- set screws
The optics are worth the price of admission, Crisp, sharp everything you're hoping for. My only suggestion for Celestron is to go back to larger set screws for the mounting plate and accessories.
I've owned my edge for 1 1/2 years now. The focus has too much movement for an ota at this price but it is smooth to operate. The focal reducers for Edge ota's aren't cheap and they still don't have one for the 9.25 Edge. The mirror lock has little effect on mirror flop and I have to refocus often. The stars are pinpoint out to the Edge of the field of view just like they advertise. I did expect the Edge to be sharper at higher powers but it's better if used at lower power. I'm not sure if the extra $1,000. for the Edge was worth it.
Having used SCTs for imaging for many years, I was always a bit disappointed with several factors in their performance. Although many performed exceptionally well and provided excellent images, the short comings always seemed to be a limitation in producing optimal or perfect images. The Edge HD series by Celestron introduced solutions to many of these limiting factors. Curvature, coma and mirror flop were the three most obvious limitations. Each of these has been addressed in a unique and effective way in the HD series. Curvature and coma have become increasingly detractors as CCD chip sizes have grown. From my experiences with a ST7 these were seldom issues but when I moved up in chip size the edges and corners of the images began showing the original SCT limitations. This was addressed by the two element corrector permanently enclosed in the focus tube. These corrector elements eliminate coma and produce a flat field with an imaging circle that is 42 mm in diameter. This opens the new HD scopes for use with ST11000 chip sizes and for the many new moderately sized chips that require corrected field to approximately 27 mm. With my scope well collimated the results are stunning and rival those of instruments costing many times more. Yes you have extra elements and yes there is some additional light loss but, with the efficiency of detectors increasing with each generation, the overall benefits far outweigh any losses. The XLT coating on these elements reduces their effect on scattered light so this although not specific to the new HD series is an excellent use of existing technical improvement. The issue of mirror flop is one that is highly debated. My experience was based on the fact that collimation would change over the course of a night based on the position of the mirror as it moved across the sky. The mirror locks now incorporated in the HD series are both effective and ingenious. They effectively clamp the mirror holder in place at 120 degrees from the focus mechanism. This has the result of providing excellent collimation at any angle. Thus by collimating at any angle, making sure that the telescope is well focused and locking the mirrors collimation is retained and is consistent thru ought the sky. I use an external auto focuser to achieve focus and with some careful manual focus methods I am able to maintain the desired and optimal 146 mm back of scope to imaging surface measurement and still provide autofocus capabilities with only a fraction of a mm off from the optimum 146 mm. This 146 mm spacing is a new concept for old SCT users and although a longer back focus would have been desirable there is plenty of real-estate to use with careful and deliberate imaging equipment choices. The addition of cool down vents was a needed modification since the scope is effectively closed without the vents. If I sound very positive about the HD series and in particular my 9.25, it is simply because this scope although evolutionary in its design is a significant improvement from previous SCT developments. Celestron has one again stepped up the deliverables and has raised the bar for low cost performance! I am looking forward to Celestron's introduction of a focal reducer/corrector for these scopes but in the same direction appreciate the extraordinary ability to use the Faststar, hyperstar capabilities that is present now in all of the HD scopes (Starizona has produced the Hyperstar for the 9.25. If you are searching for a reliable, cost effective and versatile instrument for imaging and visual use, I highly commend this line of Celestron scopes to you. I could not have been more pleased with my selection. Sincerely, Sam Bruce