Thread size for ISTAR 2 inch diagonal body

[alaskaastronomy]

I have one of the great ISTAR 2 inch diagonals.  I am interested in attaching a Baader Twistlok eyepiece holder directly to the diagonal body and started a search for the threading size/specs on the body a few months ago (late 2020).
I tried forums on other sites with no luck and contacted Ales here @ ISTAR. He did a really good of trying to track down the original CAD drawings or other documents to find the threading...no luck.


But, the problem has been SOLVED  today April 20, 2020 and Ales suggested I add this forum post for other users. 



I tried various adapters, filters ete to find the diagonal body threading. 
Filter 49mm threading was too small and the adapter just fell through the body opening.
50.8mm  (2 inch as on SCT threading) was too big.

So, I purchased two step rings with closer sizes to test the threading.

One was 50.5mm x 0.75 filter thread and it was also too big.

But the 50.0mm x 0.75 filter threading fit perfectly.







If you want to add or modify any pieces to this great diagonal directly on the body of the eyepiece side, this is the threading that you will need.







Mike

[Ales - iStar Optical]

Hello Mike,

thank you very much for posting this important information. We still have approximately 40 of these diagonals in stock but we are not planning on producing them again. We have made these units using the best materials, milled each diagonal body out of a solid piece of aluminum alloy, incorporated internal baffles, used extra thick optical glass (almost double thickness compared to what our competition uses). So all this results in added cost and these days many people (not all though) are going strictly for price. And we are unable to compete on price with other mass-produced, cheap diagonals out there. This is why we will no longer produce these diagonals in the future. But for those of you who want to have a great quality diagonal, there are still many units in stock.