SVBONY MK90 90mm Maksutov-Cassegrain Telescope OTA

The SVBONY MK90: A 90mm Go-Anywhere Telescope for High-Power Viewing

The MK90 is designed for observers who prioritize sharp, high-contrast planetary and lunar detail in a telescope that is easy to transport and set up. The Maksutov-Cassegrain design concentrates the optical power of its 1250mm focal length into a tube that is a fraction of the size of a comparable refractor or Newtonian, making it a travel scope or an instrument for quick sessions from a balcony or backyard.

Whether used for astronomy or as a powerful daytime spotting scope for nature observation, the MK90 delivers the crisp views characteristic of the Maksutov design. It serves both amateur astronomers seeking a dedicated planetary instrument and terrestrial observers who need significant magnification for long-distance viewing.

The 2-Element Maksutov-Cassegrain Optical Design

The optical system of the MK90 consists of a two-element design: a convex meniscus corrector lens and a primary mirror. This configuration corrects for optical aberrations without the need for a complex Schmidt plate, resulting in improved image contrast. Internally, a tapered baffle tube is used to block and absorb stray light, ensuring a dark background and enhancing the visibility of subtle details on bright targets.

The closed tube also keeps dust off the internal mirror, and the sturdy metal construction withstands travel.

90mm Aperture and f/13.9 Focal Ratio for Detailed Views

With a 90mm aperture, the MK90 gathers enough light to provide definitive views of the solar system's brightest objects. The long 1250mm focal length results in a slow f/13.9 focal ratio, which is the key to its high-magnification capabilities. This optical combination makes it easy to achieve the high powers needed to see Jupiter's cloud belts, the Cassini Division in Saturn's rings, and the thousands of craters and rilles on the Moon.

The trade-off for this high-power planetary resolution is a narrower field of view compared to a short-focal-length refractor. While the MK90 excels at isolating individual targets, it is less suited for sweeping across the widest star fields of the Milky Way.

Internal Focusing via the 1.25-inch Focuser

Focusing on the MK90 is achieved by turning a knob that moves the primary mirror internally along the main baffle tube. This mechanism allows for a fine degree of focus control, which is critical when observing at high magnification.

The rear of the telescope terminates in a standard 1.25-inch visual back. This allows for the direct attachment of any standard 1.25-inch accessory, including star diagonals, eyepieces, and astronomy cameras.

Connecting Diagonals, Eyepieces, and Cameras to the MK90

The MK90's standard 1.25-inch focuser provides broad compatibility with the most common accessory format in astronomy. To begin observing, you will need to add a 1.25-inch diagonal and at least one 1.25-inch eyepiece (both sold separately).

• For Astronomical Use: A 1.25-inch mirror or prism star diagonal is required to view at a comfortable 90-degree angle.
• For Terrestrial Use: A 1.25-inch correct-image prism diagonal will provide an image that is both upright and non-reversed, which is essential for daytime nature viewing.
• For Imaging: Most 1.25-inch format planetary cameras will slide directly into the focuser or diagonal.

Visual Observing: The Moon, Planets, and Double Stars at 1250mm

The MK90's optical system is optimized for high-contrast, high-magnification targets. Its long 1250mm focal length provides a large image scale, allowing you to push the magnification on steady nights to resolve fine planetary and lunar features.

With appropriate eyepieces, you can expect to clearly resolve the primary cloud belts of Jupiter, the rings of Saturn, the phases of Venus, and the polar ice caps of Mars when it is near opposition. The long focal length also suits double stars like Albireo (Beta Cygni) or Castor (Alpha Geminorum).

Imaging with the MK90: High-Resolution Lunar and Planetary Photography

The same characteristics that suit the MK90 to visual observation also make it a capable instrument for lunar and planetary imaging. The 1250mm focal length provides enough image scale to capture details on planets with modern, small-pixel planetary cameras.

By attaching a 1.25-inch CMOS or CCD camera, you can record high-frame-rate video of the Moon and planets. Using stacking software, these videos can be processed into a single, detailed image that reveals far more detail than is visible to the eye alone.

Thermal Cool-Down and Factory-Set Collimation

Like all telescopes, the MK90 performs best when its optics have reached thermal equilibrium with the outside air. Because it is a closed-tube design, it is recommended to let the telescope sit outside for a period before observing to allow it to cool down and for the image to stabilize.

The MK90 is precision-calibrated at the factory and the Maksutov design is known for holding its collimation very well, meaning periodic adjustments are not typically required. However, if adjustment is ever needed after rough handling, collimation screws are accessible on the rear cell of the optical tube.

Mounting the MK90: 70mm Vixen Dovetail & ¼-20 Thread

The MK90 has two ways to connect to a support: a UNC 1/4-20 photographic thread and a 70mm, 75-degree Vixen standard dovetail plate.

• Vixen-Style Dovetail: A 70mm long Vixen-style dovetail plate is included, which is the standard for most modern lightweight to medium-duty astronomical mounts. This provides a secure connection for tracking celestial objects.
• UNC ¼-20 Thread: The standard ¼-20 photographic thread is the same size found on the bottom of most cameras. This allows you to attach the MK90 directly to a sturdy photographic or video tripod for terrestrial use or quick, grab-and-go astronomical viewing.

What's In The Box and What You Still Need to Get Started

The SVBONY MK90 is sold as an Optical Tube Assembly (OTA), which includes the main telescope and mounting hardware. To use it for observation, you will need to supply a few key accessories.

Included in the Box:

• MK90 Maksutov-Cassegrain OTA
• Versatile Dovetail Mounting Base
• 70mm Vixen Style Dovetail Plate
• Objective Lens Cover and 1.25-inch Dust Plug

Required for Operation (Sold Separately):

• An astronomical mount or a sturdy photographic tripod.
• A 1.25-inch star diagonal (for astronomical use) or a correct-image diagonal (for terrestrial use).
• At least one 1.25-inch eyepiece. A low-power eyepiece (e.g., 25mm) for finding objects and a high-power one (e.g., 10mm) for detailed views are recommended.

A Step-by-Step Guide to Setting Up Your MK90

Setting up the MK90 optical tube on your mount is a straightforward process. Before you begin, ensure your mount or tripod is on stable, level ground.

1. Attach to Mount: Loosen the dovetail saddle lock on your mount. Slide the 70mm Vixen dovetail plate on the MK90 into the saddle and tighten the lock securely. If using a photo tripod, screw the tripod's ¼-20 bolt into the telescope's ¼-20 thread.
2. Install Diagonal: Remove the 1.25-inch dust plug from the back of the telescope. Insert the barrel of your 1.25-inch diagonal into the opening and secure it with the thumbscrews.
3. Insert Eyepiece: Insert your chosen 1.25-inch eyepiece into the diagonal and lightly tighten its thumbscrews. It's best to start with your lowest power (longest focal length) eyepiece.
4. Remove Lens Cap & Focus: Remove the main objective lens cover. Point the telescope at a distant object and look through the eyepiece. Slowly turn the focus knob until the image is sharp. You are now ready to observe.