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Celestron SCT; HD vs no HD


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For an SCT at aperture 9.25" or larger, and for someone who is keen on visual but also some rough and ready imaging of solar system objects as well as DSOs, would I notice much difference between the HD version and the non-HD version? I suspect there must be some significant difference inside as the prices are wildly different.

Thanks for any replies.

James

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The main benefit to the aplanatic SCT designs are the reduction in off-axis coma and increased field flatness, these are significant improvements for DSO imaging ... but doing long-exposure imaging at SCT focal lengths is a tough challenge due to the image scales involved, which makes them hard 'scopes to pick for getting started, and a small apochromatic refractor is much easier if DSO imaging is your ultimate goal. On-axis the distinction between the two designs is less significant, and for planetary imaging the small target size means there's little practical difference between the 'standard' and 'HD'/'ACF' type designs - see Damian Peach's imaging with a standard C9.25, for example, if you need any demonstration of what the 'old' design can do.

As for visual, how much does coma and off-axis sharpness bother you? My experience is that it is very much a personal thing and seems to concern people to different extents, some people hate any off-axis distortion while others are largely indifferent to it (thereby driving all sorts of flamewars online!). If you're unsure it might be worth trying to find someone local to you with a coma-prone 'scope (Newtonian, SCT, etc.) to find out how you find it - remember though that other issues like collimation, cool-down, etc. also play a role in image quality, and they'll affect the HD too. If you find you're after a tack-sharp image across the field of view then you'll need to save up for the HD, but it's really something you need to decide for yourself. Much cheaper to make that discovery with someone else's 'scope if you can :)

Edited by Ben Ritchie
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The mirrors are supposed to be the same, but the Edge HD versions have additional correcting lenses up the baffle tube to sort out the coma and field curvature. There's quite a substantial difference in price for that! But if you use ultra wide (82 degree) or wider eyepieces, the Edge HD makes the stars nice and sharp across the FOV, the non-HD can't. If you stick to 68-70 aFOV EPs and below, you should be OK with the non-HD.

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I had a similar choice and ordered an 8" SCT HD. Stunning images and a fantastic OTA. Alas, my mount broke so I'm selling the edge 8" and have ordered a CPC 1100 deluxe HD.

It should be said though that unless you're going to invest in wide field eyepieces you won't notice the difference.If you go the hyperstar route for imagining then the edge optics are bypassed anyway. What you do get is mirror locks and cooling vents though and according to some 'refractor' like views. I opted for the HD version as it represents the best SCT design you can get.

Just depends on your budget. I plan to keep the cpc for a very long time so the idea of choosing the older model didn't appeal.

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Out of interest, is there any practical difference between the CPC GPS and CPC HD fork mounts (other than being cosmetically different) and handset software? It's hard to tell from the descriptions, and short of doing a line-by-line comparison i'm not sure if i've missed something in passing.

I did notice

  • Re-designed drive base and drive mechanics with spring loaded RA worm block with enveloping brass teeth
  • Re-designed electronics deliver constant regulated power to the motors making them capable of driving the telescope even when not perfectly balance

although i'm not sure what effect this has in practice.

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Out of interest, is there any practical difference between the CPC GPS and CPC HD fork mounts (other than being cosmetically different) and handset software? It's hard to tell from the descriptions, and short of doing a line-by-line comparison i'm not sure if i've missed something in passing.

I did notice

although i'm not sure what effect this has in practice.

I think the changes will be minor at best.

Faster slewing. A whole 1 degree but I bet it's noisier!

None blinding power light but the cable has one too. Doh!

Screw on power cord - noting this might be more of a problem with the cord wrap issue.

Supposedly better tracking.

Personally I think they missed a trick as it would have been better to have the power connection on the base that doesn't rotate and I'd much rather they used quiet motors and forgot about the extra speed.

so in short, I think it will represent a very small set of common sense improvements. I'll confirm when mine arrives as I had the regular CPC a few years ago.

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Everyone is different... in another thread today, one of the guys was describing how he disliked slow slewing scopes :D Again, my opinion only, but the slewing speed is largely irrelevant, but the noise may or may not disturb the neighbours! Mine can go swing ;)

I don't know for sure, but there are supposed to be motor and power upgrades the the Deluxe, along similar lines to the CG5->VX changes. I'm not even convinced of any handset software differences, but it will depend on the age of stock...even the (cheaper) Nexstars have the new handset. From what I've heard, the CPC was no slouch in its accuracy and tracking, and very solid host for the ota. Again, my Nexstar surprises me sometimes and that's only single-arm!

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Get the AZEQ6, unlock the clutches and slew yourself, silently, then lock the clutch and it still know exactly where it is.

But getting back to the question, I don;t think I need EdgeHD technology. Cheers all.

James

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