Planet size

[BryansBelt]

Evening everyone,

So, I was able to find my first planet yesterday (Saturn) and it was AWESOME! I know Saturn is one of the easier objects to find, but I am in a light polluted area and barely was able to find it with the naked eye before zooming in. That brings me to my question. I have an Orion Spaceprobe 130ST. I have a 2x Barlow with a 25mm and 10mm EP. I was able to spot it with the 10mm and Barlow, but the size was still small. Is this because of the capability of my eps or my scope? If I remember reading correctly, the maximum magnification of my scope is calculated at aperture 5.1" x 60= ~300x. Is the correct? If so, I am only able to magnify an object 130x with my 2x Barlow and 10mm ep.

Hopefully this makes sense to someone. I was really excited to see Saturn and its rings, but I would really love to see it on an even larger scale.

Thanks for the help!

[Phil-lost!]

Take a look here, it was a big help to me when i got my scope. http://www.12dstring.me.uk/fovcalc.php

[John]

Planets generally do appear quite small in the eyepiece field of view, even at high power.

It's probably because we see all these images around, with big, enlarged image scales and details that we struggle to see visually. When we come to look through a scope we think "thats nice but smaller than I thought it would be".

You scope should be able to handle up to around 200x on Saturn, if the viewing conditions are stable. Even then the planet won't look huge but study it for a while and you will start to pick out more detail.

Even with my 300mm scope I generally only use 265x or maybe 318x on Saturn, the latter when conditions are good. I'd rather see a smaller but sharper and contrasty view than the blurred washed out view you get when you use more magnfication than the scope and conditions can stand.

[BryansBelt]

Thanks for the replies. That website is pretty handy. So with just a 25mm, 10mm, and 2x Barlow, what would you recommend for viewing objects larger? Another ep or a stronger Barlow?

[Tony H]

Take a look here, it was a big help to me when i got my scope. http://www.12dstring.me.uk/fovcalc.php

This, if accurate, should be required viewing for anyone seaking to buy their first scope.

Try the options your budget allows and have a look at what you can expect to see.

Great tool.

Thanks for the link.

[Phil-lost!]

I made the mistake of buying a 2.5mm eyepiece to go with my first scope because the instruction manual said that was the maximum it was capable of, yes it gave a big image but it was so blurred it looked like the scope was out of focus and its sat in a cupboard ever since. I found a better quality eyepiece made more difference, bst starguider in my case.

[BeanerSA]

Better viewing conditions, and repeated viewings, will achieve more than any expensive eyepiece.

[John]

Thanks for the replies. That website is pretty handy. So with just a 25mm, 10mm, and 2x Barlow, what would you recommend for viewing objects larger? Another ep or a stronger Barlow?

In all honesty, a larger scope.

You could try getting a 6mm eyepiece which, when used with the 2x barlow, will give you 216x magnification but you are pushing the scope and most likely the seeing conditions to their limits so the results may not be enitrely satisfactory.

A larger aperture scope (eg: 200mm) can handle higher magnifications with more ease due to it's larger light gathering area (the main mirror) and it's higher resolution limits (also due to the larger mirror).

Beyond 200mm the gains get smaller so my 300mm can't use 400x - 500x very effectively due to the limitations of our seeing conditions but it's "cruising" at 250x

[BryansBelt]

In all honesty, a larger scope.

You could try getting a 6mm eyepiece which, when used with the 2x barlow, will give you 216x magnification but you are pushing the scope and most likely the seeing conditions to their limits so the results may not be enitrely satisfactory.

A larger aperture scope (eg: 200mm) can handle higher magnifications with more ease due to it's larger light gathering area (the main mirror) and it's higher resolution limits (also due to the larger mirror).

Beyond 200mm the gains get smaller so my 300mm can't use 400x - 500x very effectively due to the limitations of our seeing conditions but it's "cruising" at 250x

That's what I was waiting for someone to say, as I figured it could be the limitations of my scope. I just bought this one as my first, so I will be keeping it around for a while.

Sent from my SM-G925V using Tapatalk

[Paul2015]

It's all good I'm fortunate to live in a dark place so can find Saturn as a bright 'star' to the SE at the moment and can just about see the rings with my 20mm EP with my celestron 70az refractor, the seeing and the poor quality 10mm EP just ruin it at 90x though

[ronin]

Very few objects are as big as anticipated and the claims on magnification are generally, well, magnified.

You have a 130 your magnification rule says diameter (ins) x60 and so 300x - something seems a bit wrong there, for whatever reason the guide here tends to be 2x dia (mm) so that is 260x. We are already somewhat different .

Now reading posts for some time rarely does anyone actually get to this "maximum", most are "disappointed" and the reality is that it is marketing hype.

On a 130mm scope you will get 150x and maybe 180x occasionally, I doubt you will get 200x at any time. Also if you want to try for 200x then expect to buy a selection of the top end eyepieces to find the one that works with the scope, each eyepiece likely being $400-500. Lets say $1500 before the right one appears.

Saturn is good at 125x and if you can get to 150x and still deliver a sharp image you are doing well.

The scope is f/5 and fortunately not one of the Bird-Jones designs, so a 5mm eyepiece will give 130x - an eyepiece alone will likely be sharper then barlow+eyepiece.

A 4mm eyepiece will give 162x and I suspect that will be the realistic maximum you will get. Not really aware of a common 4mm eyepiece. There were a couple but they have faded - maybe check the used market. The alternative being an 8mm and a 2x barlow. 8mm eyepieces come in the Celestron X-Cels, Astro-tech Paradigms and TV plossl ranges.

There is an Antares W70 eyepiece that is 4.3mm (I think) that would give 151x.

For Saturn you need a good image and contrast so check and make sure the scope is well collimated.

If after all this you still want to try for more then in the Astro-Tech Paradigms there is a 3.2mm eyepiece, that would deliver 203x if it worked on the scope - I would be a little doubtful. It's only $60 :grin:  afterall they are good and they look good with the purple anodised rings.

[brantuk]

Higher magnifications will work if you're scope is capable of it - but you need good conditions as well. When you magnify a planet or other object, you also magnify the atmosphere and all it's imperfections. So in England much over 200x and the view starts to get very grainy.

If you're high up in a desert though on a crystal clear night, you can go to 300x or 400x and more I've heard folks say. Here in the UK we also have the weather to deal with just to complicate matters - so 200x is rough average maximum in most scopes.

[Peter Drew]

Multiply the diameters of planets in seconds of arc by the magnification you are going to use and then compare that to the full Moon as seen with the naked eye (the Moon is around 1800 seconds of arc). This should show that the planets, as seen in the telescope, are larger than you think.