which eyepieces?

[alnab01]

Hi all

I have my first beginner scope - Celestron Astromaster 130EQ 650mm focal length. I am interested in observing the planets. I dont expect to see them in crisp, clear detail but obviously want to get the best observations possible. I currently have the 20mm and 10mm eyepieces supplied with the scope as well as the 15mm and 6mm and 2x barlow from the accessory kit.

Can anyone tell me what i should be looking through to observe the planets or whether what i have is sufficent for the capability of my scope.

thanks

Alan

[miguel87]

With those eyepieces you seem to have all the magnifications that you could need to observe planets. If you want better views you would need to upgrade maybe in the 100x to 200x magnifaction range. My first upgrade was to vixen npl plossls, 45 quid each and think and a significant improvement. It really depends exactly what type of observing you want to do and where you are going ti do it.

Mike

[alnab01]

what do you mean 100 - 200 magnification range. Sorry if this seems silly. I am completely new to all of this.

Alan

[alnab01]

sorry to double post but meant to say that for now i am looking at observing the planets and moon. I live in the countryside so ideal for observing when the weather suits. Would a 4mm work on this scope?

Alan

[Ricochet]

Magnification is the focal length of the scope / focal length of the eyepiece. If you were to use a 4mm eyepiece then you would have a magnification of 650/4 = 162.5X. Alternatively, you could use an 8mm eyepiece and your 2X barlow to get the same result.

I would always advise new users to consider the BST Starguider range as an upgrade on the eyepieces supplied with a telescope.

[wookie1965]

Have a read of these they  will help, depending on how much you have to spend is another thing to think about. There are plenty of eyepieces out there with a range from £50 to hundreds then you have the second hand market (astro buy and sell ) but saying that have a read through these two posts and any other questions just ask.

http://stargazerslounge.com/topic/43171-eyepieces-the-very-least-you-need/

http://www.swindonstargazers.com/beginners/eyepieces.htm

[YKSE]

Alan,

Your eyepieces and barlow cover all the needs for Moon and planetary observing, and many DSO too.

Using 6mm together with the 2x barlow will need good seeing conditions.

Magnification is dividing telescope's focal length with eyepiece's focal length, so the 6mm in your scope gives 650/6=108 x magnificaion, 6mm with the 2x barlow gives 216x.

[miguel87]

Basically you dont have anything missing. It just depends if you want to upgrade the quality of your views by buying more expensive replacements for your current eyepieces.

So your question of which eyepiece to buy depends on your favourite amount of 'zoom'. If you like hiw big the planets look in your 6mm then upgrade to a better quality eyepiece that is roughly 5-7mm in focal length.

Wide angle views arent particularly relevant to planetary observing. Do you wear glasses? Longer eye relief might make a more comfortable viewing experience. If you want the planet to look sharper you need higher quality lenses which badically means more expensive. Any eyepiece upgrades are also limited by the scope but your celestron is a decent bit of kit.

[miguel87]

I quick additional very important comment. Regardless of your quality of eyepieces, images will always get grainier/wobblier/blurrier/less crisp the more you zoom in on planets. In my personal experience with my 8 inch scope in semi rural south wales, more than 200x magnification is rarely useful.

[ronin]

You have a 130/650 scope, so as you say f/5.

Owing to the numbers a 5mm eyepiece will give 130x magnification - nice easy thing to remember if eyepiece = f number, then mag = diameter.

For Jupiter you do not actually need a great deal of magnification so lets say around the 80x area.

As Mag = Fs/Fe you get that the eyepiece needs to be around 650/80 ~ 8mm. So an 8mm eyepiece should show Jupiter pretty good.

Saturn is smaller, and my experience is that 120-130 was good on that (the time I looked the scope delivered 125x)

As 125x is very close to thje bit at the top you will need a 5mm to deliver 130x.

A 6mm will give 108x - maybe OK.

It seems to be that "5" is the turning point for scopes and eyepieces.

Faster then f/5 and you re looking at more costly eyepieces, shorter the 5mm and again you need a good eyepiece.

So your f/5 with a 5mm eyepiece is to my thinking a case where the two may work together or they may not. Simply there is variation in mirrors and eyepieces and occasionally there can just be a mismatch where the specific items dislike each other.

For a 5mm I think you are looking at something like the BST Starguider, they do an 8mm also that is generally well regarded. So if you have £100 to buy with then the 8mm and 5mm are good options. At the 6mm length is the William Optics SPL 6mm, which again gets good reports, but WO SPL's cost more. There are the Celestron X-Cel-LX's also.