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Installing spider in the wrong position?

ATM optics reflector
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#1 starhunter50

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Posted 15 August 2019 - 12:09 PM

 i had a Machine shop make me a 8 inch tube ( 80 thou thick) and they drilled the holes right at the focuser angle, not 90 deg off.

can i still install the spider cutting across the focuser light path and if not, why not ?

:-(

 

thanks guys...

 

 



#2 jtsenghas

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Posted 15 August 2019 - 12:15 PM

Aren't the spider vanes far enough towards the sky end of the tube not to intrude on the cone of light converging within the focuser from the secondary? 

 

Could you show a photo? 


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#3 starhunter50

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Posted 15 August 2019 - 12:15 PM

ok pic coming up ..

brb

Attached Thumbnails

  • spiderA.jpg
  • spider B.jpg

Edited by starhunter50, 15 August 2019 - 12:25 PM.


#4 jtsenghas

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Posted 15 August 2019 - 12:18 PM

If the vane hole is just in line with the focuser hole but doesn't interfere with focuser mounting or intrude into the return light path from the primary, no problem unless you want to mount an internal filter slide. 


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#5 Pinbout

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Posted 15 August 2019 - 12:23 PM

ok pic coming up ..

brb

yes please



#6 starhunter50

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Posted 15 August 2019 - 12:27 PM

Have a look , i did not want  strange diffraction spikes that would ruin the image ...



#7 Pinbout

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Posted 15 August 2019 - 12:41 PM

Not a problemo 


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#8 Hawkdl2

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Posted 15 August 2019 - 12:51 PM

I don't think it is a problem, but if you don't like it,  would it be that hard to remount the spider?

 

Larry


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#9 Luca Brasi

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Posted 15 August 2019 - 01:06 PM

That's how my Skywatcher is set up. Wish it wasn't though. Keeps me from installing a filter slider.

#10 Pinbout

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Posted 15 August 2019 - 01:54 PM

its also not a problem to drill 4 new holes if you really want an X instead of a + 


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#11 starhunter50

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Posted 15 August 2019 - 03:13 PM

ok , as long as there is  no draw back , im kool  



#12 jtsenghas

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Posted 15 August 2019 - 04:51 PM

As far as diffraction spikes go, each vane will produce two spikes 90 degrees from the vane. It matters not whether the cone of light from your secondary to your focal plane is downstream of a vane or not. The obstruction to the light path will still be a circle in the center with a pair of crosshairs from the vanes. Think about it, it makes no difference if the reflected light passes behind a vane.

 

Some people do in fact make new holes and rotate the spider so that they have nothing within the range of a filter slide mounted inside.  I believe Ken Fiscus, who "liked" my previous post is one who did just that on a 12" Zhumell. 

 

Depending on scope size and secondary weights, some find a little less deflection with altitude and more consistent collimation when one pair of the vanes are vertical on four vane spiders , which would be your case only if you put your focuser on top or horizontally. For a scope your size, you'll probably want to orient the focuser no lower than 30 degrees and no higher than 45 degrees when aimed at the horizon for comfortable use.

 

For a scope your size, unless the spider is truly inadequate, you shouldn't have any trouble maintaining collimation with altitude angle changes for any vane orientation.

 

Focuser orientation is entirely a matter of personal preference. I prefer to observe with my left eye and would rather pull my scope than push it when observing to the south. As a result, I build all my scopes with a right side focuser (as seen from behind the scope). 

 

Some people prefer left side focusers both to favor right eye use and to keep body heat from the prevailing winds from the west from pushing warmer air from the body across the light path when viewing to the south. This, of course, presumes a northern hemisphere prevailing wind and a tendency to view to the south. Here in Ohio such breezes are insignificant.

 

As far as your vane orientation goes, FUGGEDABOUTIT! 


Edited by jtsenghas, 15 August 2019 - 04:56 PM.


#13 starhunter50

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Posted 15 August 2019 - 05:00 PM

Kool.... then i'm all set to go.  

and as my project goes a long i will post the pics here so you guys can see the progress ,

 

Stay tuned.. 

 

N42 W82  Southwestern  Ontario.


Edited by starhunter50, 15 August 2019 - 05:01 PM.

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#14 jtsenghas

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Posted 15 August 2019 - 05:08 PM

Please start a new thread with a title something like "<your name>'s 8" f/? <dob or newt> build ".

 

If you just append to this thread newcomers will continue to remark on the vane question. If you have a question, throw it out on the thread, but be prepared for a total lack of consensus on the answer! Take what you can use and leave the rest. 


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#15 starhunter50

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Posted 15 August 2019 - 05:58 PM

Will do , thank you ..




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