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c-14 image train

astrophotography Celestron equipment imaging SCT accessories
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#1 unclewally

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Posted 08 July 2019 - 08:26 PM

Recently purchased an older grey tube c-14 ota. starbright coating. Wanted it to be versatile, visual, as well as imaging at different focal lengths. Not sure if i can use hyperstar.. the secondary mirror cell looks identical to fastar but it doesn't have the word fastar on the secondary.  Also not sure what focal reducers to use for different focal lengths. Any suggestions for the imageing train. Want to use motorized focuser, oag, fillter wheel and cmos cameras.Would really appreciate the help so i can make the right purchase. Thanks                              



#2 WadeH237

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Posted 09 July 2019 - 07:30 AM

Welcome to Cloudy Nights!

 

Can you send a picture looking into the front of the telescope, so that we can see the secondary mirror and labeling around the corrector plate retaining ring?

 

Also, what experience do you have with deep sky imaging, and what mount are you using?  There are lots of options, and that will help us to make recommendations for the imaging train.



#3 carolinaskies

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Posted 09 July 2019 - 07:36 AM

If you have Hyperstar the retaining ring simply unscrews and you can lift out the secondary.  

For imaging you have multiple choices of reducers.  Depending on what camera you plan to use each has it's pros and cons. 

The more agressive the reducer the shorter exposure is necessary and wider the field, but this comes at the cost of vignetting.   For a C14 only the Hyperstar will give you a truly wide field view. 

A focal reducer otherwise is mainly to reduce imaging exposure time as surface brightness is increased for targets like galaxies and nebulas.   However today this isn't nearly as important as in old film days since we can stack images to get greater signal to noise ratios.   

Entry level reducers like the venerable .63 are good for starting out.  For standard non-edge non-ACF optics you'll want a reducer/corrector vs straight reducer, this helps with field curvature.  

 



#4 unclewally

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Posted 09 July 2019 - 03:56 PM

 I am new to astro imaging.working on my home dome. I have a software bisque mx mount. want to keep imaging train light. thinking about zwo 1600 mono, cooled camera. I am trying to send picture of secondary. of my c 14. interested  in narrow band .want to incorporate off axis guider ,2 focusers, filter wheel.                      cant seem to  attach pictures to this reply. thanks bear with me.  



#5 unclewally

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Posted 09 July 2019 - 05:04 PM

IMG 1572 (1)
IMG 1573
IMG 1576

 

posting pictures of my c 14 secondary. not sure if it is hyperstar compatible. looks identical to fastar 



#6 WadeH237

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Posted 09 July 2019 - 06:15 PM

That looks like a Fastar secondary where the label has been removed.  If you gently turn that outer ring counter-clockwise, it will likely come off, allowing you to lift out the secondary.  Make sure that you have the scope pointed up a bit when you do this, so that the secondary cannot call out.  When you put the secondary back in, there is a pin that aligns with a slot in the secondary holder to ensure that you reinstall it at the correct rotational angle.  When you screw the retaining ring back on, stop tightening at the first sign of resistance.  Definitely do not give in to the urge to give it a quick snug.  The likely result of that will be making it so that the retaining ring won't easily come off again.  And when you apply more force to break it loose, the whole secondary assembly may rotate within the corrector plate.

 

If the retaining ring it already tightened so that you cannot easily remove it, I would suggest contacting Starizona.  They have more experience with Fastar setups than anyone (including Celestron).  They should be able to help you to get it off.

 

Regarding deep sky imaging, you may know already that this is definitely not a setup that lends itself to learning imaging.  You mount can handle it, but the focal length is such that it is incredibly unforgiving, even with an awesome mount.  I would suggest getting a short focal length refractor (600mm or less) and using it to learn the basics.  You will likely want a wide field solution anyway, so it'll be good to have the refractor in your toolkit.

 

Regarding cameras, the pixels on the ASI1600 are quite small at 3.8 microns, and you will be very, very oversampled.  This won't prevent you from taking nice pictures, but it won't be matched as well to your system (or as efficient) as a CCD camera with 6 to 9 micron pixels.

 

For an OAG, the specific model is not that important (and Celestron makes a very nice one with all the adapters included that you might want).  The key thing will be that the field of view is small enough that you may have trouble finding guide stars.  You will want the most sensitive guide camera that you can get.  I'd recommend something like a Lodestar or Ultrastar with a mono sensor.  I would also suggest considering ONAG instead.  It will give you a larger field of guide stars and would match particularly well to an Ultrastar guider.

 

Regarding two focusers, I've been down this road.  I have worked with an external Crayford focuser (the Optec TCF-S).  It works, but takes up a whole lot of back focus and affects the effective focal length and correction for spherical aberration.  I prefer replacing the Celestron focus knob with a FeatherTouch SCT focus knob.  This knob is directly supported by both the MicroTouch focus motor from Starizona or the Optec focus motor (and Starlight sells the Optec motor under the Focus Boss name as well).  Using the FeatherTouch know also allows you to use Hyperstar and retain your focus motor.

 

Finally, regarding the reducer, I have had good success with the Celestron F/6.3 reducer/corrector.  You want to make sure that all the spacing is correct for optimum results.  Starizona also offers a couple of SCT reducer/correctors that are better, but much more expensive, than the Celestron one.

 

I hope that this helps, and please let us know how it's going.

 

-Wade



#7 unclewally

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Posted 09 July 2019 - 09:51 PM

thanks for your recommendations..    I  do have a micro feathertouch focuser for the c 14 Concerned about  .mirror flop .what it will do to your imaging.  It  will be  some time till I get everything together, quite a learning curve.  In the mean time I will take all the suggestions I can get. thanks for your help . keep you posted  Determined.  The reasoning for 2 focusers  was to rough focus with the stock focuser. lock the mirror in place and fine focus with the second focuser. Possibly with a moonlight focuser,that allows you to screw the focal reducer inside the focuser.Not sure how much back focus I will have to incorporate oag filter wheel and camera.



#8 WadeH237

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Posted 10 July 2019 - 07:55 AM

Regarding mirror flop, it is an issue with the C14.  After a long slew, it can take a while for the mirror to settle.  I mainly see this when I am doing a sky modeling run, where I have it slew to 100+ points in the sky to do plate solves.  Some of the plate solve images has streaked stars because the mirror is still moving.

 

In practice while imaging, if you focus properly, mirror flop is not an issue.  By "properly", I mean that you approach final focus with a counter-clockwise turn, which is pushing the mirror against gravity.  If you need to make a clockwise turn, turn the knob too far, and then come back counter-clockwise to take up backlash and load the mirror again.  When you autofocus, it should be possible to configure the backlash compensation to do this as well.

 

Oh, and the C14 pictured will does have a mirror lock, so if you want to lock the mirror, you will need to modify the telescope.  The two methods that I have seen are Flop Stoppers, which replace the two shipping locks on the back of the scope, or with a collar that squeezes the baffle tube (and requires cutting a "hatch" in the tube, to be able to reach inside to operate it).  I don't think that either of these two solutions are still in commercial production, so you'd need to be creative.


Edited by WadeH237, 10 July 2019 - 07:57 AM.


#9 unclewally

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Posted 11 July 2019 - 10:47 AM

thanks again for your experienced expertise.  I  will keep an eye out for the flop stoppers in the mean time. I probably can make them my self.




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