Dusty Corona Australis

[richardo]

Hi All,
with my tests inbetween clouds, rain and winter type weather,
I put together this image of one of my favourite objects with what I had.
I now have a Paracorr corrector and have moved my primary mirror back in the newt to
accomodate the increase in FL.
With this, getting the right spacing and fine tuning the squaring of the CCD
to the optical train, plus dealing with distortion in the corners by my 1 1/4"
filters, it's been never a dull moment.
Thank goodness for CCDInspector! But this image doesn't really show my final
adjustments.
Have some new 2" filters coming in the next week, should finally get all
these issues sorted.
Also have just pulled down the mount to relube and adjust...
So it's been a very busy week for me on my 2 weeks holiday.

Here's a link to my home page with a link to the 1.4mb image if you'd like to
have a look.
http://www.baytop-observatory.com/

Hope you're having as much fun as me:(:sadeyes::mad2::)

Thanks for looking

All the best:thumbsup:
Rich

[multiweb]

:eyepop: Phenomenal picture there Rich. Love it! You even managed to get color and details in a little face on spiral at 5 o'clock. Top shot. :thumbsup:

[richardo]

Thanks Marc...
took me ages to sort my vignetting out as my flats didn't work well on my colour channels... I'm thinking it was a couple of LEDs to some of my devices. Lum corrected well though.
Just quietly waiting to get my new 2" filters then things will be soooo much easier.

Cheers again:thumbsup:
Rich

[strongmanmike]

Ah sigh, trials and tribulations :scared: can send us :nerd:

Lovely subtle and well composed rendition of this Malin favourite :thumbsup:

Not essential I guess but it would look even better if you just tweeked those elongated stars.

Mike

[jase]

Fine work there Rich. The time spent working the imaging train configuration over seems well worth it. Certainly a flatter field than your previous image.

You allude that the image does not show the final adjustments meaning you're posting a mediocre image or is this just a play on words? Personally, by the looks of the data set, I'd be very happy if I were you.

Thanks for sharing your efforts on this. Corona Australis is undoubtedly a prime target for a reflection neb aficionado as yourself. Looking forward to seeing what the new filters will bring.

Cheers

[richardo]

Hey Migel,
thanks there buddy.
Been a busy time trying to get things where I'm happy. I'm just about there though, so it's been a good work out.
Have just tweaked the stars... yeah I looked at them and thought, ahhh, it's more a set of test images..(do it right man:rofl:)
Yes, worth doing, worth doing as best as poss!



Thanks very much Jase!
Was a challenge with my hicups... hicups

It's been a lot of trial and error to sort these things out with the new gear; But as you say, pays off in the end.
Made harder waiting for all the things I need. But has been a steady progression in the right direction.
The face plate on my H16 just needed a tweak on one corner, I've been using CCD inspector to help out as well as my eye... and did the final tweak after the data for this image.
As I collimate prior to every sesh, I really needed to have consistency with how the corrector sits in the draw tube so it's repeatable every time without too much fuss. Collimation is spot, but there was that nagging diagonal elongation to one corner while to the opposite side stars appeared elongated horizontally. In the centre stars were ok but slightly flattened.
I'm sure I'm pretty much there now.
So hopefully when the 2" filters arrive, this will be the test to if there is any of that distortion left and if I've arrived at the sweet spot for the corrector spacing with this setup.
Am seriously very happy with the Paracorr and the way it handles stars giving a nice airy disc. Much different than the MPCC I find.

Thanks guys for your nice comments.
Always appreciated as we work through our issues:thumbsup:

All the best
Rich

[strongmanmike]

Yeh that's a bit better.

Actually you know what..? I recon your dust in the lower left quadrant is about as good as I have seen, very 3D, nice work.

Mike

[Paul Haese]

An excellent image which is smoothly processed and one I would be very proud of if it were mine. Are you aware that you captured what looks like a galaxy in the image? I really like the fine streaks of gas in the reflection nebula.

Cracker shot.

[Garyh]

That`s a brilliant rendition Rich! I love this area and this has inspired me in getting more subs!
cheers Gary

[gregbradley]

A very good image. I had no attention on the stars when I viewed the image. But star elongation in one corner may be indicative of focuser sag. Newts are a bit funny that way in the sense of all that gear hanging off the focuser which is at 90 degrees to the tube. Must put more leveraged pressure on the focuser.

The image though seems to lack a bit of punch/impact. I think the data is there though. The central blue neb stars could benefit from a bit of lassoed curves or shadows/highlights and the dust areas a bit more smoothing to reduce the graininess. And more colour contrast or saturation. As I say a technically very good image but to me just lacks that extra kick that it could. Perhaps the colours channels need more.

I am leaning myself to abandon binned colour and do unbinned colour and combine them in the lum channel as well for extra clarity. I was surprised at the difference between unbinned and binned data using an FSQED and reducer. Perhaps the faster the optics the more unbinned data loses clarity and resolution.

Greg.

[Octane]

Rich,

Fabulous image. The dust does look 3D and that gorgeous little galaxy is an added bonus. Also, I can see what looks to be a diffuse nebula just to the right of the lower-left dust region; between the blue stars, and just a little under them.

This is a really subjective call, but, I'd love to see a bit more saturation overall. I think I see where Greg's coming from. Personal taste, though. The image still stands on its own.

H

[TrevorW]

Nice Rich

[Peter Ward]

All good. Noise well controlled, with great highlight and shadow, guiding and focus are spot on. Nailed the colour balance.

A top shelf image.:thumbsup:

[richardo]

Thanks Mike and cheers for that!



Thanks Paul!
There's actually two fairly well seen galaxies with another what looks like an edge on right of the obvious one in the lower R/H area.. also with close scrutiny there's two extended minor planets making their way across, you'll see them as little lines. These were captured on Sunday night.
Yes i too think the reflective streaks look pretty cool!



Thanks Gaz!



Thanks Gregg for the comments, observations and critique.
My draw tube lays under the tube so the imaging setup is upside down and always has been, so as to reduce non symmetrical flexure and off balancing in different parts of the sky. When I built the scope I added a 4mm aluminium backing plate that curves up around half the diameter of the inner tube. If anything, it could be the Moonlight focuser, but I can put a fair amount of pressure on it with minimum movement, or what would warrant movement as the scope tracks.
The new designed SX cameras now have the facility to adjust the face plate at the front of the camera: it was never squared up before being sent to me. So I've gone back to rechecking all my mirrors, secondary offsets, so I know collimation is spot. This I had to do before being able to problem solve. I've always religiously used the Jim Fly auto collimator and sight tube for spot on refinement. Needs to be spot at this F ratio.
It is the face plate as that last test run through ccd inspector, things were as near spot on as the seeing was permitting with +/- .1 % tilt in x & y... varying in different areas, far better than when I took these series of test images to compose this image.
I agree that the colours seem a bit mute... i've actually cranked the saturation up fairly well... but there is a point of over done and I pulled it back from this point.
It could be my flats weren't great... This chip is very sensitive in the green and lacks in blue and red... as I found out when I did a G2V cal.. I might have to change my tactics on ratios but this will all come together for ernest when I have full illumination with the larger filters.
Still your thoughts about binning might be worth a try.
All will be revealed.



Thanks for the comments and observations H!
It's a hard area to process for sure. Lots of variation. Just trying to get the right balance without clipping, or over stretching..
Yeah like that little emission neb, just seems to set give a variation to the area which draws your eye to it.
(see my reply to Greg on colour) Maybe more colour data is needed. Wouldn't surprise me as the conditions were a little fuzzy. So perhaps extinction came into play here.
Still coming to terms with flat fielding... this could have had an effect when I calculated the background deviation when applying the flats.
Still, when the 2" filters arrive, will only be flat fielding the lum... the colour will be fine... maybe this will make a difference:shrug:



Thanks Trev.



Thanks very much Peter!
this is one of my favourites and wasn't going to post this image as I was simply running adjustment tests.. but once I started to put them altogether thought what the hey, I can do something with this.
Really loving having new equipment though, fun to work through the issues!:rolleyes:

Once again thanks all for taking the time with your comments and critique.:thumbsup:

Appreciated:D
Rich

[Hagar]

Very nice Rich. A very interesting piece of sky well imaged. I would lift the blue saturation a littleand get those reflection nebulas bouncing off the page, but thats just me,...
Well done

[telemarker]

Great image of a sweet part of the sky. So much going on, nebulas globs and dust wonderfully rendered. :thumbsup:

[Alchemy]

Has a nice crispness to it, the diffraction spikes have an rc look about them, very clean.
:thumbsup:

[gregbradley]

There was an interesting report by Richard Crisp about flats recently.

He proves that the least noise added by flats are those taken at about 80% level of your CCD rather than the common 1/3rd or less.

I'll have to trial that myself as I have had some flats that were quite bright and they seemed to damage the image. May have been some other factor though.

I use a white T shirt over the end of the scope and do my flats at dusk. That works well.

Greg.

[richardo]

Thanks Doug, yes it is a beautiful area.
It's the first time I've been able to have the globular Ngc6723 in the fov. So it's a bonus added to the nebula.
I did a G2V calibration when I received the new camera, and also when I replaced my MPCC with the Paracorr corrector.
The colour weight shown in this image is the product of this plus extinction multipliers were applied.
I've given as much saturation as I dare, even to do a sat layer and paint,feather in the reflection nebulosity to further saturate it looks unnatural and induces noise.
No, I'm pretty happy with what I have.
The blue channel compilation was fairly mute in comparison to the R & G, and judging from many images on the net, the blue areas of reflection don't extend a great distance from the blue star, (perhaps in wider fields) or are overly saturated,(well some I've seen are, but overly so) unless of course you take more and/ or deeper colour channel subs.
But as you mentioned, this is all personal taste.



Thanks very much Keith!
This whole area in wider field images show just how dusty it really is.
Nice to have a bit of blue to set it all off with a glob to boot!





Thanks Clive...
I think with the Paracorr corrector in comparison to the MPCC, gives a nice airy disc to the stars, quite similar to what I've seen with images taken with RC's.

I guess this scope is an RC... ah that is, to coin a comment from a friend of mine...... a 'Richie creation":rofl:

Thanks all for your comments:thumbsup:
All the best
Rich

[richardo]

Thanks for this Greg.
I've been using a light box.
I set my flats in all channels to around 29-30,000 ADU which is about 70-75% the full well depth of the KAI4021m chip.
While my Lum flats divided well after bias subtraction on flats and lights, I saw over correction in the colour channels to the corners where my vignetting is. Dust motes were corrected nicely though.
Has me baffled.
I've tried lower ADU levels with no success, I might give the 80% a go and see what happens.

Maybe I'll try the 'T' shirt flats with twilight and see how the colour gets on. Seems strange that the colour flats correct the motes but not correctly do the vignetting.:mad2:
I'm a bit over it now as I've tried and tried..

As I've mentioned, once I get the 2" filters, vignetting will no longer be an issue. I still will be flat fielding the Lum however.
But hate it when things don't do as they should.

Cheers
Rich

[Octane]

The more I look at it, the more I think it looks wonderful as is.

lol @ Ritchie Creation. That is GOLD.

H

[richardo]

Hi H,
yeah pretty funny eh!
My late Friday afternoon work debriefing buddy lays claim to it,:cheers: :drink::drink::drink::drink::drink: :drink:
he dropped this one on me and had me rolling on the floor.... classic I thought.. just classic:lol:

Cheers Humayun

Rich

[JD2439975]

Very nice indeed Rich, lovely fluffy dust. :thumbsup:

[gregbradley]

I am not sure that is correct Rich. Doesn't a 16 bit CCD do 65535 ADU? Ins't that a measure of how many shades of grey it can
differentiate?

I'll have to check but I think well depth is a different thing. It measures how many electrons each well can hold. You could be right here though. Does that mean a camera with a well depth of less than 65535 cannot differentiate all shades of grey? (mind you your typical image only sits in a fraction of those 65535 levels of grey).

But what I was saying was go 80% of 65535 = 52,428.

I may well be the one here who has it wrong so let me check that question out first.

The other possibility with a light ring or other things is uneven illumination.

Also you didn't move the camera orientation after the flats did you? It has to be the same - probably was though if the dust donuts went.

Did you use median combine?

I have had odd flats at times that did not work. I put it down to the fact they seemed too bright. Also perhaps a wrong conclusion.

I get good results doing 3 flats median combined shooting for 20,000 adu or thereabouts with at least 2 or 3 second exposures (my cameras have physical shutters that show in less than 2 or 3 secs) using a white Tshirt at dusk and median combine with bias subtraction (not that important).

Can you post one of your flats?

Greg.

[richardo]

Thanks very much Justin!
It's like where I live, dusty dusty dusty!

All the best
Rich

[Martin Pugh]

A fine image indeed Ricardo, I like the pastels in the way you have processed this.
cheers
Martin

[richardo]

Greg, mmmm, there seems to be two camps amongst the FF experts on the net.
And as I'm pretty green to flat fielding, maybe I've gone off with the wrong camp:lol:
On one count, I've read, and as I've thought, that you need between 30-50% of your full well capacity: This I can recall was from a discussion on cloudy nights with a guy who was using a H16.
Here's a link
[http://stargazerslounge.com/imaging-image-processing-help-techniques/94836-help-big-problem-flat-field-calibration.html]

And I've just had a quick look once again (hate to think how much time i've spent on trying to find definitive info on this matter :confused2:)...
that as you've said... 16bit ccds aim for around 20,000 adu... or 1/3rd there of 65,535

OK, now I'm really confused:rolleyes:

Here's another equation I found that is to give the correct target for flat fields, just to throw another spin on things, but this seems to indicate what you've been saying ..

full well/ADU gain*30-50%=target

So for my camera that equates as follows
40,000/ .6 * 30%=19,999.99rec so 20,000adu

I did have a read after you commented on Richard Crisps document pertaining to filter edges and things... interesting and I think this has solved a drama for a friend of mine...

No I didn't move the camera at all.. the donuts were gone with the rgb's.

I median combined my master bias subtracted flats to create a master flat for each individual channel.
I first wasn't bias subtracting from either the lights or the flats... things didn't work. Then I did bias subtract from both and that's when my lum flat fielded very well.
The rgb channels didn't however do that well with the vignetting.

Ok, so I'm going with you with aiming for 20,000adu....
I'll give that a try and see how things go.

Thanks for bring this to my attention..

Rich

[richardo]

Thanks very much Martin!

Appreciate you taking a peek and commenting!

All the best
Rich

[gregbradley]

Hi Rich,

Here is the link to the paper on flat fields by Richard Crisp who is a CCD engineer and who started narrowfield imaging:

http://www.astromart.com/forums/viewpost.asp?forum_post_id=720614&poll_id=&news_id=&page=3

You are right it is 80% of full well capacity not 80% of the 16bit levels (ie. 65535).

The bottomline here of his article is that the higher the % of full well used for flats the less are needed to get lower noise. The lower the % of full well used the more noise you will introduce and the more flats will be needed to achieve comparable noise levels.

So in your case of full well of 40,000 you would aim for flats of about 32,000 ADU. You would bias subtract (at the same temp).

Note the scope needs to be in focus for flats. So make sure your scope is in focus first. Important for me as I may do flats at dusk before I have imaged and thus before the scope is focused.

Illumination for the flats of course has to be even as flats are trying to even out the uneveness of illumination from both the optical path and the chip itself (it may not be uniformly sensitive across the whole chip).

Are you doing autodarks with your flats? The darks would be virtually identical to the bias being such a short exposure and isn't part of the
procedure.

With the colour channels are you doing flats 2x2 to match your colour channels 2x2? If you take a 1x1 colour flat and try to apply it you may get an error message but if not you will get weird results that don't work.
I have sometimes used a luminance 1x1 and reduced it to 2x2 in CCDstack and applied it to a colour channel when I didn't have a flat for that colour. Sometimes it worked but often it did not. Better to use another colour's flat if for some reason (like it got dark hehehe) you don't have the correct colour's flat.

The only other thing may be if your filters are loose and move around causing the lights to be different to the flats. Apart from that you would have to detail every minute step taken to see if there seemed anything odd.

It is easy to continue to shoot flats at 1x1 as you probably did your lumninance flat first and then the colours. An easy way to tell is to look at the file sizes of the colour flats versus the luminance. 2x2 is about 1/4 the file size of 1x1.


Greg.

[RobF]

Wonderful work Rich. Inspiring stuff!

[richardo]

Thanks for clearing this up concerning well depth.
Now I know where I am.

I only shoot my colour in 1xs binning. Back in 2002 I think it was when i first purchased my SX-H516, I liked the idea behind 2xs binning. Combining 4 pixels to make one and bringing the filtered light in quicker. Trying it I found I didn't like the extra work and end result so haven't binned since.

I haven't bothered with dark subtraction as I find the chip, at this time of the year, I can get away with sigma combining my subs with little or no residue of noise. Maybe in summer it might be a different story. Still generally, in summer, the temperature drops to the mid teens. The temp I use at the moment is -15C, this seems to be all that is needed to keep things fairly clean from noise.

I will attempt again to see how my flats go..... since I've had a break, I have a little more head space...

Rich



Thanks very much Rob!
It's an inspiring area of the sky

Cheers guys
Rich