Prism Shoot-Out

[Nightspore]

I decided on a shoot-out with two conventional 1.25" prism diagonals: a Takahashi TAKSD1 and a Baader Planetarium T-2. The telescope used was an Orion 90mm StarMax Maksutov.

 

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. I didn’t have much time before both planets were too low so I primarily used an 18mm Astro Hutech, 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.

 

 

It is a lightweight diagonal and I have read reviews stating that the housing is plastic. I'm pretty sure it isn't and is a light metal alloy or possibly aluminium. I'm not so sure about the base plate, but I'm not totally convinced it isn’t also metal. It could very well be be a hard type of plastic. 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 (GSO, Tele Vue). The TAKSD1 gave a bright, sharp image with no light scatter and easily revealed the Venusian phase. The conventional Baader was next, followed by the Amici. Apart from the mirror reversing I could tell no difference between the Tak’ and the Amici. There was no hint of the prism roof with the Zeiss Amici. The Baader Planetarium T-2 also gave a sharp image, although I thought it was fractionally darker.

 

 

The amount was almost imperceptible though and may have been my imagination. As Saturn became more prominent I switched all three to that.

 

 

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Nightspore]

 

Baader T-2 with 7.5mm Extension Tube

[+Bino-viewer]

Hi

Why the need for the Helical focuser ?

Doesn't it eat up more lightpath mm's ??

[Nightspore]

19 minutes ago, Bino-viewer said:

Hi

Why the need for the Helical focuser ?

Doesn't it eat up more lightpath mm's ??

I should imagine it adds a few mm. The Baader T-2 is sold with a helical (and even a nosepiece!) so I added an extension. I need the helical for fine focus on scopes with only a single speed focuser. So basically, all my Mak's and my 150mm Newtonian. The Baader helical, more or less permanently threaded into the Newtonian's GSO focuser, can cause in-focus problems with some eyepieces. 

 

Basically I suppose it is a trade-off in light path or in-focus for fine focusing.

 

 

The GSO Newtonian always had focusing problems anyway lol.

 

 

[Nightspore]

 

I was a bit concerned by stacked filters possibly touching the prism surface. Threading the Double Polariser into the diagonal nose bought it into direct contact with the visual back baffle on my Mak's.

 

 

So the solution was to use a GSO Barlow barrel as an extension tube.

 

 

Admittedly it looks a bit Heath Robinson, but I haven't had any in-focus problems.

Edited December 19, 2019 by Nightspore

[Nightspore]

 

The 7.5mm extension also helps with back-focus on my ED72.