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mbalkham

Spider upgrade - orientation of vanes

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Hi all,

I'm upgrading my spider vanes to the TS Optics double carbon spider (Teleskop-Express: TS-Optics Carbon Double-Spider for 295-310 mm inside tube diameter (teleskop-express.de)). The aim here is to be a bit stiffer and hopefully hold collimation better plus to tighten my diffraction spikes. I will also us copper foil on the vanes for the secondary heater rather than wires.

I've been trying to find advice on the orientation of the vanes relative to the focuser. Everything I see online points to one of the vanes being inline with the centerre of the focuser. However on my OOUK CT10 the stock spider is offset at 45 degrees to this. That makes collimation more tricky as the adjustments tilt/twist the secondary not relative to the optical axis (the two left thumbscrews are not parallel to the optical axis).

Question am I overthinking this just install in the existing holes or should I redrill the fixings in a more usual pattern relative to the focuser?

Thanks in advance

Matt   

20201125_095333.jpg

spider.JPG

Edited by mbalkham

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If you turned the secondary assembly and spiders 90deg in that photo, wouldn't that align the adjusters as you want them?

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Optically I don't think it will make any difference. Mechanically it might be better to avoid the focuser where the tube is already under some stress.

Regards Andrew 

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In the current arrangement, thumbscrews aren't parallel to the vanes 

20201125_101413.jpg

Edited by mbalkham

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In the new one I'm not sure if 45 degree rotation works either because of the offset of the two thumbscrews? Will wait to see when it arrives! I've also reached out to TS Optics for advice.

 

ts-double-spider-1000.jpg

Edited by mbalkham

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I went with changing the orientation. Not collimated yet but I'm sure it will be easier if I'm the same plane. Looks and feels much stiffer which must be good. Hopefully test it this weekend. 

20201208_173158.jpg

20201208_173145.jpg

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So testing tonight produced a funny set of diffraction spikes. Does this mean I haven't managed to get it square? or is this some other issue (don't think it is collimation or focus but could be tilt, focuser tube alignment, something else?). Also screenshot of ASTAP CCD Inspector for same image.

 

Canopus_Light_007_d.jpg

Screenshot 2020-12-10 at 23.43.41.png

Edited by mbalkham

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I think the split spikes are caused when the secondary isn't centered in the tube, i.e. opposing pairs of vanes don't form a straight line.

 

Looking at your images, it barely looks out... but maybe something worth checking?

 

 

Capture1.PNG

Capture2.PNG

Edited by CraigT82

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I think you might be right. I remeasured the spacing and it looks like my 4 holes are not equally spaced around the circumference (not by much). I was not far off centre but obviously not close enough and that was pulling vanes offline a little. 

I've filled the holes and will redrill tomorrow above the last lot. Will triple check all the measurements and accuracy of the pilot holes before redrilling.

I think I'm parallel to the primary. I'll check again. Will also check the focuser alignment again. 

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I think it might have something to do with effectively having 8 vanes.    🤔

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Even with uneven spaced holes, you still should be able to center the secondary.

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