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Bino-viewer

Curved Newtonian Spider Vanes.

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Bino-viewer

Evening folks.......


 


Doing a little research on' curved style' spiders in Newts.


The traditional 4 vane straight spiders can leave bright diffraction spikes around bright objects.


 


21790628359_38b39116ee_o.jpg


 


To help alleviate this you can modify the spider vanes by making them curved.


This then 'spreads' the diffraction evenly around the full 360 deg of the object you are viewing.


Here's what they look like....


 


21789813088_e645d3540b_o.jpg


 


There's a US based company that make them, based in Pleasanton California : 1800 Destiny.


 


https://id18510.securedata.net/1800destiny.com/merchantmanager/index.php?cPath=5_17


 


And here's a link to a mini review by UK astronomer Ade Ashford, which is quite a few years old now.


 


http://www.nightskies.net/scopetest/accessories/destiny/spider.html


 


 


Some observers say they reduce contrast in the image and don't like them.


 


There's not many scopes out there with them fitted as standard.


David Lukehursts scopes have them, although its a single curved arm design.


But David likes them and recommends them on his scopes.


 


I remember Orion Optics trying them a few years ago. This design was two small circular vanes either side of the secondary.


But they've since gone back to the traditional straight 4 vane.


 


I'm interested in your thoughts on this.


Anyone looked through a scope with the curved vane design  ? (either 3 or 4 vane curved)


How did it compare to the traditional 4 vane straight design ?


And is it a mod worth me considering.......??  :)


 


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Tweedledee

They obviously spread the diffraction around so it effectively becomes invisible. I doubt if you would detect any lack of contrast in the UK with all the light pollution. If you had mag 7 skies then maybe they would stop you seeing that extremely elusive nebula.


 


I'd say that if the spikes annoy you get a curved spider. I won't be changing mine at that price. You also have to factor in all the messing about drilling new holes in the OTA and removing your old secondary (without breaking it or damaging the coatings) and glueing it safely to the curved spider.


 


I reckon it would be far cheaper to simply remove the four vanes from your existing spider and fabricate curved vanes and bolt them on .


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Tweedledee

Just noticed from your photos, that on their secondary holder mechanism (nothing to do with the vanes) the spring is pulling the mirror up to the holder and keeping it in constant contact with all three adjusting screws. The standard method has the spring pushing the mirror away from the holder and its adjusting screws, allowing the mirror to come loose at times during collimating. I might modify mine to their method to see if it gives an advantage, would just need a longer bolt and washer and move the spring to the top.


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Doc

Personally I wouldn't bother unless I was building from scratch.


 


Most people buy a dob as they like hunting for deep space objects, and you will not see diffraction spikes on dim stars. You will see them on the brighter stars but after a while you get used to them.


 


I would get your dob up and running first and see what you think.


Edited by Doc

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BAZ

I think the problem with the curved ones is that they are thicker, maybe that could explain the interference. The straight ones are held in tension so can be made thinner.


I don't mind really, as Doc says it doesn't affect what I am after with the Dob.

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philjay

I restored an 8" Orion Optics Newt from the 90s the other year. This had the single curved vane secondary holder. Although agriculturally built, (OO weren't elegant in their engineering back then) it worked well. Visually I couldn't see any spikes, but then I don't really pay attention to them in traditional 4 vane newts anyway. I tried it on DSO imaging for a laugh and yep there wasn't the normal diffraction spikes


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Bino-viewer

Ironically, in this months Astronomy Now magazine, Ade Ashford again reviews the same scope (6" F/11 Newt) that he reviewed 8 years before.


 


And he criticises the 1mm 'thick'  4 vane secondary holder as causing "relatively intense diffraction spikes- a symptom sadly exacerbated buy the 3 unnecessarily wide


mirror clips holding the primary"


 


He states "that some will argue this is merely cosmetic, and will have a negligible effect on resolution" he argues the resulting scattered light does indeed reduce contrast.


 


I have the same 1mm 'thick' 4 vane secondary spider, and the big ugly mirror clips on my own OO scope.


 


And at the end of the review, he recommends using a well designed, curved vane, secondary mirror support to diffuse diffraction spikes, and smaller primary mirror clips, 


to further reduce diffraction noise.


 


Food for thought  :)


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