Meade_OTA

After several months of wait, in July 2003, I received my new OTA from Meade Instruments. This OTA is certainly the best I've purchased since I've used my first Meade SCT telescope. But for the first time, I only purchased a Meade OTA without the LX200 mount.

This OTA has all the new technologies made by Meade Instruments. The new accessories are a plus for my CCD nights. I've hesitated between a Celestron 11" Starbright carbon OTA and this Meade 12"UHTC OTA. I chose the Meade for 2 significant accessories for the success of my CCD pictures : the Meade UHTC coating, the Meade mirror lock for the primary mirror. The last accessory, the mirror lock, is to me the most important thing for the why of my choice against the Celestron OTA. With my old 12"LX200 classic, I've known several frustrations with the mirror flop. The ScopeStuff mirror lock have been a Great help.

My Meade 12" UHTC OTA has been directly selected, early in March, in the Meade Instruments factory on several OTAs and on my own criteria. The Meade technicians have ckecked the OTA with the criteria. My Meade OTA has been made in March 2003.

A Ronchi test has given some beautiful parallel lines. The star test was very good too. My OTA seems very good even if more tests would be necessary.

My 12" OTA is installed on the Losmandy DM12 dovetail plate. The weight of the Meade 12" UHTC OTA (without the DM12) is 40 lbs (18.1 Kg).

Mirror Coatings: my Meade 12" OTA is equipped with the Ultra-High Transmission Coatings group include primary and secondary mirrors coated with aluminum enhanced with a complex stack of multi-layer coatings of titanium dioxide (TiO2) and silicon dioxide (SiO2). The thickness of each coating layer controlled to within +/-1%. The result is an increase in mirror reflectivity across the entire visible spectrum; at the important hydrogen-alpha wavelength of 656nm. — the predominant wavelength of emission nebulae — reflectivity is increased from 89% to over 97%.

Correcting Lens Coatings: my Meade 12" OTA with the UHTC group include, in addition, an exotic and tightly-controlled series of coatings on both sides of the correcting lens or correcting plate, coatings which include multiple layers of aluminum oxide (Al2O3), titanium dioxide (TiO2), and magnesium fluoride (MgF2).

The UHTC logo is not visible in front of the correcting plate but on a stick under the OTA and on the Meade package.

On the following chart, we can see, at the several wavelength, the transmission of the UHTC group compared with the QE of my SBIG ST-10XME CCD camera. The UHTC Hα transmission is very good with the ST-10XME QE (83%). The OIII & SII emission lines have an excellent UHTC transmission and excellent ST-10XME QE too ( OIII = ~63%, SII = ~78%). I use these 3 emission lines for my CCD images.

Emission Line	Wavelength (nm.)	Transmission: UHTC Group (%)	ST-10XME QE (%)
Hα	656	88.46	83%
Hß	486	89.22	60%
Oxygen III	496	89.78	63%
Oxygen III	501	88.98	62%
Helium II	469	87.63	58%
Helium I	588	90.10	83%
Nitrogen II	655	88.50	84%
Nitrogen II	658	88.39	83%
Sulfer II	673	87.79	78%

The main accessory in the new Meade OTAs, is the Mirror lock for the primary mirror. I tested this accessory with success on several CCD pictures. It is very easy to use and I did not note focus variations with the mirror flop. But the use of the mirror lock changes the focus and we need use a Crayford focuser like a JMI NGF-S very accurate and solid. When the mirror is locked, the OTA focuser is locked too.