Due to bad weather in Germany, I wanted to do some modifications to my Sharpstar 13028HNT. I’d like to share my first experiences with these modifications, though there is still more to do.
A few things I wanted to try:
Create a new mirror mask (notches in the mirrormask worsen the star shape)
Eliminate internal reflections (only just started here, more to come)
Experiment with star shapes featuring 6 spikes (new secondary spider)
First, I 3D-printed a mirror mask:
No notches and 1 mm smaller diameter (to be safe)
I added velour tape on it
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The initial result looked good: the star shape improved. But I wanted something more stable, so I decided to have it CNC-machined.
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I am satisfied with the first test (comparison phots below). The material quality is fine!
The next step was blackening the surface beneath the primary mirror. Not all of it was black-painted in the original manufacturing.
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No gluing needed: The Velour holds by itself, locked in with the screws (and can be easily removed).
Finally, a real challenge (one of my first 3D-designed models): the secondary spider with three struts.
A 6-spike star shape is not very common in amateur telescopes, so I was very curious to see it on my own telescope. The secondary spider was designed with FreeCAD.
Again, I printed a 3D prototype to get a good fit. After that, the CNC machining was completed.
CNC machined spider:
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Comparison to the original spider:
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The attached spider on my carbon 13028HNT:
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(Btw, this was done by a manufacturer where you can have CNC parts and more made.)
Again, the build quality looks good to me. With no other modifications, I mounted it on the tube, performed collimation (works very well with OCAL). The collimation is very precise and easily done.
And finally, the first light! I was very excited and had waited a few weeks for this day. A quick test to see the performance on brighter and dimmer stars. But look for yourself. Don’t mind the strong crop; it was a quick test with no flats and a very short integration time.
M45:
41×60 seconds
Sony A7 III, ISO 640
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NGC 1333:
25×90 seconds
Sony A7 III, ISO 640
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Here is a comparison between the modifications:
upper left: before any modificiation (Didn’t use the Astronomik UV/IR Filter, probably the reason for stronger halo)
upper right: my new mirror mask
below: new mirror mask + new secondary spider
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So far so good! I think I need to add some velour tape to the spider as well, since reflections occur on very bright stars. The tube is already flocked.
I’m happy to answer questions :)
CS
Armin
