The telescope used was an Orion 90mm StarMax Maksutov intriguingly shown with a William Optics diagonal in this old jpg lol.
Baader Planetarium Prism Diagonal T-2/90deg and Takahashi TAKSD1
These two prism diagonals were also compared against a third which is a 1.25" Baader Zeiss Amici (also equipped with a helical focuser).
Baader Zeiss Amici
The target was primarily a setting twilight Venus, although I also intended to view Saturn as it was in conjunction with Venus on the 11th of December 2019. I didn’t have much time before both planets were too low. I mainly used an 18mm Astro Hutech ortho', giving 69x. Venus was very bright and easily seen early on with a 25mm AH orthoscopic. For Venus I also employed a Baader Double Polarising filter.
Venus/Saturn conjunction
The Tak’ was up first.
Apparently these diagonals are supplied with all Takahashi scopes. It is lightweight in design and I have read reviews stating that the housing is plastic. I'm pretty sure that it isn't and it is a light metal alloy or possibly aluminium. I'm not so sure about the base plate, it is probably a form of hard plastic so I'm not sure how it would wear over time. Unlike the Baader diagonals there is no filter thread in the nosepiece. Some have complained about the Tak's plastic collet snagging undercuts. I haven’t had any real problems although it helps if you use smoothies and barrels with shallow undercuts or those with lower lip flares (
The amount was almost imperceptible though and may have been my imagination. As Saturn became more prominent I switched all three to that. The Baader T2 helical focuser certainly makes a difference for fine focusing. Again, I had no problems with inserting and extracting eyepieces from these helicals, bearing in mind they have three set screws. I've had a lot of experience with these particular focusers as I've used them on my Newtonians for years. With a 7.5mm spacer the Baader is 70g heavier but the difference compared to the Takahashi feels negligible.
Weights:
Baader Zeiss Amici (helical focuser, 7.5mm spacer), 270g
Baader T2 (helical focuser, 7.5mm spacer), 200g
Takahashi TAKSD1, 130g
I can't choose a real winner. The Takahashi gave a bright, sharp image as did the Baader Zeiss Amici. The Baader 'bog-standard' wasn't really any different and had the advantage over the Tak' of having a helical focuser. The Takahashi and standard Baader diagonals are about the same price. The Baader Zeiss Amici's extra weight compared to the others was quite noticeable.