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About Ags

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    Main Sequence

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    Astronomy, computers, programming, photography, buying stuff
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    The Netherlands
  1. ....sounds like I got quite close with a figure of 0.8ish for an unobstructed telescope! Might revisit this now i have a much more powerful computer.
  2. I am afraid that telescop-optics.net is coming at this from a completely different paradigm, so I can't help you - they are using Fourier transforms for a mathematical solution, while I am modeling the waves travelling though the telescope. Because there are a lot of waves to sample, I can only approach the answer but never actually reach it. But Fourier stuff makes my brain hurt - so my approach was good enough for me.
  3. I think I was more focused at the time on the relative performance rather than on the individual absolute values. Due to the numerical and simulation-based approach I was not able to calculate the contrast precisely (would have required hundreds of times more processing time) but I could calculate the _relative_ levels of contrast.
  4. Even in a refractor there is contrast loss due to diffraction. I can't recall how I got a number near 0.8 for no obstruction though - that looks too low.
  5. The glass reduces the optical path due to refraction, just like a prism diagonal has a shorter path than a mirror diagonal.
  6. On the subject of spacing - my spacing is 44mm, but it won't be after I mount a 1.25" IR filter in-between lens and camera. The same applie to everyone who mounts a clip filter in their DSLR. So how critical is the spacing in reality?
  7. Yes, confused about the tilt though - if there was tilt, wouldn't there be a softness gradient across the chip, especially if the tilt is sufficient to distort individual stars? I had forgotten my IR block filter, so adding it back in should help a bit! Looking at getting some step down rings to stop the lens down F3.3. Also thinking of making a polygonal aperture mask as a last resort - I would be happier with diffraction spikes than with triangular stars!
  8. You mean 31.5, right? On the subject of lenses, I have been thinking of replacing the macro with a 100/f2.0 portrait lens. These have a very good reputation, but never seen one used for astronomy.
  9. This looks pretty good when zoomed in... https://www.astrobin.com/331725/?nc=all
  10. I think my mono camera has an advantage over you here - I can focus for each channel. The reputation of the Canon 100/2.8 is that it is very sharp for astronomy. But individual samples vary. My stars look to me like pinched optics.
  11. I have got the right spacing I think. I don't mind binning but the asymmetry extends far out into the halo of the stars so I don't think that is a solution. Maybe rotate the camera 120 degrees for each third of exposures, assuming it is the lens? I can try stopping down, but that is an anathema to me, as I am limited in capturing time.
  12. These stars are 100 x 1250 ms subs stacked in DSS. Non-L Canon 100 Macro lens af F2.8 connected to an ASI 178 MM. The picture is a center crop. The misshapen stars can be seen on individual stbs so it is not a stacking issue. Bad lens, or something more fixable?
  13. It was a full moon but I had a test run tonight on M31 and the double cluster. Now that I have a finder, the setup (ASI178MM, 100/f2.8 macro lens and AZ-GTi) is a real pleasure to use!
  14. I think S and N are a counterweight for the objective lens.
  15. Just a little orange adapter to connect a finderscope to my Canon EF to T2 adapter.
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