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Home > Diagonals & Erecting Prisms > Altair Dielectric Diagonal 99% Reflective 2" Push-fit for refractor telescope

Altair Dielectric Diagonal 99% Reflective 2" Push-fit for refractor telescope

Altair Dielectric Diagonal 99% Reflective 2" Push-fit for refractor telescope
Price: £69.99
Incl. VAT 20% ( £11.67 )
Product code: DIAG-2IN
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The Altair-EX Dielectric Diagonal is precision CNC machined with an extremely reflective, accurate and smooth mirror surface for maximum image contrast. Recommended to do justice to telescopes with good quality optics.
The multi-layer silver dielectric coatings reflect so much light, it's difficult to see the actual mirror surface when looking into a newly purchased diagonal. Dielectric coatings are more durable than aluminium ones because they do not oxidize, and are extremely scratch resistant, therefore easier to clean. This diagonal is the push-fit version which will fit telescopes with a 2" push fit aperture in the focuser. A "SCT" version is also available for customers with a Meade or Celestron Schmidt Cassegrain, which attaches directly using the standard "SCT" thread on the rear of the telescope.
The 2" barrel is threaded for filters, and it has an internal blackened thread to stop stray light reflection, increasing image contrast. A precision machined low profile 1.25 to 2" eyepiece adapter is included. Both the 1.25" adapter and 2" rear aperture have brass compression rings, which will not mar your eyepiece barrels. The low profile 2-1.25" adapter has a corresponding slot machined into the diagonal body to lower it even further. This achieves as much in-focus possible for Cassegrain users, who would like the focal length of their telescope to stay as close to design parameters as possible.
The Diagonal comes with a durable hard presentation box with protective foam insert, and two plastic end caps.
Cleaning instructions: 
Dust will enter the diagonal after opening it, and during normal use. This is inevitable and a little dust will have no effect on image quality. As a general guide, the product should be cleaned only when it gets very dusty usually once per a year or two. It is important to note you can use a diagonal for years with dust on it and it will not noticeably degrade the image. We have found that sometimes the translucent dust cap on the 1.25" end of the diagonal is so tight fitting, that the edge of the barrel can scrape the plastic off the inside of the dust cap, which can end up inside the diagonal the first few times you use it. If this is the case, you can just blow the dust off using a photographic blower (squeeze bulb type) which is quite handy to have around for eyepieces and suchlike, and it's no big problem. For stubborn dust and moisture spots from condensation, gently wipe the mirror with optical cleaning fluid and a cotton wool bud. There is no need to flood the diagonal with fluid, only a little is required. Tescos sell cheap eyeglass cleaning fluid which some customers have recommended works well (use the coated-lens type), or you can use Baader fluid which is designed for optics. Most camera shops also stock optical cleaning fluid for coated lenses. Isopropyl alcohol can also be used (90% or more concentration).

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Customer feedback

Customer Reviews

  • Author: tim walberg
    This diagonal is a high quality item and very reasonably priced. It works perfectly with my refractors so I'd recommend this product.

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