RCW54n & NGC 3572 (Gum 34?) - comparison field with Bert's RH200 added

[RobF]

Gear challenges and weather have made it hard to get anywhere with astrophotography lately. Last night was an unexpected clear one in SE Qld though, and after bumbling around I finally started to get the gear singing.

This is my first decent outing with the FSQ. I ended up on this field after looking for "something faint and red" in Starry Night that I hadn't done before. After moving around to get what I felt was at least half decent composition and getting the imaging run underway discovered later there don't seem to be too many images around this area (at least that I could find). An old image from Marco Lorenzi was about it.

Anyway, the Ha seemed good enough to warrant trying to steal some moon aflicted RGB. One of my cardinal rules broken enjoying a quite Easter afternoon - have processed during the daytime with light streaming in the windows :question:

Ha and HaRGB renditions shown.

FSQ106ED @ F5/QHY9 guided with 50mm finder/SSAG/NEQ6
Ha is 4 x 5min + 11 x 15min = 185mins total
RGB 4x5mins each unbinned

Higher res zoomable versions available here (https://picasaweb.google.com/UserRobF/RecentWork#) even though there isn't a lot more to see TBH.
(HaRGB courtesy of the PI HaRVB-AIP script for PI, version 1.0.5 - impressive stuff I thought)

Go easy on me - I've almost forgotten how to work PI its been so long :lol:

[peter_4059]

It turned out to be quite a good night last night Rob - I was kicking myself that I didn't get set up. I really like the HaRGB - great colours. Will have to look at the PI script - downloaded the latest version this morning.

[RobF]

Thanks Peter. Every time I've had a go for last month or so that old cliche has come true - clouds appear once you've set up, got aligned and focused :rolleyes:
A single 5min sub was all I have to show for the entire year otherwise.

There was no reason to expect last night to be kinder - was kind of like a dream after waking up to clouds again this morning :)

[batema]

I think it looks great in both formats. I know the weather has been less than helpful in regards to imaging as has been my 3 week old broken leg, but i would love to know your thought on the neq6 and fsq combination particularly on faint nebula. Exciting times. ahead for you Rob.
Mark

[Larryp]

Very nice:thumbsup:

[RobF]

Hi Mark

Hope the leg is back in action properly when the weather finally does clear. Must make life at the school challenging.

I've been debated upgrade options for a long time and realised changing any one thing would effectively show up the limitations of the others (Talking mainly mount/camera/OTA here).

The Newt allowed me to get in deep and narrow on a lot of things, but playing with Zenithstar refractors in recent years showed me the other (dark?!) side of seeing more FOV. As nice as it would be to have a bigger chip camera to take advantage of the big flat FSQ field, the QHY9 gives nice resolution detail even with the reducer in, and a field with about 5 times the area of the Newt.

Without a larger camera its debatable how you go on faint stuff. The 8" Newt is of course pulling in more light, but processing is challenging to handle vignetting. In the end I'm hoping the FSQ gives me a future upgrade path once I win the lotto :P

As for the NEQ6, it purrs along nicely handling the FSQ, but the PE is actually quite a bit worse than my trusty HEQ5. All the more reason to zoom out and destress on a short focal length holiday for a while ;)

[batema]

Looking forward to seeing it in action at astrofest. No worries getting around at school as i have 6 weeks medical cert so no school for me. Am on crutches for entire time so cannot. even get any of my gear out to muck around. Frustrating.

[RobF]

Thanks Larry. Was determined to get off the beaten track a bit this time rather than try the gear on an old fav.



Fingers crossed for better weather going forward. Astronomy is definitely not a "crutch friendly" hobby, but glad to hear you've got a bit of time to rest at least Mark.

[Ross G]

Very nice photo Rob.

Good detail and I really like the colour version.

Ross.

[RobF]

Thanks for checking it out Ross.
Was good to get back in the saddle.

[multiweb]

Missed that one. Awesome field. Didn't now you got an FSQ. Lucky so and so. :thumbsup:

[avandonk]

Here you go Rob 24 MB unstretched tiff.

http://d1355990.i49.quadrahosting.com.au/2013_04/NGC3576+.zip


Exposures 6x32 min in 3nm NII.


It would be interesting to see how the resolution compares to your FSQ.


Bert

[RobF]

Thanks Bert. I've zoomed right in until pixelation is starting on the same field for comparison, FSQ on right.

The tracking on my NEQ6 was pretty average on the night, so I suspect the resolution of the FSQ would have appeared even poorer if not for "mathematical averaging" based on the fair number of frames collected.


For those interested in stats, as far as I can tell:

Bert's RH200:
8" f/3 FL = 600mm
6x32mins 3nm NII (192mins total)
Theoretical image resolution = 3.09 arcsec/pix

Rob's FSQ:
4" f/5 FL = 530mm
3x5mins + 12x15mins 7nm Ha (195mins total)
Theoretical image resolution = 2.1 arcsec/pix


Observations:

Seeing can't really be quantitated between the 2 sessions (Melbourne versus Brisbane) but both were relatively close to city centres?
I'm not sure how to calculate flux gathering capacity, but 8" f/3 should be way ahead of 4" f/5 for roughly equivalent imaging time and I think that shows in terms of details and signal to noise (but then again the NII data is 3nm and the Ha 7nm so perhaps the NII is letting less light through but with better resolution and contrast?)
The RH200 stars are clearly better resolved
Focus - its possible and reasonably likely the RH200 is a bit better focused - the FSQ was done by hand with a Bhat mask then not adjusted all night - planning to add Robofocus in future - I'm pretty fussy though so I don't think it would have been out by much (if anything) - not sure how often the RH200 needs checking in this regard?
There is a little more pixelation showing in the RH200 image (more so on the original TIFF) reflecting the larger arcsec/pix value, but IMHO it hasn't hurt the image and results in an image 50% bigger per pixel, and that's before you start taking into account the massive size of the larger chip - I want a 16803!! :lol:

[RobF]

Yes, happy and broke so and so. I'm loving my imaging Marc, so I figure its an investment in the future.

[avandonk]

Thanks for that comparison Rob. Looks like the FSQ106ED and RH200 are very close in resolution and PSF. This would make data combination from both quite easy.

I always dither when collecting data. The native resolution is of course 3.09' per pixel for the PL16803 camera RH200 combination. The RH200 has better resolution than the sampling of the PL16803. By upsizing all frames by a factor of X1.5 before stacking to now give a potential resolution 2.06' per pixel this inherent resolution can be recovered. More frames gives better resolution enhancement.

This is mathematically sound according to The Sampling Theorem.

If your frames are dithered you should try upsizing x1.5 and then stacking. I am sure you will see an improvement in resolution especially with the dim small stars.

The Atlas Focuser is about as good as it gets for focussing. I can see a difference in the Bahtinov diffraction pattern with only 100 steps (8.5 micron). The critical focus zone of the RH200 is about or less than 10 micron.

Even though the RH200 is very temperature stable I heat the RH200 and most of the image train back to the filter wheel with eight dew straps 24/7. These dew straps are controlled by a PID PWM (Proportional Integral Differential Pulse Width Modulated) temperature controller that keeps the set temperature constant +- 0.1C. In summer I set this temperature to 20.0C and in winter 14.0C. This way focus does not change overnight with ambient temperature changes. In fact it does not change over many nights unless something is disturbed.

This heating of optic works better with a sealed optic, as at constant temperature there are no convection air currents. This should work very well with your FSQ. I used to do the same with my Canon 300mm lens as it had terrible focus variation with temperature.

Hope all this rambling helps.

Bert

[RobF]

Helps greatly Bert. I'd never thought of keeping the entire image train warrmed versus temp controlled focus. Makes much more sense with your observatory permanent rig of course.

I'm used to be being oversampled at FL 1000m so I'll definitely try your upsizing logic. I do dither always too, but usually only every 4th frame if shooting interleaved LRGB. Can't remember what I did for data - suspect was only every 4th Ha.

All very helpful for those starting on the CCD journey too I'd warrant.
Thanks again,
Rob