1.25 vs. 2 inch eyepieces - is there a difference?

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  • Member since
    May, 2005
1.25 vs. 2 inch eyepieces - is there a difference?
Posted by Anonymous on Thursday, June 22, 2006 9:33 AM
New to this hobby, but I am really enjoying it. I have the Orion 10XTi and I love it. Eventually I will want to buy more eyepieces (I have the 25mm and 10mm plossls that came with the scope), but I see that there are 1.25 inch and 2 inch eyepieces. Is there an inherent difference between these different sized eyepieces assuming they are similarly sized - for instance 32mm - or are they essentially the same? Thanks!
  • Member since
    January, 2004
Posted by tkerr on Thursday, June 22, 2006 1:55 PM
 aliberator wrote:
New to this hobby, but I am really enjoying it. I have the Orion 10XTi and I love it. Eventually I will want to buy more eyepieces (I have the 25mm and 10mm plossls that came with the scope), but I see that there are 1.25 inch and 2 inch eyepieces. Is there an inherent difference between these different sized eyepieces assuming they are similarly sized - for instance 32mm - or are they essentially the same? Thanks!


In simple layman terms there are a few differences other than the obvious 3/4"  larger diameter in the barrel size. Typically 2" Eyepieces are used for lower magnification and or wider field of view. A 2" barrel will allow for a wider Apparent Field Of View through the Eyepiece that a 1.25" wouldn't normally allow.  So if you had a 2" and 1.25" 32mm EP, the AFOV in the 2" would be greater, probably much greater.
There is another benefit to the 2" barrel that it also allows for larger lens elements to be used. In other words a larger eye lens so that even at higher magnifications / short focal lengths your not looking through a peep hole as you would in your standard 1.25" plossl. Even in a short focal length EP's you can be looking through an eye lens that is 1.25" in diameter. Another advantage to many of them is a more comfortable eye relief so you don't have to paste your eye to the EP.
And probably the most obviouse difference is the cost.

If you want a reasonably priced wide field eyepiece that works great in the XT10 Look at the Orion Stratus EP's. they work as both formats with a 68° AFOV. Nice comfortable eye relief and large eye lens. 
If you are looking to invest in something of even greater quality and a AFOV around 82°  the TeleVue Naglers are very nice and also very costly. Pentax makes a very nice top of the line high quality costly EP also.

Note: Too low and too wide in a fast Newtonian reflector may not be wise.


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Equipment: Orion XT10 Classic, Celestron C6 R-GT (CG5 GT mount), C80ED Canon EOS 350D, Canon EOS 50D, Meade DSI II Color CCD, Phillips SPC900NC

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