What is the main difference between the William Optics GuideStar 61 and the Zenithstar 61?
Both models use the identical FPL53 ED doublet lens, so their optical quality is the same. The primary difference is mechanical: the GuideStar 61 has a lightweight draw-tube focuser designed for guiding and portability, while the Zenithstar 61 has a more robust rack-and-pinion focuser to support heavier imaging cameras.
Can the GuideStar 61 be used as a primary imaging telescope?
Yes, absolutely. The GuideStar 61's FPL53 optics make it an excellent portable, wide-field imaging refractor. For optimal results across a larger sensor, it is best paired with an optional field flattener, such as the William Optics Adjustable Flattener for ZS61.
How does the draw-tube focuser on the GuideStar 61 work?
The GuideStar 61 uses a simple and reliable draw-tube, or "push-pull," focuser. You achieve coarse focus by sliding the tube in and out, then lock it. Fine focus adjustments are then made by rotating the lens cell assembly itself, allowing for precise focus on your guide star or imaging target.
How would the GuideStar 61 perform for guiding on a large SCT imaging the Andromeda Galaxy (M31)?
It would perform exceptionally well. The apochromatic FPL53 optics of the GuideStar 61 will produce very sharp, tight stars across the field of view of your guide camera. This allows your software to calculate a more accurate centroid, leading to smoother and more precise tracking corrections, which is essential for long exposures on a target like M31 with a long focal length SCT.
What accessories are needed to use the GuideStar 61 for imaging the North America Nebula (NGC 7000)?
To image a large target like the North America Nebula, you would need a solid mount, a guide camera (if using it as a guide scope), and your primary astronomy camera. To ensure sharp stars to the edge of your frame, a dedicated field flattener like the Adjustable Flattener for ZS61 is highly recommended. The optional 0.8x reducer/flattener would provide an even wider field of view to capture the entire nebula complex.
Is the FPL53 lens in the William Optics GuideStar 61 truly apochromatic?
Yes. The use of FPL53, a high-grade extra-low dispersion (ED) glass, in an air-spaced doublet configuration effectively eliminates false color (chromatic aberration). This provides images with sharp focus across the visual spectrum, high contrast, and no purple fringing around bright stars, meeting the definition of an apochromatic refractor.
