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14inch CDK comparison?

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#1 Gert

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Posted 10 November 2017 - 01:16 AM

Hello All,

 

How do these three compare?

  • Planewave CDK14 (F7.2, Obs 48.5%, 48lbs)
  • AG Optical 14.5 (F6.7, Obs 51.7%, 54lbs)
  • Orion UK ODK14 (F7.2, Obs ??, 26kg) (Noteworthy they give 2nd mirror diam, not obs. As if a baffle doesn't count)

Not sure what I will do with the scope. A bit of all, maybe. Don't want an SCT or Newt.

 

Thanks,
Gert

 



#2 orlyandico

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Posted 10 November 2017 - 01:57 AM

There are a number of rants here on CN about the quality of Orion UK products in general. You can search for it.

 

If I was in the market for a CDK14, I would rule them out on that basis and limit myself to the first two. I know it's not very fair but AGO and Planewave have excellent reputations, so why bother with a vendor that has attracted negative feedback.



#3 rgsalinger

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Posted 10 November 2017 - 02:23 AM

All I can say is that on the Planewave Yahoo group I have yet to see in the 9 months that I've been lurking there anyone complaining about the optics in their telescope. My 12.5 survived a 600 mile car right from my house to my remote observatory. I love the integrated heating/fan/focuser on the thing - very few dangling cables - and one piece of software controls everything.

Rgrds-Ross


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#4 ManuelJ

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Posted 10 November 2017 - 02:35 AM

Orion UK is a nice option if you like pain and suffering.


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#5 orlyandico

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Posted 10 November 2017 - 04:41 AM

+1 I was very interested in the Orion UK ODK14 because it's cheaper than the AGO and Planewave options ($8300 vs $15000 for the Planewave and $15.6K for the AGO). And money is indeed a factor. That's a huge difference.

 

Makes you wonder why there's a huge difference...

 

And... if you are unlucky... all that money you "saved" will be for nothing.



#6 Terry White

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Posted 10 November 2017 - 08:22 AM

As a prospective buyer, I too have concluded that the best high-end 14-inch class astrographs are those made by Planewave Instruments (cDK) and AG Optical Systems (iDK). I have dropped the Celestron and Meade modified SCT designs from consideration because of issues with a moving primary mirror. The main differentiators between the two are:

 

Price - (assuming fused quartz mirrors) $16,500 (cDK) vs. $15,575 (iDK)

Imaging Circle - 70 mm (cDK) vs. 60 mm (iDK)

RMS Spot Size Diameter - < 6 microns @ 70 mm (cDK) vs. < 9 microns @ 60 mm (iDK)

OTA Weight - 48 lbs. (cDK) vs. 59 lbs. (iDK)

Primary Diameter: 14-inch (cDK) vs 14.5-inch (iDK)

Customer Optical Test Report: No (cDK) vs. Yes (iDK)

 

The cDK, with it's slightly larger imaging circle, appears to be a little more future-proof in that it is more compatible with the next generation of large format CCD chips. Both OTA's are beautiful astrographs with many satisfied customers. I'm looking for your input, so please feel free to correct any errors that I may have made. Thanks.


Edited by Terry White, 10 November 2017 - 09:13 AM.

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#7 macdonjh

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Posted 10 November 2017 - 01:30 PM

I know owners of both PlaneWave and AG Optical and all are happy.  I don't think you will go wrong with either as long as you do your due dilligence and understand the differences between the scopes (like Terry White did, above).

 

If you're interested in DSO phtography, the following may not be applicable, but CFF also makes good scopes.  I really like my 14" classical Cassegrain visually, and DJ Hanson uses a similar 14" for planetary photography.  Much slower, at f/15 or f/17, than the CDKs, though.


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#8 Gert

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Posted 10 November 2017 - 02:16 PM

Hello All,

 

Thank you for the interesting feedback.

 

I'm coming from a PW CDK12 where I did check the optics on ronchi and star test. There were some polishing artefact zones that I could document. PW responded though that the zones were under their production tolerances and there would be no need for action. Optically I would place PW better than C or M but not on a level of Tak or AP. The optioal report that comes with the iDK is a bonus.

 

One thing I don't like with the CDK + iDK is the increase of central obstruction. I do like my scopes to perform visually as well and diffraction limited on-axis performance is a must. I care less about 70mm image circle diam @ <10um stars. There are very few amateurs with sensors in that class now or in the near/mid future. The claims for these image circles look like number marketing to me and I would rather have <50mm image circle on-axis diffraction limited performance and 5-10 percent less central obstruction.

 

On another note I like the closed OTA at Orion ODK. I once approached PW about offering a closed OTA in the 14 and 17 as they do in the 12 but they would not consider. They offer a cloth light sock, But for operation in a light polluted environment with possibility of dew I like OTAs that I can wipe down with a kitchen towel when wet.

 

I still don't consider M & C. I hat several of each and closed OTAs, thermal equilibrium problems, sub top-notch optics sent all of them to Astromart.

 

Clear Skies,

Gert



#9 carolinaskies

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Posted 10 November 2017 - 02:41 PM

Hello All,

 

Thank you for the interesting feedback.

 

I'm coming from a PW CDK12 where I did check the optics on ronchi and star test. There were some polishing artefact zones that I could document. PW responded though that the zones were under their production tolerances and there would be no need for action. Optically I would place PW better than C or M but not on a level of Tak or AP. The optioal report that comes with the iDK is a bonus.

 

One thing I don't like with the CDK + iDK is the increase of central obstruction. I do like my scopes to perform visually as well and diffraction limited on-axis performance is a must. I care less about 70mm image circle diam @ <10um stars. There are very few amateurs with sensors in that class now or in the near/mid future. The claims for these image circles look like number marketing to me and I would rather have <50mm image circle on-axis diffraction limited performance and 5-10 percent less central obstruction.

 

On another note I like the closed OTA at Orion ODK. I once approached PW about offering a closed OTA in the 14 and 17 as they do in the 12 but they would not consider. They offer a cloth light sock, But for operation in a light polluted environment with possibility of dew I like OTAs that I can wipe down with a kitchen towel when wet.

 

I still don't consider M & C. I hat several of each and closed OTAs, thermal equilibrium problems, sub top-notch optics sent all of them to Astromart.

 

Clear Skies,

Gert

If you'd like a semi 'closed tube' feature you could always spend the money for custom panels attached to the truss system or make a 'false' tube wrapping the truss in material similar to dew shields.  A simple and effective methodology while still maintaining the benefits of a truss system.  If that wasn't enough, I suspect you could custom order a carbon fiber tube to fit your choice of optics.    



#10 Riccardo_italy

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Posted 10 November 2017 - 04:34 PM

I have an OOUK VX8L and it works well.

 

Don't know anything about their CDK.....



#11 Jared

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Posted 10 November 2017 - 06:35 PM

Hello All,

 

How do these three compare?

  • Planewave CDK14 (F7.2, Obs 48.5%, 48lbs)
  • AG Optical 14.5 (F6.7, Obs 51.7%, 54lbs)
  • Orion UK ODK14 (F7.2, Obs ??, 26kg) (Noteworthy they give 2nd mirror diam, not obs. As if a baffle doesn't count)

Not sure what I will do with the scope. A bit of all, maybe. Don't want an SCT or Newt.

 

Thanks,
Gert

Hey, Gert,

 

Fit and finish is better on the AG Optical scopes than you are used to on the PlaneWave.  Probably little if any difference functionally, though. These scopes are a touch faster than your 12", so the central obstruction is just that much larger.  May not be desirable from your perspective, but I'd basically consider these dedicated astro graphs.  Delivery dates have sometimes been quite long with AG Optical (depending on the backlog for the person figuring the mirrors) so double check before you make a decision.  I agree with the others that I would avoid Orion UK based on the number of complaints I have seen here over the years.  No direct experience, but when you are talking about something as big and difficult to ship as a 14" CDK, I'd stick with the U.S. based companies for U.S. customers.  Warranty work on something like this... Best to just avoid the question. I think your odds of success are much higher with PlaneWave or AGO.  The people at both companies are great to work with.  Heck, I learned all I needed to about Orion UK when I went to the front page of their website.  They promise that while other optics may deliver views like this...

 

blur.jpeg

 

Their's will show you this...

 

sharp.jpeg

 

"No Question."

 

Encke gap, no question, huh.  And they are in the UK, for heaven's sake, which is not exactly renowned for its fine seeing conditions!  Those kinds of over the top claims just turns me off.  


Edited by Jared, 10 November 2017 - 06:49 PM.

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#12 Gert

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Posted 10 November 2017 - 09:24 PM

...

Heck, I learned all I needed to about Orion UK when I went to the front page of their website.

...

Love it! Is that the department store 2inch 500x power scope advertising on astrographs? :-)

 

Cheers,

Gert



#13 orlyandico

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Posted 10 November 2017 - 09:31 PM

There's this person in Germany, Klaus Helmerichs, who will sell you a carbon fiber tube of whatever size you want. It won't be cheap ($600+) but a drop in the bucket compared to the cost of the CDK14.

 

CFF is a fairly new company and there are very few scopes out there.. but I read a report of a bad experience with one of their DK's that required rework. Granted, one report. But how many CFF DK's are out there?



#14 Gert

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Posted 11 November 2017 - 04:05 AM

Hello All,

 

I promised the optics test documentation from the CDK12. This is a prime focus star-Foucault image. That's as close to the actual mode of operation of the optics as can be.

 

CDK125_Null_Test_20100313_1s.jpg

 

Clear Skies,

Gert


Edited by Gert, 11 November 2017 - 03:17 PM.


#15 Axunator

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Posted 11 November 2017 - 04:33 AM

 

CFF is a fairly new company and there are very few scopes out there.. but I read a report of a bad experience with one of their DK's that required rework. Granted, one report. But how many CFF DK's are out there?

I presume none because reflectors they make are either classical Cassegrains or Ritchey-Chretiens...



#16 orlyandico

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Posted 11 November 2017 - 06:03 AM

My mistake.

 

Some months back there was supposed to be a shootout between a CFF (probably a classical Cass) and a Mewlon 250 which is a DK. I conflated the DK with the CFF.

 

It's here on the forums somewhere..

 

 

 

 

CFF is a fairly new company and there are very few scopes out there.. but I read a report of a bad experience with one of their DK's that required rework. Granted, one report. But how many CFF DK's are out there?

I presume none because reflectors they make are either classical Cassegrains or Ritchey-Chretiens...

 



#17 Axunator

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Posted 11 November 2017 - 11:15 AM

 

Some months back there was supposed to be a shootout between a CFF (probably a classical Cass) and a Mewlon 250 which is a DK. I conflated the DK with the CFF.

 

It's here on the forums somewhere..

 

 

Yes, it's discussed at least here: https://www.cloudyni...lescopes/page-3 (see post #65). Sounds like a very interesting shootout, hopefully they can/could finally conduct it and report soon...



#18 DuncanM

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Posted 11 November 2017 - 03:36 PM

As a prospective buyer, I too have concluded that the best high-end 14-inch class astrographs are those made by Planewave Instruments (cDK) and AG Optical Systems (iDK). I have dropped the Celestron and Meade modified SCT designs from consideration because of issues with a moving primary mirror. The main differentiators between the two are:

 

Price - (assuming fused quartz mirrors) $16,500 (cDK) vs. $15,575 (iDK)

Imaging Circle - 70 mm (cDK) vs. 60 mm (iDK)

RMS Spot Size Diameter - < 6 microns @ 70 mm (cDK) vs. < 9 microns @ 60 mm (iDK)

OTA Weight - 48 lbs. (cDK) vs. 59 lbs. (iDK)

Primary Diameter: 14-inch (cDK) vs 14.5-inch (iDK)

Customer Optical Test Report: No (cDK) vs. Yes (iDK)

 

The cDK, with it's slightly larger imaging circle, appears to be a little more future-proof in that it is more compatible with the next generation of large format CCD chips. Both OTA's are beautiful astrographs with many satisfied customers. I'm looking for your input, so please feel free to correct any errors that I may have made. Thanks.

Most mirrored OTAs wll have issues with mirror movement because the mirror cells cannot rigidly lock the mirror in place without inducing stress into the mirror.  My limited experience with modified Cassegrain designs suggests that they are difficult to collimate. Overall, IMHO, their advantages (in the 14in size range) over an SCT based design are minimal. Additionally I would research Newtonian astrographs before making a final decision.



#19 orlyandico

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Posted 11 November 2017 - 03:50 PM

Getting back to this topic..

 

Anyone considering a CFF cassegrain would do well to get in touch with the folks who were supposed to conduct that shootout.

 

 

 

 

Some months back there was supposed to be a shootout between a CFF (probably a classical Cass) and a Mewlon 250 which is a DK. I conflated the DK with the CFF.

 

It's here on the forums somewhere..

 

 

Yes, it's discussed at least here: https://www.cloudyni...lescopes/page-3 (see post #65). Sounds like a very interesting shootout, hopefully they can/could finally conduct it and report soon...



#20 Alterf

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Posted 11 November 2017 - 05:37 PM

In addition, anyone interested would do well to contact the many others who own one, who are CN members.  I've had mine for 18 months or so.  It is a wonderful telescope.  It has excellent optics and mechanics.  From the get-go, without any mods, I've been able to image with 20-minute subs at >2300mm.  Numerous sample images are available on the blog linked below. 

 

CFF also has an active Facebook page, and interested people are welcome there. 

 

Finally, anyone interested in a CFF telescope should contact the company itself.  CFF is a very small company but also very open about what they do.  At the least, one should also contact CFF and ask whatever one is wondering about.

 

Val



#21 Jared

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Posted 12 November 2017 - 01:11 AM

Most mirrored OTAs wll have issues with mirror movement because the mirror cells cannot rigidly lock the mirror in place without inducing stress into the mirror.  My limited experience with modified Cassegrain designs suggests that they are difficult to collimate. Overall, IMHO, their advantages (in the 14in size range) over an SCT based design are minimal. Additionally I would research Newtonian astrographs before making a final decision.

 

I can't say your experience matches mine, though I have not owned scopes larger than 12.5" so it's possible things are different in 14" and 16" sizes.  I find that CDK's are actually quite easy to collimate; like an SCT you only need to worry about the secondary.  If the primary is off (or the secondary is out of center) the only symptom is imperfect field illumination, and a flat resolves that.

 

I have not noticed significant collimation issues from the mirror mounts or in the OTA on either of the two 12"+ class telescopes I have owned.  None.  

 

Advantages over a 14" SCT from an iDK/CDK?  Several.  

- Typically better cooling/faster equilibration due to open tube design / 

- Larger unvignetted field of view

- Often more back focus available

- Less susceptible to dewing

- Larger flat field (than either a Celestron Edge and much larger than a Meade ACF)

- Slightly faster than an ACF or a Celestron with dedicated reducer

 

I'm not saying those differences are necessarily worth the cost; that's up to the purchaser.  The advantages are more than minimal, though.  As far as imaging  Newtonians... In this size range wouldn't you need to have something custom made?  Including the Wynne corrector?  ASA tops out at a little under 12".  I suspect it is difficult to make something stiff enough at a reasonable weight to handle a heavy camera hanging off the side of the tube once you cross a certain size threshold. That sort of load not attached to the back plate must be a real challenge.  Maybe you know of some 14" class Newts?  Everything I could find was a Cassegrain of some sort--Officina Stellare (various designs), Starizona Hyperion, AG Optical, PlaneWave... 


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#22 Edwin

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Posted 12 November 2017 - 03:53 AM

There was a second hand CFF 14" for sale on a Dutch astro-website yesterday for EUR 5500, but I cannot find it back right now. It is probably already sold, not strange for that asking price.



#23 Richard Whalen

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Posted 12 November 2017 - 07:31 AM

Hello All,

 

I promised the optics test documentation from the CDK12. This is a prime focus star-Foucault image. That's as close to the actual mode of operation of the optics as can be.

 

CDK125_Null_Test_20100313_1s.jpg

 

Clear Skies,

Gert

Hi Gert,

 

No expert but looks like rough optics with zones to me. Do they make their mirrors in house or sub them out? I wonder what their production tolerances are? You should post this over in the ATM forum, several optical test experts there.



#24 DuncanM

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Posted 12 November 2017 - 03:43 PM

 

Most mirrored OTAs wll have issues with mirror movement because the mirror cells cannot rigidly lock the mirror in place without inducing stress into the mirror.  My limited experience with modified Cassegrain designs suggests that they are difficult to collimate. Overall, IMHO, their advantages (in the 14in size range) over an SCT based design are minimal. Additionally I would research Newtonian astrographs before making a final decision.

 

I can't say your experience matches mine, though I have not owned scopes larger than 12.5" so it's possible things are different in 14" and 16" sizes.  I find that CDK's are actually quite easy to collimate; like an SCT you only need to worry about the secondary.  If the primary is off (or the secondary is out of center) the only symptom is imperfect field illumination, and a flat resolves that.

 

I have not noticed significant collimation issues from the mirror mounts or in the OTA on either of the two 12"+ class telescopes I have owned.  None.  

 

Advantages over a 14" SCT from an iDK/CDK?  Several.  

- Typically better cooling/faster equilibration due to open tube design / 

- Larger unvignetted field of view

- Often more back focus available

- Less susceptible to dewing

- Larger flat field (than either a Celestron Edge and much larger than a Meade ACF)

- Slightly faster than an ACF or a Celestron with dedicated reducer

 

I'm not saying those differences are necessarily worth the cost; that's up to the purchaser.  The advantages are more than minimal, though.  As far as imaging  Newtonians... In this size range wouldn't you need to have something custom made?  Including the Wynne corrector?  ASA tops out at a little under 12".  I suspect it is difficult to make something stiff enough at a reasonable weight to handle a heavy camera hanging off the side of the tube once you cross a certain size threshold. That sort of load not attached to the back plate must be a real challenge.  Maybe you know of some 14" class Newts?  Everything I could find was a Cassegrain of some sort--Officina Stellare (various designs), Starizona Hyperion, AG Optical, PlaneWave... 

 

As I say, my experience with these types of scopes is limited.

 

SCT's can be/are fitted for forced air circulation for cooling

 

Open tube designs also have drawbacks:

 

Dust and optical coating deterioration

More likelihood of insect and animal infestation

larger CO

 

I was thinking of a 12in Newtonian such as the Astro-Tech 12in F4 but there are some high-end OTA's available in the 14in range:

http://www.telescope...ules.com/htn400

and

http://www.telescope...lescopes-stores

 

and for imaging, these would seem to have most of the advantages of the modified cassegrain designs.



#25 akulapanam

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Posted 12 November 2017 - 07:21 PM

I would strongly consider Officina Stellare either in 12" or 16" size as well. The nice thing about the RIDK is they are diffraction limited over a wider spectrum and have smaller spot sizes.

OS like Planewave is also a large company delivering professional Optics whereas AG is a guy in a garage. OS will also literally fly across the world to support their products

Edited by akulapanam, 12 November 2017 - 07:24 PM.

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