Telescope Reviews: Saturn with oberwerk 20X80 lw's

I can "see" Saturn's rings with 15x70s, but not with 12x50s, although at 12x50 I can easily make out an elongated shape. I can see distinct black space between the rings and the disk with 16x70 Fujinons. With 20x80s, the rings are clearly separated from the disk and have a distinct curvature all the way around. But at these magnifications you could not even hope to see any detail in the rings. Nor could you hope to see distinct separation of the disk from the rings at any location other than the ansae.

The separation between the rings and the disk is about 7 arcseconds. People with excellent visual acuity can see things when they are magnified to an "apparent" size of about 160 to 180 arcseconds. Few can see better. That would mean you need 160/7 = 22x magnification to see this 7" separation. But Linear features are easier to see than point sources, so the needed magnification can be somewhat less.

The Cassini division is only 0.7 arcseconds wide, but is a very high contrast linear feature. Simple calculations would lead you to believe it might take 160/0.7 = 228x magnification to see the Cassini division. However these are some real results obtained with small scopes.

500mm/90m ref - 5mmU.O.ortho=100x – good contrast view, Cassini 30%-40% around,
500mm/90m ref - 6mmU.O.ortho=80x – Cassini only suspected

480mm/78m ref - 7mmU.O in 2xUltima=140x – difficult view but seen
480mm/78m ref - 4mmU.O.ortho=120x – barely seen maybe 30%,
480mm/78m ref - 5mmU.O.ortho=100x – only momentarily suspected on following ansae

600mm/76m newt cas - 5mmCel.ortho=120x – rings very distinct, but No Cassini.

The 78mm AT1010 ref is a better scope than the 76mm Swift newt cas. The 90mm is an orion ST90.

These results help illustrate that linear features can be seen easier than might be expected. That helps explain why I can see the space between the rings and the disk at only 16x rather than the predicted 22x. But all of this should give you a pretty clear indication that about all you could hope to accomplish viewing Saturn with binoculars is just barely seeing the separation of the rings at the ansae.

Because of the tilt of the rings, even when they are open to us at maximum as they were last year, the visual separation between the rings and the disk in front of the disk is only 3.5 arcseconds, only half of what we see at the ansae. (Maximum tilt 30°. Sine 30° = 0.5. 7 arcseconds x sine 30° = 3.5 arcseconds.) If I can see the separation at the ansae at 16x and in front of the disk the separation appears only half as wide then I would need twice as much magnification, a minimum of 32x magnification to see the separation of the rings in front of the disk. Now that the tilt of the rings is getting more edge on, it would take even a little more magnification.

I can see 3 of the 4 stars in the Trapezium with my 16x70s. On rare occasion, I have split all 4 components of the Trapezium with my Obie Dlx 20x80s. The closest two are about 8" apart. I have also seen all four with the 20x80s masked down to 20x50.

You have plenty of aperture to see 8" doubles or see the 7" separation of the rings from the disk. Even a 60mm aperture would suffice. It's magnification you need to see it.

edz

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