Anti Star Spike Mask for Newtonians

[Catanonia]

Just seen this on another group and thought I would share it.

A diffraction mask that apparently removes star spikes from secondary mirror vanes in Newtonians.

https://www.thingiverse.com/thing:1260926?fbclid=IwAR2YhQg6gAeTeblz4GIq8g7J8iLOLhl4n6IliEY5ceXxL_nsbk2L2Xqkh9g

Never tried one myself and I have no association to the link, just thought I would share it.

[Annehouw]

I have experimented with that, and they do work. There is a slight downside in that it will take away a bit of contrast.

In the end I decided not to use them. I do not dislike spikes anyway.

There was a discussion on this a while back for use in a alt-az telescope. As spikes rotate in that configuration, there is a need to fix it in that case.

Discussion here: https://pixinsight.com/forum/index.php?threads/diffraction-spikes-rotation-on-alt-az-telescope.14364/#post-88091

[Whirlwind]

On 11/01/2022 at 08:54, Annehouw said:

I have experimented with that, and they do work. There is a slight downside in that it will take away a bit of contrast.

In the end I decided not to use them. I do not dislike spikes anyway.

 

I wonder whether they could be used on a RASA as well to hide diffraction spikes from cables that would otherwise cause no symmetric effects?

[vlaiv]

8 minutes ago, Whirlwind said:

I wonder whether they could be used on a RASA as well to hide diffraction spikes from cables that would otherwise cause no symmetric effects?

If you bend cables into semi circle - you'll do the same - there is no need for special mask and blockage of the light.

Diffraction happens on a straight edge - in direction perpendicular to that edge. If you make edge curved - each little section will diffract in direction perpendicular to it and if you have semi circle - this will spread in 360° effectively creating halo rather than one strong spike.

Just make sure you have semi circle and not semi ellipse or otherwise you'll end up with elliptical halo around bright stars, see here for discussion on that:

 

[Whirlwind]

1 minute ago, vlaiv said:

If you bend cables into semi circle - you'll do the same - there is no need for special mask and blockage of the light.

Diffraction happens on a straight edge - in direction perpendicular to that edge. If you make edge curved - each little section will diffract in direction perpendicular to it and if you have semi circle - this will spread in 360° effectively creating halo rather than one strong spike.

Just make sure you have semi circle and not semi ellipse or otherwise you'll end up with elliptical halo around bright stars, see here for discussion on that:

Yes, sorry I was aware that you could do it this way.  I was thinking more that it provides a structure to attach the cables to.  As noted if you get it wrong it has effects.  If you have a mask template that fit around the opening then you could attach the cables to backside of the mask to hide them completely and providing a known attachment path (rather than trying to arrange the cables in a certain way that might then move during imaging etc).

[vlaiv]

3 minutes ago, Whirlwind said:

Yes, sorry I was aware that you could do it this way.  I was thinking more that it provides a structure to attach the cables to.  As noted if you get it wrong it has effects.  If you have a mask template that fit around the opening then you could attach the cables to backside of the mask to hide them completely and providing a known attachment path (rather than trying to arrange the cables in a certain way that might then move during imaging etc).

Good point.

3d printed structure that integrates nicely with camera mounting and some sort of support on aperture edge would do the trick.

https://www.cloudynights.com/topic/594770-curved-spider-vanes-for-imaging/

In general, if you have particular design - you can easily see what sort of PSF you'll get and hence star profiles.

All you need is software capable of doing FFT transforms (power spectrum in particular).

Here is example in ImageJ and FFTJ plugin - take any aperture (white value 1 is clear and black - value 0 is masked), do FFT of it and look at power spectrum and blur it a bit with gaussian blur to simulate seeing. Stretch to see star image.

[Annehouw]

2 hours ago, Whirlwind said:

I wonder whether they could be used on a RASA as well to hide diffraction spikes from cables that would otherwise cause no symmetric effects?

Here are two similar (same?) off the shelf solutions: https://www.firstlightoptics.com/adapters/buckeyestargazer-cable-router-for-front-mounted-cameras.html and https://www.teleskop-express.de/shop/product_info.php/language/en/info/p12999_Wega-cable-guide-for-Celestron-Hyperstar-and-RASA-8-.html

[vlaiv]

3 minutes ago, Annehouw said:

Here are two similar (same?) off the shelf solutions: https://www.firstlightoptics.com/adapters/buckeyestargazer-cable-router-for-front-mounted-cameras.html 

Like the solution, but completely baffled by this detail:

 

[ollypenrice]

2 hours ago, vlaiv said:

Like the solution, but completely baffled by this detail:

 

I'll guess: counterweights horizontal, bubble level horizontal, camera properly orientated. I do it myself!

Marcel Dreschler uses a 4-vane 'spider' to route his cables on a RASA 11.

Olly

[Catanonia]

6 hours ago, vlaiv said:

Like the solution, but completely baffled by this detail:

 

I use a similar 3d printed semi circle cradle to route my Rasa cables. The spirit level is interesting...

[Catanonia]

Spider Vane for Diffraction Spikes on a Rasa