Equipment Library

The Seattle Astronomical Society maintains a library of small and medium size telescopes that may be checked out for a period of 1 month by members in good standing. If you are new to astronomy, this is an excellent way to learn how to use a telescope and to begin viewing the wonders of the night sky, without having to invest immediately in a telescope of your own. To check out a telescope, please check out our equipment available for loan.

If you have any questions about borrowing equipment, or do not see a specific piece of equipment please reach out to our Equipment Manager.

Available Immediately

The following list of equipment is immediately available to borrow.

Celestron NexStar Evolution 6

Currently there are 6 requests to borrow this.


The Celestron NexStar Evolution 6 includes integrated WiFi and can be controlled with your smartphone or tablet by connecting your device to NexStar Evolution’s built-in wireless network. A SkyAlign alignment procedure is built into the Celestron mobile app for setup of the "GoTo" mode that provides automatic slewing to a selected object. Use the planetarium interface to display a list of celestial objects currently visible based on your time and location. NexStar Evolution includes its own built-in battery and will operate for up to 10 hours on a single charge. Ergonomic handles help with setup. Manual clutches in both altitude and azimuth offer flexibility to manually point the telescope when powered off. The 6-inch NexStar Evolution tracking accuracy is accurate enough to get started in astroimaging by attaching your DSLR camera.

The telescope also includes a StarPointer finderscope, a 1.25” star diagonal, eyepieces, and an AC adapter.

Available Soon

Available Eventually

The following list of equipment is currently loaned out to a member, and may include other members waiting to also borrow.

Orion Resolux 10.5x70 Astronomy Binoculars

Currently there are 2 requests to borrow this.


Large-aperture astronomical binoculars are intended for viewing star clusters, nebula, and galaxies. 10x magnification will provide good wide field views of larger deep sky objects such as the Great Orion Nebula and the Pleiades star cluster. At a dark sky site it will provide good views of Milky Way star fields and larger objects such as the Andromeda and Triangulum galaxies (M31 and M33). 

Like any binoculars, the Resolux 10.5x70 will provide pleasing views of the moon.

The Orion Resolux binoculars feature BAK-4 prisms and anti-reflection multi-coatings on all optical surfaces. The eyepieces focus individually and provide 18mm or more of eye relief They.have a 5.0-degree field of view.

A binocular tripod mount is provided in the SAS loaner package, but these 10.5x70 Resolux binoculars are hand holdable for short viewing sessions, especially if you can relax in a reclining lounge chair (not provided) while stargazing..  

Orion StarBlast 4.5

Currently there are 2 requests to borrow this.


The Orion StarBlast 4.5 EQ reflector telescope is suitable for beginner and intermediate astronomers. It comes with an equatorial tracking mount and adjustable-height tripod. Two eyepieces from the Orion Expanse series, which have a large 66 degree apparent field of view, are included. A 15mm Expanse eyepiece provides 30x power magnification, and a 6mm Expanse eyepiece provides 75x magnification.  An Orion EZ Finder II reflex sight is provided to aim the StarBlast 4.5 Equatorial Reflector Telescope anywhere in the night sky. The EZ Finder II projects a small red-dot onto a viewing window and the user must move the telescope until the red-dot is aimed at the intended area of the sky

ZWO ASI120MC-S Imaging Camera

Currently there are 2 requests to borrow this.


The ASI120MC-S is a color USB3.0 camera. primarily intended for planetary imaging, but it can be used for deep sky imaging with some limitations.

Orion StarMax 127 EQ

Currently there are 2 requests to borrow this.


Note: This equipment includes an equatorial mount that must be set up properly. For visual use, just point the polar axis of the mount approximately toward the  north.  

The StarMax 127 telescope is a Maksutov-Cassegrain design that folds a long focal length into a relatively short and easy to handle optical tube. The long focal length (1540mm) makes it easy to reach high magnification for observation of the moon and planets. The 127 mm aperature is large enough for nice views of brighter deep sky objects.  Includes an adjustable tripod and equatorial mount with manual slow-motion controls. The equatorial makes it easier to track the moon and planets at high magnification, but can be confusing for beginners. The Equipment Manager can provide advice on setting up and using an equatorial mount.

Currently Unavailable

The following list of equipment is not available to members until we are able to replace or repair parts.

Ultrastar Color Imaging Camera

Note  This item is being serviced and it is not available for check out.

This Ultrastar camera is being combined with a new telescope and mount to make a complete astrophotography loaner package. It will be available soon.

The camera and the required cables are included in this loaner. he user must supply a telescope, tracking mount and computer. The Ultrastar is an advanced version of Starlight Xpress 'Superstar' guide camera and it has a similar resolution of 1392 x 1040 pixels. However, the CCD chip has 70% more area and the QE is considerably greater, at around 75% peak. It is useful as both a guide camera and an imaging camera, which is especially well suited to 'Live Viewing' mode. A program called 'Lodestar Live' is capable of controlling the Ultrastar in Live view. It can also color convert and stack images from single-shots.

Telescope Types

Types of telescopes

Copyright NIAAS, North Ireland Amatuer Astronomical Society

What are those numbers?

Types of telescopes

Copyright 2008-2012

The f-ratio is the focal length divided by the diameter of the telescope. Magnification is the focal length of the telescope divided by the focal length of the eyepiece.


To find the f-ratio of a telescope 10 " in diameter with a 45" focal length:

Divide 45 " F.L. by10" D. to get an f-ratio of 4.5.

Compute Magnification

First, convert focal length to mm: 45" = 1146 mm, then:

1146 mm focal length divided by 35 mm eyepiece equals 33 magnification.

More Information

If you are interested in learning more about telescopes, we recommend: