Hello,
I was testing the Kenko x1.4 converter on the 5D MkIII fitted to the Mewlon 180 to see if it could tame the off axis coma that DK’s are known to have. The clouds kept rolling in, in waves, so not much chance of any long exposure tests on DSO showpieces. Instead, I slewed to Saturn and had a bash at seeing how many satellites I could dig out at an effective focal length of some 3000mm at F16.8.
I tried ISO 800, 1600, 3200, 6400 and 12800 with exposures varying between ½ sec and 30 secs and discovered that I had recorded 8 of the Saturnian satellites, with a very ill-defined clump of pixels located at one of the indicated positions of Phoebe, at magnitude 16.68. SkyTools Pro 3 showed Phoebe at one position in its orbit whilst Starry Night Pro Plus 6 showed Phoebe’s position some 180 degrees away at the other end of its orbit. Sky Safari Pro running on my iPad was congruent with the SkyTools view and over the years, I have come to trust the accuracy of SkyTools when in conflict with other astronomy applications.
The Sky X Pro showed Iapetus in a completely different location to SkyTools and SNP which were both in agreement. Anyhow, I’m not going to claim Phoebe for this session as I had to use averted imagination to dig out the alleged clump of pixels from the background. Interestingly enough, with a 30 sec exposure at ISO 12800, I was able to locate mag 16.3 and 16.4 stars with a high degree of confidence, although I think that Phoebe at mag 16.68 was just outside this limit.
The frames were aligned and stacked in Images Plus and then imported as Layers into CS6 for the faint inner moons, the planetary disc and the fainter stars. As the series spanned almost 30 mins due to intermittent cloud cover, there was some minor orbital movement of the satellites which I have not corrected for, I used their positions as is.
I have included a couple of stretched frames of the ISO 3200 and 12800 images and a screen print from SNP from where I derived the orbits.
Cheers
Dennis
Saturn:
Earth Distance: 8.8 AU
Sun Distance: 9.8 AU
Magnitude: 0.19
Size: 43"x 17" (disc = 19” x 17”)
Diameter: 120536.0 km
Satellites:
Name Mag PA° Sep"
Mimas 13.0 73.4 22.6
Enceladus 11.8 89.4 37.1
Tethys 10.3 85.3 45.2
Dione 10.5 213.8 21.4
Rhea 9.8 263.5 77.9
Titan 8.4 264.6 183.6
Hyperion 14.3 280.1 202.7
Iapetus 11.2 183.3 138.3
Phoebe 16.6 110.1 1111.6
