Celestron 20mm Erecting Eyepiece Help

[Stormflagflying]

Hi,

This is my first post to this group. I'm really looking forward to being part of this community as I take my first step into the stars ?
I was fortunate enough to receive a Celestron 130eq Telescope for Christmas (I have had to wait 57 year for my first Telescope but I now have one). The problem I have is that when I insert the 20mm erecting eyepiece and then look through it, the circle that you see (not sure of the correct name) is not full and looks like it is eclipsed at the top for about 40 percent of the circle. If I take it out of the Telescope and look through it I get a full circle and just to confuse matters even more if I insert the 10mm eyepiece into the Telescope then I do get a full circle to view the image on. So I'm not sure if the 20mm erecting lens is faulty?  I have raised the issue with Celestron Tech support but so far have had no response so I thought I would post here as I am keen to get out and get using it.
Appreciate you thoughts
Terry

[rwilkey]

Hi Terry, welcome to the Lounge.  Firstly, the 20mm 'erecting' eyepiece is mainly for daytime use.  The circumstances you describe sounds like what we call kidney-beaning, ie. you need to get your eye in the right position to get a full view, you might be viewing too far away or too close to the eyepiece, so that the view appears to wobble or dissappear altogether.  With the 10mm eyepiece you have to get your eye closer and this may explain the better view. 

Edited December 30, 2018 by rwilkey

[lenscap]

Hi, and welcome to SGL.

As said it may be kidney-beaning, or if  viewing with the scope way out of focus you may be seeing the shadow of the secondary mirror & spider.

If so , this should disappear when you focus on a distant object.

My first scope came with one of these Celestron erecting eyepieces and the biggest improvement to my viewing experience happened when I discarded it in favour of a second-hand 20mm generic Plossl eyepiece which cost me less than £15 because;

      - the erecting EP showed targets the opposite way up to my other eyepieces- confusing

      - the built in erecting prisms limit the apparent field of view to less than 30 degrees, versus about 50 degrees for a Plossl. Since you use a low power EP to get a larger FOV this rather defeats the object.

     - the light loss through the prism set makes the view noticeably dimmer than a normal eyepiece of that focal length.

Enjoy your Astro journey.

 

 

[Floater]

Welcome to SGL. The above extremely quick and erudite posts are testament to the fact that you’ve found a good place to be.

Have fun. ?

[Alan64]

51 minutes ago, Stormflagflying said:

Hi,

This is my first post to this group. I'm really looking forward to being part of this community as I take my first step into the stars ?
I was fortunate enough to receive a Celestron 130eq Telescope for Christmas (I have had to wait 57 year for my first Telescope but I now have one). The problem I have is that when I insert the 20mm erecting eyepiece and then look through it, the circle that you see (not sure of the correct name) is not full and looks like it is eclipsed at the top for about 40 percent of the circle. If I take it out of the Telescope and look through it I get a full circle and just to confuse matters even more if I insert the 10mm eyepiece into the Telescope then I do get a full circle to view the image on. So I'm not sure if the 20mm erecting lens is faulty?  I have raised the issue with Celestron Tech support but so far have had no response so I thought I would post here as I am keen to get out and get using it.
Appreciate you thoughts
Terry

Hello,

I'm afraid you won't get much use out of the 20mm.  The field-of-view will be quite narrow when compared to a 20mm Plossl.  Entry-level kits do not include the best of eyepieces and accessories, so you'll want to complement the experience with a Plossl or two, or three.  The included 10mm is most certainly usable, but it's not a Plossl, either.  Plossls are the barest minimum if you're wanting performance, and they're not expensive...

https://www.365astronomy.com/GSO-Super-Plossl-Eyepieces/

I would suggest a 32mm from that listing, and to help find your way around the sky.  That will serve as your lowest power(20x), for hunting, for observing the star-studded fields of the Milky Way, the Pleiades, and the galaxy in Andromeda. 

A 20mm Plossl will give you a power of 33x, and for closer look.  You can barlow the 20mm Plossl, for a simulated 10mm, with a 2x barlow...

https://www.365astronomy.com/GSO-2x-Barlow-2-Element-Achromatic-Barlow.html

...and for a power of 65x.  A 130mm aperture is capable of reaching even higher powers, however the manufacturer equipped that model with a spherical primary-mirror, instead of the accepted and expected parabolic.  A parabolic primary-mirror is the standard for f/5 Newtonians.  Why they chose to do that is somewhat unknown.  Therefore, it will be more difficult to reach, say, 150x, whilst at the same time enjoying sharp and pleasing views.   But you can certainly attempt 150x, and where the planets and other objects come into their own; for a closer look at the craters of the Moon, and for the splitting of double-stars.  The focal-length of a 130mm f/5 is rather short, at 650mm.  Let's see what it would take to reach 150x, when the time comes...

650mm ÷ 150x = roughly a 4mm eyepiece

In that event, you would need a 12mm Plossl and a 3x barlow, and for a simulated 4mm(163x)...

https://www.rothervalleyoptics.co.uk/antares-x3-achromat-fmc-barlow-lens-125.html

Or, if you already have a 2x barlow at the time, you can get either an 8mm or 9mm eyepiece.  With the 2x barlow and the 8mm, you would have a simulated 4mm(163x); with the 9mm, a simulated 4.5mm(144x).

Those are merely examples and suggestions.

Eyepieces are fully the other half of a telescope.  The two are one and inseparable.  You can't use one without the other, unless a camera takes the place of an eyepiece, as when imaging with a telescope.  The eyepieces and other accessories do not have to be acquired all at once, and they should be chosen carefully, as the eyes from individual to individual differ.  For example, if you wear prescription-eyeglasses, and find that you need to wear them at the eyepiece, then you may need eyepieces with longer eye-relief, and in order to see the full field-of-view.  Eye-relief is noted within the specs of the listings of most eyepieces; usually, 20mm of eye-relief is preferred by eyeglass-wearers.

Eyepieces, barlows and other accessories only have to be acquired once, as long as they're not lost or broken, and they can be used with any other telescope(s) that may be acquired in future.  I have over twelve telescopes, but only one of each focal-length of eyepiece, mostly.

You can motorise the RA-axis of the kit's mount, and with an economical 9V-battery(a lithium-type during the winter) motor-drive...

https://www.firstlightoptics.com/celestron-astromaster-series/motor-drive-celestron-astromaster-geq-93514.html

Such will allow you to track an object automatically, hands-free.  It will even cause an object to stand still there in the center of an eyepiece, and for as long as you'd like.

[Stormflagflying]

Thank you all so very much for your quick responses and the completeness of the information you have provided me with. I am very impressed (Plus I learnt a new term 'kidney-beaning' and lots of other stuff that I am going to have to look up :-). 
I suspect I will be a familiar poster for a while as I discover this new fascination. I'm looking forward to it.

Happy New Year to you all.

Terry

[Karan05]

On 31/12/2018 at 00:25, Alan64 said:

Hello,

I'm afraid you won't get much use out of the 20mm.  The field-of-view will be quite narrow when compared to a 20mm Plossl.  Entry-level kits do not include the best of eyepieces and accessories, so you'll want to complement the experience with a Plossl or two, or three.  The included 10mm is most certainly usable, but it's not a Plossl, either.  Plossls are the barest minimum if you're wanting performance, and they're not expensive...

https://www.365astronomy.com/GSO-Super-Plossl-Eyepieces/

I would suggest a 32mm from that listing, and to help find your way around the sky.  That will serve as your lowest power(20x), for hunting, for observing the star-studded fields of the Milky Way, the Pleiades, and the galaxy in Andromeda. 

A 20mm Plossl will give you a power of 33x, and for closer look.  You can barlow the 20mm Plossl, for a simulated 10mm, with a 2x barlow...

https://www.365astronomy.com/GSO-2x-Barlow-2-Element-Achromatic-Barlow.html

...and for a power of 65x.  A 130mm aperture is capable of reaching even higher powers, however the manufacturer equipped that model with a spherical primary-mirror, instead of the accepted and expected parabolic.  A parabolic primary-mirror is the standard for f/5 Newtonians.  Why they chose to do that is somewhat unknown.  Therefore, it will be more difficult to reach, say, 150x, whilst at the same time enjoying sharp and pleasing views.   But you can certainly attempt 150x, and where the planets and other objects come into their own; for a closer look at the craters of the Moon, and for the splitting of double-stars.  The focal-length of a 130mm f/5 is rather short, at 650mm.  Let's see what it would take to reach 150x, when the time comes...

650mm ÷ 150x = roughly a 4mm eyepiece

In that event, you would need a 12mm Plossl and a 3x barlow, and for a simulated 4mm(163x)...

https://www.rothervalleyoptics.co.uk/antares-x3-achromat-fmc-barlow-lens-125.html

Or, if you already have a 2x barlow at the time, you can get either an 8mm or 9mm eyepiece.  With the 2x barlow and the 8mm, you would have a simulated 4mm(163x); with the 9mm, a simulated 4.5mm(144x).

Those are merely examples and suggestions.

Eyepieces are fully the other half of a telescope.  The two are one and inseparable.  You can't use one without the other, unless a camera takes the place of an eyepiece, as when imaging with a telescope.  The eyepieces and other accessories do not have to be acquired all at once, and they should be chosen carefully, as the eyes from individual to individual differ.  For example, if you wear prescription-eyeglasses, and find that you need to wear them at the eyepiece, then you may need eyepieces with longer eye-relief, and in order to see the full field-of-view.  Eye-relief is noted within the specs of the listings of most eyepieces; usually, 20mm of eye-relief is preferred by eyeglass-wearers.

Eyepieces, barlows and other accessories only have to be acquired once, as long as they're not lost or broken, and they can be used with any other telescope(s) that may be acquired in future.  I have over twelve telescopes, but only one of each focal-length of eyepiece, mostly.

You can motorise the RA-axis of the kit's mount, and with an economical 9V-battery(a lithium-type during the winter) motor-drive...

https://www.firstlightoptics.com/celestron-astromaster-series/motor-drive-celestron-astromaster-geq-93514.html

Such will allow you to track an object automatically, hands-free.  It will even cause an object to stand still there in the center of an eyepiece, and for as long as you'd like.

I just bought GSO ED 3x Barlow but it makes 20mm quite hazy when i see jupiter or saturn... Do u think theres a problem with Barlow.. or something else... ...