Eyepieces

[Sanj Ara]

I recently bought an 8' Skywatcher Dobsonian. It came with 1.25' 10mm and 15mm eyepieces. What is the best eyepiece for viewing the moon, Jupiter and Saturn?

[romx]

The 10mm is the best for planets, for wider shots of the moon so you want the 15mm or for a closer view the 10mm, really I suggest something under 10mm for planets as they may appear quite small in the 10mm

[glynnlondon]

Your 10 mm ep will be the highest power so that will give you most magnification for the moon and planets.

The 10 mm tho is not of the highest quality so a lot of people will purchase a planetary eyepiece around the 8 mm range of better quality.

[Dave In Vermont]

We've heard from many people who have your telescope-model that. yes. the supplied 10mm eyepiece is of rather poor quality when compared with some of the others that are available. But I'll refrain from making suggestions of good eyepieces. Rather I'll explain roughly how this works in regard to what sort of views you can expect.

A good 8" Dob is an excellent telescope, and the Skywatcher's are among the best. Congratulations! And yes indeed, a high magnification is great for the planets and our Moon. But the high-power views through a telescope will give you a smaller view of the sky. Likewise a lower-power eyepiece will give a wider field-of view (FOV). And some objects in space are quite large and extended in size, so a low-power eyepiece will be best for viewing these. Nebulae are examples of some things that might be large. Your 8" Dob will allow you to see many, many things. And this is what the size, or aperture of the telescope determines - the number of objects you can see. This stays the same regardless of the power of an eyepiece. 8" aperture brings you dimmer objects that a 6" can't show you due the the brightness of these objects not being high enough to see. This is called magnitude. A higher number equals a dimmer object. A magnitude of 11 is for a dimmer object than a magnitude 10 object is. An 8" telescope can keep someone able to find and explore new objects every night for the rest of one's life!

About eyepieces (EP's): An eyepiece with a lower focal-length equals an EP that gives you a higher power. So the 10mm EP gives a higher power than the 25mm. To find the magnification any EP provides is found by dividing the telescope's Focal-Length (FL) by the FL of the eyepiece. Your 8" Dob has a focal-length of 1200mm. So:

1200mm / 10mm = 120X. Simple as that. The 25mm EP = 48X

I hope this helps you to understand how these things work!

Clear and dark skies -

Dave

[Sanj Ara]

Thanks for the great comments and explanations. Very helpful. 

[Timebandit]

Hi. Yes nice scope you have there so well done on choice. If you are looking to upgrade your high magnification eyepiece for planets and moon without spending big bucks then I suggest looking at the 8mm televue plossl which is a great little eyepiece in faster type scopes and gives very sharp views . 

[Linda]

You might also want to buy a 25mm eyepiece to get a wide view. Good for finding objects and for viewing wide clusters.

[Dave In Vermont]

Linda - I'm willing to bet the poster meant to type '25' rather than 15. These Dobs come with a 10mm & 25mm eyepieces. But you're right! And some good wide-fields as well.

All the best -

Dave

[Mak the Night]

For planetary/lunar viewing I'd aim for eyepieces which will give you 150x - 200x - 250x spread of magnifications. Investing in a decent 2x Barlow may be helpful. As an example, I use a Celestron 9mm X-Cel on my 130mm (900mm focal length) Newtonian combined with a 2.5x Barlow and sometimes with a 2x Barlow to give me 250x, 200x and if used without a Barlow 100x. In that way, one eyepiece more or less becomes three eyepieces.

[Sanj Ara]

Dave you are correct. I made a mistake. It's a 25mm plossl not 15mm as the post says. I will try to get the 8mm televue plossl as I think my 10mm eyepiece may not be the best. I'm guessing I would also need a moon filter. I read that dual filer is better than a single. Any suggestions on this point?

[Mak the Night]

7 minutes ago, Sanj Ara said:

Dave you are correct. I made a mistake. It's a 25mm plossl not 15mm as the post says. I will try to get the 8mm televue plossl as I think my 10mm eyepiece may not be the best. I'm guessing I would also need a moon filter. I read that dual filer is better than a single. Any suggestions on this point?

I'm one of the few people I know who really rate the 8mm TV Plossl. I'm not too keen on the rubber eyecup though and I usually roll it right down.

[Louis D]

52 minutes ago, Sanj Ara said:

I will try to get the 8mm televue plossl

Be aware that many folks don't like the TV 8mm plossl's short eye relief.

[Mak the Night]

32 minutes ago, Louis D said:

Be aware that many folks don't like the TV 8mm plossl's short eye relief.

Yeah, that's a good point, I keep forgetting many observers wear glasses. Although, at 6mm, I think it compares with similar eyepieces with the same focal length.

TeleVue 8mm Plossl

[glynnlondon]

1 hour ago, Sanj Ara said:

Dave you are correct. I made a mistake. It's a 25mm plossl not 15mm as the post says. I will try to get the 8mm televue plossl as I think my 10mm eyepiece may not be the best. I'm guessing I would also need a moon filter. I read that dual filer is better than a single. Any suggestions on this point?

I personally wouldn't bother with a moon filter. You can stop down your telescope by leaving the dust cap on the front and removing the smaller cap. Or some use sunglasses to cut down the glare.

[LukeSkywatcher]

8mm BST for planets. Good eye relief and pretty cheap.

[Sanj Ara]

Is the GSO 1.25 plossl 9mm a better choice?

[AlentejoSkies]

I'd also add that it's good to use what you have - almost whatever you have - for a while and develop a sensitivity to what you want to do next (although it's for sure also good to ask advice so that even if you take the next step quite quickly it will be a good one...)

[Mak the Night]

A 9mm or 7mm Celestron X-Cel would work. With a 200mm aperture a 0.9 (13%) Neutral Density filter would be good for the Moon. Baader make good filters, although the Baader Neodymium is my favourite Moon filter, if I use one.

[romx]

for a relatively cheap price  the vixen npl lenses are rather good visually I have a 8mm one and it does nice views of jupiter and saturn (when im lucky enough to have a chance to see saturn) and it brings some really decent detail of the moon although the planets are fairly small you can see some nice details especially in jupiter and some banding if the rings of saturn even in the heavily light polluted skies around me I am definitely planning a 6mm one of those

[Louis D]

4 hours ago, Mak the Night said:

A 9mm or 7mm Celestron X-Cel would work.

Be careful.  Those are Celestron X-Cel LX eyepieces.  The Celestron X-Cel line that preceded them were vilified in the online forums for their kidneybeaning and other faults.  Occasionally, newbies will buy well priced used X-Cel eyepieces thinking they are getting X-Cel LX eyepieces instead; then they complain about how poorly they perform compared the hype.  When they post a photo of the eyepiece, veteran observers immediately see the problem.

[Dave In Vermont]

40 minutes ago, Louis D said:

Be careful.  Those are Celestron X-Cel LX eyepieces.  The Celestron X-Cel line that preceded them were vilified in the online forums for their kidneybeaning and other faults.  Occasionally, newbies will buy well priced used X-Cel eyepieces thinking they are getting X-Cel LX eyepieces instead; then they complain about how poorly they perform compared the hype.  When they post a photo of the eyepiece, veteran observers immediately see the problem.

That is very much great information that it deserves repeating!

I had bought the 5mm X-Cel back when the first came out. I had never gotten around to testing it out in my menagerie of instruments when I read the reviews. They had won the prestigious "Worst Eyepiece Ever!" award! And this from the largest astro-forum of all. Oh lucky me!

It's still here, staring up at me from it's nest.

Great advice, Louis!

Dave

[Sanj Ara]

Based on this discussion one thing is clear. Figuring out which eyepiece to buy is freaking difficult. And experience seems to be the best guide. Since I'm light on that its great to be able to tap in to the collective experience of all of you. 

[Dave In Vermont]

Well thank you! That's what we do here - share knowledge back & forth.

Something to learn: An eyepiece that's great in one telescope may be horrible in another telescope. This usually applies to the different types of telescopes we all commonly use or see around, Newtonian reflectors, refractors, Cassegrains. From here we need to think about the different sub-groups that define a specific telescope's variety: Take refractors for an example of narrowing the criteria. Is the refractor a 'fast' refractor? We'll call the cut-off as F/7. So if someone has a fast-refractor, we can think this means their refractor is a fast refractor as they said it was an F/5. Now along comes someone else who says they have a 'slow' refractor as it is an F/10. So a variety of eyepiece may work well on a slow-refractor of F/10, while bringing on armegeddon when tried in an F/6 fast-refractor.

I'll let this soak in for tonight - lest we wander into the different varieties of eyepieces and their compositions of lens-configurations. I hope your medical-insurance covers nervous-breakdowns.....  

So Sayeth the Grim-Reaper -

Dave

[Mak the Night]

9 hours ago, Louis D said:

Be careful.  Those are Celestron X-Cel LX eyepieces.  The Celestron X-Cel line that preceded them were vilified in the online forums for their kidneybeaning and other faults.  Occasionally, newbies will buy well priced used X-Cel eyepieces thinking they are getting X-Cel LX eyepieces instead; then they complain about how poorly they perform compared the hype.  When they post a photo of the eyepiece, veteran observers immediately see the problem.

I believe the originals didn't have filter threads either. Luckily I never used one of them and I only know them by their dodgy reputation. It makes you wonder why Synta/Celestron didn't give them a totally new name. I've seen pictures of the original X-CEL and I'm pretty sure at least some of them had silver coloured draw tubes, probably aluminium, which distinguishes them somewhat. I'm new to the X-CEL LX, what's surprised me was how good they are for 59 quid! From what I can gather they are the same optically as the Meade 5000 series but I have no idea who the OEM is. No doubt Synta are being secretive about that.

I even like the twist-up eyecup, usually I'm not a great fan of eyecups under around a 30mm f/l, and the supplied bolt case is useful. It's rare I get so enthusiastic about something that doesn't have TeleVue or Baader written on it lol.

[Dave In Vermont]

Okay - if it's 'Show & Tell Time' - I'll play!

I went and dredged-up the Beast Itself - the Infamous Celestron 5mm X-Cel.

And it is a silver-tube and it's got filter-threads in it. So without further ado, here's it is in all it's glory:

 

 

 

So MTN - would you like to buy it from me?

E'gads!

Dave