Refractor Diffraction Spikes

[jif001]

I thought I’d have a go at printing a mask for my refractor (102mm) to create those diffraction star spikes you get with a Newtonian - and it worked! This is simply a Bahtinov mask taken from Thingiverse and modified to replace the slits with a cross having a 2mm square section. The test image of the Pleiades illustrates the effect. The arrow allows for consistent alignment between sessions.

[Peter Drew]

Very good, now add a central obstruction and see how much performance is reduced.     🙂

[Dr_Ju_ju]

Also add a rotator, so that you can 'tune' the spikes to the direction you prefer   😎.....

[andrew s]

Don't  be put off @jif001 it's not a real astro image without diffraction spikes. They add a touch of class that purist refractor boys and girls just fail to appreciate . 👹

Regards Andrew 

[jif001]

Agreed - stuff like this means that us Frac types have the best of both worlds 👍🏻

[michael.h.f.wilkinson]

Why not just convolve the image with the required diffraction pattern?

[michael.h.f.wilkinson]

7 minutes ago, jif001 said:

Agreed - stuff like this means that us Frac types have the best of both worlds 👍🏻

Same for cat people with their SCTs, Mak-Newts or Schmidt-Newts

[jif001]

4 hours ago, michael.h.f.wilkinson said:

Why not just convolve the image with the required diffraction pattern?

Why not just take a blank image and paint some stars on it? 🤔

[michael.h.f.wilkinson]

5 hours ago, jif001 said:

Why not just take a blank image and paint some stars on it? 🤔

That is completely different. Adding vanes to the scope is mathematically the same as convolving the image with the corresponding PSF

[John]

It seems an interesting idea, to me, to carefully capture and process photons that have travelled many light years to reach here and then to add an optical effect created by unncessary hardware added a metre or so away from the imaging chip

But, I'm not an imager, so what do I know

 

 

Edited January 20, 2021 by John

[Sunshine]

Pretty cool! I want one too.

[jif001]

10 hours ago, michael.h.f.wilkinson said:

That is completely different. Adding vanes to the scope is mathematically the same as convolving the image with the corresponding PSF

The effect is the same, but tweaking an image in software doesn’t really fit under the heading ‘DIY Astronomy’ 🤷🏻‍♂️

[jif001]

9 hours ago, John said:

It seems an interesting idea, to me, to carefully capture and process photons that have travelled many light years to reach here and then to add an optical effect created by unncessary hardware added a metre or so away from the imaging chip

But, I'm not an imager, so what do I know

 

 

The whole process of astrophotography is about changing the record of those photons that we carefully capture. If we didn’t then all we would have is a bunch of linear images that would offer very little interest. No two images of the same target will be the same as a result of different ways of ‘post processing’, and let’s not forget that SHO is a complete misrepresentation of reality. 
There’s also a certain aesthetic appeal to star spikes in an image. The real point here is that if you want them with a refractor, you can have them: you could think of this mask as a form of optional ‘pre-processing’. Overall, what you do to capture and process your images is a matter of personal taste and preference. 👍🏻

[tooth_dr]

I saw this on the facebook group yesterday.  I think these spikes look a lot better than those added in on post processing, and M45 is one of those images that really works with spikes.

However would I add this to my refractor - nope.  It's bad enough having them on one scope.

Did you say you modified an existing mask from thingiverse?  Is it possibe to modify STL files or was it available as a part file?

 

Thanks

Adam

[jif001]

I took an existing .stl file and modified it, creating a hole to delete the Bahtinov pattern then adding the vanes 

[jif001]

Here’s an earlier test with 1mm vanes (rather than 2mm used for the Pleiades). Interesting how the lines are broken - some destructive interference going on? 

[Merlin]

Personally,I don't like diffraction spikes and much prefer nice, sharp, star images

[jif001]

24 minutes ago, Merlin said:

Personally,I don't like diffraction spikes and much prefer nice, sharp, star images

Won’t necessarily use it much myself, just an interesting experiment.