Takahashi FOA-60Q
Selecting a solar scope was a bit of a journey. I have written a separate blog about it. For reasons mentioned in the blog, I chose to put a solar scope together from individual components. As telescope I opted for the Takahashi FOA-60Q. The FOA-60 is a small 60mm fluorite apochromat refractor. The optional EXQ1.7x focal extender is screwed into the main tube between the objective lens and the focuser. Not only does it almost double the length of the tube, it also reduces the spot sizes significantly, making it one of Takahashi’s sharpest telescopes with a Strehl ratio of 99.8%. With the extender, the telescope is referred to as FOA-60Q, and is a perfect tool for solar or lunar observation and photography.
Aperture: 60mm
Focal length: 900mm
Focal Ratio: f/15
Image circle: 44mm
Length: 702mm
Weight: 2.1kg
Cradle
The tube is mounted on a Vixen style plate using an original Takahashi 68S-GT cradle. This 0.5kg cradle with 68mm inner diameter offers more than sufficient support for the FOA-60Q tube. The 58mm wide bottom part of the cradle makes for a solid connection to the mounting plate.
Sol-Searcher
Aligning a solar scope is tricky because there are no stars to use during the day. Tools like the Televue Sol-searcher help by letting sunlight pass through a small hole, creating a dot on a panel behind it. Point the mount’s GoTo to the Sun and adjust the altitude and azimuth to line up the dot. This usually gives a good enough polar alignment.
Vixen style plate
The Takahashi cradles are part of a separate eco-system of mounting options. And it can be a bit challenging to find proper devices to mount them on regular Vixen or Losmandy clamps. This special Takahashi-Vixen dovetail bar is designed by ADM specifically for the 58mm-sized Takahashi rings.
Dual-speed Focuser
Solar imaging will be focused using manual focus. The standard focuser on the FOA-60Q is only a single-speed focuser. A dual-speed focuser from MoreBlue was added to the scope to have a finer control over the focusing process.
M56
Ring sizes in the Takahashi world are always a bit special. Many of the smaller telescopes are based on the M56 thread-size and so is the FOA-60Q. Takahashi publishes for each telescope a system chart which is extremely helpful.
Spot Diagram
The FOA-60Q is a particularly sharp telescope, mainly due to the corrections taking place in the EXQ1.7x extender unit. The scope has a theoretical Strehl ratio of >99.8%, which is better than the TOA-130 and TOA-150 telescopes. The spot diagram shows this impressive sharpness.