Seeing/Collimation/Imaging Dataset:
This page compares imaging results using my scopes under different seeing conditions. My Celestron 9.25 inch SCT had a minus 60 degree corrector plate malrotation which I did not fix until August 29, 2009 and this caused some image softening. The Mewlon and Gladius are in top form. Seeing conditions are estimated by calculation of stellar PSF at approximately the same altitude above the horizon as the imaging target. The Antioniadi scale and/or the Pickering scale are also used. When I have time, the telescope extrafocal, focal, and intrafocal collimation performed just prior to target imaging and an animated gif of the focused star are shown. Clear Sky Chart seeing predictions and jet stream location and wind speed are also listed when possible. I usually get a couple of days a month of 5/10 seeing with the rest being worse. Seeing better than 5/10 is rare in my area and occurs maybe a couple of times per season. 7/10 seeing might occur a few times a year and I think I experienced 8/10 seeing once a few years ago. I still have not seen genuine 9/10 or 10/10 seeing conditions in my area after many years of frequent observing. The best seeing in New England seems to occur toward the last days of a gentle stalled frontal boundry over the ocean just off the coast, producing a gentle breeze coming out of the south and moving inland from coastal waters. When this pattern occurs, the jet stream is usually far away and usually to the north and west of me. Image examples X. and XI. below were taken during such a weather system. But unfortunately, it is not a very common weather pattern in my area. My more usual weather pattern of west to east air flow in the typical high pressure system is generally not associated with very good seeing in my area, possibly because it is coming in over the Berkshire hills and more local hilly terrain to the west. The jet stream is typically not far away with these high pressure systems.
Star testing/Collimation Technical Notes:
The test star is chosen at about the same altitude above the horizon as the moon when possible. Either a 3x or 5x barlow lens is used for calculating the star PSF. The FWHM of the smallest and largest smear of the central core/Airy disk of the star at focus was measured in pixels and converted to arcseconds. With the 3x barlow there are 0.4345 arc second/pixel based on measurements of a lunar crater (given Copernicus has a diameter of 93 km and has an angular diameter of 48.5 arcseconds). The 5x barlow gives 0.261 arcsecond/pixel using the same method. The PSF gives a good indication of the seeing conditions and is an objective rather than a subjective measurement. A sample PSF calculation for Arcturus using an image from Example 1 below is:
I. Imaging Results Under Extremely Bad Seeing Conditions (Seeing 1/5; Antoniadi V (worst); Pickering 1; Zenith PSF 5.3 to 10.0 arcseconds)
Test Done Using 9.25 inch F10 SCT at 1305 x on August 8, 2009 at 00:30 to 03:00 UT. Weather: clear and calm with fair transparency. Polar jet stream directly over Massachusetts with strong upper level winds of about 80 knots. Clear Sky Chart seeing prediction was 2/5. Stars twinkled moderately to the naked eye and Jupiter was steady. Visually at 94x the lunar surface and Jupiter boiled with extremely rapid fluctuations. No fine detail at all could be seen. Temperature approx. in the mid 60s F. No dew. Test star: Arcturus at 66 degrees above horizon. Moon about 49 degrees above horizon. Jupiter about 44 degrees above horizon. The PSF for Arcturus measured with a 5x barlow varied between 5.74 and 10.74 arcseconds. The PSF at the altitude of Jupiter was between 7.4 and 14 arcseconds.
Sample Imaging Results for the Moon and Jupiter:
Janssen 1.5x barlow 9.25" SCT Mewlon 250 F18 on 9-13-09-09 01300 UT (same seeing)
II. Imaging Results Under Below Average Seeing Conditions (Seeing 2/5, Antoniadi IV, Pickering 3, Zenith PSF 3.2 to 4.5 arc seconds)
Test done on August 8, 2009 0100 to 0330 UT using a 9.25 inch SCT with 3x barlow and Lu075M camera. Partly cloudy and calm with average transparancy. Predicted seeing 3/5 by Clear Sky Chart. Some twinkling of stars by unaided eye. Jupiter did not provide a steady image in the eyepiece at 94x and intermittantly boiled at the edges. The shadows of two moons could be seen on Jupiter, but no fine festooning or fine detail could be seen associated with the main belts. The edge of the polar jet stream was over central Massachusetts with upper level winds of about 50 to 60 knots. Arcturus, the test star, was 66 degrees above the horizon and showed a PSF between 3.48 and 4.95 arc second at focus using a 3x barlow. The PSF at the zenith was between 3.2 to 4.5 arcseconds. The moon was 45 degrees above the horizon during imaging. Jupiter was 40 degrees above the horizon for a PSF of between 5.0 and 7.2 arcseconds.
Janssen Formation. 3x Barlow. Tycho under high sun. 3x Barlow.
III. Mewlon 250. August 15, 2009 0100 to 0300 UT, Poor Seeing. (seeing 2/5, Antioniadi III, Pickering 4, Zenith PSF=3.2 arcseconds)
A weather front bringing overcast to the area had passed through and the jet stream was over the Atlantic Ocean rather than over my town. Seeing was predicted by the Clear Sky Chart to be 3/5 or better, but in reality measured seeing based on the PSF of Arcturus was much worse than this and was more like 2/5. Arcturus was 66 degrees above the horizon with a PSF measured with the Mewlon of 3.5 arc seconds. The intra and extra focal star test images boiled badly. The zenith PSF was 3.2 arc seconds. Jupiter was 44 degrees above the horizon with a PSF in the area of about 4.6. It tried to overcome the seeing to some extent by taking a larger than usual number of frames of Jupiter with my ToUcam and ended up stacking the best 250 of 6200 frames. Transparency was good and the sky was clear with no wind. The Mewlon image of Jupiter is sharper than that taken with the Celestron 9.25 inch scope under better seeing (see III above) conditions, and this likely reflects the presence of some substantial spherical aberration in the Celestron scope which I caused some time ago by improperly aligning the corrector plate.
Jupiter:
IV. August 16, 2009 0345 UT. Mewlon 250, Average Seeing (2 to 3/5; Antioniadi III, Pickering IV, Zenith PSF = 2.1)
The sky was clear with below average transparency due to haze. There was no wind and no dew formation. Arcturus was 66 degrees above the horizon and Jupiter was about 44 degrees above the horizon during the star test and imaging. The star test was begun about 0130 UT and Jupiter imaging at about 0300 UT. The PSF of Arcturus varied between 2.3 and 3.6 arcseconds. The best Zenith PSF was 2.1 arc seconds. The best PSF at Jupiter was 3.0. There was some question as to whether the Mewlon needed a small collimation tweak looking at the outside focus pattern, but inside focus looked fine. The brick patio was wet with cool water which was allowed to completely evaporate before the scope and mount were set up. The back of the mewlon was left open to cool the mirror. A small fan was used to gently ventilate the mirror from the side intermittantly. Jupiter was imaged at F24 with a ToUcam Pro camera. Image capture was poor because camera settings were too dim and this badly affected processing for this imaging run.
Jupiter
V. August 18, 2009 0330 UT Above Average Seeing (Seeing 3/5 and sometimes 4/5)
Mewlon 250 at F24 with ToUcam Pro. Best 1260 of 1475 frames. Clips was too long so planet rotated just a bit causing some blur. Capture rate was 10 fps. Seeing was 3/5 and occasionally 4/5. Atmosphere was transparent. There wasn't time to do a star test but seeing was close to 1 arcsecond near Jupiter. The jet stream was far away for a change.
VII. Jupiter August 26, 2009 0200 UT. Seeing seemed to be below average at an estimated 4/10 at 0200 UT, and worsening to 3/10 by 0300 UT. The image of the planet boiled very badly in the eyepiece at 94x. Stars at the zenith twinkled badly. Since I had the Mewlon 250 and ToUcam already set up, I took a few avi clips. This one was taken at F18 with an IR block filter in place and the image was made from the best 781 of 1348 frames. I expected to see nothing but a blur after processing and was surprised to see some detail emerge. I credit this on very painstaking focusing on the brighest of Jupiters moons that was visible. It was difficult to get an exact focus because of seeing conditions, but I think this is the only reason that detail appeared in the images of the planet. Had bad seeing been combined with bad focus, then nothing but a big blur would have been produced.
VIII. Jupiter August 27, 2009 215 and 250 UT. Very poor seeing estimated at 3/10. Jupiter boiled badly in the eyepiece.
IX. September 7, 2009 0200 UT. Seeing predicted to be 7 to 8/10, but appeared to be 5 to 6/10. Mewlon 250 @F18, EM-200 mount, DMK31 mono camera with Astronomik RGB filters. Best 600 of 1000 frames per channel. Channel images sharpened before assembly into final color image. Alignment in Registax, centering in AIP4WIN, Magic Focus sharpening in PS CS2.
X. September 21, 2009 about 00:53 UT. Seeing 6/10. Mewlon 250 at F18, DMK21 firewire camera. Best 750 of 1000 frames per R, G, B channel. Better seeing allowed more detail than usual to be captured, at least for me. 6/10 seeing is fairly rare in my part of New England.
XI. Jupiter. September 22, 2009 00:15 UT.
Seeing 5/10. Mewlon 250 @ F18, DMK21 firewire camera (best 633/1000 frames per channel processed and stacked)
