Once the telescope's computer has been initialized to the sky, any of over 4,000 targets can be selected from the onboard database by using the hand controller. Choose each target by scrolling through menus while reading object names and information from the controller's LCD readout. Large, softly backlit control buttons are easy to see and press, even when wearing gloves on cold nights, although I have found that the brightness of the LCD readout tends to drop off as the temperature approaches freezing. In practice, the NexStar 4GT's goto system works adequately provided it was properly initialized and has a fresh set of batteries. Although the motors are noisy when slewing from object to object, the selected target is usually within the field of the 25-mm eyepiece. Once in a while, however, the telescope will go into a "death slew," seemingly spinning around aimlessly. To bring the scope back to its senses, press one of the direction keys, then "Enter" to try again. Sometimes, this will happen when the batteries are running out of power, for which the NexStar 4GT has quite an appetite. A fresh set of batteries will be fully drained after only a night's worth of use. To save the expense of new batteries every clear night, buy the optional AC adapter or Celestron's Power Tank, which allows portable operation. Optically, the NexStar 4GT has its pros and cons. Images are rather dim due to the small aperture, although most that I have examined seem to give reasonably sharp views. The Moon and brighter planets certainly put on a good show. Jupiter shows two or more belts and Saturn's rings display Cassini's Division, although not as clearly as through a 4-inch refractor. Double stars, such as Castor in Gemini, are cleanly split. Like the Meade ETX telescopes, the NexStar 4GT has a built-in "flip mirror. " By turning a small knob, an internal mirror diverts light either up through the star diagonal into the eyepiece or directly through an opening where a camera body can be attached for photography. The NexStar's mounting, however, is really only suitable for short exposures of the Moon or terrestrial scenes. One reason why longer exposures are not recommended is the accuracy of the motor drive's tracking. While aiming precision is adequate, the telescope does not track the sky as accurately as some other telescopes, including the ETX. Even after the telescope has been initialized precisely, objects tend to drift out of the field of view, requiring users to press the direction buttons on the hand controller to keep up. Overall, I'd judge the Celestron NexStar 4GT a good second telescope for someone who is looking for a "grab and go" instrument for quick viewing sessions. Although slightly larger than the Meade ETX90EC, its small aperture still limits it to brighter objects only. If money permits, I would recommend the Celestron NexStar 5i or Meade ETX125EC, both of which have better optics and larger apertures. -Phil Harrington, author of Star Ware Pros: Compact, light weight design Goto computer control Ease of setup Cons: Small aperture Short battery life Poor tracking precision Noisy motors.

The smc PENTAX XF8. 5 and XF12 are standard unifocal eyepieces, offering a focal length of 8. 5mm and 12mm, and a magnification of 46 and 3.

The Relative Brightness Index (RBI) ranges from 9(10x) to 1(30x) and the Twilight Factor ranges from 17. 32(10x) to 30(30x). Interpupillary Distance (IPD) ranges from 60mm to 74mm and Eye Relief is approximately 8mm - 10mm.