A couple of links to online tools that are very useful when trying to select eyepieces. 1.) Televue's Eyepiece Calculator (http://www.televue.com/engine/TV3b_page.asp?id=212&plain=TRUE). Very useful when starting out with a new scope or expanding your current eyepiece collection. Naturally, it only lists Televue brand eyepieces, but the basic info still applies to other brands with similar focal lengths and similar apparent fields of view. Two approaches to consider when choosing eyepieces: Increase magnification in even increments (Example: 40x - 100x - 160x - 220x), or decrease the true field of view in even percentages ( Example: 4 degrees - 2 degrees - 1 degree - 0.5 degree). Red asterisks will appear on the chart when the exit pupil of the scope/eyepiece combination exceeds 7mm, or the magnification exceeds the calculated maximum based on the scope's aperture. Televue also recommends not to exceed 350x magnification, regardless of the scope's capabilities. 2.) Astronomy Tools (http://astronomy.tools/) A lot of good stuff here. The FOV calculator by itself is a great tool. After selecting a Messier or NGC object, selecting a telescope, and selecting an eyepiece, it calculates the focal ratio of the scope, the magnification, the true field of view, the exit pupil, and the Dawe's limit. When you click on "Add to View", it projects a circle on the star field showing the true field of view for the scope/eyepiece combination, and shows the relative size of the Messier or NGC object within the field. Great when trying to figure out which eyepiece will give you enough field if view to take in very large objects like M31, the Andromeda galaxy, or enough magnification to view a very small object, like the elliptical dwarf galaxy M32, which happens to be a companion galaxy to M31. Besides having an eyepiece mode, the FOV calculator also has a camera mode. This is useful to determine which celestial objects can be adequately framed by your scope/camera combo, and which objects are either too large or too small compared to the camera's field. Again, the camera's field and the relative size of the Messier/NGC object will be projected when you click "Add to View". And if you decide to try your hand at astrophotography, there's a CCD Suitability calculator that will help you find a camera that's a good match for your telescope's focal length by calculating the resolution, or how many arc-seconds of sky are covered by each individual pixel on the camera's CCD chip. Sky conditions and the use of a focal reducer/field flattener also figure into the results, so be sure to include them.