diffraction spikes

[nightfisher]

How do you avoid diffraction spikes when observing planets with a newt, i guess you just get the planet "of axis", between the spider vanes?

[cotterless45]

Never noticed them observing planets with a Newt. Have you thick intrusive vanes ?

I was awaiting the multiple transit this morning , just got one moon going halfway when thick cloud rolled in,

Nick.

[ollypenrice]

How do you avoid diffraction spikes when observing planets with a newt, i guess you just get the planet "of axis", between the spider vanes?

All of the aperture contributes to all of the image so you can't locate the planet between the vanes!

The only solution (and a very good one) is to use a curved spider along these lines. http://www.rfroyce.com/spider_cv_8/spider.htm

WHat happens here is that each segment of the corve produces a diffraction artifact in a different place.

Olly

[John]

My 12" dob has curved vanes. I don't get any diffraction spikes. The diffraction is still there but it's evenly distributed across the FoV. Whether the sum total of diffraction is greater, the same or less than conventional vanes I don't know as I've not compared it directly to a conventional 12" but I'm very pleased with it's overall performance particularly on lunar and planetary detail

[ollypenrice]

David Lukehust uses them, as indeed do Obsession, so that probably says it's a good idea.

Olly

[Moonshane]

increase the aperture LOL

I find they (same thickness) were intrusive on my 6" f11 so I changed to a curved spider vane with good results. My 12" f4 hardly shows them at all.

[nightfisher]

I barely notice CA in an achro frac, but spikes in a newt really get to annoy me, i dont think i will bother with a newt upgrade. Thanks for the replies, stopped me making a mistake

[Dannae]

The choice and style of spider is effectively a choice of what you want to see in your star images. A straight vane causes diffraction in a 2% area.  A curved vane’s diffraction is equal to its curvature, thus a 90 degree curve in a vane equals a 90 degree swath of diffraction.

I've looked through curved, looped 3 and 4 vane and I put myself in the rigid 4 vane camp. My heart says the views are 'cleaner' in a curved vane system but my head says there is more total diffraction.

Curved spiders are often thicker than their 3 or 4 vane counterparts which are held in tension but I feel that it comes down to what you want to see and what is most pleasing. Perhaps splitting close doubles would be preferential with a 4 vane if you move the companion out of the spike of the brighter star whereas planetary views smack bang in the centre of the eyepiece might appear better with a curved.

Just my 2 vanes

Regards

Dannae

[philj]

A case of unsightly spikes eh Jules :-)

That 8" OO newt I rebuilt the other year had curved secondary holder vanes which gave acceptable views. Stick with the refractors, you know it makes sense :-) :-)

[RikM]

Using a larger aperture with an off-axis aperture mask does the trick.

[Peter Drew]

The main problem usually with refractors is that you are financially stuck with a small telescope. 

[Moonshane]

The choice and style of spider is effectively a choice of what you want to see in your star images. A straight vane causes diffraction in a 2% area.  A curved vane’s diffraction is equal to its curvature, thus a 90 degree curve in a vane equals a 90 degree swath of diffraction.

I've looked through curved, looped 3 and 4 vane and I put myself in the rigid 4 vane camp. My heart says the views are 'cleaner' in a curved vane system but my head says there is more total diffraction.

Curved spiders are often thicker than their 3 or 4 vane counterparts which are held in tension but I feel that it comes down to what you want to see and what is most pleasing. Perhaps splitting close doubles would be preferential with a 4 vane if you move the companion out of the spike of the brighter star whereas planetary views smack bang in the centre of the eyepiece might appear better with a curved.

Just my 2 vanes

Regards

Dannae

This rings true with me actually. The planetary views are far superior (cleaner) with the curved spider but the views of double stars were slightly better with the straight four vane system. Lunar views are the same. I took the view that overall, the curved spider was worth it.

[Dannae]

Peter Drew, on 09 Dec 2014 - 1:50 PM, said:

The main problem usually with refractors is that you are financially stuck with a small telescope. 

Been there, still stuck with it

[moriniboy]

I'm thinking of upgrading the vanes on my AE newt to curved ones by using 4 stainless steel 0.5mm rules, should be interesting....

They only cost £1.29 each off feabay and if it does not work I will just convert back to stock.

[nightfisher]

I barely notice CA in an achro frac, but spikes in a newt really get to annoy me, i dont think i will bother with a newt upgrade. Thanks for the replies, stopped me making a mistake

As above, i wont be upgrading to any other newt

A case of unsightly spikes eh Jules :-)

That 8" OO newt I rebuilt the other year had curved secondary holder vanes which gave acceptable views. Stick with the refractors, you know it makes sense :-) :-)

Yes phil, refractors or better still for planets......Maks.....no coma, no spikes, no CA, easy on the mounting system............decision made

[Astro_Baby]

The main problem usually with refractors is that you are financially stuck with a small telescope. 

Get a Mak All the aperture for lots less - course then you are stuck with a very high F ratio but nothing is perfect

[nightfisher]

Get a Mak All the aperture for lots less - course then you are stuck with a very high F ratio but nothing is perfect

Got one, i did own the 180 pro, but downsized to a 150 pro about a year back, was a good move as its more grab an go than the 180

[Qualia]

For general star observing, I see diffraction spikes as a thing of great beauty. There's a sense of elegance about them. On planetary viewing, however, there can be a subtle loss of contrast, the delicate bluring of Jupiter via the spider vanes but, of course, aperture makes up for this sliight loss, revealing a whole new world of detail to discover. I guess this is the reason why there's no perfect scope to own, each has something to offer which the other type simply won't be able to match.

[Macavity]

Riddle me this then... (A split spike!) 

I sense orthogonal veins are not quite... orthogonal?

(Collimation / techniques have improved since then!) 

[HD-AP]

Hi

My sinden optics 10 inch  f8 newtonian has an optical window ,so no diffraction spikes .

But to be honest in my larger newts with spiders ,diffraction spikes don't bother me that much .

[Stu]

On 12/12/2014 at 22:06, HD-AP said:

Hi

My sinden optics 10 inch  f8 newtonian has an optical window ,so no diffraction spikes .

But to be honest in my larger newts with spiders ,diffraction spikes don't bother me that much .

That 10” f8 must be quite something! Love my 8” f8, but the extra aperture and no spikes must be great!

Most of the time the spikes don’t bother me, particularly on planets. I don’t go looking for them but they are definitely there.