• English
  • French

Zoom the image with the mouse

Celestron M42 Spacer Ring Kit - 7.5mm, 12mm, 30mm - 93618

In Stock - Ships Today if Ordered by 2pm! (Tues - Fri)

We will price-match Canadian astronomy dealer pricing

Ask a Question About This Product

  • Adjusts back-focus between your camera and telescope for the best astroimaging results
  • Kit includes 3 spacer rings of different lengths (7.5mm, 12mm, 30mm)
  • Threads to your T-Ring and T-Adapter with standard male and female T-Threads

To achieve the best astroimages, it is important to attain the proper back-focus distance for your camera relative to the telescope it is being used with. If the back-focus distance your camera consumes is not exact, the performance at the corners of full frame imaging sensors will suffer—stars will appear elongated and not as pinpoints.
Example: RASA 8 with a ZWO ASI 183 MC PRO camera

  • Required back-focus distance for RASA 8 with included M42 camera adapter: 25mm
  • Back-focus consumed by ZWO ASI 183 MC PRO camera: 17.5mm
  • To achieve equal back-focus distance, a 7.5mm M42 spacer ring is required

Celestron's M42 Spacer Ring kit includes three different length spacer rings to achieve the proper back-focus distance with our popular Celestron optical tubes and T-thread camera adapters.
How to Use
Depending your method of astrophotography (DSLR or CCD/CMOS), there are two ways to use the M42 Spacer Ring. If you are using a DSLR, place the desired M42 Spacer Ring between your T-Ring and your T-Adapter for your optical tube. If you are using a CCD or CMOS camera, place the desired M42 Spacer Ring between the camera and the T-Adapter for your optical tube.

Below is a quick guide to help you determine which spacer ring to use for our EdgeHD, Schmidt-Cassegrain, and RASA 8 optical tubes:

Spacer Ring Size: Works best with:
7.5mm Provides proper spacing with RASA 8 for many ZWO cameras
12mm Provides proper spacing with RASA 8 for many Atik cameras
30mm Converts ZWO camera w/filter slider to 55mm back-focus standard for use with Schmidt-Cassegrain & EdgeHD

The M42 Spacer Rings are machined aluminum black anodized. The internal surfaces are blackened and glare-threaded to provide the highest contrast. Each spacer ring has a knurled surface, providing a great gripping surface for threading/unthreading. The M42 Spacer Rings are compatible with M42 x 0.75 (T-thread) camera adapters.

Returns Policy

You may return most new, unopened items within 30 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).

Items that have been opened, damaged or are otherwise unsaleable will be subject to a minimum 10% restocking fee, to be assessed by Telescopes Canada upon receipt of the returned goods

You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).

If you need to return an item, simply login to your account, view the order using the 'Complete Orders' link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.


We can ship to virtually any address in the world. Note that there are restrictions on some products, and some products cannot be shipped to international destinations.

When you place an order, we will estimate shipping and delivery dates for you based on the availability of your items and the shipping options you choose. Depending on the shipping provider you choose, shipping date estimates may appear on the shipping quotes page.

Please also note that the shipping rates for many items we sell are weight-based. The weight of any such item can be found on its detail page. To reflect the policies of the shipping companies we use, all weights will be rounded up to the next full pound.

Typographical Errors and Order Cancellations

Telescopes Canada reserves the right to cancel an order due to an error in pricing by Telescopes Canada or one of our suppliers, equipment being no longer obtainable, or other events which are out of our control.

Client-Initiated Cancellations

Client-initiated order cancellations are accepted prior to delivery of the equipment to the customer, thereafter it is a return.

Thread: M42 x 0.75
Spacer lengths: 7.5mm (.29"), 12mm (.47"), 30mm (1.18")
Construction: Aluminum black anodized
Interior: Blackened and glare threaded
Exterior: Knurled grip surface, each ring labeled with its length

Questions & Answers

Have a Question?

Be the first to ask a question about this product