Planetary features using the GO 100mm f5.3?
Posted 23 November 2012 - 11:15 AM
1. resolving the rings of Saturn including Cassini's division
2. seeing the Great Red Spot on Jupiter
3. seeing the shadow cast on Jupiter's surface by any of its 4 moons
4. seeing the polar ice cap on Mars when Mars is farthest from the Earth, 10 degrees above the horizon, on a windy night (no, just kidding!!)
Garrett will, of course, gladly sell me more eyepieces. Should I spring for the 10mm Plossls (53x) or perhaps the 12.5mm (~40x?)? Or be satisfied looking at double stars at 23x?
Posted 23 November 2012 - 12:49 PM
Now, if you want to insist on using this instrument, you could consider getting an eyepiece giving 100x or more and using just one side of the binocular. But be aware that such instruments are not built to optical quality specifications anywhere near that of a basic telescope.
Posted 23 November 2012 - 01:10 PM
Just the same, depending on how well figured your binos are, some planetary viewing is possible. I've watched Jovian shadow transits, seen the GRS, the Cassini division rarely, Plato craterlets on Luna, but not much detail on Mars (not enough mag.). I have to admit, though, that my 80mm apo refractor shows more detail on any of these targets than the binos. Just sayin' that it can be done but there's a lot of CA at these higher mags, even in an f7.5 instrument.
If your BTs are the only optics you have out, it's worth a try at planets but it's better just to use the BTs up to maybe 75x on clusters, DSOs, etc. and of course the lower mags where the BTs excel. Serious planetary observation still is best with a telescope!
Posted 23 November 2012 - 02:53 PM
75x is really the maximum, however that is still pushing the envelope. 60x gives me the best image of superficial details of Jupiter and Saturn and that’s on a steady, night, Mars ? - no.
Tracking becomes problem at the higher mags. Yes, you will see some detail on the brighter planets but really I do not think the large BT 's were designed for that purpose. I have a long tube F.15/108mm refractor for planets. Yes, keep trying but at a later date getting, at a minimum, a ED80 mm on solid mount with a RA drive and let you see more. Even better still a ED100 which can be acquired relatively cheaply – they make very nice planetary scopes. Yes, you will be using one eye to observe but most optical instruments are a compromise.
Posted 23 November 2012 - 06:40 PM
Posted 24 November 2012 - 11:51 AM
Posted 24 November 2012 - 03:34 PM
I viewed Jupiter at 86X. At that magnification the chromatic aberration blurs detail quite badly, and the Oberwerk is an f/6. An f/5.3 achromat is only going to have worse CA.
Planets need high power, and not only will CA be excessive at high power, but collimation has to be absolutely perfect. You will be able to see the NEB and the SEB on Jupiter at lower power, but the power needed for the GRS will likely not be doable on an achromatic binocular.
Mars is a very poor sight in binoculars. The CA alone makes high power viewing very poor. And it's tough focusing a binocular on Mars.
Saturn: doesn't take much to see the rings, and you might detect the Cassini division at around 80X, but collimation will have to be perfect.