Takahashi 1.25" Prism diagonal


Availability: More on the way

This premium 1.25" Takahashi TAKSD1 compression ring prism star diagonal is the diagonal that Takahashi puts with all of their complete telescope systems - even those costing as much as $30,000.
Our Product #: TAKSD1
Takahashi Product #: TKA00547

Product Description

This Takahashi TAKSD1 premium 1.25" star diagonal uses a high quality prism instead of a mirror. The prism has 100% internal reflectivity and the entry and exit faces of the prism are multicoated for minimum light loss. The lightweight (only 3 ounce) diagonal will work with any 1.25" accessory telescope other then a reflector.

The diagonal uses a non-marring molded compression ring to hold the eyepiece in place, rather than a set screw that can scratch the barrels of your eyepieces. The compression ring is tightened by a ribbed thread-on collet around the eyepiece holder. Rotate the collet in one direction and the compression ring tightens on the eyepiece to hold it firmly in place. A simple twist on the collet in the opposite direction loosens the compression ring's grip on the eyepiece. With a collet, instead of a thumbscrew as most diagonals use, there is no chance of losing the thumbscrew in the dark (along with the ability to hold your eyepieces safely in your diagonal).

The Takahashi TAKSD-1 is standard equipment with every Takahashi complete telescope package. Do you think that Takahashi would limit the performance of their telescope systems costing up to $30,000 with a less than exceptional star diagonal? Takahashi wanted the best 1.25" diagonal for their telescopes. Should you settle for anything less than the best for your scope?

Tech Details

Weight 3 oz.
Warranty 5 years


Review by:
Diagonals of all kinds are on the market, some bargain, some very costly. The Takahashi 1.25" prism right-angle diagonal is a sure bet if you want to get a quality diagonal without spending a small fortune. I've used it with an 80mm f/7.5 ED refractor as well as a 100mm f/9 ED refractor. It is invisible. That is, it does not visibly degrade the image at all. I tested it on planets and the moon using the diagonal in the refractor and then straight through, without the diagonal, and see no difference regarding sharpness, detail, chromatic aberration, internal reflections or scatter. It just doesn't get better than that.
The twisting adjustment of the compression ring takes some getting used to if you are familiar with the more common set screw types. But it is an overall better way to hold the eyepiece in my opinion.
This is my goto diagonal and it never fails me. Highly recommended (Posted on 9/7/2019)
Review by:
The Takahashi prism diagonal is an excellent performer. I directly compared it to a well known premium mirror diagonal costing hundreds of $ and could see no performance difference. The diagonal is lightweight which is a real bonus for the lightweight fast APO's on the market today. There are two mechanical aspects to be aware of. First, the diagonal is not threaded for filters. Second, the locking mechanism requires an awful lot of turning if your eyepiece has an undercut. This is more of an issue if you are swapping back and forth between an eyepiece with an undercut and one without. However, you cannot beat the optical performance so this are minor issues. (Posted on 7/25/2019)
Review by:
Don’t let the plastic body dissuade you this is a finely made prism diagonal at a great Price! (Posted on 11/16/2018)
Review by:
This is my everyday diagonal for a five-inch triplet refractor (actually, I have two - I like having back-ups). This is a quality item from a manufacturer who can justly be called the Japanese Zeiss, and at a surprising low price. If you do your research online, you'll find that this prism diagonal is in the top echelon of diagonals and outperforms many highly-regarded mirror diagonals, especially in planetary work (talking especially about Jupiter). Buy it - it's a steal. (Posted on 8/4/2017)
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