Curved spider vane

[JemC]

A couple of weeks ago i was contemplating changing my SW 130P-DS for a refractor for imaging due to developing a dislike of the diffraction spikes created by the spider vanes,  to cut a long story short  one of the suggestions was to carry out a little DIY and change them for a curved spider vane,

after posting that i was not to confident in my own DIY skills, along popped a nice gentleman from Todmorden Astronomy centre, @Peter Drew who kindly offered his services to help me out,

The end result of that conversation was this, 

A big thank you goes to Peter for sorting this for me, 

all i need to do now is try it out and see what the difference is,

[John]

I'll be very interested to hear what differences this design change makes

I have curved secondary vanes on my 12" dobsonian.

 

 

[JemC]

8 minutes ago, John said:

I'll be very interested to hear what differences this design change makes

i will post an update once i have had a chance (weather permitting) to try it out with before and after images,

[Dave In Vermont]

Count me in on waiting to hear - and see - what your findings are! I don't suppose you're a astro-photographer? A photo or two would show us the conclusive results - but it's not necessary. Just your words would be fantastic!

I love the  'proactive' approach you've employed -

Starry (without the 'spikes') Skies,

Dave

 

p.s. - A thank you to Peter, too!

[JemC]

11 hours ago, Dave In Vermont said:

Count me in on waiting to hear - and see - what your findings are! I don't suppose you're a astro-photographer?

Consider yourself counted Dave 
I would say i am trying to be an astro-photographer  all be it not at the level of a lot of the good people on here, 

As soon as i can get a clear night i will be trying it out and will post my findings with an image taken before modification and one taken after modification, i am keeping my fingers crossed that i am going to like the outcome that the curved vane produces,

Regards
James

[Stu]

That looks like a really neat job! Hopefully it will have good results.

[Space Hopper]

Interested myself too with how this performs.

Looks an innovative design.

I have been thinking of modifying my own scope and purchasing my own curved vane.

Theres a US company that supply them.....

http://www.1800destiny.com

[John]

Here are the supports on my Orion Optics 12" F/5.3:

 

[FenlandPaul]

Really interested to hear of the difference you see. I prefer Newts over fracs (not trying to start a fight here - just my own preference on using them - my brain is wired better for using a Newt than frac) but the thing I do love about fracs is the pinpoint stars.

John- did you for yours yourself? If so what difference did you see? 

[JemC]

30 minutes ago, FenlandPaul said:

Really interested to hear of the difference you see. I prefer Newts over fracs (not trying to start a fight here - just my own preference on using them

You won't start a fight 

i will be posting before and after images as soon as i can try it out, just need all this rain and cloud to move on,

[John]

1 hour ago, FenlandPaul said:

...John- did you for yours yourself? If so what difference did you see? 

They were an option offered by Orion Optics back when my scope was made. They don't offer it now - presumably most folks were content with the standard 4 vane design ?

With mine, I don't see diffraction spikes. There is diffraction of course but it is spread out more evenly across the field of view. I'm not over bothered by diffraction spikes when I use newtonians though - my scope had these fitted when I bought it used.

 

[Rusted]

A curved spider design still needs to be stiff. Which may require thicker vane material than a straight one.

If it sags [at all] the apparent thickness of the curved vane will increase by rotation away from the optical axis.

Some users swear by them. Some theorists swear at them, for smearing their diffraction effects across the image.

[JemC]

1 hour ago, Rusted said:

Some users swear by them. Some theorists swear at them, for smearing their diffraction effects across the image.

 At the minute i can't swear by or swear at them, not had chance to try it out yet due to working late and being cloudy 

I can say that it has been put together really well by @Peter Drew and looks to be quite sturdy/stiff,
I am hoping with fingers crossed that i get a clear spell this weekend then i can try it out.

[JemC]

On 16/04/2017 at 00:22, John said:

I'll be very interested to hear what differences this design change makes

 

On 16/04/2017 at 03:10, Dave In Vermont said:

me in on waiting to hear - and see - what your findings are!

 

On 16/04/2017 at 16:51, Stu said:

fully it will have good results.

 

On 16/04/2017 at 18:21, Tubby Bear said:

Interested myself too with how this performs.

 

On 16/04/2017 at 20:40, FenlandPaul said:

Really interested to hear of the difference you see

 

Well i managed to get out last night for a short while to try out the 130P-DS with the curved spider vane that i had installed by @Peter Drew,
The seeing was not brilliant (well to me anyway)and there was or seemed to be a thin layer of cloud knocking about which did not help matters, but at least i was out,

Please bear with me on this as i am a little out of my comfort zone, not really used to writing  up any report/findings on equipment used.
Focusing was done by eye, no aids were used, maybe i should get a bahtinov mask to help with that,

So! what do i think, 

From a visual point,
bearing in mind that i have not done a great deal of that and this is just my own opinion, there seemed to be little difference to the view,
Was i expecting it to give a better view...To some degree Yes,
Did it give me a better view..No not really,
Was i dissapointed with the view...Certainly not and to be honest i quite enjoyed looking through it for a change (should do that a bit more)

i did not or could not see any of the loss of contrast(with my eyes at least) that some people have said curved vanes can cause,(but that could be put down to a lack of experience of actually looking through a telescope,)

Does it get rid of the diffraction spikes, to a certain degree yes, but not completely, It does as some of the other SGL members have said spread it around, whether that is for the better or worse remains to be seen,as i don't feel that the amount of time i have had using it really does it justice,so i will be trying it out again at some point,(nights are getting shorter now)

From an imaging point initial findings are,

Is there a notable difference with the curved vane...Yes, you do not get the 4 diffraction spikes as with the normal spider vane, However you do or at least with the little imaging i did last night still get some diffraction but most of it is spread around the object,

Is this better...my imeadiate thoughts..yes somewhat but if i was to be honest i think i was expecting more,

Could it be better...I certainly think so, i think with better seeing conditions and better focusing i do think the images could be improved somewhat,

I would have liked to be able to image some of the areas that i have done previously to compare, IC434, NGC2244, M45 but unfortunately these are now not visible from my location.
Is it going to stop me wanting to get a refractor for imaging...at the moment NO but it is early days with it yet, but i won't be getting rid of the 130P-DS either just yet,
More time is definately needed with it.

Overall i am happy with what i got from it in such a short time last night and i am looking forward to at least trying to improve on that over the coming months,

i have attached two images
both 60 seconds, iso 400 

the first image is with the standard 4 vane spider 
the second with the curved spider
not the best ones to be comparing with, but it does give some idea of what i got and the difference to some extent,

 

 

[John]

What an open and balanced report - thanks for posting it

Look forward to hearing more on this.

[AKB]

Great to see some objective comparison.  Thanks for that.

Since both Matsukov and SCT designs get away with corrector plates, I've often wondered how easy it would be to get an optical quality plain glass disc to support the secondary.  Would perhaps need to be coated too, so not a cheap option.

AK

[John]

5 minutes ago, AKB said:

...Since both Matsukov and SCT designs get away with corrector plates, I've often wondered how easy it would be to get an optical quality plain glass disc to support the secondary.  Would perhaps need to be coated too, so not a cheap option.

AK

For a newtonian it's called an optical window I believe and the approach has been used in the past although it's mostly through DIY efforts these days I think. Getting an optical window of decent quality (optical flatness) is harder than it might seem apparently and I think it will need coatings of some sort. 

 

[25585]

@iPeace 

[ollypenrice]

An excellent report.

More imaging will be needed to reach a firm conclusion, I think.

Olly

[Tom OD]

I d be curious to see how temps change the shape of the that vane. Surely it would knock the whole system out of collimation during a night?

Whereas the 3 or 4 vanes going across teh tub diameter might expand equally and not have the same effect.

Tom

 

[Tom OD]

Just found this by chance on Peters home page. What a great chart of diff pattterns.

 

[Moonshane]

Good report and 'mirrors' what I found will my 6" f11 and curved Destiny vane bought for it. In fact I didn't really get on with the curved vanes and changed back. I found the view felt 'cleaner' with four vanes.

Were the stars of the same magnitude in your test?

[Stu]

I do wonder if the double circle ones, like in John's 12" f5.3 are best. Although they have a larger surface area, so generate more overall diffraction, having two complete circles ensures, I guess, more complete cancelling out of any spikes.

The Portaball I had used three curved vanes and whilst it did not have diffraction spikes, the stars weren't a lovely refractor shape either.

[25585]

2 hours ago, Stu said:

I do wonder if the double circle ones, like in John's 12" f5.3 are best. Although they have a larger surface area, so generate more overall diffraction, having two complete circles ensures, I guess, more complete cancelling out of any spikes.

The Portaball I had used three curved vanes and whilst it did not have diffraction spikes, the stars weren't a lovely refractor shape either.

Stu, what is the pattern like for your Heritage, with its single strut?

[Stu]

It's a line. A single strut creates two spikes, one the same side as and the other 180 degrees opposite, forming a line. It's actually much better than I expected it to be.

A four vane spider actually creates 8 spikes, but pairs of them coincide so you only see 4. So actually a 3 vane spider shows 6 because they don't coincide.

This link has good info:

http://www.astronomyhints.com/spider.html