Images from 21 February

[Paul Haese]

Got down to the observatory over the weekend and imaged the following images:

NGC5128 (http://paulhaese.net/NGC5128.html)
NGC3579 (http://paulhaese.net/NGC3579.html)

Both images are deep runs of 25 minute subs. Data is contained on the bottom of each page.

Comments are most welcome as well as criticism.

[h0ughy]

Hi Paul,

i like the result you were able to get with Cent A - after seeing Mike Sidonio's effort on this and comparing yours, you managed to get a nice result.

[strongmanmike]

:scared::scared::scared::scared: is...that.....Centaurus A????? Nooooooooooooo:eyepop:....:help:

Sorry, Super images Paul, you have to be happy with these.

Looks like you have the guiding working but you are braver than I going 25min, I wouldn't trust everything to go right and would be too frustrated if I lost a few subs at 25min each :scared:

Not sure you could make any meaningful improvements to these? excellent mate!

Mike

[renormalised]

Nice piccies, both of them. Good effort, Paul!!:):)

[Tilt]

Big subs! Nice results, good detail in both images.

Michael

[strongmanmike]

Yeh and just wait till you see them both on a decent monitor :doh:....:lol:

[h0ughy]

I have actually gone through and readjusted the TV - lowering the contrast significantly and adjusting the brightness - then re calibrated. I was within 3% of the target output on both black and white which was a lot better than before (it changed to 200% on white and 60% on black and the sharpness module in the TV was set incorrectly when you were here , but i have learned that the tele has a user setting - which i adjusted) Now Mr Sidonio your Cirrus looks superb, your pinkish bits in the lagoon look superb, even showing different star colours blues, yellows , orange ones. your CG4 shot shows colours within the dirt LOL, and omega cent shows the star colours in the group - even the witch head look great. So nnaarrr :P SNOT perfect like on yours but its good:whistle:

[strongmanmike]

So what all this means Paul is that Houghy "would" have seen your images as gastly but now they must look good, Houghy was previosuly looking at images and thinking Oooh nice when in fact they were crapola :whistle: but he had nothing to compare with so he didn't know any different, now he knows, bit like needing glasses and not knowing it until one day you get a pair and cripes :eyepop:...:thumbsup:

[Quark]

Very nice images Paul.

As a comparison I am comparing these two images to David Malins published in his most excellent book "The Invisible Universe", published in 1999.

Your images demonstrate just how far amateur equipment has advanced over the last 10 years.

I think your image of Cent A is exceptional, it reveals a great amount of quite delicate structure in the dust lane. It loses very little in comparison to the photographic plate of Davids.

When I first looked at your image of 3579 a rather elongated star within a tight loop of nebulosity toward the bottom of the main part of the nebula and to the left of centre caught my eye. This is actually two stars that appear in Davids image with clear separation. I realize that there is no comparison between the AAT and a Takahashi refractor but the detail that you have captured, albeit on a smaller scale is very impressive when compared to the images in Davids book.

Regards
Trevor

[dcalleja]

Brilliant images. Outstanding detail.

[Paul Haese]

Thank you all for the comments.

Mike you are a funny man.:D

Trevor, I constantly marvel at how far all amateurs have come in the last 5 years; let alone the last 10. Equipment and careful attention to details is what drives most of us. Personally, everytime I fire up the scope I just try for more detail, sharper images and better processing. I find that comparing images of many other people helps with the colouring of these images. The main thing for me is that this is all fun. I like imaging in varying capacities, but it has to be good fun.

For guys wanting to know how to get better images, I work on this policy. Not saying my images are better than anyone elses (in fact they are in many ways not great). However, I try to take as many deep subs on one target as will allow. Images get really smooth after 10 or so subs. Lots of darks are also important especially this time of the year. And; more importantly I have found that going more than 10 minutes produces very good signal which when combined with the numbers of subs cancels noise quickly. I gather this is somewhat the same for the true astro cameras too. For DSLR's though I stick to this rule.

Thanks once again.

[spearo]

Great shots both of them especially Cen A awesome!
frank

[leinad]

Fantastic Paul!!; thanks for sharing your advice on technique also.

Can I ask at what ISO level you took these long subs?

Did you also use a time delay between exposures? I was wondering how the DSLR performed with heat/time x exposure from one to the next , inc darks.

[bloodhound31]

I am a big fan of Centaurus A mate. Beaut job. So sharp, well focused and realistic.

Champion effort mate.

Baz.

[Paul Haese]

leinad,

I sue ISO800 and with an interval of 8 seconds between images. Unfortunate what I think you are looking for is someones experiences with an uncooled 40D or similar camera. My camera has been modified by Central DS with a peltier cooling unit. The chip is usually around 19 degrees below ambient and as such has little if any noise. I cannot really help you with an uncooled unit on such long subs. Although one of the other chaps that was there last night was using such a camera and doing 30 minute subs. He had prepared his darks the night before and just applied them when processing. So you can take long subs with an unmodded camera, but lots of darks are necessary to remove the noise.

[jase]

Both very spectacular images Paul. No arguments from me about going deep. No reducer on the 102? Imaging at F/8? My only comment is that I'd like to see a little more blue coming out of those stars. Spec class M stars are looking good, but the O and B type could do with some more saturation I feel. Great details on display, quite a visual pleasure that sets the scene for DSLR imaging. Well done.

[prokyon]

Great pics!!! :thumbsup:

[Paul Haese]

Thanks Jase,

No reducer but I have a flattener. Can you tell me how to bring out the saturation in those star types. Always more to learn.:)

[Octane]

Paul,

Fantastic work.

That is a magnificent Centaurus A. Kudos to you for keeping the background nice and even. Wonderful star colours and excellent guiding.

Regards,
Humayun

[Omaroo]

Very nice indeed Paul! :) As previously mentioned - a textbook effort.

[jase]

This is a tough one Paul. You're in with a chance of NGC3579 given there are subtle blue hues present. The use of the colour range tool is not going to help however as the fuzziness range will pick too much. I think in this scenario, I'd duplicate the layer, apply curves to the blue channel to bring out the highlights. Blend the layer back as "Lighten colour". You are likely to need to mask the highlights and drop the opacity however. Once you've got a distinctive blue, the colour range tool may then be more successful and selection to bring up the saturation further. Alternatively, If you only want to fix up a few of the brighter stars you could simply go to channels, highlight the blue channel, then click on RGB eye so you see all channels (RGB), but only the blue channel is selected. Then use the sponge tool with saturation selected. Run over the stars that look blue to boost their saturation. In the process, you can also desaturate the red and green channels (also using the sponge tool), but be careful as this can be quite drastic and sometimes difficult to balance Would suggest altering (lowering) the opacity and flow of the sponge tool - keep an eye on the white point as it can turn a weird hue that results in some effort to restore. Zoom right it and avoid touching the saturated areas if possible.

NGC5128 is a different story. There isn't much in the way of blue stars to begin with. The subtle blue fold beside the dust lane is present, but not much with the stars.

I can't help but think that your long exposures has all but saturated this information. Its probably worth checking for it though...perhaps use DDP to validate this as it will manage the stellar profile very well i.e. the bell curve shaped histogram across the star compared to a table top (where you've hit saturation). This is present in the NGC5128. Even the small angular stars reach the 256 level and table top out, thus are saturated (see attached). A bell shaped curve will provide better colour saturation as the star reaches the top of the curve. Table topped stars are usually crunchy, sharp or abrupt in appearance. Not often are they totally void of colour however, but contain a small tight ring around the saturation. The idea of the bell curve is the expand the tight ring into a gradient towards the star centroid. A large bell curve will look like the star is out of focus...this should clearly be avoided.

If you've lost the colour information (unlikely), I'd still recommend going deep, but take a few 300s subs to manage the stars. This is a common technique used with astro CCD's to manage the stellar profiles. Managing stars is probably one of the more complex components of imaging. I still get it wrong, but when you pull it off, the aesthetics of the image really shine.

Apologies for the Mr. Squiggle type unhappy face in the attached.

[marc4darkskies]

Two excellent shots there Paul. Well done!! :thumbsup:

Cheers, Marcus

[Paul Haese]

Thanks Jase, I will give this a try when I get some time. Excellent tut. Just have to get my head around this. Learn something new everyday.

Thanks Marcus.

[gregbradley]

Great results Paul. I agree with Mike, 25 minute subs is a bit of tough one.
I cut my subs back to 10 mins as I got rounder stars. 25 minutes will show up any slight error in your polar alignment as even though you are autoguiding it won't compensate for rotation from polar alignment errors.
Also flexure is more likely to show up in longer exposures -gusts of wind, stray clouds, etc etc.

I don't think there is any difference between 2 x 10 and 1 x 5 stacked and 1 x 25mins in terms of signal to noise ratio. It is more a thing in narrowband to do long subs as the signal from those are so low that it is hard to get above the noise hence longer subs.

Greg.

[Garyh]

Ohh, nearly missed these lovely images! Great work Paul! :thumbsup:
25min subs, you don`t have flexure problems that`s for sure! You must be using a slow iso?
cheers Gary

[jase]

For ABG there is quite a difference - regardless of filter. Remember, today's sensors respond to light in a linear fashion. The longer you go, the more light collected. So for the dim regions of an image, a single 30min long sub will give you a better S/N ratio than taking 3 x 10 min subs. Also, the latter doesn't make an image any deeper. You're still only collecting 10mins of light, thus noise will continue to reveal itself in the dim regions when you stretch it hard to get out the faint nebulosity. Clearly, the issue with one sub is that you've got some work to do in removing chip defects, cosmic ray hits, etc, so obviously more subs the better to reject the outlier pixels. You can measure the ADU levels to confirm the theory. The recent DSLR images presented on this forum attest to going long - stunning results indeed.

[Paul Haese]

Hey Jase, us guys from the Clayton group just love going long. We are trying to go longer on each outing just to see how far we can go. Mark (WYSIWYG) did a 60 minute on the trifid, and had the moon not been present it would have been a superb image.

There is a chance for burning out image as Greg has suggested, but linear capture does seem to help with not having to stretch the data. I guess this is really a balancing game with DSLR. A different matter for you guys with mono though.