Curved vane secondary supports

[Stu]

I'm looking into these with the possible intention of fitting one to my 12" newt.

Interested to hear of experiences with sourcing and retro fitting them. I can't seem to find any UK suppliers for them so any info on this would be great.

At the moment, I'm favouring a single 180 degree curve on the basis it has the shortest length, so minimizing diffraction. I've seen this one from Prostar

http://www.fpi-protostar.com/crvmnts.htm

Any thoughts?

Cheers,

Stu

[Brian Nordstrom]

Stu that's almost exactly what I made for my 5 and 10 inch newts , I made the curve diameter 1.5x the diameter of the OTA eg. the 5inch with its 6inch top tube has a dia. of 9 inches .

I read this some where and it seems to work very well , this design really works for knocking off those pesky diffraction spikes , see my reply on your other thread .

Brian.

[Joseki]

I ordered one from the US, this one: http://www.1800destiny.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=1D&Product_Code=MCVS&Category_Code=CVS

 with the optional upgrade for dew heater wiring.  It worked out pricy and the upgrade meant it took longer to dispatch but overall happy with it.  It was for a ATM project so it wasn't replacing an existing one though.  It was easy to mount and works well as far as I can tell.

That site also has a discussion of different styles of spiders but they're not independent so could be biased.

http://www.1800destiny.com/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=1D&Category_Code=cvss

[Stu]

Stu that's almost exactly what I made for my 5 and 10 inch newts , I made the curve diameter 1.5x the diameter of the OTA eg. the 5inch with its 6inch top tube has a dia. of 9 inches .

I read this some where and it seems to work very well , this design really works for knocking off those pesky diffraction spikes , see my reply on your other thread .

Brian.

Hi Brian

I must be being slow today, can't get my head around those numbers, can you explain or show a diagram?

Cheers,

Stu

[Stu]

Thanks Joseki, will have a look at those.

Stu

[John]

Shane has just ordered and fitted a set to his 6" dob I think Stu. I can't recall what brand they were though. I have them on my Orion Optics 12" of a different design (see photo below) and I don't get diffraction spikes at all. The diffraction is there of course but it's evenly distributed across the FoV.

David Lukehurst (the renowned dob maker) favours the single curved vane in his dobs up to around 14" I believe.

Not having used my scope with straight vanes I can't judge the difference the curved vanes make although I suspect they help towards it's excellent performance

[cassiewoofer]

Hello Stu, I have made a curved secondary vane for my home build 12" using a metal ruler as you can see in the post:-

http://stargazerslounge.com/topic/202483-first-light-with-unfinished-12-truss-dob/

I think the shape i.e. curvature could be improved, but it is self gripping with the ends just butted up aginst some rivetted on PVC plastic pipe.

Obviously it needs painting black.

The real challenge was drilling holes in the thing to attach the sec. holder.

In the end I used an angle grinder to cut two slots just wide enough for the two screws.

This could save you a lot of cash if you have the time.

[Brian Nordstrom]

Ha ha ha , all you do is measure the diameter of the OTA , ( my 5 inch has a 6inch tube OTA )  so 6inches x .5 = 9inches so the curved spider is rolled to a 9inch diameter and cut so the secondary is in the centre of the 6inch OTA and mounted in two places inside the 6inch OTA tube .

If you look at the photos of  the 'Protostar' one its the diameter of the curved piece that holds the secondary .

Cassiewoofer's  12 inch curved spider is almost identical to what I did on my 2 Newts , awesome stuff !.

I just TIG welded 2 tabs ( one each end ) and bolted to the inside of the OTA at the right place , and a 1/4 inch tube in the centre to mount the secondary holder that's a 1/4 threaded rod attached to a  piece of  wooden broom handle  inside a  piece of PVC pipe slightly smaller than the secondary mirror about 30mm long and cut at 45* with the mirror silicone'd on and a small  steel tab screwed to the PVC at the bottom to hold it in place .

A 1-1 scale drawing helped a lot in finding all the right dimentions .

My 10 inch Newt's OTAis 12 inches so the spider's curve is 12inches x.5 = 18inches in diameter ,,, or there about's .

Hope I explained this , I know the photo of my 5inch is in a hard drive in a draw somewhere ,, just gotta dig it out .

Brian.

[Stu]

Thanks Brian :-). I seem to have woken up now and that makes total sense. Thank you

Stu

[Stu]

Shane has just ordered and fitted a set to his 6" dob I think Stu. I can't recall what brand they were though. I have them on my Orion Optics 12" of a different design (see photo below) and I don't get diffraction spikes at all. The diffraction is there of course but it's evenly distributed across the FoV.

David Lukehurst (the renowned dob maker) favours the single curved vane in his dobs up to around 14" I believe.

Not having used my scope with straight vanes I can't judge the difference the curved vanes make although I suspect they help towards it's excellent performance

Thanks John. I'd seen you secondary support before but haven't seen them available anywhere. I spoke to OO about them and they said not to use a curved vane spider, that they weren't any good?

Anyway, I think, given that I have a choice, I am favouring the single 180 degree arch as this appears to minimize the total length and so reduces overall diffraction, whilst still obeying the 180 degree rule to cancel out spikes evenly.

Stu

[Stu]

Cassiewoofer, you scope looks amazing, really nice job!

Looking at the support though, I think you would get better performance if you modify it to go through a full 180 degrees. It looks from the photos as though it is only around 90 or 100 and I suspect this may be causing some uneven cancelling of diffraction, maybe giving smearing or loss of contrast? Might be worth experimenting with?

Cheers,

Stu

[John]

Thanks John. I'd seen you secondary support before but haven't seen them available anywhere. I spoke to OO about them and they said not to use a curved vane spider, that they weren't any good?

Anyway, I think, given that I have a choice, I am favouring the single 180 degree arch as this appears to minimize the total length and so reduces overall diffraction, whilst still obeying the 180 degree rule to cancel out spikes evenly.

Stu

The scope came with them Stu and for £250 with 1/9th wave Hilux OO SPX optics I'm not complaining

They can't be doing any harm given the scopes ability to split Sirius and resolve sub arc-second detail on the lunar surface

I wonder if OO's decision to drop them was more due to other reasons ?

Any rate, I have a feeling that observing conditions, well figured optics and good collimation probably contribute much more to the performance of a newtonian than the precise shape of the secondary supports.

[Stu]

The scope came with them Stu and for £250 with 1/9th wave Hilux OO SPX optics I'm not complaining

They can't be doing any harm given the scopes ability to split Sirius and resolve sub arc-second detail on the lunar surface

I wonder if OO's decision to drop them was more due to other reasons ?

Any rate, I have a feeling that observing conditions, well figured optics and good collimation probably contribute much more to the performance of a newtonian than the precise shape of the secondary supports.

Not doubting the capability of the scope John, I'm sure it is excellent, and the curved vanes will be helping that.

I'm mainly interested in whether they were original factory fit or sourced as a retro fit as I haven't seen them for sale anywhere else.

I don't buy the OO line anyway, I think there is merit in these types of supports. Ultimately I'd like to try the wire style to see how that performs but that can wait (for a long time!)

I think with all these things it is a case of tuning for small improvements. Collimation and cooling are major ones, optical figure is obviously also important but with more effect under good seeing and at high powers. Things like flocking and secondary support config I guess are likely show small incremental improvements too.

Stu

[John]

My vanes were an option from Orion Optics when the scope was made in 2005. Martin Mobberley's 10" F/6.3 was basically the same spec:

http://www.cloudynights.com/item.php?item_id=634

I've got an 8" F/5 newt with straight vanes at the moment as well so it will be interesting to see the differences (apart from the aperture). With that last night I could see diffraction spikes on stars brighter than around mag 2 and on Jupiter as I approached sharp focus but not at focus, funnily enough. Despite being used to "no spike" views I quickly forgot about them last night and just enjoyed the views 

Having flocked a couple of newts in the past and really not noticed any difference (to my eyes anyway) thats not high up my "to do" list for my current scopes. 

[Robny]

I'm also interested in these, but a little confused. I see how it geta rid of the diffraction spikes. But, the literature on the website (op) 'the diffraction is spread symmetrically around bright field objects'

Does this mean you will get a halo effect on the image or view.

Does anyone have an pics taken with this setup or similar you could show for comparison?

Many Thanks

Rob

Sent from my GT-I9505 using Tapatalk

[Stu]

Ah yes, I've seen that on CN. As you say, interesting why they have now dropped this option and recommend against it.

Anyhow, thanks for the info will do some more reading and think about it some more. Be nice to get the chance to use the scope as it is for a few decent sessions!

Stu

[AlexB67]

As far as theory would have it from what I recall, one the supposed drawbacks of the curved spider is that they take more energy  out of the central airy disk, not due to their shape but due to construction they need to be a bit thicker causing extra scatter. I suppose some of it comes down to  what you want from it, less obvious spikes,  and a little less contrast and how noticeable it would be    I wonder if OO are coming from that angle.

If the whole secondary support is light and you can keep the curved design thin, all good, but in Newts of 12 inch and higher the weight is factor.

In theory at least there is an argument for the ultra thin wires type design as discussed in this paper

http://adsabs.harvard.edu/abs/1959AJ.....64..455E

Seems to make sense in a way, but what do I know about these things, nada in practice 

[Stu]

I'm also interested in these, but a little confused. I see how it geta rid of the diffraction spikes. But, the literature on the website (op) 'the diffraction is spread symmetrically around bright field objects'

Does this mean you will get a halo effect on the image or view.

Does anyone have an pics taken with this setup or similar you could show for comparison?

Many Thanks

Rob

Sent from my GT-I9505 using Tapatalk

Rob, my understanding of this is that the diffraction still occurs (based upon the total length of support vane), but with a properly designed curved support the diffraction is evenly spread around the object as a halo rather than concentrated into spikes.

I would imagine that for splitting tight doubles, the halo is better than spikes which can fall in an inconvenient position.

Ultimately you can't beat the laws of physics and the total amount of diffraction will be the same.

Stu

[AlexB67]

Crunching my sandwiches I came across this. Coming to think of it makes a lot of sense, despite what that first papers says, ( but it also depends  a bit on target such as brightness, for example  - do you want to optimise for double stars, planets, lunar etc. this is also a factor.

Overall in terms of area the extra thickness due to curved spiders is for instruments this size and their impact on contrast and strehl ratio is fairly negligible - at least I don't think the loss in contrast is anything to worry about.

http://www.telescope-optics.net/spider.htm

[cassiewoofer]

Cassiewoofer, you scope looks amazing, really nice job!

Looking at the support though, I think you would get better performance if you modify it to go through a full 180 degrees. It looks from the photos as though it is only around 90 or 100 and I suspect this may be causing some uneven cancelling of diffraction, maybe giving smearing or loss of contrast? Might be worth experimenting with?

Cheers,

Stu

Thanks Stu!,

Yes, I will play with the shape of the mount, I was just working on memory from this article I had read a year or so ago.

http://images.cheezburger.com/completestore/2009/8/2/128937212003588066.jpg

http://images.cheezburger.com/completestore/2009/8/2/128937212003588066.jpg

[cassiewoofer]

Opps! obvioulsy the wrong link!

This is what I meant to copy!

http://www.garyseronik.com/?q=node/141

[faulksy]

sorry stu, havnt read all the thread but i no moonshane was thinking or has bought something similar, pm him he will sort you

[faulksy]

thats weired see this stu, its shanes report

http://stargazerslounge.com/topic/201988-diffraction-spikes/

[Stu]

Thanks Cassie, funny! Was wondering what a Lego Steven Hawking had to contribute to the thread :-).

I even think some of the ones shown in that link are not optimal as they do go through a full 180, but I'm sure they do reduce or eliminate the spikes.

Sti

[John]

I don't see halos or similar though my 12" dob but I'll be bringing it to the SGL star party in April and folks would be most welcome to see what they think themselves 

From the construction of mine I can see that they are more complex to install than a conventional set and perhaps OO decided that the benefits were not outweighed by the cost / complexity of installation and also that maybe few folks selected that option.

My scope was previously owned by a decent imager galled Kev Wildgoose. Here are a couple of images taken with the scope by him with the scope (me not being an imager of any sort !):