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Kendrick Newtonian Heaters
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We have Primary Mirror Heaters for 8" to 18" mirrors. They are very effective in the prevention of dew on Newtonian telescope optics, particularly for those who have Dobsonian telescopes with open truss tube designs.
There are many types of holders for Newtonian secondary mirrors on the market and we have attempted to address many of these and their various sizes with Standard Elliptical, Split and Wrap-around styles. Standard Elliptical Heaters are very effective at preventing and/or removing dew and frost from your secondary mirror. Our Split Heaters are designed to be used with larger secondary mirrors that are attached to mirror stalks (as opposed to being inside a secondary mirror holder). As the heaters are flexible, they can easily be placed around a mirror stalk. Wrap-around Heaters are an elegant solution to the problem of the dewing over of the exposed secondary mirror on Celestron, Meade, Orion, Sky Watcher and other dobsonian telescopes that have exposed secondary mirrors that are glued to a stalk.
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Primary Mirror Heater Elements |
We have primary mirror heaters for 8" to 18" mirrors. They are very effective in the prevention of dew on Newtonian telescope optics, particularly for those who have Dobsonian telescopes with open truss tube designs.
These are installed behind the mirror in between the mirror and the mirror cell and are held in place by putting a thin skim of silicone caulk (easily found at any hardware store) onto the heater and allowing the heater to dry to the back of the mirror. We do not recommend using heaters that would wrap around the outside of the optic as the thickness of Newtonian primary mirrors make this method ineffective due to the mirror mass. It is much better and much more effective to heat a primary mirror from behind.
The heaters require the use of a Dew Controller. Any Kendrick Controller model will work great. These heaters can be used with a temperature sensor on some models of our Elliptical and Primary mirror heaters, when used with our our DigiFire FX-PRO Controller (#2001-FX-PRO), and soon to be released Premier Controller (late summer 2020).
It is recommended that the Primary Mirror heaters be used at a low controller setting (ie: 15% to 20% in order to prevent optical distortion. The high wattage is built into the heaters to help clear dew or frost that is already on the optic. Once cleared reset your controller to a lower setting.
| Primary Mirror Heaters Electrical Specifications (all heaters are 12 volts) | |
| #2023 8" Primary Mirror Heater (heater diameter is 7.0"/178mm) | 0.8 Amps, 10 watts at 100% Controller setting. |
| #2024 10" Primary Mirror Heater (heater diameter is 9.1"/231mm) | 0.9 Amps, 11 watts at 100% Controller setting. |
| #2025 12" Primary Mirror Heater (heater diameter is 11.0"/279mm) | 1.6 amps, 20 watts at 100% Controller setting. |
| #2112 14" Primary Mirror Heater (heater diameter is 12.25"/311mm) | 1.6 amps, 20 watts at 100% Controller setting. |
| #2026 16" Primary Mirror Heater (heater diameter is 15.1"/383mm) | 4.75 amps, 60 watts at 100% Controller setting. |
Secondary Mirror Heater Elements | |||||
 Standard Elipticle heater |
 Split heater |
 Wrap-around heater |
Our Standard Elliptical heaters fit behind the secondary mirror and work best in Newtonian telescopes that have the removable type of secondary mirror housing.
The Split heater is also meant to be attached to the back of a secondary mirror but is to be used with larger secondary mirrors that are attached to mirror stalks. As the heater is flexible, it can easily be placed around the mirror stalk and then the heater is glued to the back of the mirror.
The Wrap-around heaters can be used with secondary mirrors that are attached to stalks* or can be wrapped around the outside of a mirror holder**.
*Some stalks connect to the secondary mirror using double sided foam tape. This tape will insulate the stalk from the mirror, making it difficult for the heater to do its' job.
**Using a Wrap-arpound heater on a typical secondary mirror holder will increase the size of the secondary mirror obstruction but it will be very effective. If your secondary mirror is larger than 1.83" in width, we recommend using the Standard Elliptical heaters.
Which one fits my scope?You will need to study how your secondary mirror assembly is constructed and take some measurements. As much as we would like to have one of every telescope in our shop, well, we can't do that. Manufactureres also don't share CAD drawings or even dimensions. Here are some basic guidelines to steer you in the right direction. NOTE: Heaters CANNOT be trimmed to fit (it will sever the heating element)!
Guide to choosing the right secondard heater We make several styles of secondary mirror heaters. Ideally, a heater that is able to make direct contact with the back-side of the mirror works best with lower power consumption:
- Elliptical heaters work for models that have the mirror sitting inside a hollow tube. They are usually stuffed with synthetic wool as the method of keeping the mirror (and an Elliptical heater) in place.
- "Split" heaters work for mirrors that are glued to a "stalk" and have the back-side of the mirror exposed around the perimeter.
- Wrap-Around is for those mirrors that have no means to affix a heater in direct contact with the back-side of the mirror. These wrap-around the "stalk" and in turn transfer heat to the mirror. They work quite well. Generally, set the Dew Contoller a bit higher as the heat does need to travel to where the mirror is attached.
More information on these various heaters can be found below.
Standard Elliptical Secondary Mirror Heaters |
These heaters are very effective at preventing and/or removing dew and frost from your secondary mirror. Using your Kendrick controller, you may turn the power up high to quickly clear the optics of moisture if they are dewed or frosted over or you may use a very low power setting to keep the optic barely above air temperature and prevent the formation of dew or frost.
These heaters work best in Newtonian telescopes that have the removable type of secondary mirror housing pictured here. They can also be used with secondary mirrors that are attached to stalks. To use them in this situation, the mirror will need to be removed from the stalk, the heater glued to the back of the mirror and the mirror (with the heater) glued back onto the stalk. If you do this, be careful that the mirror is firmly attached to the stalk again as you will not want it falling off onto your primary mirror!
Installation Sheet Instructions for S2, S3, S4 Heaters (PDF)
| FITTING DIMENSIONS | |
| Diagonal Mirror Heaters Fitting Specs | |
| #2016 S2 | Fits minor axis of 1.83" to 2.14". (Heater dimensions: 1.75" x 2.625" or 45mm x 70mm) |
| #2017 S3 | Fits minor axis of 2.60" to 3.50". (Heater dimensions: 2.5" x 3.625" or 63mm x 90mm) |
| #2018 S4 | Fits minor axis of 4.00" and up. (Heater dimensions: 3.75" x 5.5" or 95mm x 140mm) |
| HEATER SPECIFICATIONS: | |
| Diagonal Mirror Heaters, (All are 12 volts) | |
| #2016 S2 | 0.16 amps, 2 watts at 100% Controller setting. |
| #2017 S3 | 0.25 amps, 3 watts at 100% Controller setting. |
| #2018 S4 | 0.25 amps, 3 watts at 100% Controller setting. |
Split Secondary Mirror Heater |
Our Split heaters are designed to be used with larger secondary mirrors that are attached to mirror stalks (as opposed to being inside a secondary mirror holder). As the heaters are flexible, they can easily be placed around a mirror stalk. The heater is glued (glue not supplied) to the back of the mirror.
These heaters have plenty of power to clear a fogged over secondary when set to high power. Under normal operation, they should be run at 30% to 50% controller setting, depending on conditions.
To be effective to its full potential, it will need to be covered with foam or some kind of insulating material so that the heat is directed into the glass and not the atmosphere. A self adhesive, neoprene insulator is provided with the 2029-M, 2029-XM, 2029-L and 2019-XL heaters.
Kendrick 2029-M Split Ring Secondary Mirror Heater Installation Sheet (PDF)
Specifications (note: All electrical specs stated at 100% controller setting):
| 2029-M Wire length: 610 mm (24") Connector: RCA plug Wattage: 5.5 watts Center hole dimensions: 37 mm x 51.5 mm Minor axis dimension: 67 mm Major axis dimension: 96 mm |
R200SS Wire length: 380 mm (15") Connector: RCA plug Wattage: 2 watts Center hole dimensions: 50 mm x 72 mm Minor axis dimension: 71 mm Major axis dimension: 100 mm |
2029-XM Wire length: 610 mm (24") Connector: RCA plug Wattage: 7 watts Center hole dimensions: 45 mm x 64 mm Minor axis dimension: 80 mm Major axis dimension: 110 mm |
2029-L Wire length: 610 mm (24") Connector: RCA plug Wattage: 8 watts Center hole dimensions: 45 mm x 66 mm Minor axis dimension: 85 mm Major axis dimension: 116 mm |
2029-XL Wire length: 610 mm (24") Connector: RCA plug Wattage: 8 watts Center hole dimensions: 81 mm x 112 mm Minor axis dimension: 108 mm Major axis dimension: 148 mm |
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Wrap-around Secondary Mirror Heater |
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These heaters are an elegant solution to the problem of the dewing over of the exposed secondary mirror on Celestron, Meade, Orion, Sky Watcher and other dobsonian telescopes that have exposed secondary mirrors that are glued to a stalk.They will effectively control and prevent dew on the exposed secondary mirror.
This heater is a formed, flexible heater that wraps around the stalk of the secondary mirror holder. As there is no way to put a heater behind these types of secondary mirrors, this heater must be wrapped around the stalk. The heater then heats the stalk, which in turn heats the secondary mirror.
As the heater needs to be secured against the stalk in order to keep it in place you must use the elastic band (included) or electrical tape (not included) to do this. We are occassionally asked if these heaters will affect the glue that holds the mirror to the stalk. The answer is NO, they will not. These heaters do not get anywhere near warm enough to do that. They apply a gentle warmth that is enough to keep the dew and frost off your secondary mirror and that is all.
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The heater wires can be taped down against one of the spider vanes (we recommend black electrical tape for this) and the heater wires terminate in a male RCA connector.
We include a neoprene wrap-around insulator with each heater. This greatly enhances the performance of these heaters as it prevents the warmth generated by the heater from dissipating into the atmosphere. The insulator will need to secured in place with tape (we recommend black electrical tape for this) or an elastic band.|
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There are several ways to route the wires accross the Spider Vanes. You can use the "quick connectors" and wire lead or a thin, adhesive backed, foil "conductor" (soldering required). The kit includes a 48" RCA Extension Cord and RCA "coupler".
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| HEATER ELECTRICAL SPECIFICATIONS: | |
| Wrap-Around Diagonal Mirror Heaters, (All are 12 volts) | |
| #2028-S | .33 amps, 4 watts at 100% controller setting. |
| #2028 | .8 amps., 10 watts at 100% controller setting. |
The wattage fairly high for a heater of this type but this is necessary if you ever need to clear your secondary of dew that has already formed. With your Kendrick controller you can reduce the ceuurent draw of these heaters to very little. Our recommended controller setting for these heaters is 10% to 20%. Your observing environment will determine what setting you must use.
2028 Wrap-Around Diagonal Mirror Heater Installation Sheet (PDF)
| SKU | Description | Price | |
| 2028-S | Wrap-around Secondary Mirror Heater for mirror on 1.25 inch stalk | CAN $78.00 | |
| 2028 | Wrap-around Secondary Mirror Heater for mirror on 2 inch stalk | CAN $102.00 |
Dewguard Temperature Sensing Secondary Mirror Heaters |
Discontinued
The Dew-Guard Temperature Sensing heaters (DG1, DG2 and DG3) have been out of production since 2012. Not to worry, there are still many options for keeping your seconday mirror dew & frost free!
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Suite 104, 2775 Dundas St. West, Toronto, ON M6P 1Y4 Phone 416 762 7946 Fax 416 762 2765 |
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