Eyepieces: 1.25", or 2" or those that do both?

[keefnet]

Hi. I just got my new 250PDS and Alt-EQ6 GT setup yesterday and only got the stock supplied 2" 28mm eyepiece. I'm travelling to the US in a couple of weeks and was looking to pick up a few additional eyepieces -- cost and expected quality led me to these;

Celestron X-Cel LX Series Eyepiece - 1.25-Inch 12mm 93424, or Celestron Ultima LX Series Telescope Eyepiece - 1-1/4 in - 2 in 13mm - 93368

then: Celestron Ultima LX Series Telescope Eyepiece - 2inch 22mm - 93375, or Celestron Ultima LX Series - 1-1/4 inch - 2 in 17mm 93369

Some are 1.25 and 2" compatible. Now I have teh scope I see how that fits but does the fact they are 1.25 compatible men they are less "light" visible than a proper 2" only EPA?

And, I don't seem to see a 2" Barlow lens, so assume that really, the 2" just means better eyepiece comfort.

Also more general, to complement the 28mm I got withteh scope, is the general consensus that a 13 and 17 or 22 would be a good addition to start with, or I was thinking should I try a 5 for maximum mag without using the barlow?.

Appreciate the advice as I have never had a scope before.

Also, feel free to see my galary pics of the unboxing and final setup (a few pics anyway).

[John]

The only advantage of the 2" size eyepieces is that they offer a wider field of view than the 1.25" size can as their barrels and optics are physically larger. The ones with the hybrid 1.25" - 2" barrels are actually 1.25" eyepieces but the option to use them in a 2" focuser is provided for convenience and security for the ones with larger bodies.

It's common to use 1.25" eyepieces for medium - high powers and a 2" or two for low power / wide angles, if your scope can take them.

[keefnet]

Thanks John - so the fact that Barlow's seem to be mostly, if not all, 1.25" is due to the fact they'll increase magnification normall used more so for planetary viewing so don't benefit from a 2" design.

I suppose a dual fit 1.25"/2" EP fitted to a Barlow wouldn't be any worse than a 1.25" EP, just maybe a little more comfortable - or am I really missing the fact that the lens part you look into would actually be the same size, justa wider mount/body?

I'm not also thinking of a coma lens -- wondered if that makes any difference being 1.25" and used with a dual capable EP?

[John]

If you mean coma corrector then these are usually wide enough to accommodate 1.25" or 2" eyepieces. They are only really in newtonian scopes of F/5 or faster. Many folks don't use one though.

You can get 2" barlows and they work with either size of eyepiece. 2" eyepieces and barlow lenses do have larger glass elements in them which contributes to why they cost and weigh more.

Things can get bulky when you combine large eyepieces with a 2" barlow. The picture below shows my 8mm Ethos eyepiece, which is a 1.25" eyepiece with a 1.25" - 2" barrel, in the smallest 2" barlow you can get, the Antares 1.6x. Together they have a focal length of 5mm which is the same as the two 1.25" eyepieces next to it:

[keefnet]

Thanks for comparison picture -- I see why some reviews of 2" EP's on Amazon.com say they are like a soda or beer can. As I have a f4.7 10" Newtonian, I'll probably invest the extra 20-30% in 2" EP's, at least a couple of them in the 13 to 22mm range (I'll see what my stock 28mm images are like before I decide on a potentially better quality 28 or 32mm), then probably stick with 1.25" for a 5mm.

[rwilkey]

Hi Keefnet, better to invest in eyepieces, I made the 'mistake' of buying a SW 2" Barlow when I bought my first 2" ep, but found that widefield low power ep's don't actually Barlow very well, as the eye relief is way out and the exit pupil is double the size, and impossible for the eye to take in, so it just doesn't work. I was using the 32mm PanaView with the Barlow. So consequently I have never used the 2" barlow in anger, although you can use it with 1.25" ep's, it is just too damn lumpy. So stick to ep's and learn by my mistake!

[Naemeth]

Thanks for comparison picture -- I see why some reviews of 2" EP's on Amazon.com say they are like a soda or beer can. As I have a f4.7 10" Newtonian, I'll probably invest the extra 20-30% in 2" EP's, at least a couple of them in the 13 to 22mm range (I'll see what my stock 28mm images are like before I decide on a potentially better quality 28 or 32mm), then probably stick with 1.25" for a 5mm.

Unfortunately, F/4.7 is very unforgiving of budget eyepieces, and also exhibits more coma than in F/5. Coma can be corrected of course, but it can be rather expensive for a good quality coma corrector.

As for 1.25" or 2", it's kind of a moot point, you'll use both. For high power eyepieces, you usually use 1.25" eyepieces, but with the Ethos range, even the higher power ones are 2" just to accommodate the field stop, and if you just go for 1.25" you will miss out on more widefield views (mind you, I personally wouldn't go above a 5mm exit pupil, or about an 25mm eyepiece). The TeleVue Plössls deliver good views (so I've read anyway) for a good price, so you could look at them. The ones you would want are all 1.25".

Generally, 0.965" = Cheap and low quality (or 0.968, can't remember which it is, and there are exceptions to this)

1.25" = Standard for most scopes, many eyepieces available for high and low power, reasonably cheap

2" = More expensive, a lot of larger scopes have the facility for both 1.25" and 2", and they are heavier

3" = More expensive again and a lot heavier, scopes don't often have a focuser for this

4" = Rare. See here for some examples

HTH .