| This click-stop Tele Vue zoom is fully multicoated, with an 8mm to 24mm focal length range and a soft rolldown rubber eyecup. It is set up to accept optional TeleVue Dioptrx astigmatism-correcting auxiliary lenses and with optional TeleVue digital camera adapters for “digiscoping" (afocal imaging using digital cameras). The Tele Vue zoom has click-stops at 8mm, 12mm, 16mm, and 24mm for quick changes to precise preset magnifications (for example if a pair of zooms are used in a binoviewer). It uses a lanthanum rare earth glass field lens for a long eye relief that’s suitable for virtually unvignetted eyeglass use. As with all zooms, except for the unique short focal length TeleVue Nagler zoom, the apparent field of view of this eyepiece decreases as the focal length increases. This results in a 20% narrower field of view at low powers and a 10% wider field at high powers than you can achieve with similar focal length single magnification eyepieces. This is just the reverse of what most people expect from eyepieces – which is a wider field at lower powers, where you’re usually observing larger objects that don’t need as much magnification to fit in the eyepiece field. Likewise, the usable eye relief changes as the focal length is changed, in this case decreasing in the middle focal lengths and increasing to a maximum at the focal length extremes. If these minor anomalies are not a problem for you, a zoom offers the convenient ability to precisely match the observing magnification to the seeing conditions, as well as offering a virtually infinite number of magnifications in a single reasonably-priced eyepiece. With a 2000mm focal length telescope, such as an 8" f/10 Schmidt-Cassegrain, the 40° apparent field at the longest 24mm focal length will result in an actual field of view that’s 0.48 degrees across at a magnification of 83x. The usable eye relief is 16mm at this focal length.
At an eyepiece focal length of 16mm, this zoom has a 42° apparent field (giving a 0.34° actual field at 125x with the same 8" f/10 Schmidt-Cassegrain) and 12mm of usable eye relief.
At an eyepiece focal length of 12mm, the apparent field is 45° (a 0.27° actual field at 167x with the same 8" f/10 Schmidt-Cassegrain). The eye relief is again 12mm.
At an 8mm eyepiece focal length, the zoom’s apparent field increases to 55° (a 0.22° actual field at 250x with the same 8" f/10 Schmidt-Cassegrain). The usable eye relief is 15mm at this focal length.
The TeleVue click-stop zoom includes the standard fold-down eyeguard and TeleVue dust covers, (as used on Radians, etc.) The eyecup slips off the zoom body to expose a groove around the top of the eyepiece for installing an optional TeleVue digiscoping adapter or TeleVue Dioptrx astigmatism-correcting auxiliary lens, as shown in the feature image below. There is a safety undercut on the chrome barrel that engages the thumbscrew of your star diagonal or eyepiece holder to keep the eyepiece from falling should the thumbscrew accidentally loosen during use. The wide knurled rubber grip ring provides a sure grip and easy adjustment of the magnification in cold weather, even when wearing gloves or mittens.
|
Printer friendly version
Email page link to a friend
Do you have a question about this product?
