Longs Focal Length scopes 16" RC vs. CDK 12.5 vs. C14 Edge HD

Mind if I ask why you don't want the 16” Gso rc anymore? Might help others with their suggestions

• With EdgeHD 14 you get half the field size compared to the CDK 12.5”.

• If you want perfectly round stars all the way to the corner, with EdgeHD 14 you will be constantly dealing with mirror flop.

• With a closed-tube design and a much larger mirror, the cooldown time for the EdgeHD 14 is going to be significantly longer.

• If you also want stunning planet images and views, EdgeHD 14 has the ‘edge’.

Collimated fine before repositioning primary.

Might be worth checking how it's mounted?

Best of luck either way, small galaxies are worthy of your efforts :)

So the RC was fine until you moved it? If that’s the case I would exhaust all options in getting your RC sorted before spending money on an entirely new optical system. How were you collimating in the past? RCs aren’t difficult to collimate if done with the right process. Unless some mechanical component was damaged during the move you should be able to get it back into good collimation.

If you have already exhausted all options then then CDK is definitely the way to go. I would just hate to lose aperture if it isn’t strictly necessary.

With a scope of that age you may be right and it’s just losing the battle to time. If it’s losing collimation mid-operation then the primary mirror cell could be your problem. Maybe consider looking into replacing the cell. If it’s possible it could save you a lot of money.

JohnAdastra · May 12, 2026 at 07:24 AM

Our group is seeking a potential scope replacement for a GSO 16” RC at our dark dry site. Two alternatives within our price range seem to be the CDK 12.5” and the Celestron 14” EdgeED. Each has acceptable focal lengths though the optical designs are a bit different between each. If anyone has experience with one or more of these telescopes, we would to hear your honest opinion about the ins and outs and any relative experience you may have had - good or bad. The scope is to be used for astrophotography with high quality filters and a full frame ASI6200MM mono cam. We’re looking to take some high end photos and potential APODS. Please get back if you can help.

Thanks,

John

Putting aide the issues with your current scope, I’ll try to answer your question. I’ve owned an Edge 14 and a CDK20. Both have pros and cons. Both companies can ship very high quality optics; unfortunately, they can also both ship very mediocre optics. Overall the mechanics of Planewave scopes are far superior to Celestron. Still both telescopes can be configured to produce spectacular results. The CDK 12.5 will provide a larger field of view but both scopes can fill a large sensor (36 mm x 36 mm) with corner to corder pinpoint stars. With the Celestron, you should plan on retrofitting it with an Optec SMFS focuser so that you can lock the position of the primary. In my view, both of those scopes can produce excellent results (if you get a good one). You can check out my gallery to see the images that I used to produce with my former C14 Edge. Naill McNeal also has a gallery with a lot of excellent images taken with his C14 Edge. The biggest differences between the two scopes are the price, the quality of the components, and the field of view.

John

PS I won a number of IOTDs and one APOD with data from my former C14 Edge…so if that’s your goal, you might do pretty well with one of those scopes!

Reg Pratt · May 13, 2026, 04:36 PM

With a scope of that age you may be right and it’s just losing the battle to time. If it’s losing collimation mid-operation then the primary mirror cell could be your problem. Maybe consider looking into replacing the cell. If it’s possible it could save you a lot of money.

Tanks Reg. We have gone down a thorough list of troubleshooting and process of elimination. There is a aftermarket mirror cell for $3K, but we might just be adding to the sunk costs without a certain chance of resolution. A replacement scope appears more likely.

John

Jeff Herman · May 14, 2026, 02:50 AM

If you have a good corrector for your GSO RC it might be worth resurrecting it as it could have the potential to out-perform a CDK.

That’s an interesting scope Jeff. Perhaps we’ll look into that brand which seems well designed. We got a corrector for the RC and have tried it with and without, but the collimation issue still is a problem. We haven’t got to the point where we've done an imaging run either way due to all the unsuccessful collimation tries.

Another option would be an AGOptical iDK. Although AGOptical is no longer around, the entire “company" (all equipment, designs, etc.) was sold to Scarlet Astronomy Systems and it looks like they are finally about to get product out the door. I think AGOptical's thermal control/management system is simpler than the PW system and it looks like SAS had refined it further. Just a thought…and yes, I love my AGOptical 14.5iDK.

https://scarletastro.com/pages/production-updates

If I was going to buy a 15000USD CDK telescope I’d get it from PlaneWave for 3 reasons. First, the integrated control system for the rotator/focuser/fans/heaters is all all made by PW and is supported by PW using the PWI4 control system. If I have a problem, I call PW and I do not have to involve other vendors. The second reason is that I’ve owned 3 of these and it takes maybe 30 minutes to collimate one even when something serious has happened to the scope. The final reason is that I KNOW that the scopes are well made as I’ve had two nasty collisions over the past ten years and never had a bit of damage - just needed to collimate and that’s that. In the long run, support at this price level is more important than spot diagrams, IMO.

@JohnAdastra ,

I realize you’ve put some effort into troubleshooting your scope, but have you really gone back to square one with regard to optical alignment? By this I mean, have you 1) made sure the spider is centered, 2) aligned the focuser on the center of the spider with the secondary mirror removed (using the focuser baseplate adjustment screws on the back of the scope), 3) replaced the secondary, 4) centered the secondary mirror spot in the focuser, and proceeded systematically from there? And do you do fine collimation with the DSI method or SkyWave software on real stars?

All of this sounds harder than it really is. I probably spent a half day on bench collimation and a night or two on fine collimation. But this effort was well worthwhile, and I have found the collimation of my GSO 10-inch truss tube RC very easy and incredibly stable. I check collimation every few months and as needed but have not had to make an adjustment in a year. And as a backyard imager without an observatory, this is with me re-mounting the tube on a per-session basis.

Also, when you say the stars change over the course of the evening, it makes me think your imaging train might be sagging. What focuser do you have? The stock one is not very good, in my opinion. I installed a Prima Luce Labs 3-inch Esatto focuser, which is absolutely rock solid. Are your connection points threaded and secure? No compression fittings anywhere? Nothing loose?

Of course, the CDKs and iDKs being discussed are excellent scopes, but you already have an excellent scope. I would try everything possible to troubleshoot the one you have before spending big on something else.

Regards,

Glenn