13 replies to this topic

[sink45ny]

 When the fifth 30lbs counterweight is added tomorrow I'll be ready to drift align the mount.

[astro_1]

Really nice looking scope !!

[RalphMeisterTigerMan]

Question: what are the benefits of a Corrected Dall-Kirkham over a Ritchey-Cretien? I know that astro-imagers use both, I'm not quite sure of the differences when it comes to imaging.

 

RalphMeisterTigerMan

[jhayes_tucson]

The CDK has a flat field and it's easier to make.

 

John

Edited by jhayes_tucson, 06 December 2018 - 05:05 PM.

[chuckscap]

Depending on design it can have a much smaller CO but then you sacrifice FOV, a good tradeoff in my opinion.

[sink45ny]

Question: what are the benefits of a Corrected Dall-Kirkham over a Ritchey-Cretien? I know that astro-imagers use both, I'm not quite sure of the differences when it comes to imaging.

 

RalphMeisterTigerMan

Planewave sells both CDK's and RC's and here is a paragraph from the own literature.....  http://planewave.com...optical-design/

 

Having an aberration free telescope design means nothing if the optics cannot be aligned properly. Many Ritchey owners never get to take full advantage of their instrument’s performance because the Ritchey is very difficult to collimate. Aligning the hyperbolic secondary mirror’s optical axis to the optical axis of the primary mirror is critical in the Ritchey design, and the tolerances are unforgiving. The secondary mirror of the CDK design is spherical. It has no optical axis and so the centering tolerance of the CDK secondary mirror is comparatively huge. With the help of some very simple tools, the CDK user will be able to set the secondary spacing, collimate the optics and begin enjoying the full performance potential the instrument has to offer within a few minutes.

 

Note: I have never collimated a CDK or an RC.

Edited by sink45ny, 06 December 2018 - 11:50 PM.

[drprovi57]

Having owned a 14.5” RCOS (RC design) and now a 17” CDK - I can say that collimating CDK for optimal performace is a big plus - also one can find CDK’s in the F5 and F7 range - hard to find RC designs below F8 with out focal reducers.  Also most RC’s still require a field flattener for today’s large CCD chips.  

 

Jason

[sink45ny]

Having owned a 14.5” RCOS (RC design) and now a 17” CDK - I can say that collimating CDK for optimal performace is a big plus - also one can find CDK’s in the F5 and F7 range - hard to find RC designs below F8 with out focal reducers.  Also most RC’s still require a field flattener for today’s large CCD chips.  

 

Jason

Jason what mount are you using? I have an AP-1600, the CDK17 is a monster, it needs 6-30lbs counter weights. 

Edited by sink45ny, 08 December 2018 - 08:51 PM.

[drprovi57]

Steve - I am now using a Paramount ME 2 - I believe it is rated around 240Lbs instrument capacity.  It has no issues pointing and tracking with CDK 17 along with cameras, guidescopes, even with added SW Esprit 100 and camera - I regularly perform unguided imagingusing ProTrack on ME2.. even with long FL - stars are round to the edge of my FLI PL11000 camera

 

jason

[dcbaros]

I am jealous. Great looking scope.

[andysea]

+1 for what Steve said about RC vs CDK collimation, I never collimated a CDK but that is also my understanding. 

[akulapanam]

Its only easier if the primary is fixed (the Planewave is).  If not the same skill / process is required for a CDK, Harmer Wynne, RC, Classical Cass, etc...  The disadvantage of course is that fixed primaries can develop astigmatism over a long period of time .

Edited by akulapanam, 12 December 2018 - 11:57 PM.

[drprovi57]

This “collimation” topic comes up frequently regarding RCs and CDKs - Steve points out a key difference in optical design that makes the CDK’s ‘much more” forgiving in collimation compared to RCs - I have owned RCOS 14.5”, Planewave CDKs, and my present 17” OG Optical and have collimated them all using all the different techniques (Tak scopes, lasers, stars, CCD imaging, etc) and the bottomline:  one will find collimating a CDK design (with or without fixed primary) far easier than RC design - its all about the optical design...  I can share more on collimating these scope, but would take this thread off subject... enjoy the CDK they are great scopes

 

Jason

 

Edited by drprovi57, 13 December 2018 - 06:29 AM.

[sink45ny]

Finally got it drift aligned tonight. Now the fun begins, get the primary camera reattached and focused. Then focus the OAG.

A single 300 second image stretched but no calibration frames.

Edited by sink45ny, 26 December 2018 - 03:59 AM.