Celestron NexStar5 Frequently Asked Questions Date updated: 01/05/00 Note: This FAQ was created from the contributions of many individuals, some of whom submitted questions directly, others who provided the material that I then assembled, and some of whom have posted this information on public webpages they have created. In cases where the author submits the question and requests it, I have posted their address so that readers can contact them directly. When information is drawn from public webpages, a link to that webpage (and attribution) is included. Information culled from reading emails and newsgroup postings is not credited but the input is appreciated just as much as the attributed sources (thank you all in advance). If you have any questions, comments, or corrections, please send them to russbag@mail.com You can find the text version of this FAQ here: n5_faq.txt ------------------------------------------------------------------------ Contents Eyepiece/Magnification: Problems: * How to Determine Magnification * Why does my NexStar 5 sometimes (or Power) of the NexStar 5 (or slew uncontrollably ("runaway") any telescope)? * How to Determine True Field of View (FOV)? NexStar 5 Technology: * What is the latest firmware? What features change with each revision of the firmware? Can the firmware be upgraded by the user? Is there firmware in the handset? * What do the digits of my serial number mean? What is the relationship between the firmware in my scope and its serial number? * What is inside the NexStar 5? * What happens if you damage the NexStar 5 - can it be fixed? ------------------------------------------------------------------------ Eyepiece/Magnification Questions ------------------------------------------------------------------------ How to Determine Magnification (or Power) of the NexStar 5 (or any telescope)? [top] by George Greenfield (greenfield@proaxis.com) Magnification (or power) for a telescope is calculated by dividing the focal length of the telescope by the focal length of the lens being used. The focal length of the NexStar is 1250 mm. This will stay constant for all our calculations. What changes is the focal length of the lens. The focal length of each lens will be printed on its side. The NexStar comes with a 25 mm lens, so the magnification with this lens is 50x (1250/25=50). Selecting lenses with different focal lengths will change the magnification of the scope. The shorter the lens focal length of the lens the higher the magnification and visa-versa (the longer the focal length of the lens the smaller the magnification). Remember, only so much magnification is useful, however. On a "good seeing" night (dark, clear, transparent, calm…) magnifications of about 50 to 60 times the diameter of the aperture of the scope is the best most scopes will do. The NexStar with a 5 inch aperture will not usually provide useful views at much over 300x (5X60=300). The view will tend to be dark and not so clear. Many objects like open clusters, nebula, the Andromeda Galaxy, etc… are best viewed with lower magnification. The moon and the planets, when the seeing is good, are wonderful to view with higher magnification. Following is a table with various lenses and their respective magnifications with the NexStar. The table also includes magnifications using a Barlow - a device that effectively doubles the magnification of each lens. Telescope Lens Focal With 2x Focal Length Length Magnification Barlow 1250 4 313 625 1250 5 250 500 1250 6 208 417 1250 7 179 357 1250 8 156 313 1250 9 139 278 1250 10 125 250 1250 12 104 208 1250 15 83 167 1250 18 69 139 1250 20 63 125 1250 25 50 100 1250 30 42 83 1250 35 36 71 1250 40 31 63 ------------------------------------------------------------------------ Determining True Field of View (FOV) [top] by George Greenfield (greenfield@proaxis.com) An eyepiece’s apparent field of view is the angular diameter, expressed in degrees of the circle of light that the eye sees when looking through the lens when it is not attached to the telescope. The true field of view is the angle of the sky seen through the eyepiece when it is attached to the telescope. True field of view is approximately determined by the following formula: True Field of View (FOV) = Apparent field of Eyepiece / Magnification Where Magnification = Telescope Focal Length / Eyepiece Focal Length (see FAQ "How to Determine Magnification) The apparent field of the eyepiece is usually stated with the eyepiece literature and it varies from eyepiece to eyepiece and lens design to lens design. For example the 25mm Plossl eyepiece that comes with the NexStar 5 has an apparent field of view of 52 degrees. The magnification of the 25mm eyepiece with the NexStar is 50x. So the FOV of this eyepiece with the NexStar is: FOV = 52 / 50 FOV = 1.04 degrees (about twice the diameter of the moon) ------------------------------------------------------------------------ NexStar 5 Technology ------------------------------------------------------------------------ What is the latest firmware? What features change with each revision of the firmware? Can the firmware be upgraded by the user? Is there firmware in the handset? [top] Aaron Wallace has the definitive page on this subject at his site (http://www.koessel.com/nexstar/ under Software). I have reproduced it here: Internal Firmware For older NexStars, the firmware version was displayed on the hand controller when the NexStar was powered up for all the numbered versions below. However, this doesn't happen with newer units, or with units that have an upgraded hand controller. The version number, when displayed, consists of four numbers, separated by decimal points: 2.12.12.6. The four numbers are the version of the main EPROM, the ALT controller, the AZ microcontroller, and the hand controller, respectively. There have been two versions of the main EPROM--2 and 3. 3 adds the moon as a GOTO object, but only with hand controller .7 or later. Thus, people with 3.13.13.6 won't have the moon as a GOTO object until upgrading the hand controller. There have also been two versions each of the ALT and AZ microcontrollers: .12 and .13. It's not clear what .13 fixes, although it seems to address the runaway slewing problem. Some scopes have .12 ALT and .13 AZ microcontrollers (12.12.13.6). There have been several versions of the hand controller. Version .7 is needed (along with EPROM 3) for moon support; it may also address some European settings problems. Version .9 fixes the RS232 lockup problem. This version of the hand controller does not display version information on startup, which can be a problem if the hand controller is updated (for the RS232 fix) on a NexStar with older firmware in the base. Here are some versions that have been encountered: 2.12.12.6Initial release. Actually, works very well! 2.12.13.6Fixes "runaway slewing" problem. 3.13.13.6Moon is not a GOTO object. This seems to be a newer base shipped with an older hand controller. 3.13.13.7Adds moon as GOTO object. Resolves problems with European settings. Someone with an older version of the firmware who 2.x.x.9 upgrades hand controllers to fix the RS232 bug will not have the moon as a goto object, and may have the runaway slew problem. The latest known version. (Note: Hand controller no 3.13.13.9longer displays version number. The version information was determined by disassembly.) Let [Aaron] know if you encounter another version or discover how to determine the firmware version of the new "unnumbered" version. The firmware resides in two socketed EPROMS and three microcontrollers (two in the base, one in the hand controller). Apparently, these can be mixed and matched to a certain extent (see chart above). There is no way to update the firmware via software, and Celestron requires returning the base and/or the hand controller to update the firmware. Celestron doesn't seem to have settled on an upgrade policy for owners with older versions yet. I would imagine that the firmware would be upgraded under warranty if it contains a bona-fide bug. Also, it seems that when scopes are replaced under warranty, they are supplied with the latest firmware. ------------------------------------------------------------------------ What do the digits of my serial number mean? What is the relationship between the firmware in my scope and its serial number? [top] It has been reported that 60001 was the first NexStar 5, so count up from there. As to firmware vs. serial number, the trend is as you would expect: later scopes (larger serial numbers) have later firmware. However, this trend may have been messed up a bit by scopes being recycled by Celestron (e.g. replaced under warranty then the older serial number scope is updated/repaired and sent to someone else as a warranty replacement). At least some recycled scopes have the latest firmware. ------------------------------------------------------------------------ What is inside the NexStar 5? [top] There are at least 3 sources of information on this subject. Jordan Blessing took the covers off a NexStar 5 and posted the pictures and description on the web (http://home.att.net/~celestron/nexstar.htm). Engineers from Meade apparently took one apart and provided some technical details to Mike Weasner (http://www.weasner.com/etx/etx-nexstar-specs.html). Aaron Wallace has posted some detailed information on his site's Software page (http://www.koessel.com/nexstar/). The internal details from the Weasner site (not all of this data is from the Meade examination): Focuser: Micrometric, moving primary mirror. Focus knob/shaft mounted in dual race ball bearing assembly. Mount Design: Fork type, single tine, solid aluminum with plastic skin. Spur gear drive, metal gears Memory: 256 Kbytes EPROM containing 18,473 total object designations (over 100 text descriptions) Processors: Four processors, 2 - PIC17C44, 2 - 16C63 Battery: 8 AA internal (top loaded). Life: 5 hours (alkaline using demo mode). Power consumption: 176 mA (idle), 190 mA (tracking), 390 mA (1 motor slewing), 600 mA (2 motors slewing). ------------------------------------------------------------------------ What happens if you damage the NexStar 5 - can it be fixed? [top] A lot of you may be curious about what happens if a telescope is seriously damaged by toppling over at a star party or being dropped. We have only one data point on the N5 but it is a useful reference. An owner had the misfortune to have his N5 tumble out of its case and down a set of concrete steps. The damage to the scope was: broken corrector plate (the front lens of the scope), broken finder, and cosmetic damage to the tube and fork arm. Celestron indicated that they could repair the scope and return it to its original performance. He shipped the scope to Celestron. It took about a month to get it back. The cost to repair was $275 for the optical repairs and $100 to replace the cosmetically damaged tube and arm. Reported performance is like new. ------------------------------------------------------------------------ Problems ------------------------------------------------------------------------ Why does my NexStar 5 sometimes slew uncontrollably ("runaway") [top] This problem has been called uncontrolled slewing, runaway slewing, runaway OTA (Optical Tube Assembly). For the remainder of this article it will be called simply "runaway". Runaway's symptom is that the N5 is instructed by the hand controller, the N5 computer, or an external computer, to move in one or both axis and doesn't stop, at least, not before the user has tired of watching its slow gyrations and turns off the power. The facts on runaway: * Most often, runaway occurs in just one axis, rarely it occurs in both axis (quite an amusing sight when it does). * There is no evidence that runaway damages the scope. * The only way to stop it is to turn off the power switch (you can not restrain the motion of the scope without damaging it). This means that you lose your alignment settings. * It has been confirmed that both the keypad and RS-232 computer input become ineffective during runaway, as if the computer inside the N5 is "locked up", which it might be. * Runaway has been observed with fresh internal batteries, weak internal batteries, AC external power, and battery external power. * Runaway has been reported for nearly all revisions of the firmware (the latest firmware, 3.13.13.x) is so new that we have little data on it. Celestron's position to date (12/28/99) is that runaway occurs when the scope is powered by an external power source through the coaxial power jack (as indicated above, N5 owners have reported runaway when operating on a fresh set of internal batteries). Celestron says runaway occurs when a loose fit between the jack center pin and the plug causes minute electrical interruptions (spikes) which cause the computer to lose control of the drive motors. The correct response is to shut the scope off. To correct the loose fit, Celestron has advised owners to use a small screwdriver or penknife to gently spread the two halves of the coaxial power jack's center pin about 1 mm apart. This is to provide greater friction when the power plug is inserted in the jack. Some owners have had to do this operation repeatedly as regular use of the coaxial power jack pushes the pins back together (there is some concern in the owner community that repeated spreading of the pins will cause them to break). Some owners have placed a thin piece of rubber, cut from a rubber band for example, between the pins to keep them from squeezing back together. External voltage spikes are not the only source of runaway behavior - Aaron Wallace at http://www.koessel.com/nexstar/ (an excellent site) has written about another runaway problem and his text is reproduced here for your convenience (the original page is under the Problems link at the above site): Running in Circles Sometimes, the scope will go 'round and 'round counter-clockwise indefinitely. If this happens, you can press one of the arrow keys to stop the infinite slew, and re-GOTO the object, without the need to re-align the scope. It's not clear what the cause of this problem is, but it seems to be fixed in firmware version 2.12.13.6 and later. Note that these are two different runaway problems and with the exception of the very latest firmware (3.x.x.x - too new for trouble reports) owners have reported the type of runaway that can't be cleared with the hand controller with all versions of firmware. ------------------------------------------------------------------------ End of NexStar 5 FAQ comments: russbag@mail.com updated: 01/05/00