topic Re: Any Canon EOS-RP to Celestron C90 adapter(s)? in Camera Accessories

Any Canon EOS-RP to Celestron C90 adapter(s)?

JTTraverse — Sun, 21 Dec 2025 23:40:06 GMT

I recently was given a Celestron C90 1000mm f/11 lens (fwiw it's the black model with wide gold band, looks very similar to the orange model). The original owner used a 2.5" adapter tube to attach it to a Canon T90 camera, which I think had an 'FD' lens mount.

I happen to own a Canon RP camera that I would like to use with this C90 lens, but it's been a strain trying to get specifics on what sort of adapter I would need. Unless there is a ready-made adapter exactly for this, I've presumed that I'll need a T-adapter as well as the right T-ring. So, does anyone know exactly what it will take to make this work?

I do understand that the spacing of the T-adapter and T-ring is vital for correct focus on this camera. One suggestion was to try an EF-EOS R adapter on the camera and then simply use an EF T-ring and T-adapter to attach it. But it seems to me that there must be a simple solution, like a T-adapter that screws directly onto the C90 lens mount and the other end attaches directly to the camera lens mount, or an RF T-ring on the camera.

If anyone has experience with this, or knows a right solution to make this work, I'd appreciate the help.

Thanks!!

Re: Any Canon EOS-RP to Celestron C90 adapter(s)?

Tintype_18 — Mon, 22 Dec 2025 19:45:44 GMT

Can't answer your question but that is one big lens. What do you photograph?

Re: Any Canon EOS-RP to Celestron C90 adapter(s)?

Waddizzle — Mon, 22 Dec 2025 20:19:07 GMT

When Canon released the Ra, I believe users were using the RF-EF mount adapters.

Re: Any Canon EOS-RP to Celestron C90 adapter(s)?

FloridaDrafter — Mon, 22 Dec 2025 23:18:45 GMT

Hello, JT!

You may... MAY... be able to use a T-mount made for the EF mount and get the R=>EF mount adaper. This depends on how thick the T-mount adapter is, which I'm not familiar with. If it's too thick, it will mess with where the image circle falls on the sensor, if it works at all 🙂

Newton

Re: Any Canon EOS-RP to Celestron C90 adapter(s)?

ebiggs1 — Tue, 23 Dec 2025 15:29:39 GMT

Check out the Celestron T Adapter C90. That is what I used but I didn't have an R series.

Re: Any Canon EOS-RP to Celestron C90 adapter(s)?

Waddizzle — Tue, 23 Dec 2025 17:57:39 GMT

All the above suggestions are correct. The key piece of information that hasn’t been mentioned is that you are going to need more than one adapter.

The telescope needs a T-mount adapter. Next you’ll need a T-mount to EF adapter. Finally, you’ll need an EF-RF mount adapter on the camera. That’s three adapters.

Let’s review that. The scope needs a T-mount adapter. The camera needs the RF-EF mount adapter.

Sitting between them you’ll need a T-mount to EF mount adapter.

Re: Any Canon EOS-RP to Celestron C90 adapter(s)?

Waddizzle — Wed, 24 Dec 2025 14:20:14 GMT

I quick search shows that there T-mount to RF mount adapters from several manufacturers. This would be a far less costly approach than my previous suggestion of using a RF to EF adapter. This type is a direct connection to the scope.

The image is neither a suggestion or an endorsement. This model was at the top of my search list.