Magnification needed for viewing outer planets

[ianrich77]

Hi All,

Was wanting to know what magnification I need to view the surface texture of planets like Jupiter? i.e. the cloud formations and the red spot etc...

I have a 130mm Newtonian with 650mm focal length.

Thank you,

Ian

[Roobi]

Exactly what i was wondering also, seems we have similar scopes. I have the astromaster 130eq 5.12" and 650mm focal length. i tried my 10mm ep with a 2x barlow lens which i believe should give me 130x mag, and i got a nice view of jupiter and it's moons, but it was still pretty small. I think the highest mag we can go to is 325x but apparently that will give us blurry images. Hopefully someone can help us out hey :)

[mental4astro]

Hi ianrich77, :welcome: to IIS!

There are two main things that govern the image quality seen. The first is the optics, and the second is the atmosphere.

First optics:

The rule of thumb for maximum magnification obtainable by a given diameter of apeture is:

50X per inch of apeture.

So for your 5" scope, this would be 250X. This is regardless of focal length! It is a factor completely governed by the size of your apeture. Your may push it to 60X per inch but then the quality of your optics needs to be really good. Here we deal with the real world.

Second atmosphere:

The majority of the time, the highest useable power will be between 100X and 150X. The reasons is turbuance in the atmosphere becomes much more readily visible the higher in power we go. The ocassions when the atmosphere allows for a good stable image at higher than this range diminishes the higher we go. Even so, at sea level, we are usually limited to 300X.

Don't feel short changed. In the last year, I've only had 2 occasions when I was able to use 360X on my 17.5" scope to view Jupiter for a good image, just. Theoretically I should be able to go to 875X. I've got no chance at sea level.

Also, the hotter the day, the worse the turbulance. Most stable viewing occurs in the early, early morning.

[ianrich77]

Thanx for the info,

My last question is that there are more things to look at than just the planets? Would my telescope be good at viewing close ups of the moon, spiral galaxies, closer planets, comets and such?

I checked my manual and it states that the maximum viewing magnification of my telescope is 330x without image blurring or distortion.

You also said that the atmosphere in relation to your altitude affects image quality?

Cheers :)

[mental4astro]

First altitude. Have you noticed how all the big professional scopes are not only located in remote areas, but these areas are also on the top of some pretty serious mountains? This is why Australia misses out on the really big optical telescopes as we don't have tall enough mountains. The higher you go, the less atmosphere, and the less turbulance you will be subjected to. The greatest elevation close to my home is two hours away for a height of 1000m. Though better than sea-level, I still don't escape turbulance for the vast majority of the year. You will see this distortion as a blurring of the image, where the object resists focusing, and when you hit on it, it blurrs again. The effect is the same as a mirage, where warm air being of different density, seems to move around a distant object.

I too have a 5" scope, a Celestron C5. The main difference between our scopes is that mine has a focal ratio of f/10, while yours is f/5. This makes yours able to see certain objects a little easier than in mine, like faint galaxies.

The main reason I mentioned my scope is that this way you can tell I won't be pulling your leg not only on what you can see, but how they will appear.

You will see beautiful deep sky objects like nebulae, open clusters, globuar clusters (some of which can be resolved in a 5" scope, meaning you will see its individual stars), and the brighter galaxies. What you won't see are the pretty colours you see in pictures, nor the arms of spiral galaxies. A five inch scope is just not big enough. You will see galaxies as faint ghostly shapes. Experience observing will be your best friend in identifying what you see. A dark-sky site will also be your best mate here too.

Planets: The Cassini division in Saturns rings will thrill, as too identifying Titan, its largest moon (see my post here with regards to this, though in here the post is for an 8" scope, you can do the same with your 5": http://www.iceinspace.com.au/forum/showpost.php?p=542286&postcount=10 ).

You will be able to make out a tiny disk with Uranus, plus its faint greenish colour (you can also see it in 7X50 binos, so a 5" scope is no problem). Neptune is also a sinch, though no disk, but its give-away characteristic being its blue colour is just too deep to be a star. With both of these you will need specialist maps to pin down. Sky and Telescope publishes these yearly.

Mars when close enough to us, will even show an icey-white polar cap!

Comets? No problem when they are around and bright enough, but not like in picture again. Moon? Boy, you are in for a treat. Not only craters, but valleyies, escarpments, ridges.

Your scope's manual states 330X without distortion! OK. Fine. Try it out. That is the best way to know.

There are a number of star charts available from the Stickies in the beginners forum. This is my favourite for just starting out: http://www.asahi-net.or.jp/~zs3t-tk/atlas/atlas.htm . Print it out and have a go.

[Robh]

Manufacturers of telescopes generally quote theoretical values for magnification and resolution as if in a vacuum. The specs can be used to compare the capabilities of various scopes but it can also give the impression the scopes are better than they really are. In practice, these values are rarely (or perhaps never) attainable. Alexander is right in saying that outside factors will essentially limit your scope's capabilities. Seeing will limit sharp viewing to below 250x most of the time, regardless of the size of your scope. Rarely will you be able to exceed this and actually gain clearer detail. Skyglow and transparency will also affect your limiting magnitude (the dimmest objects you can see).
However, having said this, there are many exciting and wonderful objects to observe with your scope!

Regards, Rob.