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# William Optics RedCat 51
- URL: https://macobservatory.com/william-optics-redcat-51/
- Published: 2019-07-06T00:17:14.000Z
- Updated: 2026-03-10T15:58:56.000Z
- Author: Andrew Burwell
- Tags: Reviews

![](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/img_0353-format-original.webp)

I’ve been really interested in the[William Optics RedCat 51](https://agenaastro.com/william-optics-redcat-rc51ii-gen-2-51mm-f-4-9-petzval-apo-refractor-telescope-red.html?aw%5Faffiliate=eyJjYW1wYWlnbl9pZCI6IjQiLCJ0cmFmZmljX3NvdXJjZSI6IldpbGxpYW0gT3B0aWNzIFJlZENhdCA1MSBSZXZpZXciLCJhY2NvdW50X2lkIjo0NX0&ref=macobservatory.com)since the original announcement. A few web bloggers got ahold of early versions of this scope, and took some really fantastic wide field images with it. Once the scope finally released early reports from purchasers showed lots of issues. Poor coma and off axis issues were prevalent. I waited for the initial manufacturing run to go out of stock, and ordered when they started the second run hoping any issues would be cleared up and I would get one without problems.

The day finally arrived. Agena Astro had them in stock, and I was quick to grab one. It arrived last week to cloudy skies, and I only had it out for a few minutes. Since then, i’ve been able to get it out for a full night of Hydrogen Alpha imaging on the Elephant Trunk nebula. I paired it up with an older[Orion StarShoot AutoGuider](https://amzn.to/2LFWMRC?ref=macobservatory.com)that I had laying around, a[ZWO Mini Guide Scope](https://agenaastro.com/zwo-30-f-4-mini-guide-scope-for-asi-cameras-30f4.html?aw%5Faffiliate=eyJjYW1wYWlnbl9pZCI6IjQiLCJ0cmFmZmljX3NvdXJjZSI6IldpbGxpYW0gT3B0aWNzIFJlZENhdCA1MSBSZXZpZXciLCJhY2NvdW50X2lkIjo0NX0&ref=macobservatory.com), and my existing[ZWO ASI1600MM-Pro](https://agenaastro.com/zwo-asi1600mm-p-cmos-monochrome-astronomy-imaging-camera-pro.html?aw%5Faffiliate=eyJjYW1wYWlnbl9pZCI6IjQiLCJ0cmFmZmljX3NvdXJjZSI6IldpbGxpYW0gT3B0aWNzIFJlZENhdCA1MSBSZXZpZXciLCJhY2NvdW50X2lkIjo0NX0&ref=macobservatory.com)main camera,[ZWO 8-slot filter wheel](https://agenaastro.com/zwo-eight-position-electronic-filter-wheel.html?ref=macobservatory.com)and Astrodon filters.

![](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/img_0356-format-original.webp)

At first I couldn’t figure out how to focus. It turns out that the scope shipped with the lens hood flipped around covering the focus. I had to unscrew it and reattach the other direction. It makes the scope quite compact for traveling, and I intend to pair it with my Sky-Watcher Star Adventurer when I head out of town in the future. To set up for imaging, I had to reach the prescribed back focus distance, and I used one 16.5 adapter, the filter wheel and space to sensor to achieve 55mm of distance. William Optics also offers DSLR adapters that attach to the back of the scope where you can hook up your Canon or Nikon camera with no additional spacers.

Once set up to image, I placed it on my[Celestron AVX mount](https://agenaastro.com/celestron-advanced-vx-mount-91519.html?ref=macobservatory.com), and loaded up[EKOS](https://macobservatory.com/an-overview-of-ekos-astrophotography-suite-on-the-mac/)to begin imaging for the evening. A quick[Polar Alignment](https://macobservatory.com/celestrons-all-star-polar-alignment-procedure/), and I was off imaging. I picked a target that would fully fit into this wide field of view, the entire Elephant Trunk nebula. Here’s the first night of imaging with around 6 hours of HA data. I calibrated and stacked the image with[Astro Pixel Processor](https://macobservatory.com/processing-a-bi-color-narrowband-astronomy-image-in-astro-pixel-processor-on-the-mac/).

![](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/elephant-trunk-format-original.webp)

I ran the final image through PixInsight’s FWHM/Eccentricity and image analysis tools. The final image shows very little issues with the scope. There is an interesting aberration with the largest stars, it looks a bit liked pinched optics. I have an e-mail out to William Optics to confirm and see if I can fix it by adjusting the screws around the lenses. There is very little coma in the final image.

![](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/arberration-inspector-format-original.webp)

The above image shows the very slight coma in the extremes of the corners. It’s practically invisible zoomed out, so I can live with that. But one of the benefits of a Petzval scope like this is that it’s supposed to be corrected for these issues, and provide an extremely flat field. The field is definitely flat, but the coma still exists however minor it is.

![](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/img_0357-format-original.webp)

![](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/img_0358-format-original.webp)

## Recent images taken with the RedCat 51

![SH2-240: Spaghetti Nebula](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/image-asset-99.webp)

[Image details](https://www.astrobin.com/oszrxq/0/?ref=macobservatory.com)Feb 14, 2022William Optics RedCat 51,ZWO ASI294MM-Pro,Rainbow Astro RST-135E

![The SADR region](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/image-asset-100.webp)

[Image details](https://www.astrobin.com/87g9uf/0/?ref=macobservatory.com)Sep 21, 2021William Optics RedCat 51,ZWO ASI294MM-Pro,Rainbow Astro RST-135E

![NGC 2264: The Cone Nebula](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/image-asset-134.webp)

[Image details](https://www.astrobin.com/y75pcp/C/?ref=macobservatory.com)Apr 12, 2021Rainbow Astro RST-135,William Optics RedCat 51,ZWO ASI2600MC-Pro

![M42: The Orion Nebula (with a little Horse Head)](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/image-asset-135.webp)

[Image details](https://www.astrobin.com/klatjd/?ref=macobservatory.com)Dec 15, 2020ZWO ASI2600MC-Pro,William Optics RedCat 51,Rainbow Astro RST-135

![IC 2118: The Witch Head Nebula](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/image-asset-136.webp)

[Image details](https://www.astrobin.com/uslf5x/B/?ref=macobservatory.com)Dec 15, 2020William Optics RedCat 51,ZWO ASI2600MC-Pro,Rainbow Astro RST-135

![NGC 7023: Iris Nebula](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/image-asset-137.webp)

[Image details](https://www.astrobin.com/slqzkz/?ref=macobservatory.com)Dec 15, 2020ZWO ASI2600MC-Pro,William Optics RedCat 51,Rainbow Astro RST-135

![Constellation Auriga nebula group](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/constellation-auriga-nebula-group.webp)

[Image details](https://www.astrobin.com/m07iyx/?ref=macobservatory.com)Dec 15, 2020William Optics RedCat 51,ZWO ASI2600MC-Pro,Rainbow Astro RST-135

![M31: Andromeda Galaxy](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/andromeda.webp)

[Image details](https://www.astrobin.com/r5lct1/?ref=macobservatory.com)Dec 15, 2020ZWO ASI2600MC-Pro,Rainbow Astro RST-135,William Optics RedCat 51

![M45: The Pleiades](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/image-asset-138.webp)

[Image details](https://www.astrobin.com/waz84a/?ref=macobservatory.com)Nov 3, 2020ZWO ASI2600MC-Pro,Rainbow Astro RST-135,William Optics RedCat 51

![Sharpless 2-129: Flying Bat Nebula](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/image-asset-139.webp)

[Image details](https://astrob.in/2g5chb/0/?ref=macobservatory.com)Jun 18, 2020ZWO ASI2600MC-Pro,ZWO ASI1600MM-Cool,10Micron GM1000 HPS,William Optics RedCat 51

![IC 1871: Soul Nebula](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/soul-nebula-1.webp)

[Image details](https://astrob.in/heqipl/0/?ref=macobservatory.com)Dec 4, 2019ZWO ASI1600MM-Cool,Celestron Advanced VX,William Optics RedCat 51

![NGC 1499: California Nebula](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/california-nebula.webp)

[Image details](https://astrob.in/l9rojg/0/?ref=macobservatory.com)Dec 4, 2019ZWO ASI1600MM-Cool,William Optics RedCat 51,Celestron Advanced VX

![IC 1805: Heart Nebula](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/heart-nebula.webp)

[Image details](https://astrob.in/yfb6y5/0/?ref=macobservatory.com)Oct 28, 2019William Optics RedCat 51,ZWO ASI1600MM-Cool,Celestron Advanced VX

![Crescent Nebula Widefield](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/crescent-nebula-widefield.webp)

[Image details](https://astrob.in/y8t56l/0/?ref=macobservatory.com)Oct 10, 2019Celestron CGX,William Optics RedCat 51,ZWO ASI1600MM-Cool

![M31: Andromeda](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/m31.webp)

[Image details](https://astrob.in/p69bi4/B/?ref=macobservatory.com)Sep 9, 2019Celestron CGX,ZWO ASI1600MM-Cool,William Optics RedCat 51

![The Veil Nebula: supernova remnant](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/o7obyj5i5zip_1824x0_wmhqkgbg.webp)

[Image details](https://astrob.in/417276/0/?ref=macobservatory.com)Jul 31, 2019William Optics RedCat 51,ZWO ASI1600MM-Cool,Celestron CGX

![NGC 7000 & IC5070 - North American Nebula & Pelican Nebula](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/fvdcl5qlpxs6_1824x0_wmhqkgbg-1.webp)

[Image details](https://astrob.in/417021/C/?ref=macobservatory.com)Jul 31, 2019William Optics RedCat 51,Celestron CGX,ZWO ASI1600MM-Cool

![Sadr Region - RGB-Ha](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/vk2labdthtsj_1824x0_wmhqkgbg.webp)

[Image details](https://astrob.in/416061/0/?ref=macobservatory.com)Jul 19, 2019William Optics RedCat 51,ZWO ASI1600MM-Cool,ZWO ASI071MC-Pro,Celestron CGX

![Sadr Region](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/sadr.webp)

[Image details](https://astrob.in/415913/B/?ref=macobservatory.com)Jul 18, 2019William Optics RedCat 51,ZWO ASI071MC-Pro,Celestron Advanced VX

![IC 1396 - Elephant Trunk Nebula](https://storage.ghost.io/c/8d/3a/8d3ae6c9-185e-49c7-b8a6-36d44545d9f9/content/images/2026/03/dfvjnh3zmcny_1824x0_wmhqkgbg.webp)

[Image details](https://astrob.in/413987/C/?ref=macobservatory.com)Jul 7, 2019Celestron Advanced VX,William Optics RedCat 51,ZWO ASI1600MM-Cool