What type of eyepieces are standard in celestron astromaster 130

[jnp]

Hi,

I am thinking of getting some more eye pieces for my scope, but need to know how the existing 10mm and 20mm (terestial - but with prism removed) compare with Plossl, super plossl etc? What type of lens have I got and how many degree field of view etc.

thanks

John

[kniclander]

I would guess the e/ps you have are plossls with an apparent FOV of about 50degrees.

[John]

I've had a good look around the web and I can't find the actual eyepiece design noted anywhere. As kniclander says they are probably plossls with the 20mm having an additional lens to provide a "right way up" image (which you have removed I think).

They probably compare reasonably well with the normal budget plossls on sale so it's probably better to expand your set a little rather than replace them if thats what you were thinking.

John

[jnp]

I have dismantled the standard 10mm lens ( :? hopefully no damage done). It has two seperate lenses, a plano convex near the eye and a doublet (so 3 lenses in total). I thought plossl had 4 or more elements?

I'm on lookout for 2 ep. A 32mm or longer to help find dark objects (I hate the red dot finder thingy - see other thread), and a decent 5 or 6mm to planets.

My dilema is probably very common, eyepieces get exponentially more expensive and I'm not sure my meagre 4" mirror will do a good eyepice justice. I do realise that a cheap 5mm will just give me a fuzzy blob thought, I borrowed a very cheap 3x barlow form a £60 Lidl telescope - very poor!.

There are Celestron plossls on ebay with 52 deg FOV for £15 inc post that have "plossl" displayed (this is why I dont think mine are plossl). Has anyome been able to compare those with say the Meade 4000 series (£35 inc post)?

[John]

Sounds like the 10mm is a Kellner-type design (sometimes called Modified Achromats -MA's). A 32mm plossl would be a good idea - no point in going for anything longer in the 1.25" format as the 32mm will show all the sky that's possible in that format. I thought the Astromaster 130 had a 130mm F/5 mirror (5.12 inches aperture and 650mm focal length) ?.

You generally get what you pay for with eyepieces and most scopes will benefit from decent ones. If your current eyepieces are both MA's then I think a decent plossl will perform better.

If you can get them 2nd hand the Meade 4000's are pretty good for the £15-£20 or so each they cost.

John

[jnp]

Yes, the scope is quite "fast" at f/5 (4inch with 650 focal length).

Second hand stuff seems to go at silly proces on ebay, almost same prices as new.

Thanks for the comments

[John]

Second hand stuff seems to go at silly proces on ebay, almost same prices as new.

Try the SGL for sale section or this place:

http://www.astrobuysell.com/uk/

John

[jnp]

As 32mm is mentioned as the lowest strength eyepiece, will I actually see more sky with say a 66 degree FOV eyepiece than say a 52?

(Correction: my scope is 5 inch - i said 4 inch before. I dont want to confuse anyone)

[John]

As 32mm is mentioned as the lowest strength eyepiece, will I actually see more sky with say a 66 degree FOV eyepiece than say a 52?

(Correction: my scope is 5 inch - i said 4 inch before. I dont want to confuse anyone)

The 1.25 inch format eyepieces are limited (because of the barrel size) in how "wide" they can be. At the 32mm focal length that limit is 52 degrees, at 24mm it's 70 degrees and at 18mm it's 82 degrees and so on. At 40mm that limit is 43 degrees - and that looks rather narrow (like looking down a well) although the amount of sky seen is that same as a 32mm 52 degree eyepiece - just at lower magnification.

Low magnficiation views tend to be more affected by light pollution and look rather washed out. Appying a bit more magnification helps relieve this which is why people tend to like wide angle eyepieces - you see the same amount of sky, magnified more, with less light pollution effect so things like DSO's stand out a little better.

To answer your specific question, a 32mm 66 degree eyepiece would show more sky than a 52 degree one but they can't make it in the 1.25" format - so you would need to get a 2" eyepiece. In the 1.25" size 66 degree eyepieces are around 20mm in focal length.

I hope that makes some sense !.

John

[jnp]

That makes perfect sense. Eyepieces with high fov will be wasted in my setup due to barrel limit. Great explanation below.

Incidentally i have recently spolit myself using 15x70 binoculars which are a pleasure to use. Seem to have a huge apparent fov.

[dayglowill]

Hi John,

I've got an astromaster 130 myself. Although I've only used it a couple of times since I bought it, I would say that the the included eyepieces are adequate but pretty much every other eyepiece I own is better.

The Konus plossl 10mm and 17mm eyepieces that came with my Konus scopes are a little better than the ones with the Astromaster, not enough that I'd recommend buying them new as replacements though.

My Meade Series 4000 26mm and Celestron X-Cel 10mm both perform wonderfully with this scope and I would happily recommend either.

My feeling is that Astromaster is certainly capable of doing justice to "mid-price" eyepieces.

Will.