Celestron EdgeHD 8" + CGX

Worth knowing before you buy

Why do my stars look fuzzy even after collimation?

Thermal equilibration is the primary culprit—the EdgeHD 8's sealed baffle tube traps heat and takes 3–4 hours to cool down completely, significantly longer than standard SCTs. Poor atmospheric seeing, high magnification beyond 25× per inch of aperture, and astigmatism in your observing eye also contribute.

Is the EdgeHD 8 good for visual observation compared to a standard C8?

When properly cooled and collimated under good seeing, the EdgeHD produces sharper stars across the entire field due to its coma-corrected design, especially off-axis. However, owners note that in poor seeing conditions or without adequate thermal equilibration, a standard C8 or C8 XLT may deliver better practical results because their simpler optical path cools faster.

How long does the EdgeHD 8 take to cool down?

Multiple owners report 3–4 hours for complete thermal equilibrium in winter conditions, compared to around 1–2 hours for standard SCTs. The closed baffle tube design with optical elements at the rear restricts air circulation and heat escape.

What collimation method works best for the EdgeHD 8?

Using a high-speed camera with Metaguide or similar software provides more reliable collimation than visual Ronchi or Airy disk methods, which are difficult to perform accurately under typical seeing conditions. Multiple owners emphasize that collimation must be verified on an actual in-focus star image at the edge of the field, not just by achieving a concentric donut in the out-of-focus pattern.

Does back focus distance matter for visual use like it does for imaging?

While back focus is critical for imaging to achieve proper spacing and avoid optical anomalies, visual observers report it has minimal practical impact as long as focus is achievable with the eyepiece and diagonal combination you choose. However, using a shorter visual back (like the 2-inch shorty) instead of the longer supplied back may improve cooling slightly by reducing tube length.

Should I buy the EdgeHD 8 or stick with a standard C8 for visual use?

Choose the EdgeHD if you observe under consistently good seeing conditions, have patience for long cool-down periods, and value a sharp field edge-to-edge. Choose the standard C8 XLT if you want faster cool-down, shorter thermal equilibration time, or observe under average to poor seeing where the simpler design performs comparably.