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Extreme asymmetry in diffraction spikes Sky-Watcher Explorer 150PDS · John Walsh · ... · 26 · 717 · 4

Cassiopeia1 0.00
John Walsh
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Update on the issue I had.

Firstly thanks to everyone for the suggestions and advice.

I flocked the spider as per manufacturers advice and got collimation as close as I could. 

I got the TS GPU coma corrector. Aside from fixing coma it had the hoped-for effect of pushing out the focus point by 20mm so my draw tube barely intrudes into the OTA at all now.

The only downside I can see so far are some bizarre blue & red blobs that appear to be some sort of internal reflections. I can live with that for now though I think. I can include some images of these artefacts if anyone is interested. They really are quite odd-looking..

Here is the first image I managed since doing the aforementioned alterations. 

It’s just 2 hours per panel in a 2-panel mosaic but I’m pretty pleased with it so far.

M45 - Pleiades Mosaic
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Gondola 8.11
Tony Gondola
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I don't know if you've made progress with this but in terms of spider refraction, vane thickness has a direct impact on how the effect shows up in an image. Thick vanes will give you short but bright spikes. Thin vanes will give you very thin and dim long spikes. I believe it's the same amount of energy, it's just being distributed differently. What you really have to think about is what are those choices doing to your image and every single star rendered, even if it's not obvious? What I can tell you is the more vanes you have the more the contrast in your image is being reduced. I don't understand why companies that design spider upgrades continue to use 4 vanes when higher performance would be had with just two at 90 degrees to each other. A single vane would be even better but no one really wants a single pair of spikes like that.
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