. Do you use a set WB or just adjust it in post production?

My tracker has been modified twice so far, I replaced the original hinge with a fire-door ball-bearing hinge which significantly increased rigidity, and I added a red-dot finder as sighting along the hinge just didn't work for me (having glasses doesn't help matters). I still think there's too much flex in the ply though. I have my eye on an AstroTrac, but want to see whether interest wanes before investing

[wayne2418]

Re: Pleiades Cluster

[Dave_S]

Re: Pleiades Cluster

Steve, bear in mind that I added nothing to your image, but just removed the unwanted elements, such as gradient, colour cast, and colour noise.

Everything else in your image was fine, the content was all there.

I don't astro image with a DSLR, but specialist astro-imaging CCD cameras (Starlight Xpress SXVF-H9, and SXVR-H16) which have no WB adjustment, and produce what is effectively a RAW image, so everything is done in post-capture processing.

The other attribute that they have is that the CCD is cooled down to -20 degrees below ambient (SXVF-H9), and -30 for the SXVR-H16). This is done with a Peltier Cooler, and keeps the thermal noise of the CCD down to respectable levels. Especially important with long exposures (10-20mins).

You can't do this with a DSLR, and hence if you go for long exposures, noise will be an issue.

The Pixinsight software, which is a dedicated astro-image processing programme, has a couple of very clever, and unique 'Tools'.

One is the Dynamic Background Extraction tool, which is very effective at removing gradients, and the other a Selective Colour Noise Reduction tool.

Effectively, DSLR astro imaging is limited the brighter objects, and wide-field imaging, much like your M45 image, where you can get away without very long exposures. The Great Orion Nebula (M42), is an ideal object for a DSLR.

For objects that are down at Mag 30, its too much of a challenge for a DSLR.

A lot of people that are astro imaging with a DSLR are using modded cameras, and the EOS 350D was very popular, although any EOS camera can be modded for astro.

I wouldn't advocate modding your 'every day' DSLR, as doing so would render it unsuitable for normal photography. Second hand cameras like the EOS 350D for example can be picked up for very little money now, and there a several people that will mod them for you, which I believe involves removing the IR filter.

Flexure in any mount, can be very problematical, and certainly ruin an image. Its not hyper critical with the really wide-field stuff, when using a camera lens, but as you up the focal length, it becomes much more of a issue.

Processing astro-images is a very different game to processing normal photographic images, and is quite a 'learning curve'.

I've been doing it for some 12 years now, and am still learning new things.

In the main, we are dealing with very feint objects, and achieving a good Signal to Noise Ratio (SNR) is a challenge.

In processing we will subtract Bias frames, Dark Frames, and Flat Field Frames, from the image frames during the image calibration stage, before we get into the real processing.

I'll not go into details on this here, as its quite involved, and would take a lot of typing.

Dave

[S_J_P]

Re: Pleiades Cluster

The idea of cooling CCD's wasn't something I realised was available for amateurs, it's quite staggering what equipment and techniques are available nowadays

I think I shall muddle along with my DSLR and I'll take a look at the Orion Nebula over the dark winter nights.

Thanks for the comprehensive reply Dave