Ngc 6744

[stars2go (Colin)]

Hi Folks

Have been a "lurker" for quite a while but have just gotten a reasonable image with my Plane Wave CDK-700 and thought I would submit it for your critical examination. This is the second image I have taken with the scope, the first was a dismal failure. The leap from a Tak TOA-130 to the CDK has been a steep learning curve.

This image is the result of about 7 hours under the skies over 4 nights in July. The imaging site is a small farmlet about 40k from Perth city central in what I would call about Bortle 3. Gear was set up under the stars waiting installation of a Sirius dome.

Image taken with...
Plane Wave CDK-700 (Alt-Az) with focuser & de-rotator
MMOAG and Lodestar auto-guiding
FLI Centreline filter wheel and FLI PL-16803 camera

Image collected using MaximDL and developed from LRG at 300 Sec subs, B at 400 Sec and Ha at 900 Sec. Stacked with CCDStack and processed further with PS-CS6. Focusing via a Plane Wave algorithm using multiple stars (typically 50 or so) from the main image field.

Comments and criticisms welcome

Colin Eldridge

Image is here....
http://astrob.in/full/16778/

[Martin Pugh]

Hi Colin
that would be an image taken with an $185,000 telescope?!

Bloody hell!

As for the image itself, it is noisy for 7 hours exposure taken with a 28" telescope at f6.6. You also have what appears to be either a column defect or a satellite trail (black line) going through the image.

I would also add that focus appears a little soft.

Enough criticism! Sorry - I am clearly jealous of your CDK 700.

Martin

[stars2go (Colin)]

Hi Martin
Your comments are spot on. Lots of learnin to do. Soft focus more an issue of poor guiding at the moment though I have a plan of action for that.
Yes there is a column defect that was not properly calibrated out... sigh...
Regards
Colin

[alpal]

Looks great except the focus but how come when you say

Focusing via a Plane Wave algorithm using multiple stars (typically 50 or so) from the main image field.

Your guiding looks ok as the stars are round unless:
(1) your star centroid algorithm was off? - guide star too big or too small.
(2) some other software setting not matching the dynamics of the mount.
(3) maybe the seeing was no good?
(4) target low in angle?

Still it's an impressive start for a mighty expensive dream telescope.
I look forward to seeing many more pics.
Thanks for sharing.

[stars2go (Colin)]

Hi Al
I think my problem is best described under your point 2. Guiding with Maxim was jumping around quite a lot with RMS errors over a two minute time period of about 1 pixel (=0.4 arc seconds). More experimentation with aggressiveness and max move, in the pipe line.
Thanks for the comments
Colin

[dvj (John)]

Well I think we are all impressed by your equipment!

A telescope that large is going to be subject to soooo many variables.

- seeing. If you don't have it, it will always be soft.
- thermal cool down time, I doubt if the mirror would ever reach temp during the night unless you are in an envronmentally controlled building matching nighttime temps.
- collimation
- tracking
- CCD Pixel Size. I might be looking for a camera with larger pixels.

But wow, you are off to a great start.

Is this located in the southern hemisphere?

jg

[alocky (Andrew lockwood)]

Not bad for a beginner!
I can't remember seeing a better image of the Pavo Spiral anywhere. It's one of my favorite supernova search regulars. I wonder if your autoguider is chasing the seeing a bit? Atmospheric turbulence over Perth is certainly one of the limiting factors, more so than thermal considerations.
I assume there's not much you can do about the smeared diffraction spikes?
Cheers, and please keep them coming!
Andrew.

[strongmanmike (Michael)]

For a second attempt image with anew scope it's not bad at all. To me it looks like seeing might have been against you..? I have this problem at my current location - inner Newcastle

Yes, awesome telescope and imaging gear

Mike

[stars2go (Colin)]

Thanks everyone for you kind comments.
DVJ (John) has also nailed my problems in this early image with fairly poor seeing and also non-optimised guiding. Thermal cool down does not seem a problem with 12 fans circulating air around the primary. John, Perth is down South at -32 degrees Lat.

[strongmanmike (Michael)]

Got any drool photos of your observatory..?

Mike

[stars2go (Colin)]

Hi Mike
Still in bits in my shed. 5 meter Sirius. Have to wait until a paddock dries out before I can get a truck on it. Truck and obs would sink in the clay without a trace if I attempted it now.
Colin

[Peter Ward]

Very tidy start Col... I was very curious to see how well the beast would go at sea-level.

I suspect seeing will always be problematical with that sort of aperture....to that end Perth Observatory (Bickley) mounted their Lowell scope on a 15 metre tower to significantly reduce low level turbulence.

Looking forward to seeing more from such an impressive set-up.

[alocky (Andrew lockwood)]

The Lowell at Perth was mounted up on the tower to get clear of the turbulence the trees were expected to produce, but it didn't help, and the 1m Lowell was going to be subsequently installed at ground level (until it all went horribly wrong). To rub salt into the wounds, the 24 needs urgent remedial work to repair concrete cancer. Maybe Colin can take up the slack with his higher spec beastie- such an instrument would be capable of genuine scientific contribution!

The jetstream seems to be our biggest problem in Perth, the kind of steady seeing I grew up with in SE Qld just never seems to happen here. I can count on one hand the number of nights my 25 has reached its potential, and have room for a few more.
Cheers,
Andrew.

[Paul Haese]

Looking forward to your further contributions here. Nice scope for sure but I can tell you where to put the scope. Exmouth up to Broome is the sweet spot for seeing and you can be assured to see a few other imagers up there in the coming years. One of the best planetary images I have ever seen was taken from EXmouth 2 years ago. You can find it here. Look for 30 August 2010 under Jupiter. If that sort of seeing does not temp you, I don't know what will.

To the image. Calibration needs some attention and noise control techniques will improve the image. You might consider selective sharpening too. For a second image with that kit, I am going to keep an eye out for you in the future.

[tilbrook@rbe.ne (Justin Tilbrook)]

Absolutely awesome Colin!!

This is a a tuff one, at least with my setup. Tried it several times but looked crap.

Just shows what good equipement, plenty of data and processing skill can produce.

Cheers,

Justin.

[alpal]

Originally Posted by stars2go

Hi Al
I think my problem is best described under your point 2. Guiding with Maxim was jumping around quite a lot with RMS errors over a two minute time period of about 1 pixel (=0.4 arc seconds). More experimentation with aggressiveness and max move, in the pipe line.
Thanks for the comments
Colin

I hope you can sort it out soon.
You've done very well as that's only your 2nd pic!
I think most people would have been mucking around for 6 months just to get one pic.
You've obviously got the field de-rotator working which would have worried me.

With the kind of money you've spent I bet you'll put adaptive optics on it one day?
AO needs a bright star & you will have more to chose from with such a large mirror 0.7m mirror.

I can't wait to see your next pics.

cheers
Allan

[Ross G]

Hi Colin,

Nice looking photo.

That is one amazing telescope!

Good luck and hoping to see some fantastic photos.

Ross.