12 replies to this topic

[philsan300]

I have a C14 XLT that I upgraded (changed the tube to a carbon fiber tube and installed mirror locks). I also added the Starizona Large Format focal reducer/field flattener. I'm pretty happy with the pictures I take with it, although it's a lot of work making sure I have good collimation, little to no tilt, great focus, and other things like making sure the corrector plate is correctly centered.

 

I recently bought a new CDK12.5; what an amazing scope that is. No corrector plate, the Hedrick focuser and Dew controller are amazing, it holds collimation like forever, the ease of use is a welcome pleasure.  There is no comparison to the quality and ease of use.

 

Because both scopes (the C14 with the reducer) have similar fields of view (2665 for the C14 and 2541 for the CDK) and speeds (7.5 vs. 8), I'm going to sell one. I originally bought the CDK to replace the C14. However, once you have the C14 really well collimated, focused, and with little or no tilt, then due to its larger aperture, it collects 25% more photons than the CDK. My subs have more detail. For me, at the end of the day (night actually), what matters most is the data on the subs, not how easy it was to get it.

 

The mount I use is an AP900 the, camera is AASI2600mm pro, I use ZWO large OAG, Wanderer rotator, tilt adapter, ZWO 7 position filter wheel. One other difference is that the train on the CDK is 68mm in diameter up to the camera which is 54mm. The wider train gives my OAG a lot of room, and I believe helps minimize flexure on the train.

 

I can't afford a CDK 14,  but any input on which scope to keep would be greatly appreciated.

 

One last thought, will using 25% longer subs compensate for the 25% greater aperture? I have had really cloudy nights (pun intended) lately and have not tested that.

 

Phil

Edited by philsan300, 15 March 2025 - 11:49 AM.

[WadeH237]

However, once you have the C14 really well collimated, focused, and with little or no tilt, then due to its larger aperture, it collects 25% more photons than the CDK. My subs have more detail. For me, at the end of the day (night actually), what matters most is the data on the subs, not how easy it was to get it.

It seems that the answer is pretty clear...

[philsan300]

Wade, thanks for the quick response.

Beautiful work on your astrobin site and nice shout out to The Expanse!

[ngc2218]

I have a C14 XLT that I upgraded (changed the tube to a carbon fiber tube and installed mirror locks). I also added the Starizona Large Format focal reducer/field flattener. I'm pretty happy with the pictures I take with it, although it's a lot of work making sure I have good collimation, little to no tilt, great focus, and other things like making sure the corrector plate is correctly centered.

 

I recently bought a new CDK12.5; what an amazing scope that is. No corrector plate, the Hedrick focuser and Dew controller are amazing, it holds collimation like forever, the ease of use is a welcome pleasure.  There is no comparison to the quality and ease of use.

 

Because both scopes (the C14 with the reducer) have similar fields of view (2665 for the C14 and 2541 for the CDK) and speeds (7.5 vs. 8), I'm going to sell one. I originally bought the CDK to replace the C14. However, once you have the C14 really well collimated, focused, and with little or no tilt, then due to its larger aperture, it collects 25% more photons than the CDK. My subs have more detail. For me, at the end of the day (night actually), what matters most is the data on the subs, not how easy it was to get it.

 

The mount I use is an AP900 the, camera is AASI2600mm pro, I use ZWO large OAG, Wanderer rotator, tilt adapter, ZWO 7 position filter wheel. One other difference is that the train on the CDK is 68mm in diameter up to the camera which is 54mm. The wider train gives my OAG a lot of room, and I believe helps minimize flexure on the train.

 

I can't afford a CDK 14,  but any input on which scope to keep would be greatly appreciated.

 

One last thought, will using 25% longer subs compensate for the 25% greater aperture? I have had really cloudy nights (pun intended) lately and have not tested that.

 

Phil

I would keep the CDK. You can compensate by taking more subs. 

[GaryShaw]

Hi

You sound like you love the CDK … so why the question?

Gary

[KGoodwin]

It seems to me that the spot sizes are tighter with the CDK, and unless you have incredibly good seeing I doubt that you could get extra resolution from the extra 1.5” of aperture. So I have to wonder where the extra detail on the C14 subs is coming from. Perhaps it’s actually better contrast from the smaller secondary obstruction, the additional brightness from the extra aperture, or the lack of diffraction effects from having no spider on the C14?

If you’re going to sell one you’ll certainly get a better return on selling the CDK, though. I don’t like the Headrick focuser and replaced mine, but otherwise it’s an incredible scope and the resale value will be much better than trying to get a return on a custom tube, upgraded C14.

[robbieg147]

For me it's a easy choice the CDK, I am curious how does your AP900 handle the C14?

[philsan300]

Robbie, the total RMS error I get using the C14 on my AP900  ranges between .2" and .5" depending on seeing and wind. On a good night it stays between .2" and .3".   I think I am going to end up selling the C14 and the AP900, throw in a few more $$$ and get an AP1100 to cradle the CDK. That way I can take longer subs (combined with more subs that I have been using) to make up for the difference in aperture.

 

Gary, thanks for the analysis, it makes sense. The differences between the subs are there but subtle, and I don't like the diffraction spikes. I like NGC2218's idea of taking more subs.

 

Phil 

[Beaverpond Astro]

I'll second Kyle's comment.  Keep the CDK and upgrade the focuser if you can.

[Hillbrad]

Hey Phil I have two setups at my spot right now..iDK17” (similar design as a cdk) and a 16” LX200. They both are great scopes but I find myself getting more quality and consistent data with the 17” on most nights.

Also I will add that some nights if there’s wind, my idk gets the better guiding numbers because it’s hollow and doesn’t have a big dew shield on it to catch the wind.

Brad

[philsan300]

Hi Brad, 

Just looked up the specs on your IDK17" ... wow!!!!  What mount is it on?

I do have a question about the open truss telescopes, do you get a lot of light interference if are not in a really dark zone?

Thanks

Phil

[rgsalinger]

Well, to me, the purpose of owning a CDK is to use a full frame camera with it. Yet, if you get better data (somehow I am skeptical) then you have to keep the C14, sell the CDK and then save up for a CDK14. 

[Hillbrad]

Hey Phil yeah the 17” is a lot of fun for small galaxies! It’s on an ap1600 and the 16” lx200 is on a cem120. They both give very similar guiding numbers on nights of good seeing.

The open truss tube hasn’t had any light leak issues when there’s no moon… but I have noticed if I’m doing narrowband stuff and the moon is really bright, sometimes I can see some gradients from it. But if it concerned me enough I could always slide the light shroud up higher.

Either way it’s a hard choice to make! One more consideration…do you ever do planetary imaging? The C14 gives you a much better option for that.

Brad

Brad