1 1/4" or 2" EP?

[skygawker]

Hello to all on the forum from a rookie. Hope someone can help me. Is bigger better when it comes to barrel sizes? Does anybody know the pros and cons of both sizes? My 10" dob was supplied with 2 X 1 1/4" ep's but has a 2" focuser and an adapter so before I begin buying more ep's and some filters I'd like to know which is better. Any advice much appreciated.

[dannat]

2" ep's are generally preferred but the cost of them is a lot higher than most 1.25", you generally have to buy decent quality ep's to get good viewing, buying secondhand is often a good idea.

[rmcpb]

2" eyepieces are only necessary for wide angle low power eyepieces where the light cone is too big to fit through a 1.25" tube otherwise the smalleer tube diameter works just as well.

Some people try to use 2" exclusively as it saves fiddling with the adaptor when switching between a 2" and 1.25" eyepiece but I would consider this an expensive exercise for no gain.

Basically get good eyepieces in the style/size that works for you and forget the 2" v 1.25" issue. If it works then its right.

Keep looking up.

[JethroB76]

Two inches may allow for wide fields etc but have the draw back of often being heavy beasts which can be a pain for dob owners, especially top heavy scopes like the lightbridge.

I agree with Rob, just buy the eyepieces best suited to your needs (and budget). And yes, buy second hand where possible.

[csb]

Do 2" ep's give better eye relief?

I have just bought my first 2" (via Ice ads) to compare it to 1.25" (haven't used it yet). The lens is wider than in a 1.25" - Does this have any benefits?

[Starkler]

Nope, there is no direct relationship between the size of the eye lens and eye relief.

There are excellent eyepieces available in both 1.25 and 2 inch formats, just as there are poor eyepieces available in both formats.

As Rob stated, the reason for having the larger 2" barrel is to allow the bigger light cone necessary with low power wide field eyepieces.

In a few cases, there are 2" eyepieces with focal lengths not requiring to be 2" format for field size reasons, but rather mechanical reasons due to having large glass elements in the design, eg Televue ethos and the old Meade series 4000 UWA.

[skygawker]

Thanks guys. I may just get a 2" 32mm for those big open clusters and star rich parts of the milkyway. Good point about the dob tube's center of gravity though, even a relatively light-weight addition like a telrad throws out the balance a little. Will need to look at coming up with a counterweight system.http://www.iceinspace.com.au/forum/../vbiis/images/smilies/thumbsup.gif

[OneOfOne]

The biggest benefit for having a larger lens at the eye is that it is much easier to find in the dark! The lens of a Plossl from about 10mm or shorter gets pretty small and can be hard to find in the dark, whereas the lens in all of my Pentaxs are the same size...from 40mm down to 5mm, which are much easier to line up with your eye. Most wide angle designs tend to have the same size eye lens.

[asterisk]

Siebert make lighter 2" lenses which are less of a problem with dobs and lightbridges.

http://www.siebertoptics.com/