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Curved Spider Vanes for imaging?

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#1 Ivandn

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Posted 12 October 2017 - 12:46 PM

Hi, 

 

I just started serious imaging having recently acquired a real mount Orion Atlas, and a guide setup. So far its been pretty good but still a lot to learn in the way of fine-tuning the setup. 

I am pretty happy with the first few images out of my 6" reflector but I'm really not feeling the diffraction spikes. I know the recommendations are to use refractors but I can't afford a good APO right now. 

 

I'm (cautiously) intrigued by the concept of curved spider vanes and having round stars. It seems like the popular (and only?) choice is 1800Destiny.com but I've not seen many images on Astrobin or otherwise that are using curved spiders.

 

So I'm wondering a few things and would greatly any input and especially if you do use curved spider vanes:

1) Is there a good reason why they aren't as common? (do people prefer diffraction spikes?)

2) Do they significantly compromise rigidity to a point where imaging is not recommended? 

3) Does anyone have images or found images online from on reflectors with curved vanes? I'd love to see them!

 

Thanks!

~Ivan

 

 

 

Equipment:

Celestron 6" Omni XLT

Orion Atlas EQ-G

Sony Nex5

ZWO120mms + ZWO 60mm F/4.6 guidescope



#2 Jeff Struve

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Posted 12 October 2017 - 12:51 PM

I'll be interested in seeing responses...

 

  • I think they may not be as common because most folks process their pics, and there is a way to remove the spikes (I can't stand them!)
  • I don't think that there is a compromise...
  • Not I!

 

Thanx!



#3 ChrisWhite

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Posted 12 October 2017 - 12:57 PM

I like the spikes, but i image with an 8" need so I might be in denial. Lol!

Best way to produce images with less intrusive spikes is to increase your integration times so that you don't have to stretch as aggressively. I'm talking 10, 20 or more hours on an image.

You'll enjoy the benefits of strong data signal as a side effect. Hahah

#4 Ivandn

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Posted 12 October 2017 - 01:06 PM

Best way to produce images with less intrusive spikes is to increase your integration times so that you don't have to stretch as aggressively. I'm talking 10, 20 or more hours on an image.

That's good to know and it definitely makes sense. When combining images from multiple nights, do you avoid changing anything in the rotation so the spikes match up? I don't have a way to tether my camera so plate solving is tricky at best.

 

If the spikes don't match up, can they be processed out when stacking images from 2 nights, if say integration time is more or less equal? ( I do realize framing will be messed up doing that)



#5 calypsob

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Posted 12 October 2017 - 01:19 PM

This is the best method for removing spikes, no need to go curved http://serge.bertore...r/antiaigr.html   This will almost completely eliminate the spikes, I think that by dithering aggressively you could really end up with round stars.  If you additionally mask the mirror clips then you can have a diffraction free light path with nice round stars.  You can download and print mask aigrettes here https://www.thingive...m/thing:1260926 They could be rescaled for a larger scope in a slicer like cura though I would recommend redesigning them completely to fit your application using the geometry provided on Serge's website.  Design Spark Mechanical is a free 3d non parametric extrusion program and you could whip one of these up in 2 seconds specifically for your scope.   


Edited by calypsob, 12 October 2017 - 01:20 PM.

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#6 ChrisWhite

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Posted 12 October 2017 - 01:35 PM

It doesn't matter if your camera rotates, as long as your scope doesn't rotate. You want to get your camera close simply so you have maximum overlap of field of view from night to night. Since your newt is mounted on a dovetail and doesn't rotate, no problem.

If your mount is not perfectly relatively level between sessions then the spiders might change position relatively with the sky, which can result in double spikes or spikes that don't lineup perfectly, so just make sure you get your mount precisely positioned from night to night.

I move my mount in and out each day. I just never touch the leg extensions and mark exactly where in my lawn each leg goes. It's precise enough to make sure the spikes line up from night to night.

#7 pfile

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Posted 12 October 2017 - 01:36 PM

 

Best way to produce images with less intrusive spikes is to increase your integration times so that you don't have to stretch as aggressively. I'm talking 10, 20 or more hours on an image.

That's good to know and it definitely makes sense. When combining images from multiple nights, do you avoid changing anything in the rotation so the spikes match up? I don't have a way to tether my camera so plate solving is tricky at best.

 

If the spikes don't match up, can they be processed out when stacking images from 2 nights, if say integration time is more or less equal? ( I do realize framing will be messed up doing that)

 

 

spikes are weird, while you might think that they are related to the camera angle, they are not... they are related to the angle between the sky and the vanes themselves. so if you rotate the camera and then register the rotated frames, the spikes will still line up.

 

the only situation where the spikes will change is if you rotate the OTA itself, or rotate the vane holder, either of which would change the angular relationship between the sky and the vanes. when your telescope is on a rail, you can't really change the OTA rotation, but i suppose it is possible if you are using rings.

 

rob



#8 Ivandn

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Posted 12 October 2017 - 02:21 PM

 

spikes are weird, while you might think that they are related to the camera angle, they are not... they are related to the angle between the sky and the vanes themselves. so if you rotate the camera and then register the rotated frames, the spikes will still line up.

 

the only situation where the spikes will change is if you rotate the OTA itself, or rotate the vane holder, either of which would change the angular relationship between the sky and the vanes. when your telescope is on a rail, you can't really change the OTA rotation, but i suppose it is possible if you are using rings.

 

rob

 

Ahh that makes sense, I had to stop and think about that one for a bit.

 

What if I move my scope to a different location , but kept the scope in the same rotation on the rings, should it all still match up?

 

 

 

This is the best method for removing spikes, no need to go curved http://serge.bertore...r/antiaigr.html   This will almost completely eliminate the spikes, I think that by dithering aggressively you could really end up with round stars.  If you additionally mask the mirror clips then you can have a diffraction free light path with nice round stars.  You can download and print mask aigrettes here https://www.thingive...m/thing:1260926 They could be rescaled for a larger scope in a slicer like cura though I would recommend redesigning them completely to fit your application using the geometry provided on Serge's website.  Design Spark Mechanical is a free 3d non parametric extrusion program and you could whip one of these up in 2 seconds specifically for your scope.   

Thats brilliant! I'm definitely looking into this, thanks!! I fear it may be a little too much obstruction for a small 6" but it is cool!



#9 leveye

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Posted 12 October 2017 - 04:26 PM

They work pretty well but still leave a crazy pattern. You may or may not like it. Here is a test using a destiny 3 vane curved spider. I loved the quality of it and still use it.

 

Star test Jan  destiny 3 vane curved (1 of 1).jpg.jpg


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#10 Ivandn

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Posted 12 October 2017 - 06:28 PM

They work pretty well but still leave a crazy pattern. You may or may not like it. Here is a test using a destiny 3 vane curved spider. I loved the quality of it and still use it.

 

attachicon.gifStar test Jan destiny 3 vane curved (1 of 1).jpg.jpg

Thats exactly what I was looking for, thanks leveye! I'm sufficiently impressed at the roundness of the stars, the bloat and diffraction.

 

When you said it will leave a crazy pattern are you referring to the link (http://serge.bertore...r/antiaigr.html) shared by calypsob?

 

Calypsob - Do you have any images with the vane mask? I'd be curious to compare them to the curved vane image 

 

If not, I might even cut some out on cardboard and do some star tests on them



#11 pfile

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Posted 12 October 2017 - 06:40 PM

Ahh that makes sense, I had to stop and think about that one for a bit.

 

 

 

What if I move my scope to a different location , but kept the scope in the same rotation on the rings, should it all still match up?

 

 

 

it should all still match up... but another strategy for dealing with this would be to deliberately change the spike orientation such that they can be rejected as outliers during integration. it would probably be kind of a pain to do this though.

 

rob


Edited by pfile, 12 October 2017 - 06:40 PM.


#12 ram812

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Posted 12 October 2017 - 08:52 PM

I'd also be curious about the effect of any dew control wires on a curved vane.By the way, I like the effect on leveye's shot, that looks pretty clean to me!grin.gif



#13 Ivandn

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Posted 29 November 2017 - 02:30 PM

Many thanks to all that replied, I pulled the trigger on a 1800 Destiny curved spider vane. Below are 2 test shots of a bright star before and after.

 

I didn't realize I had changed the ISO and the stars are different so they are definitely not equal comparisons in terms of the amount of exposure and diffraction. While I upgraded the spider I also flocked the tube but I doubt that made much difference in the tests. 

 

The stars appear more hexagonal than round and brighter stars tend to have 6 short stubby spikes that make them look more star-of-david like.

 

I also added an image i did of M45 as I figured this would be a good subject to test diffraction spikes. C&C welcome!

 

Straight Vanes.

Camera: Sony Nex 5 (modified)

ISO: 800

Exposure: 120s

Star: Vega

Telescope: Celestron Omni XLT 150

 

Vega ISO800 120S Straight vanes.JPG

 

Curved Vanes.
Camera: Sony Nex 5 (modified)
ISO: 400
Exposure: 120s
Star: Capella
Telescope: Celestron Omni XLT 150

 

Capella ISO400 120s Curved Vanes.JPG

 

M45 Pleiades

Camera: Sony Nex5

Lights: 98 x 120s

Darks: 23 x 120s

Bias: 30 

Flats: 30

Processing in Pixinsight

M45 Curved Spider Vanes.JPG




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