William Optics ZenithStar 73mm ED APO Refractor

The William Optics Zenithstar 73 is an ED Apochromatic Doublet Refractor Telescope designed and built for professional astrophotography. The super high quality Ohara Fluorite (FPL-53) ED glass made with Taiwanese manufactring precision make the Zenithstar 73 an outstanding deep-sky imaging telescope.

The Ohara FPL-53 ED glass with an f/5.9 ratio negates all false colours and gives razor sharp images with high contrast images. When you join the William Optics Field Flattener (sold separately) to the Zenithstar 73mm telescope, it gives edge to edge results in deep sky imaging.

The example astrophotpgraphs shared on this webpage should give you an idea of what you can expect our of the Zenithstar 73 ED APO.

Its an ideal instrument for wide-angle deep sky imaging with a variety of DSLR Camera or dedicated professional astrophotography cameras. One can even use the Zenithstar 73 for Solar System observation / photography as well as moon craters and also for day time terrestrial observation and photography.

The quick setup time of the telescope allows users to reach out to the telescope more often when the clouds suddenly clear up. The Zenithstar 73 is small, CNC machine crafted and highly portable, an overall package / value for money for any budding / professional astrophotographer.

The scope is small and light enough with an overall weight of 2.8kg approx to work with nearly any medium-duty equatorial GoTo mounts with a recommended payload capacity of 5 kg.

Ohara FPL-53 vs FPL-51 ED Glass

The dispersion properties of ED and SD glass elements are important in determining the overall colour correction. The abbe index is used to quantify the ‘partial dispersion’ of a particular glass. Pure Fluorite offers the highest partial dispersion at around 94.99 V, Ohara FPL-53 glass is very close to Fluorite at 94.93 V and is often referred to as Synthetic Fluorite.  FPL-53 is also noticeably better than Ohara’s lower spec’ FPL-51 glass which offers an abbe index of 81.54 V.

Fast Optics with a Wide Field of View

Thanks to its fast optics (F/5.9), this refractor collects a lot of light in a short period of time. Image exposures of 2-3 minutes at ISO 1600 are likely all you will need to capture deep details of your target.

If you have ever struggled with framing up a large target such as the North America Nebula or Andromeda Galaxy, the Z61 is a breath of fresh air. The ultra-wide 360mm focal length means collecting photons on HUGE areas of the night sky in a single frame.

Even with a crop sensor camera like the Canon T3i/600D, the focal length of 576mm is still more than wide enough for the big targets.

Highly portable and Lightweight

A high-quality refractor at this size is the perfect travel scope. When combined with a portable camera mount, you’ve got a very capable deep-sky imaging rig that can pack up into a backpack or travel container.

A collapsible carbon fiber tripod, the iOptron SkyGuider Pro, and the Z61 is probably the most portable deep sky astrophotography setup you can have.

Deep Sky Imaging with the Zenithstar 73 APO

If you are new to deep sky astrophotography but have dabbled in tracked night sky shots including the Milky Way – this is likely the best possible next step for you.

An Affordable Imaging Refractor

The William Optics Zenithstar 73 currently retails for Rupees 66000.00.  The price includes the telescope only, as you can add a number of extras to your order. This includes everything from a color-matched dovetail plate to the photo adapter for your DSLR camera.

Astrophotography Performance in Compact Package

The Ohara FPL-53 ED Glass is a top of the line material found only in the best apochromatic refractors. This makes the Zenithstar 73 an excellent choice for those looking for a primary imaging telescope. This APO doublet captures sharp, high contrast images free of false color.

The Z73 is very compact and portable. It weighs only 5.5 lbs, which means that you don’t need a large equatorial mount with a heavy payload to use it for astrophotography.

Ultra-Portable Telescope

It is often said, that the best telescope is the one you use most often. With a retracted length of 330mm and convenient mounting options, you’ll have no excuse not to deploy the Z73 for a night of deep-sky astrophotography on a moment’s notice.

Impressive Features

The built-in star-spikes Bahtinov mask makes focusing your DSLR camera through the telescope quick and easy. Simply point the telescope at a bright star, and position the central spike evenly between the “X”.

The telescope is held securely inside the mounting rings and can be adjusted back and forth to improve balance if necessary.

The Perfect F-Ratio

The William Optics Zenithstar 73 APO has an f-ratio of F/5.9. The focal ratio of a telescope represents its light gathering ability, and the Z73 hits the sweet spot. In my experience with the Z73, the combination of 430mm at F/5.9 was just right for collecting long exposure astrophotography images of the Butterfly Nebula and Heart Nebula.

Although it is small, the 73mm objective is more than enough to gather impressive long-exposure deep-sky images. The wide field of view is particularly effective on large targets such as the Andromeda Galaxy, The North America Nebula, and the Heart Nebula.