PDA

View Full Version here: : Viewing Contrast Planets


steve000
09-05-2012, 08:55 PM
Hi Folks

What would be peoples opinion on the best contrast telescope for viewing planets.
I ask because Jupiter is basically just a big white disk with feint banding even at my 4mm through a Barlow.

Saturn looks nice but not great and mars is just a big white/orange disk.

When imaging with my webcam I get decent Jupiter but just a pale orange disk for mars, Saturn is OK but not great. (attached)
I have a 6" newt with a 2x Barlow and a spc880 flashed to a 900

Collimation has made little to no difference, in the attached pic it probably needs collimation as it has been a while

My thoughts are a little achromatic refractor or a little cassegrain either mak or schmidt

Thanks

Steve

janoskiss
09-05-2012, 09:31 PM
It sounds like you're pushing the magnification too far. You'll get the best contrast on planets with 1.5-2mm exit pupil, best detail (when seeing allows) with 1.0-1.5mm exit pupil, or so. Not knowing what our scope focal length / f-ratio is I cannot say what eyepiece will give you that, but I am sure that a 4mm in a barlow is way too much power. You should be using EPs between about 1 and 2x the f-ratio of your scope, e.g., in an f/5 you'd use a ~5mm for high power (detail), ~10mm for high contrast, ~7mm for best compromise between these. Well made and well set up Newtonians perform very well on planets.

Cheers :)

PS. Aperture rules.

steve000
10-05-2012, 05:54 AM
Hey thx for the reply, sorry I should have said its a 1200mm 6" scope. I often use 4mm and 6mm eyepieces as well as my 10mm but I find the target too small except Jupiter so I Barlow it up. Ignoring size even under the 6mm which is one of my favorites I still find the contrast is limiting.

KG8
11-05-2012, 04:50 AM
I aperture rules for sure, probably the best you'll get from a 6"
You could try a 3 step collomation, working right down to an in-focus adjustment with the Airy disk but at the end of day 6" is 6"

janoskiss
11-05-2012, 04:14 PM
Steve, it could be that your expectations are too high for that scope, or something about the way the scope is set up / made (that you might be able to improve on, e.g., blackening, baffling), quality of EPs - probably too many variables to know really what is going on just from what you're able to tell us here.

Best way to learn is to go to a star party look through lots of scopes to get an idea of what you can expect from various scopes, and get some experienced astronomers to look through yours and give you feedback.

Cheers.

steve000
14-05-2012, 08:33 AM
Hi All,

Thanks for the feed back. I thought it post 3 more images, this time from this weekend, seeing was good, I was out in the country so it was darker and I just colimated so it was spot on.

Results a little better, but I think I am at the limits of my scope :(

gb_astro
14-05-2012, 02:30 PM
Steve, with a newt you should get much better results with the object at centre of frame.
Why are your examples all near the edge?

gb.