Dielectric Star Diagonal - 1.25" - D1030

Excellent build and optics quality.

I bought this diagonal to check out some short fl acromats to be used for finders. I noticed some artifacts that looked like astigmatism with the 1.25" mirror diagonal I had on hand. Most of my 1.25" focuser scopes are slower f ratios and I've not had any issues with the prism diagonals I've always used. However, my f/6 RFT is much better with a 2" Lumicon enhanced aluminum mirror diagonal, which replaced a heavy brass 2" prism. As I've been intending to buy a better small mirror diagonal I decided to try this D1030. The image was cleaner and there was no noticeable astigmatism. Diagonal quality definitely made a difference. It appears to be an OEM product from Taiwan but is of very high quality.

Item arrived on time, very securely held in a small box within a larger box. As always with Stellarvure good attention to detail. I use this diagonal with the Stellarvue SV 50 ED APO as a finder on my SV 102 ED refractor. Very good quality all around. On calm nights I'm able to obtain very tight clean star images at 100x most nights with the 50mm finder. Excellent optics leave nothing to be desired.

The finest telescope in the world is part of a system. The telescope is certainly the most critical component of the system, but the mount, drive, diagonal, lenses, and any filters are all part of the total system. There is an old saying that a chain is no stronger than its weakest link, and this certainly applies in astronomy. The humble mirror diagonal is a case in point. A good diagonal should be optically flat to avoid distortion in the optical chain, it should have high reflectivity (to avoid wasting what light your telescope collects, and the mirror should be mounted very accurately to maintain collimation. I inherited my first diagonal from the package that represented my first serious telescope. When I started using it with my first Stellarvue refractor, I noticed that, with the diagonal in place, collimation was a bit less than perfect - not characteristic of the instruments from Vic's shop. A few simple tests with a garden variety laser pointer quickly showed that the mirror was not optically flat, the angle of the mirror was not precisely 45 degrees across its surface, and that the mirror showed stress at all mounting points. The result of all this was the purchase of one of Vic's mirror diagonals. Back to my redneck optical lab and the mirror was as perfect as my testing could determine. Its performance with Stellarvue refractors was as perfect as one could ask for. I now use it with all my telescopes, including an SCT and an MCT. When using an instrument that requires routine collimation (such as an SCT), using a high quality diagonal assures high-quality alignment. If you are shopping here, you are looking for quality. Don't short-change a fine telescope by using a second-rate diagonal!

The diagonal that came with my 5-inch SCT had some annoying flare lines when looking at bright stars or planets. When I removed the diagonal and used an eyepiece straight-thru, the lines disappeared. I wanted a better diagonal and I saw Stellarvue's 1.25-inch dielectric offered at a reasonable price. I don't claim to be an optician, but I am impressed. I could not detect any difference in image quality when using this diagonal versus using the eyepiece by itself. Image brightness and sharpness are unchanged and there are no annoying flares or lines. Also, the larger thumb screw is a nice touch, along with the compression-ring design, making it easier to use than my old diagonal. Insertion and removal of eyepieces is much smoother. A star diagonal really ought to go unnoticed, but I'm liking everything about this one, including its good looks.