Diffraction spike mask?

[Dave_D]

Can any of our French speaking members translate, or give their opinion on this?

http://serge.bertorello.free.fr/antiaigr/antiaigr.html

Google translate is a bit 'iffy' on  it, but it looks like a way to reduce diffraction spikes.

Could be an interesting little project

Its also on thingiverse

Masque Aigrettes Telescope Newton 200mm (Astronomy) found on #Thingiverse https://www.thingiverse.com/thing:1260926

[AKB]

This is just another way of spreading the diffracted energy across the whole image.  It will therefore reduce the contrast somewhat (although, given that the secondary does that anyway, it's probably not too much of an issue.)  It does the same thing as curved secondary supports, but can be designed more specifically for the primary dimensions.  It would be easy to try, since they suggest that you could simply make them clip-on for easy attachment (although take care to ensure that they are firmly enough attached!)

I quite like diffraction spikes.

 

[Peter Drew]

Hmm. Not keen on this myself, I think the curved vane approach is a better system with less contrast reducing effect in practical terms.  Quelle domage. 

[furrysocks2]

I love this one...

Quote

The price to pay is a small extra occultation of a few hundredths of a magnitude which is perfectly negligible.

 

[Moonshane]

Looks a bit whacky but I might give it a try.

I did this 

 

[Dave_D]

16 minutes ago, Peter Drew said:

I think the curved vane approach is a better system with less contrast reducing effect in practical terms. 

Quite true, but i only do imaging (when i get the damn chance that is lol), but as my 3D printer arrives in the next couple of weeks, i might just pop it's cherry with this

[hughgilhespie]

At last!

I have always wanted to say this - thank you so much Mr. Google!

The legs of the spider cause a diffraction in privileged directions and thus create the egrets.

Vive les egrets!!

Regards, Hugh

[John]

27 minutes ago, hughgilhespie said:

At last!

I have always wanted to say this - thank you so much Mr. Google!

The legs of the spider cause a diffraction in privileged directions and thus create the egrets.

Vive les egrets!!

Regards, Hugh

I'm still trying to figure out how and where to fit 2 trombones to my scope

 

[YKSE]

There're some methods discussed here

http://www.cloudynights.com/topic/491137-how-to-minimize-spider-vane-spikes/

My guts feelings says a black-painted apodizing mask might be the most simple and effective (as it's Dick Suiter has tested it) way forwards.

[Peter Drew]

Having just read the CN thread regarding spider diffraction it seems to me that there more mileage potential for discussion than there is for practical use.  

[Ben the Ignorant]

I read french. This is another Don Quixote fight against diffraction spikes, but it only reduces contrast, and increases scattering. Non-symmetrical spiders cut the wavefront in amorphous slices that cannot be reunited properly at the focus plane. Longer (because of their curvature) and/or thicker vanes damage the wavefront, too.

It might not show very much at prime focus, but at higher magnifications the loss is visible. Asking the scope makers to provide smooth wavefronts, and then degrading them with weird obstacles in the light path.

Look at pics from the large professional observatories, they don't remove the spikes. Spikes are like the grain in a canvas painting, or the veins in sculpted wood, they belong to the artist's tool, and never bothered me at all, ever. Every attempt at reducing them also reduces the scope's visual and high-res performance.

The best system is thin, straight symmetrical vanes, 2 or 4 in number. Three thin straight vanes at 120° also works well, because the three slices in the wavefront have the same exact shape; despite not being symmetrical, when they are reunited at the focal plane the result is fine. You get six spikes but they are very slender, and kinda pretty for my taste.

Adding things in front of the aperture is bound to damage the wavefront, there's no escaping its physical laws.

[rwg]

Putting bits of black stuff in any sort of mask shape in front of the aperture doesn't damage the wavefront in the same way that a misshaped mirror would. A bad mirror leads to interference effects from path differences (some light travels longer distances than other light due to the wobbly shape of the mirror) and also to focus position not being uniform across the whole mirror surface. Just cutting out light from some areas is a different kettle of fish entirely - it only produces diffraction effects which can be either significant or not depending entirely on the aperture pattern.

If you can still find a copy of Maskulator then that will let you play around to your heart's content simulating what the effects of different aperture masks are from spider legs to bahtinov masks to whatever. Unfortunately the original author's web site has gone, but I expect there are copies out there.

cheers,

Robin

[furrysocks2]

http://www.cloudynights.com/topic/547413-where-to-find-maskulator/

[YKSE]

2 hours ago, Peter Drew said:

Having just read the CN thread regarding spider diffraction it seems to me that there more mileage potential for discussion than there is for practical use.  

You're certainly correct about many of hte posts in that CN thread 

On the other hand, there's no dedicated section called "Lounge" there, and considering the most popular section here....

[Ben the Ignorant]

1 hour ago, rwg said:

Putting bits of black stuff in any sort of mask shape in front of the aperture doesn't damage the wavefront in the same way that a misshaped mirror would. A bad mirror leads to interference effects from path differences (some light travels longer distances than other light due to the wobbly shape of the mirror) and also to focus position not being uniform across the whole mirror surface. Just cutting out light from some areas is a different kettle of fish entirely - it only produces diffraction effects which can be either significant or not depending entirely on the aperture pattern.

True, the way the damage is done is different, but the result is the same. Some of the light that should make it to the Airy disk will go the rings, that's the loss of contrast.

[furrysocks2]

I've been working on a new newt with a camera at prime focus. I currently have a design for the top end with rather wide vanes (8-10mm).

Here's my attempt with Maskulator from just now:

To me that looks precisely like I'd be trading spikes for loss of contrast? I think I prefer the spikes.

[Moonshane]

That's exactly the conclusion I came to when I tried a curved vane system in my 6" f11 newt. I felt that although the stars looked initially a bit neater with the curves, they were not tighter and probably less tight than with vanes and overall I felt sharpness was better with the standard four straight vanes so I changed back. I found that observing for small/faint double secondaries when the PA put them in the 'gaps' was best. There's always a compromise one way or another.