William Optics

Zenithstar 61 II APO with UniGuide guidescope

A compact and light telescope setup for wide-field viewing and astrophotography

e could sum up the William Optics Zenithstar 61 II APO refractor as tiny and serious or seriously tiny; it’s a small, portable instrument with a 61mm air-spaced, colourcorrected doublet lens, which definitely packs a punch, especially when used for astrophotography.

Externally, it’s an attractive telescope that feels well made; attention has been paid to creating a visually attractive product. The main tube is white with a black clamping ring and focuser barrel, while a choice of colours – grey, gold or red – is used on the dust cap, dew shield, eyepiece clamp and mounting bar. If you decide to add on the optional UniGuide guidescope, this can be purchased with a matching colour as well.

The ZS61-II’s 61mm objective lens has a focal length of 360mm, giving it a mid-range focal ratio of f/5.9. Being so small and portable, this wide-field scope is ideal for capturing views of the star fields and nebulae that are visible from dark-sky locations. The scope can also be used for taking photos of the Moon and planets and – with safety precautions adhered to and a suitable filter – the Sun; just don’t

Wexpect detailed close-ups with such a short focal length. It would be ideal for eclipse chasing, however, as its naturally wide-field coverage is ideal for the expansive nature of the Solar corona during totality.

Visual testing

During visual testing we found stars appeared sharp and bright in the middle of the field, while clusters came vibrantly to life. The wide, generous field of view was great for putting regions such as the Double Cluster and Orion’s Sword in context. Looking at a bright Moon, we were pleased about the absence of unwanted colour fringing; the air-spaced FPL-53 doublet lens doing a great job. While imaging, we found that the Bahtinov mask provided in the removable dew shield made it a breeze to reach accurate focus. This was also due partly to the ZS61-II’s dual-speed rack and pinion focuser, which we liked as it felt very positive and responsive.

The ZS61-II’s focused image circle will illuminate a full-frame DSLR sensor. Using a Canon 6D we noticed a small amount of vignetting – when the brightness of an image falls away towards the extreme corners of the frame – but nothing that couldn’t be corrected