3 replies to this topic

[Astrokg]

I bought a 0.956" to 1.25" diagonal which sells on AliExpress and Amazon. It turned out to be really bad and not a patch on the original 0.96 prism diagonal that came with my vintage telescope. The plastic back easily opened, I found they had used a normal mirror with mirror surface on the back - not a true diagonal with mirror on the front surface.

I found that prisms were readily available, I documented the steps to make a prism diagonal from the cheap diagonal below. It is comparable to the original prism 
Diagonal that came with the vintage scope.

The only really important point is that nothing should touch the hypotenuse of the prism as it is the glass to air boundary that provides the inner reflection action. The design handles this in the square blocks that prevent anything touching back surface.

The only special tool needed is a block plane to plane the wooden blocks to an exact thickness to snugly fit.

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[Astrokg]

Steps 

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[Astrokg]

Finished

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[deSitter]

I bought a 0.956" to 1.25" diagonal which sells on AliExpress and Amazon. It turned out to be really bad and not a patch on the original 0.96 prism diagonal that came with my vintage telescope. The plastic back easily opened, I found they had used a normal mirror with mirror surface on the back - not a true diagonal with mirror on the front surface.

I found that prisms were readily available, I documented the steps to make a prism diagonal from the cheap diagonal below. It is comparable to the original prism 
Diagonal that came with the vintage scope.

The only really important point is that nothing should touch the hypotenuse of the prism as it is the glass to air boundary that provides the inner reflection action. The design handles this in the square blocks that prevent anything touching back surface.

The only special tool needed is a block plane to plane the wooden blocks to an exact thickness to snugly fit.

Wow they used a cut up bathroom mirror - SMDH. Never saw that before.

 

In most good diagonals a swatch of blackened fabric or cardboard is placed over the hypotenuse, an optical surface, to protect it. A leaf spring then fits between the back cover and this swatch to seat the prism. Unless something it is actually stuck to the hypotenuse, like mold or a fingerprint, it will not "frustrate" the total internal reflection.

 

-drl