Free Shipping On Many Items

The Telescope Authority
Since 1947

View Shopping Cart

Your Cart is Empty

TPO 2" Deluxe Dielectric Mirror Diagonal


- Read
  • Call for Availability

  • Extended Backorder

Add to Wishlist

Got questions? Click for live chat

  • 99% Reflectivity Dieletric Coatings
  • Maximizes Light Output
  • 2" to 1.25" adapter included
  • Comes with 2 inch to 1.25 inch Adapter

Product Details

  • The Third Planet Optics 2 inch dielectric mirror diagonal features 99% reflectivity, dielectric coatings to maximize light output of your telescope system. Our custom made diagonal uses a BK7 mirror polished to 10th wave accuracy or better for best possible image quality.

    The TPO 2 inch dielectric diagonal also features a CNC machined housing. This housing is designed to retain the optimal collimation of the mirror and assure the best optical performance. The CNC machined aluminum housing will provide outstanding results for years of use. This diagonal also includes brass compression rings on both diagonal and the included 2 inch to 1.25 inch adapter, assuring gentle treatment of your eyepieces. Some other brands use set screw locking mechanisms that can mar the barrel surface of your favorite eyepieces. Avoid scratches and gouges by using the OPT dielectric series diagonals. The OPT dielectric diagonal is threaded to accept 2 inch filters.

    Third Planet Optics dielectric diagonals provide outstanding performance with low prices to provide amateur astronomers with excellent value! OPT backs this diagonal with a full 2 year warranty against manufacturer defects. TPO Product Number: OS-D2DI

  • specifications

    Angle90 degree
    Diagonal Barrel Size2"
    Free ShippingYes
    Optical Coatings99% Dielectric
    Warranty2 Year Warranty
  • included items

    • 99% Reflectivity Dieletric Coatings
    • Maximizes Light Output
    • 2" to 1.25" adapter included
    • Comes with 2 inch to 1.25 inch Adapter

Product Reviews

Customer Reviews
4.3 Based on 6 Reviews
Write a Review Ask a Question
  • Reviews
  • Questions

Thank you for submitting a review!

Your input is very much appreciated. Share it with your friends so they can enjoy it too!

Filter Reviews:
    John G.
    New Zealand New Zealand
    TPO 2" Diagonal

    It appears to be a very well made piece of kit that does what it supposed to do. It has a quality feel to it which instills confidence in use. For the cost it would be hard to beat.

    Worst fitting diagonal in 30 years.

    This is the only diagonal I have ever owned that hang up while being inserted or removed from a visual back. It is also the only only where the eyepieces also hang up while being inserted or removed. This also occurs with the 1.25" adapter. I really don't like having to **** an eyepiece 3 or 4 times to get it out of a diagonal. Or, to have to **** the diagonal several time to get it out of the visual back. That is definitely not good. Additionally, the nose piece is way too long. Without a filter the diagonal sticks out approximately 1/th of an inch from the back of the visual back. With a filter it's a full half an inch. This is half way beyond the cut in where the clamp is supposed to fit to hold it in place. I can only guess what it would look like with a short visual back. The fix for filters appears to be to cut about 5/8" of the nose and rethread it for filters. However, it would still be about .5-1mm too wide on the nose piece and the same .5 to 1mm too small in the eyepiece holder. Consequently, this diagonal isn't one I can use as eventually it will either badly mak up both the 2" and 1.25" eyepice barrels and/or destroy the brass retaining ring. I currently have 3 diagonals and this is the only one I have problems with. It's the only one I have *ever* had such poor fitting problems with.

    Awesome Diagonal

    This has got to be one of the best diagonals out there at any price. I bought it to use with my 12 LX90 Schmidt Cassegrain and it's a Great piece of workmanship. I star tested my scope with it and was supprised at my scope and this diadonal, as I had perfect star diffraction patterns at 476x. Also the images are clear and bright with no edge blur, the diagonal is very, very well made with excellent fit and finish and as for the price, I think you would really have a hard time finding better quality at any price, but for $89.95, It's unheard of. I could go on and on and might as werll say a little more, I've had diagonals with the brass inserts that was so hard to get the eyepieces in and out I just wanted to throw them away, well this diagonal lets them slide in and out as smooth as glass. Ok, bottom line, if you want a really nice diagonal at a GREAT price this is it. Smallscope PS. You will also have a hard time finding any nicer folks to buy your astro equipment from than OPT, there're nice folks and there're shipping department is faster than anyplace I've used.

    Albuquerque T.
    Very Happy With This Great Diagonal

    During my transition to 2” eyepieces with my Celestron C11 SCT (F/10 I wanted a good quality, 2” diagonal with high reflectivity that didn’t cost me an arm and a leg. This diagonal fit those criteria perfectly. It has a high quality feel to it and my views were clearly improved over my existing 1.25” Celestron diagonal. I would highly recommend this diagonal to anyone. Note: If you’re an 10” or larger SCT owner and using long focal length eyepieces, make sure you don’t have standard 1.5” SCT threads anywhere in your light path as it will not allow the full light cone through to your eyepiece. I’m using this OPT diagonal in my SCT with a visual back adapter that accepts 2” accessories. (Astro-Physics sell 3.25”-to-2” adapters for Meade and Celestron scopes Clear Skies…

    Shawn E.
    Great for the $

    I own have owned a few 2 diagonals over the years including Tele Vue and AP diagonals. I picked this diagonal up, as the price was right and I had heard good things about it. Optically it is every bit as good as the best diagonals and mechanically is just a step below, but still well made. This is a wonderful diagonal for under $100.

    OPT 2 Deluxe Dielectric Mirror

    Pleasantly surprised by the above average quality for the price of this diagonal.