Review of Planewave CDK17

[gregbradley]

I have had this scope now for quite a while and I thought I would writeup some sort of a quick review of it.

It is very well made. I like the nicely machined aluminimum parts and the carbon fibre truss. Very nice and solid and no flex.
Overall impression is a nicely crafted piece of machinery. The focuser motor area could do with a cover as it looks a little exposed with its cables and a couple of cable ties. It would be nice also if the scope were provided with an end cover or at least one available as an option. It does come with a mirror cover but it is awkward to install and takes paint off the baffle. My wife made me a nice cloth cover for the end of the scope with elastic. It is white material so I can shoot flats in the daylight with my observatory roof closed and they are perfect so that was very very handy.

I did order the spandex light shroud and that works very well and is easy to use.

The scope is not super heavy (well 68KG) but being large it is awkward to handle so it is a 2 man operation to mount it. I do not see any flex at different angles, it can be on its side way over on the mount and no problem.

Mine is mounted on a Paramount ME which moves it around like it is nothing.

The large dovetail mounting plate is good and I can shift the scope in it by myself to adjust balance.

The focuser is very good and is quite repeatable althought I find coming from one direction to focus and going past it then back it often does not land on the same spot for sharp focus but its easy enough to use and that is a minor point.

My scope had very bad flaring from nearby bright stars that was affecting the occassional image. Joe from Planewave took this on board and made a new type of secondary mirror shroud which fixed this problem and he sent it to me free of charge which was great.

The flat black internal paint is quite weak and comes off fairly easily as I noticed when flocking my secondary mirror shroud and also where the mirror cover goes over the baffle it takes a bit of paint off. Minor really.

I find the mirrors need to equalise in temperature before a fully sharp focus can be achieved. Also focus will shift slightly if the temperature differential drops in the night. It may take 1.5 to 2 hours to overcome a 2C difference in temperature. The electronic fan control allows for automatic temperature control but that is really an unnecessary feature at least in Sydney as the fans full on seem to be needed to keep the mirror close to ambient all the time. Only rarely have I seen the mirror temp drop below ambient and if it does its only by about .1C which is neglible.

The scope does not have dew control built in but I believe it can be ordered as an option. I did not order that and I have noticed a dew problem only twice now out of 50 uses and even then it was only right near the end of the night anyway.

I have not cleaned the mirror yet but it appears to be an easy procedure with the truss design allowing easy access to the mirror.

Focus is not the same night after night like my 12.5 RCOS but it is often the same or very close so that is good performance but you do need to check focus each time as it may have shifted a small amount. The scope with the electronic focuser option has a fairly large critical focus zone so getting precise focus takes a bit of getting used to and means exact focus seems to be within about 20 microns or more and you could mistake a momentary piece of poor seeing with a shift in focus.

I have been imaging using a FLI Proline 16803 camera and also a FLI Microline 8300 camera. The 16803 is a heavy camera and the adapters Planewave make are unusual in that they are several plates bolted together but they are very rigid so I have not found any hint of flex in the focuser which is a really good feature. Although because it is a muliple plate adapter screwed together with allen key head scews one layer could be slightly loose and you would not know. I took my imaging rig off which became a larger chore than necessary because of this approach and I found the base plate was a little loose. Also when I loosened the very bottom plate it had spacers that fell out that I did not know were there. This is typical US style engineering which is practical but a little less refined than a Japanese made product like a Takahashi. US style engineering though goes for strength which at the end of the day is more important.


With the 16803 camera, stars are pinpoint to the corners and the scope will take in a lot of light fast. Images are easy to take.

I did find with the larger chipped camera the vignetting associated with the design shows up. It means I have to be careful with my flats which do not fully correct it and I often have to use background evening out techniques in processing. This is a large chip thing as the 8300 does not have this issue. Stars are pinpoint to the corners of the 16803 images but it does take this extra processing emphasis to correct it. It does mean though that narrowband imaging in a light polluted location with a large chip will only work on bright objects. I took about 6 hours of Ha on the Helix during a bright moon period with the 16803 camera and they were useless. The bright central hot spot of the optical design drowned out the delicate Helix and it could not be recovered with flats. Narrowband during no moon periods would be fine. Heavily light polluted areas though would require a smaller chipped camera with larger pixels as the ideal setup.

It is hard to comment on the sharpness of the optics as the large aperture shows up the effects of seeing very easily. They are sharp but perhaps not like an Ion Milled 14.5 RCOS (at 2 or 3 times the price).

But a future trip to my dark site where the seeing this time of year is often very good and no light pollution will show the potential of the scope much more clearly.

I did a collimation last night and it was easy. The procedures worked well and the tools for checking spacing were easy to use. Collimation was only slightly off after nearly a year and shipping from the USA and spacing seemed accurate or very very close.

All in all a wonderful scope which I am enjoying and it opens up a lot of possibilities in the imaging world.
But it is limited by the seeing so if you are in an area where the seeing is not so great then it won't shine until those few stable nights.
A 6 or 7 inch refractor is less seeing affected and it may be the better choice for urban imaging or image the many brighter objects only.

I have an F4.45 reducer on the way so that probably will reduce the effects of seeing quite a bit and make the scope even more versatile. I am not aware of a reducer for any RCOS or other similar scope so that is a real plus. Hopefully it works really well. Stay tuned for a report.

I must add to this review that in light of the cost US$22,000 it is way way cheaper than its competitor 16 inch RCOS at around $50,000 but a bit more expensive than the Orion Optics UK 16 inch (at the time of ordering OOUK seemed to be overwhelmed by a lot of orders and were also still developing the scope). OOUK have since delivered a few CDK type designs and I believe after a few initial problems have probably sorted them out. There is also a new competitor to Planewave CDK for a similar price. Planewave though have moved forward in leaps and bounds and have several highend mounts, several large aperture CDKs and have brought out a rotator now or are about to (I don't see it as a necessity unless you are doing remote imaging).

Overall I am very happy with this scope, it is a keeper. I thought it would be a little sharper but that may be the seeing in my area. Certainly on brighter objects it has been very sharp. It does require the right camera to match it which would be a camera with at least 9 micron pixels. 6303E, 11002, 16803, 09000 chipped cameras would be ideal. A Proline 4240 camera with 13micron pixels and 95% QE may be ideal.

Greg.

[multiweb (Marc)]

Good write up Greg. It's always good to hear that a rig is performing within its specs. Now to a dark site.

[allan gould]

Nice write up Greg, but its way out of my league

[bert (Brett)]

Its nice to see an informal warts and all review. So many reviews tend to be almost an ad!

Thanks for taking the time to write this, Greg.

[gregbradley]

Originally Posted by multiweb

Good write up Greg. It's always good to hear that a rig is performing within its specs. Now to a dark site.

I getting a plate to fit to my pier at my dark site so I can take the PME and the CDK down. It'll be a 2 man job but if I go there for a week with a good weather forecast in the no moon period and if work were all setup it would be worth the effort.

Originally Posted by allan gould

Nice write up Greg, but its way out of my league

In your instance Allan it would not suit your location anyway so you are not missing out on anything. It really needs decent seeing and dark skies
(like any scope) but some scopes perform better in an urban light polluted environment where the seeing is often poor to make matters worse.

Originally Posted by bert

Its nice to see an informal warts and all review. So many reviews tend to be almost an ad!

Thanks for taking the time to write this, Greg.

I know what you mean Bert. Planewave have been good to deal with and except for a messup on the shipping cost they've been great.

[RobF (Rob)]

Thanks for taking the trouble to write up this and many previous similar sorts of reviews Greg. I'm way out of the price league too, but its nice to day dream, and you never know when you'll pick up a bit of info that might help somewhere, even if the problems are on a completely different scale.

Looking forward to your Gold C AIC talk too.

[Bassnut (Fred)]

Another very usefull, readable and unbiased review. Top work Greg, I look forward to them, its the kinda gear Im interested in too, bonus.

[gregbradley]

Originally Posted by RobF

Thanks for taking the trouble to write up this and many previous similar sorts of reviews Greg. I'm way out of the price league too, but its nice to day dream, and you never know when you'll pick up a bit of info that might help somewhere, even if the problems are on a completely different scale.

Looking forward to your Gold C AIC talk too.

Thanks Rob. I look forward to meeting you there.

Originally Posted by Bassnut

Another very usefull, readable and unbiased review. Top work Greg, I look forward to them, its the kinda gear Im interested in too, bonus.

You're welcome Fred. I was thinking of you with your planned narrowband work with this or similar scope. It would be fine but I think most practical with a smaller chipped camera. The ST10XME setup you are using is probably an excellent match. Slightly small pixels at 6microns but the ST10 with such high QE seems to get away with it with large scopes. Vignetting would not be an issue, thats a 16803 chip issue.
You could use a large chip in your location but I think you would find you would be limited to the brighter objects (which you have mostly already done) or NB imaging when there is no moon (there goes half the time).
I was thinking of getting a 3200 chipped camera to see how it went with it at some point. The 8300 isn't a good match at all (pixels too small) but I think it would work well if its a night of good seeing (how often is that after you consider out no moon, no cloud and then good seeing out of what is left??) Its not a lot of nights here.

The CDK12.5 is slightly different to the CDK17 in that it is F8 and is also an awesome scope.

Sometimes the aperture is a pain. Last night imaging Lagoon, focus was difficult because it would look sharp, I'd take another focus image (without changing focus) and it would look out of focus -it was just a bit of poor seeing. Wow.

Generally I try to image fairly close to either side of the meridian.

Greg.