Recently Browsing 0 members
No registered users viewing this page.
By Padraic M
I spent the full night out last night and got 6 hours of Ha lights on the Bubble and the Horsehead. Reasonably pleased with the results, but even though I followed my usual process and got good focus statistics in APT, I am slightly out of focus with roundy stars and some are even slightly donutty. Samples are attached below.
- After getting close to spot-on focus, the APT Bahtinov Aid showed a focus distance oscillating from -0.02 to +0.02. Seeing seemed good to the inexpert eye. Not so sure about transparency as there was some thin, wispy cloud throughout the night. So, I started the night's imaging with focus 'Close' rather than 'On' focus.
- Different subs show different quality stars, ranging from small donuts to circles.
- HEQ5 Pro Rowan; SW Esprit 80 with field flattener, SW stock manual Crayford focuser; ZWO EFW Mini; Baader 1.25" 3.5nm Ha filter; ZWO ASI1600MM Pro binned 1x1 @ -20c.
- AA Starwave 50mm guidescope with ZWO ASI290mm Mini guidecam binned 2x2.
- All subs are 300s, gain 139, offset 10.
- Polar alignment with Sharpcap to 17 arcsec ("Excellent"); capture with APT; guiding with Phd2. Focus with Bahtinov mask and APT Bahtinov Aid. Stacked in DSS with Darks, Flats and Dark Flats.
- Mount is well balanced in RA, but is very camera-heavy in Dec.
- PHD2 guiding was around 2"/px. Imaging pixel scale is 1.9"/px.
- Do I put the round stars down to seeing, given that the Bahtinov Aid focus distance was bouncing equally above and below zero?
- Can poor seeing cause the donut stars?
- Would an electronic auto-focuser do any better in this situation?
- Would the Seeing Monitor in Sharpcap give useful information? I didn't think to use it last night.
- Could my guiding performance, and possibly the Dec balance, have affected the image quality in this way?
- What are my options in future - abandon imaging for the night? Bin all images in software 2x2 or 4x4 to sharpen the stars at the expense of lower resolution?
- Other suggestions?
Sample 1: Detail from a single 5-min sub of Bubble nebula at 100% showing round stars, and a blurred bubble.
Sample 2: Detail from a different sub of the Bubble nebula at 400% showing donuts
Sample 3: Detail from a 5-min sub of the Horsehead nebula at 100%, showing both round and donut stars
Finally, both images stacked, calibrated and stretched, scaled to 4x4 in Gimp. 28x300s Ha on bubble, 22*300s Ha on horsehead.
I would like to share with you an article written by me on high-resolution solar imaging in different wavelengths. Glad that the European Physics Journal (EPJ) Web of Conferences published it. You can read it at:
You can see the different layers of the Sun in high-resolution images using different setups.
By Padraic M
How can I set up APT so that it always connects by default to my imaging camera? I have an irritating problem that APT will regularly connect to my guide camera, even though that camera is already connected in Phd2.
I have created two APT shortcuts on the desktop, one specifying camera 2 (which usually is the guidecam) and the other specifying camera 1 (which is usually the imaging camera), but it looks like cameras 1 and 2 are not absolutely assigned to the ASI1600mm (imaging) and ASI290MC (guiding).
At APT startup, in the log it will say 'Connected to ASI1600mm' and then imediately say 'sensor size 5.6mmx3.2mm'. Then I know I have a problem as it's obviously not the 1600! I can usually sort it out by disconnecting, Shift-Connecting (to get the camera selection dialog), and selecting cameras 1 and 2 until I get the correct sensor size.
There must be a better way?