Subject: Warning for Electric Focuser Installations! Sent: Saturday, July 28, 2001 7:06:08 From: firstname.lastname@example.org (Clay Sherrod) A problem that is becoming unfortunately all too common with incoming Meade ETX telescopes for Supercharge service is a loose primary mirror that literally is rolling around freely within the optical tube assembly (OTA) upon arrival. In EVERY case (I have just seen my 12th one) this has been the result of improper installation of the optional Meade or JMI electric focuser. I highly recommend both of these focusers for observing ease and pleasure, but - through no fault of either manufacturer - careless or incomplete installation WILL result in releasing the expensive and delicate primary mirror from any tethering whatsoever. The results are disastrous. Here is the source of the problem: 1) When the Meade telescope is purchased new and unused, the focus rod is typically found tuned completely clockwise, which forces the rod all the way forward into the OTA, thereby securing the primary mirror firmly; known to most, this rod actually moves this mirror in and out from telescope's rear cell. 2) The focus rod is actually THREADED into (like a long bolt) the rear cell of the telescope through the small opening that you can see when looking behind the focus knob; it is this thread that actually HOLDS both the rod and subsequently the mirror itself into place! 3) If you take OFF the chrome focus knob (as you must do when installing the electric focuser) with the knob and rod turned completely clockwise (which pushes the mirror outward toward the front of the scope along the long baffle tube), chances are the rod will be COMPLETELY LOOSE FROM THE THREADED portion of the rear cell! This can allow the rod to easily slip into opening, become detached from the slot behind the primary mirror, and ultimately result in the mirror being totally unattached inside the telescope. If the telescope is turned downward (lens end down), the mirror WILL slip off the "sled" on the baffle tube and ultimately crash into the front baffle and lens, resulting in serious damage. 4) The end results can be: a) a damaged surface on the main mirror; b) a cracked or chipped mirror; c) damage to the secondary baffle tube; d) damage to the corrector plate; and more likely....e) all of the above. ---------------------------- HERE IS HOW TO ENSURE THAT YOU DO NOT INCORRECTLY INSTALL THE ELECTRIC FOCUSER: 1) Whether the scope is brand new or used, make sure that you have turned the focus knob COUNTERCLOCKWISE until at least 1/2" of the rod is visible between the rear of the OTA and the back flat back of the knob closest to the OTA; this will assure that the focus rod is properly engaged in the treaded portion of the rear cell; 2) Prior to removing the chrome focus knob, aim the OTA UPWARD at about 45 degrees as a precaution should the rod become disengaged, at least the main mirror will NOT slip down into the tube; 3) Carefully use a QUALITY Allen wrench (SIZE: 0.05") to gently break free the tiny set screw in the knob to release it from the shaft. Unfortunately the Allen wrench of this size which comes standard with the Meade electric focuser is NOT precision tooled and results frequently in stripping of the inside of the tiny screw such that it must be drilled out to remove. 4) Without delay, attach (using the same wrench) the large brass gear from the electric focuser package to the rod to insure that something will act as a retainer of the rod should it become disengaged from the threads. 5) Proceed according to instructions to attach the remaining focuser hardware. If you are considering adding the electric focuser, DO NOT take these warnings and instructions lightly! As much as I enjoy Supercharging a telescope, I certainly do not like to see them come in here with damaged focus rods, mirrors, or baffle tubes. If the rod for whatever reason BECOMES DETACHED and is "loose" in the OTA, NEVER SHIP THE TELESCOPE without contact me or Meade first. The mirror WILL BE loose in the OTA, and shipping will certainly result in damage as the mirror moves freely against every component within that tube. If this happens to you, feel free to contact me at email@example.com immediately for instructions on the proper precautions to ship. I urge owners with this problem to NOT facilitate repair themselves; this is NOT a home project if the mirror comes detached. P. Clay Sherrod Arkansas Sky Observatory
Subject: Re: Additional Warning on ETX Focuser Sent: Thursday, August 30, 2001 16:28:08 From: firstname.lastname@example.org (Clay Sherrod) Gary, you are absolutely correct and I am forwarding this onto Mike Weasner for inclusion in the ETX website. Thank you so much....Meade really should update this information as I am dealing with a LOT of damaged optics from this.... Thanks again - Clay Sherrod mweasner ----- Original Message ----- > Dr. Clay > > I read your warning at weasner's great site about carelessly > mounting the ETX electric focuser, including: > > As you suggest, the focus shaft should be turned > counterclockwise to expose perhaps a half inch of the > shaft BEFORE removing the knob. > > Note: This also applies to installing a Flex-Focus type device, > or anything else that will leave the end of the shaft "exposed". > > You correctly say: > 4) Without delay, attach (using the same wrench) the large brass gear > from the electric focuser package to the rod to insure that something > will act as a retainer of the rod should it become disengaged from the > threads. > > The instructions that come with the focuser: > say to put the gear on the shaft so that the gear is FLUSH with > the end of the focus shaft. That is WRONG. They use the term > "approximately flush with the rear of the shaft". > > INSTEAD: The gear must be slid FURTHER onto the shaft (as far > as it will go), until is UP AGAINST the same shoulder that the knob > was against. > > It is only the knob (or the gear) that keeps the > shaft from going too far clockwise and disconnecting from > the threads. > > Cheers, Gary
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