| This Astro-Tech 20mm Titan is a very wide 70° field medium power 1.25” eyepiece at a very economical price. The calculator below will let you see just how wide the field will be with your particular scope. For example, it will give you a wide 1.23° field and a bright 4.4mm exit pupil at 57x with a 10” f/4.5 Dobsonian. This will give you almost five minutes to observe an object as it drifts from one side of the eyepiece’s flat field to the other in such a scope. That’s plenty of time for multiple observers to look at the object or for you to absorb as much detail as possible before having to reposition the scope. With short focal length refractors, the 20mm Titan is a low power, very wide field eyepiece. With the 400mm focal length Astro-Tech AT-66, for example, it provides 20x, a 3.3mm exit pupil, and a huge 3.5° field of view that’s seven times as wide as the Moon. While it’s particularly well-suited for use with Dobsonian scopes and short focal length refractors, it can provide “picture window onto space” images with any telescope type. Even medium and long focal length telescopes provide impressive views. Use this 20mm Titan on an 8” f/10 catadioptric scope and you still get a 0.7° field at 100x, perfect for the Moon and globular clusters like M9, M13, and M22. The low price of this eyepiece also makes it a very affordable choice to buy in pairs for binoviewer. Its 11mm eye relief is quite reasonable for this focal length, although it can somewhat limit the field for eyeglass wearers. Since the Astro-Tech field is substantially wider to begin with than most other eyepieces in this price range, most eyeglass wearers won’t find the minor vignetting to be a drawback. Those who don’t wear glasses will see a huge field at only a fraction the cost of many more exotic wide field eyepiece designs.
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