The TMB® 100 9 – named a Sky & Telescope Hot Product for 2010 – is a new and more affordable 9mm 100° field eyepiece designed for “picture window on space” high power solar system and deep space observing. It has dual 1.25” and 2” barrels that allow it to be used with any telescope accepting 1.25” or 2” eyepieces without any adapters needed. Its very wide field makes it particularly convenient for lunar, planetary, globular cluster, and smaller nebula observing with Dobsonians. It gives you twice as long to observe with a Dob before an object drifts out of the field and the scope has to be repositioned than the time available with orthos, Plössls, and similar narrower field eyepieces.
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Astronomy named the TMB 9mm 100° field eyepiece a Star Product for 2010, saying “the TMB 9mm 100° fits nearly all telescopes both large and small, making this one of the most versatile wide-field eyepieces sold today.”
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The 100° apparent field of this new 9mm TMB® eyepiece is nearly 50% larger in area than the field of 82° eyepieces. You could get a similar true field with a longer focal length (but narrower apparent field) eyepiece, but the 9mm TMB® 100 has the benefits of the higher power and darker sky backgrounds that are inherent in its shorter focal length. You can use the field of view calculator below to see just how much sky the 9mm TMB® 100 can reveal with your telescope.
There is a soft rolldown eyecup to shield your eye from ambient light (from a neighbor’s security light, for example) to improve your image contrast. This eyecup has been carefully sized to position your eye at the correct eyepoint to avoid vignetting of the image, unlike similar eyepieces with overly long eyecups. At a true usable eye relief of 12mm, The TMB® 100 9 would normally somewhat vignette the field of view for eyeglass wearers. However, since the 100° field is so wide that you can’t see the full field without having to move your head from side to side to take it all in anyway, vignetting in the conventional sense is not a problem.
Then why, you might ask, do you need a 100° field eyepiece if your eye can’t take in its full field? It’s what we call the “picture window on space” effect. Stand a few feet back from an ordinary window in your house and look out at the world. The window frame on either side cuts off your view of the world and you see only part of the landscape. That’s the view though a conventional eyepiece. The eyepiece field stop acts like a window frame and cuts off part of your view. Now stand a few feet back from a picture window and look out again. The window frame is outside your eye’s field of view and all you see is the outside world. That’s the view through the 100° field 9mm TMB® 100. The eyepiece simply seems to disappear and you are looking out at space through a picture window. Which would you prefer – the cramped view through an ordinary window, or the unobstructed view through a picture window? The sensibly-priced 9mm TMB® 100 gives you that wide screen “picture window” view of the heavens that most observers find simply enchanting.
The 9mm TMB® 100 has high contrast, comfortable eye relief, and full field sharpness – with well-controlled astigmatism, field curvature, geometric distortion, and lateral color. Its eight lens elements are fully-multicoated on all air-to-glass surfaces for high light transmission and contrast. The optical plan is shown in the feature image below. The eyepiece body is encased in a broad rubber grip ring that provides a sure and comfortable grip in cold weather or heavy dew conditions.
The 9mm TMB® 100 has both 1.25” and 2” barrels, allowing it to be used in both 1.25” and 2” focusers and star diagonals. The 1.25” barrel has a safety groove machined into it to engage your focuser thumbscrew. This will help prevent the eyepiece from falling should the thumbscrew accidentally loosen while observing. The 1.25" barrel is threaded to accept standard 1.25” neutral density, light pollution, and color filters. The separate 2” barrel threads onto the eyepiece body, around the 1.25” barrel, to allow use with 2” focusers and star diagonals without the need for an adapter. The 2” barrel is threaded to accept standard 2” neutral density, light pollution, and color filters. The two barrels are shown in the feature image below.
The affordable 9mm TMB® 100 is smaller and lighter than competitive 100° field eyepieces of similar focal length. It measures only 4.75” long with the rolldown eyecup extended, and 4.5” long with it rolled down. It weighs only 14.4 ounces when set up for 2” focuser use and 13.6 ounces in its 1.25” configuration. This makes balancing a Dobsonian less of an issue when using this TMB® eyepiece than it can be with competitive 100° field eyepieces. The eyepiece comes with dust caps for both ends of the eyepiece. A plastic bolt-type storage case is standard equipment. |
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