CDK14 vs. CDK17 - Forums

Hi,

I’ve narrowed my search for a new telescope for remote observing to a Planewave. I plan to put this telescope in New Mexico, hopefully at Howling Coyote Observatories, with median seeing conditions of 1.5 arc-seconds. The mount I will be using is an AP1600 with encoders, and the camera is a QHY600M (FF, 3.76 micron pixels, with and without a reducer).I have read nearly all the excellent forum discussions and analyses by John Hayes, Rouzbeh Bidshahri (Rouz Astro) and others regarding Planewave telescope choices (CDK12.5, CDK14, CDK17, CDK20), and see that so much depends on the camera sensor, pixel size and seeing; and that sometimes the smaller aperture is better. My choice is down to the CDK14 and the CDK17. I realize that the CDK17 is much heavier, but once I set it up, I won't be moving it.

Which one is best for my potential seeing and the equipment that I will be using? I could almost decide on my own, based on what I've read, but I'm looking for the final word! That’s where I need advice; I don’t want to make a mistake at these levels! I would appreciate all thoughts/suggestions. Thank you.

All the best,

BobH.

We run telescopes for HCRO as their official provider of subscription services. There’s a CDK700 system that should be fully online in April but I can tell you that if the site is good enough to support the CDK700 you can feel confident a CDK17 will be just fine. Our testing showed excellent data on the 700. There’s already plans to deploy even longer focal length systems there (also for subscriptions and data) so I think you’ll enjoy the site and a CDK17 nicely.

Hi,

Thanks for that information; good to know. I really have been conflicted, but understood that the site was exceptionally dark. I appreciate.

Bob H.

I have a CDK 14 at a site that has seeing that averages maybe 1.5 and commonly approaches or slightly exceeds1.0. To be honest there are a couple CDK 17 there that are not producing higher resolution images than I do with the 14. Of course that could be partly the ancillary equipment such as the SXAO or just the fact that I am picky and have a high reject rate that I impose on my data.

My take is that the only reason to go for the 17 instead of the 14 would be the faster speed, not the extra FL, and I think you would be quite happy with either. I have no experience with Howling Coyote so can't comment on the seeing there but I have had setups at Dark Sky NM and Deep Sky West and neither of those had seeing close to what I have at the California site I am at now. Sadly, they are full-up right now.

Hope that helps.

Hi Bill,

It sounds like you have found an excellent location. Thanks for your critically important hands-on input! Part of the equation in making this decision is that I’m stepping up from a 7” f9 Astro-Physics refractor, which has been an excellent performer and quite an easy scope to manage. I want more aperture and a faster scope. You mention FL: The CDK14 would already be quite an improvement for my intentions, and I plan to use this scope some of the time with the 0.66 reducer, making this scope a f4.7. Would the CDK14 feel like enough of an improvement in light gathering? I think it would.

I occasionally fly small planes, the most sophisticated being a Cessna 182RG. My impression is that the CDK14 might feel like that plane, while the CDK17 would be like stepping into a Lear jet! I want to be careful to not take on more than I can manage. Should I want to bring this scope back to my observatory in Maryland (near Washington, DC), the CDK14 might make sense, but the CDK17 definitely would not, given the poor seeing and the massiveness of that scope. I definitely couldn’t manage to put it on the mount myself. It’s this balancing act, literally and figuratively, that has made this decision more difficult … and then there is the cost, which only I can answer. All of this, and your comments, lead me to give more serious consideration to the CDK14, even though the CDK17 seems the obvious choice should the scope remain in a very dark environment. Thanks again for taking the time to respond.

BobH.

Hi Bill,

It sounds like you have found an excellent location. Thanks for your critically important hands-on input! Part of the equation in making this decision is that I’m stepping up from a 7” f9 Astro-Physics refractor, which has been an excellent performer and quite an easy scope to manage. I want more aperture and a faster scope. You mention FL: The CDK14 would already be quite an improvement for my intentions, and I plan to use this scope some of the time with the 0.66 reducer, making this scope a f4.7. Would the CDK14 feel like enough of an improvement in light gathering? I think it would.

I occasionally fly small planes, the most sophisticated being a Cessna 182RG. My impression is that the CDK14 might feel like that plane, while the CDK17 would be like stepping into a Lear jet! I want to be careful to not take on more than I can manage. Should I want to bring this scope back to my observatory in Maryland (near Washington, DC), the CDK14 might make sense, but the CDK17 definitely would not, given the poor seeing and the massiveness of that scope. I definitely couldn’t manage to put it on the mount myself. It’s this balancing act, literally and figuratively, that has made this decision more difficult … and then there is the cost, which only I can answer. All of this, and your comments, lead me to give more serious consideration to the CDK14, even though the CDK17 seems the obvious choice should the scope remain in a very dark environment. Thanks again for taking the time to respond.

BobH.

Yes, with the reducer it should be much faster, but of course the sampling would also be poorer so depending on the seeing it might or might not be sampled enough. Things like BXT benefit from what used to be thought of as somewhat oversampled so there is that.

I used to fly as well and have a SEL license and took instrument training way back in the 1980s. Gave it up after around 400 hours due to it's lack of practicality. Mostly 172 but occasional use of 172RG (aka Cutlass), 182, and P210. Cutlass was my favorite. Just high-end enough w/o being too heavy.

Hi,

I agree about the reducer, but I can decide whether or not to use it depending on conditions. I do like having the option so I'm glad Planewave makes one.

I've flown most of those planes. Now I stick with astrophotography!

Bill McLaughlin:
I have no experience with Howling Coyote so can't comment on the seeing there but I have had setups at Dark Sky NM and Deep Sky West and neither of those had seeing close to what I have at the California site I am at now. Sadly, they are full-up right now.

The median annual seeing based on the data from the installed Alcor seeing monitor is 1.5" FWHM. That is the same median annual seeing that Chile gets. The min in Chile is of course lower than HCRO, but at the median the sites are competitive from that standpoint. There are many nights of sub-arc seeing at HCRO. I think it is important to note that the site is located in Pie Town, NM and not Animas or Rowe, which usually have worse seeing.

NASA has their VLA located about 40 or so mins from the site, which is usually a good sign you are in the right place for astro.

Hi Bill,

Those are impressive skies. I've spent much of my life near cities, so am looking forward to consistently dark skies without needing to travel.

Not that it matters for this discussion, but I am not replacing the AP 7" refractor on a 1200 mount which is in my observatory in Maryland; I just don't plan to take it to NM. For the darker skies of the West, I want more aperture for DSO and that's why I'm pursuing the PW scopes.

Bob

Hi Bill,

Those are impressive skies. I've spent much of my life near cities, so am looking forward to consistently dark skies without needing to travel.

Not that it matters for this discussion, but I am not replacing the AP 7" refractor on a 1200 mount which is in my observatory in Maryland; I just don't plan to take it to NM. For the darker skies of the West, I want more aperture for DSO and that's why I'm pursuing the PW scopes.

Bob

Pie Town (and thus HCRO) is along the New Mexico Route 60 Dark Sky Corridor. Super dark and super good seeing there.

Not that it matters for this discussion, but I am not replacing the AP 7" refractor on a 1200 mount which is in my observatory in Maryland; I just don't plan to take it to NM. For the darker skies of the West, I want more aperture for DSO and that's why I'm pursuing the PW scopes.

That makes a lot of sense. Not just the darkness but the seeing especially is better in the West although the seeing can still vary a lot even in the West since the terrain near the observatory (within 50-100 miles) can have a big effect on the seeing.

I spent a night at a sight about 15 miles east of Pie Town and experienced the darkest skies I have ever seen. Other than a small light dome from Albuquerque to the north east, it was perfect. The fact that it's well over 7000' in elevation doesn't hurt as far as transparency goes. I don't know about the seeing though. Having lived in both the north and southern parts of the state for 40 years, I can tell you that the seeing is generally not great. The environment tends to have large day/night temp. swings which doesn't help. That said, the best seeing I have encountered in my life was at the Sun Spot solar observatory in the Sacramento mountains just outside of Alamogordo so there are places, usually west facing mountain ridges that can be amazing due to laminar air flow. Overall, while amazing seeing can be found in isolated spots, in general it tends not to be great. In fact, I get much better seeing here in Oklahoma, especially in the winter months.

Dear Bob

Some time ago I was also considering both scopes you mention, I ended up owning a CDK14". It is true that at natural focal length the CDK17 gathers more light and offers more focal length. Here a nice discussion post about it (CDK14 vs CDK17 Analysis - Experienced Deep Sky Imaging - Cloudy Nights); however the CDK14 with the reducer it does a good job and there are many users getting fantastic results.
Then, I start considering other factors, such as the weight of these scopes. While the CDK14 weights only 22Kg, the CDK17 scales up to 48 Kg, these 3 inches are adding a lot of weight. This was a critical point, because I needed a mount to move the scope, and aiming for a 10micron mount , the load capacity of the mount adds a lot to the budget. Then there are many other things to consider when coming from a refractor, as it was my case (had an Esprit 120ED), but this is off topic.

I got the CDK14 and a 10micron GM2000 HPS II combi, these are not cheap equipment, what I mean is that both together offers an exceptional performance for a reasonable amount of money. Having the CDK17, with a GM3000 HPS to move such heavy load, would increase a lot the budget.

That was my main reasoning that helped me to take a decision, where I compromise a reasonable amount of money for an exceptional equipment.

CS

Obdulio

Tony Gondola:
the best seeing I have encountered in my life was at the Sun Spot solar observatory in the Sacramento mountains just outside of Alamogordo

That would make sense. There is also Apache Point Observatory and Sloan Sky Survey right close to there as well and the White Sands plain/desert lies just to the west so that might give good laminar flow. The only negative is that blowing sand can sometimes be an issue as well as the Miller moths...

I spent quite a lot of time in the area building the ORION observatory across the street from New Mexico Skies.

So you know the area well. it's interesting that at the Museum observatory just at the base of those mountains the seeing is generally awful. The 16" there was very rarely usable.

Hi Obdulio,

I try not to think that I have budget. I remember when I was considering an addition to my house and the architect asked if I had a budget. I said no. He said Bill Gates has a budget! So, I do and the 17" is considerably more expensive; something to consider. The weight of the CDK17 is a major concern/consideration for me, especially if I might want to use it back in Maryland. I appreciate your input and I'm glad you found the perfect combination. Hopefully I will, as well.

BobH.

I would I've been having fun watching this discussion. The scopes in question are well out of my league but if I imagine myself in that position I would ask the question I always do, what is the balance between image improvement and cost. The difference in resolution is trivial so in my mind, what you are getting an increase in image scale at twice the price considering the mount issue. That would be a no from me, I'd go with the 14.

Thanks everyone for the input. I'm now definitely settled on remote observing from the area around Pie Town, NM. Even though my plan is remote imaging, I want to set up this entire rig in Maryland … mount, scope, camera, communication, etc. … everything working well together before transporting it to NM. Here in Maryland, I have no help for setting up a telescope, but could manage a CDK14 on my own, and the 14” would probably not be too much scope for the seeing. The CDK17, on the other hand, is a beast by my standards, and I believe its aperture would be wasted in Maryland, given the light dome of Wash., D.C. and Baltimore.As things go in life, at some point, the scope could end up permanently in Maryland. That said, is the 17” so much better in the NM dark skies than the 14” that I should overcome all obstacles and get the larger scope? That sums up my dilemma. As my brother likes to say, this is a first-world problem!

Thanks everyone for the input. I'm now definitely settled on remote observing from the area around Pie Town, NM. Even though my plan is remote imaging, I want to set up this entire rig in Maryland … mount, scope, camera, communication, etc. … everything working well together before transporting it to NM. Here in Maryland, I have no help for setting up a telescope, but could manage a CDK14 on my own, and the 14” would probably not be too much scope for the seeing. The CDK17, on the other hand, is a beast by my standards, and I believe its aperture would be wasted in Maryland, given the light dome of Wash., D.C. and Baltimore.As things go in life, at some point, the scope could end up permanently in Maryland. That said, is the 17” so much better in the NM dark skies than the 14” that I should overcome all obstacles and get the larger scope? That sums up my dilemma. As my brother likes to say, this is a first-world problem!

Going to send you a private message about your deployment plans, JFYI.

Tony Gondola:
I would I've been having fun watching this discussion. The scopes in question are well out of my league but if I imagine myself in that position I would ask the question I always do, what is the balance between image improvement and cost. The difference in resolution is trivial so in my mind, what you are getting an increase in image scale at twice the price considering the mount issue. That would be a no from me, I'd go with the 14.

Hi Gondola,
Based on this discussion, and my belief that this scope will eventually find its way permanently to Maryland, now has me leaning more toward the 14". That scope is much more manageable than the 17", and certainly at less cost. I've been using 4" to 7" refractors for decades and believe even the 14" will be quite impressive. Also, I don't want to forget that I do have a life outside of astrophotography (I know, hard to imagine)! Thanks again for the thoughtful input.
Bob H.

I cant help you with your scope choice, but I have a scope at HCRO since August and just spent 4 nights there. The site is amazing, I've never seen such dark skies. The site owner lives on site and is an amazing host. Highly recommended!

You’ve already received a lot of good advice but here’s my two cents. In my view, the CDK17 is in a sweet spot. Planewave did a good job with the design and I’ve seen spectacular results come from their 17” systems. Having a bigger scope puts you in the position of being able to take advantage of the seeing when it’s better and it will work no worse than the 14”. As for the size, get a shop crane to put it on the mount. Harbor freight sells a nice one that isn’t all that expensive and that’s what I used to move my CDK20 when I was setting it up. There are pictures of it here: https://www.astrobin.com/dlko5b/N/#rC. You can’t go wrong with the 14” but if it were me, I’ll always go for the bigger aperture.

John

John Hayes:
You’ve already received a lot of good advice but here’s my two cents. In my view, the CDK17 is in a sweet spot. Planewave did a good job with the design and I’ve seen spectacular results come from their 17” systems. Having a bigger scope puts you in the position of being able to take advantage of the seeing when it’s better and it will work no worse than the 14”. As for the size, get a shop crane to put it on the mount. Harbor freight sells a nice one that isn’t all that expensive and that’s what I used to move my CDK20 when I was setting it up. There are pictures of it here: https://www.astrobin.com/dlko5b/N/#rC. You can’t go wrong with the 14” but if it were me, I’ll always go for the bigger aperture.

John

Hi John,
I appreciate your advice, especially since you've had quite a lot of involvement with PW scopes.\. I've been following your building out of the Planewaves for Chile; very impressive project! Your experiences is what got me taking a close look at the PW scopes. I have decided that the 17" makes the most sense, especially hearing it from you. I was trying to balance the various future contingencies ... New Mexico and Maryland ... but as you say, the 17" won't be worse than the 14" in bad seeing. As for the weight/size, once I set it up, it's not likely to be moved.
Thanks again. I appreciate you taking the time to respond.
Bob H.

Chris White- Overcast Observatory:
I cant help you with your scope choice, but I have a scope at HCRO since August and just spent 4 nights there. The site is amazing, I've never seen such dark skies. The site owner lives on site and is an amazing host. Highly recommended!

Hi Chris,
I've been hearing the same from many who have visited this site or have a scope there. I appreciate the recommendation.
Bob H.

Congratulations on the CDK17 Bob, I am right there with you.
I had a TEC 180 FL (1260mm FL f/7) set up on a SB Paramount ME II (with absolute encoders) and Moravian C1x-61000 at my home in coastal San Diego CA. I grew frustrated with the limited clear nights, so after about a year and half I decided to move it to HCRO. This past January I drove out there for the setup. I was amazed by the conditions there and the service Greg (owner) and Shane (technician) provided during my 2 days at HCRO. As a result, my TEC 180 rig is producing great data. My point here is that there is no need to make sure your new setup works before shipping it to HCRO. Greg and Shane can handle all of it.

Where this gets interesting is that I was so impressed with the service at HCRO and quality of the data I decided that CDK 14 or 17 would allow me to acquire data from even more potential targets. I ended up finding a CDK17 on Astromart and also selling my TEC 180. It was my discussion with Greg at HCRO that made me decide to go with the CDK17. Greg described the optics on the CDK17 as the sweet spot (similar to John Hayes). I will be going to Animas NM in mid-March to pick up the CDK17 and drive it to HCRO where Bill Long (Dark Matters) will be helping with the setup. I am looking forward to really making use of the sky conditions at HCRO to their fullest with the CDK17.
Cheers - Gene