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C6 Hyperstar mirror lock bodge


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#1 Mike Hawtin

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Posted 22 May 2013 - 01:46 PM

I originally set out on the Hyperstar journey to take deep narrow band images but straight away ran into problems with mirror flop limiting my subs to about 300 sec, so time to put my thinking cap on and get the big hammer out.  Actually the big hammer was in fact the edge of a 1/2" chisel as my first effort was to reduce the play between hollow shaft and the mirror/tube bore by whacking the shaft o/d, this raised some nice bruises which did in fact reduce play between the two parts but not by enough to go for more than about 400 sec.  So plan B was to cut 3 slots in the main cell casting through which I ran three lengths of 2mm x 15mm aluminium bent over at one end and attached to the back of the primary with double sided tape (I tried silicone adhesive first but it flexed too much).  To secure the exposed end I screwed 3 steel angle brackets to the back of the main casting and fitted M6 machine screws to them, these mirror support struts had slots filed on the exposed ends to allow them to move freely against the angle bracket/lock bolt.  The struts being clamped after focusing by lock *****.  Clamping these up initially moved the primary around but adding two washers with a dab of grease between them soon fixed that and permitted a nice firm clamp with only a very small shift which does not affect focus or collimation.  I am now a pretty happy bunny as I can reliably go to 900 sec subs with no noticeable flop.  I know my methods are crude and will make the engineers among you weep but I have no workshop and have to do everything on the kitchen table with simple hand tools.  I think one of the main reasons this crude mod actually works is due to the small primary, a larger diameter mirror would need much more support to work well.  The final touch to improve star shapes was to use an aperture mask to bring the effective diameter down to 120mm, I will have a fiddle with this to see if I can increase it but even at 120mm I am satisfied with the performance.

 

Mike

 

 

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#2 Waldemar

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Posted 21 May 2015 - 11:24 AM

Hi Mike,

 

I realize this post is 2 years old, but I want to comment on it anyway, if only for starting imagers who are thinking of buying such a system:  

300 sec subs with a HyperStar??? that is the equivalent of 7500 sec (over 2 hours!!!) without the HyperStar (± 25x). This will flood your CCD. 1-2  minute subs for faint objects is the absolute max...

The whole idea behind a HyperStar is about the possibility of taking very short subs, in order to avoid guiding problems on sub high-end mounts.

When I still had a HyperStar on my C-11, I rarely made subs over 30 sec. (which is the equivalent of 12,5 minutes)

I got rid of it, (both C-11 and HyperStar) because of the more than critical focusing with such a fast system and because it is really not easy to use filters.

Another down for me was the field curvature (spherical aberration) and the incredible critical placement of the camera.

 

Just my 2 c. 

 

Have fun anyway!!

 

Regards

Waldemar



#3 stargzr

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Posted 14 June 2017 - 09:15 PM

Hi Mike,

 

I realize this post is 2 years old, but I want to comment on it anyway, if only for starting imagers who are thinking of buying such a system:  

300 sec subs with a HyperStar??? that is the equivalent of 7500 sec (over 2 hours!!!) without the HyperStar (± 25x). This will flood your CCD. 1-2  minute subs for faint objects is the absolute max...

The whole idea behind a HyperStar is about the possibility of taking very short subs, in order to avoid guiding problems on sub high-end mounts.

When I still had a HyperStar on my C-11, I rarely made subs over 30 sec. (which is the equivalent of 12,5 minutes)

I got rid of it, (both C-11 and HyperStar) because of the more than critical focusing with such a fast system and because it is really not easy to use filters.

Another down for me was the field curvature (spherical aberration) and the incredible critical placement of the camera.

 

Just my 2 c. 

 

Have fun anyway!!

 

Regards

Waldemar

Waldemar,

 

Just saw your reply regarding the HyperStar modification.  I am sorry, but I must disagree with you regarding exposure times with the HyperStar system. It is true that you can take "snapshots" of brighter DSOs (bright globular and open clusters, the Orion nebula, etc.) But...if you want to get good color and detail on fainter DSOs such as galaxies, then longer, guided subs are a MUST.  I have not had the experience you mention, ie;, overloading or flooding the sensor on a longer exposure.  I use a C-11 with HyperStar (f/2) and a Starlight Express SXVR-H694C 1-shot color CCD imager.  The skies at my observatory are normally in the 21.35 to 21.45 range (SQM-L readings).  I have taken up to 10 minute (600 sec) subs, with no over-saturation. IMHO, longer subs like these are needed to really capture color and detail in galaxies. Just my 2-cents worth.

 

Ron Abbott

Land of Oz Observatory

http://www.astrolandofoz.com






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