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Over the Edge, to a CDK

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#1 Ettu

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Posted 08 March 2021 - 01:40 PM

As has been discussed here almost from the introduction of Celestron's Edge design, That it (I am only speaking to my experience with the C11) is capable of outstanding photos, to the corners of a full frame dslr. or a 52mm circle) BUT the loose primary can drive one to drink trying to get the possible potential performance out of it. Consistently, from one area of the sky to another, with long (over 3-5 min) exposures, or after a meridian flip.

 

It was a lot of money to get a Planewave CDK 12.5", only justified in my mind (and to my wife) because I intend to be continuing in this hobby for years to come, and I just can't put up any more with the wasted time of less than capable subs. Planewave's recent $2000.00 price drop finally put me "Over the Edge", and I bought one.

 

After 2 wks now, and with a few good nights to test it out,

Here are my pro and con comments about the switch

 

Plus Side
Sharper, brighter stars, out to the edge of a full frame (36x24mm) DSLR
Much less affected by main mirror boundary layer thermals.
Very little focus change with temperature change.
Extremely sturdy construction.
Extremely sturdy, and squared up to image plane, adapters.
Generous back focus, except with their custom focal reducer (see below)
No image shift, no matter what.
Use of a guide scope, if you prefer that method of guiding, is limited only by how rigid the mechanical interconnection.
4 point secondary adjustment.
Includes a high resolution, zero image shift, absolute position focuser.
20% larger fov,
1/3 less exposure time.
Good weight to size ratio 47 lbs bare, nearer 60 lbs with the focuser and its controller, and the dew heaters and controller.
Temperature, and mechanical stability of the CDK is many many times better.

 

Minus Side
At more than twice the price, when both scopes are at their best, the CDK's images are not twice as good.
Somewhat steeper vignette gradient toward the borders of a 52mm circle. Note: this is a first  impression/observation, not definitively measured.
Bright stars have spikes, if you don't like such things, or are not used to seeing them.
Price doesn't include the focus controller which you have to buy to operate the focuser.
If you want dew heaters, they should be ordered at the time of purchase, as they are not easily added afterward. The Kit, which includes the controller, is not cheap.
There is no humidity sensor, nor any way to link one to the dew control.
Beware! The optional f5.3 focal reducer, reduces the back focus to 1.8”
High shipping weight, 180lbs. Be prepared to receive!
There is an extra $200 crating charge.

 

 

As I look over my list, I must admit, it could give a reader pause about upgrading, but frankly, after wrestling with the Edge for about 5 yrs, it is absolutely wonderful to get top of it's capability photos out of an imaging scope, Every Time. Limited only by my shortcomings, such as, I don't have the sensor quite flat with the image plane yet, and I have the OAG pickoff mirror just a tad too far in.

In other words, it has been worth it for me, and looks like it will be far into the future.


Edited by Ettu, 08 March 2021 - 02:11 PM.

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#2 cougarone

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Posted 09 March 2021 - 09:43 PM

Thanks for the review.  I have been on the fence for either the 12.5 or 14.  Is there a reason why you went for the 12.5 instead of the 14 ? Someday I will make the jump just not sure yet. 



#3 Ettu

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Posted 10 March 2021 - 09:21 PM

Thanks for the review.  I have been on the fence for either the 12.5 or 14.  Is there a reason why you went for the 12.5 instead of the 14 ? Someday I will make the jump just not sure yet. 

You're welcome...

Why the 12.5, ? Simply the price I could afford.

If price were no object, the 14". As I'm sure you've noticed,  it's a little faster, a little better spot diagram, a little more aperture, the same FL and same weight.

But that's just it, it's not 50% (per the price) better. But yes, it is a little better. Also, If you have a camera with a sensor bigger than the full frame dslr, it makes even more sense.

 

Just a couple of comments I can add since the OP. 

If you have humidity issues, you almost certainly will need the dew heaters and controller. The quartz glass mirrors are so slow to change temperature, that if you don't heat them up toward dawn, they'll soon be below ambient and will condense moisture for sure every time. Not good. Their software has provision for this issue, to set it to aggressively heat for the hours of your choosing.

On the evening (temperature drop) side of things, I was pleasantly surprised how little a 2-3 deg C ambient-to-mirror differential affected the seeing due to thermals across the mirrors, or in the tube. The C11 Edge is notoriously sensitive and noisy, even with an insulated tube and vent fans. The first night out with the CDK, I thought I had lucked out with exceptional seeing, with 1/2 the normal tracking "noise". But now, with practically every night being less than I'd normally expect, there must be something more going on. My opinion: the thermal exchange at the boundary layer is a lot slower - hence a lot less effect. It's interesting, the noise I now see seems to be more like atmospheric seeing, not complicated or drowned out with scope issues.

 

Just as a side note, talking to the follows at Planewave, the larger scopes are the ones they're selling the most of, by far. And are way behind. (backordered) At the time I purchased my 12.5", it was the only scope they had on hand, not already sold. So, once I'd made the decision, it was kind of nice to be able to get it before the nights start getting shorter and warmer.


Edited by Ettu, 10 March 2021 - 09:33 PM.



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