Explore Scientific HR Variable Coma Corrector 2-inch, NO Camera Adapters Included

Product Overview

The Explore Scientific HR Variable Coma Corrector is a 2-inch corrector for Newtonian reflectors, designed by the optical designer Harrie Rutten and EMC coated to hold down internal reflections. This is item HRCC02-01, the version supplied without camera adapters. In Explore Scientific's own words, “this model does not come with the adapters that allow for a direct screw-on connection to a camera.” Published figures are 1 lb (0.45 kg), 69.3 mm in diameter and 147.2 mm tall.

The optics are the same as the HRCC02-00 version. The difference is what is in the box, and the price reflects it. If you want to screw a camera straight onto the corrector, buy the HRCC02-00 instead — we stock both.

Who It's For

Visual observers with fast parabolic Newtonians, and imagers who already own the thread adapters they need. Coma is inherent to the paraboloid: it grows with distance from the optical axis and worsens sharply as the focal ratio drops, so an f/4 mirror shows comet-tailed stars well inside the field of a wide-angle eyepiece. This corrector is the standard remedy and Explore Scientific specifies it for fast mirrors from around f/3.9.

Buying this version is the right call if you are using it visually with 2-inch eyepieces, or if you have a drawer of M42 and M48 adapters already and would rather not pay for another set. If neither is true, the HRCC02-00 with adapters included usually works out cheaper than buying this and sourcing adapters afterwards.

Key Features & Design

• 2-inch coma corrector for parabolic Newtonian reflectors, specified for fast mirrors from around f/3.9
• Camera adapters are not included — no direct screw-on camera connection out of the box
• Optical design by Harrie Rutten
• EMC coating to suppress internal reflections and ghosting on bright stars
• Variable spacer with markings, so the corrector can be set for different telescopes
• 1 lb (0.45 kg), 69.3 mm diameter, 147.2 mm tall

Optical Design

A parabolic mirror focuses sharply on axis and nowhere else. Off axis, rays from different zones of the mirror land in slightly different places and the resulting flare is coma — stars grow a one-sided tail pointing away from field centre, lengthening the further out you look. The effect scales roughly as the inverse square of the focal ratio, so halving the f-number quadruples the coma. That is why the fast Newtonian you want for wide fields is also the one that shows the aberration worst.

The corrector sits in the converging beam ahead of focus and applies an equal and opposite aberration, pulling those tails back into points. Its distance from the eyepiece field stop or sensor determines how completely it does so, which is why the spacer is marked rather than fixed — different telescopes want different spacings and the markings let you find yours and return to it. The EMC coating earns its place because a multi-element group sitting in a converging beam is otherwise a good source of ghost images from bright stars.

Recommended Uses

• Wide-field visual observing in a fast Newtonian or Dobsonian, sharpening stars at the field edge
• Deep-sky imaging where you already own the M42 or M48 adapters the connection needs
• Star parties and outreach with fast mirrors, where edge-of-field coma is most obvious to newcomers

Compatibility and Accessory Notes

This corrects coma; it is not a focal reducer and will not shorten your focal length or speed up your system. It is designed for parabolic primary mirrors — Newtonians and Dobsonians — not refractors, which want a field flattener instead. It fits a 2-inch focuser and needs enough in-travel to reach focus with the corrector in place. For camera use you will need to add the thread adapter yourself: Explore Scientific points to a T2 camera adapter, and their 2-inch to 1.25-inch adapter (item 510365) is a related part we also stock. Tell us your camera and telescope and we will work out which adapter and what spacing you need before you order.

Good to Know Before You Order

Read the title twice before you buy — this is the corrector on its own. There is no camera adapter in the box, so a DSLR or astro camera cannot screw directly onto it as supplied. The HRCC02-00 version includes both M42x0.75 and M48x0.75 adapters and typically costs less than this listing plus adapters bought separately, so it is the better value if imaging is your intention. Reaching focus is the other common snag: adding a corrector moves the focal plane, and some Newtonians need a low-profile focuser to get there. We can check that with you.

Frequently Asked Questions

Why is this cheaper than the other Explore Scientific coma corrector? Because the camera adapters are not included. The corrector itself is the same — same Harrie Rutten design, same EMC coating, same marked spacer.

Can I still use it with a camera? Yes, once you add the right thread adapter. It is not supplied here, and buying it separately usually costs more than the gap to the HRCC02-00 version. Ask us and we will price both ways for you.

Will it work on my f/5 Dobsonian? Yes — it is designed for parabolic Newtonians and specified for fast mirrors from around f/3.9. Reaching focus is the thing to check, not the optics.

Does it change my focal length? No. It corrects coma and leaves the focal ratio alone. A focal reducer is a different product.

Bottom Line

The Harrie Rutten HR coma corrector, corrector only, at a lower price than the adapter-equipped version. The right buy for visual observers and for imagers who already own their adapters. If a camera is in your plans and your adapter drawer is empty, take the HRCC02-00 instead — our Bolton team will tell you honestly which one suits you.