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Everything posted by Ags

  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.
  16. My ASI 178 MM has opened up so much for me - EEA, planetary and lunar imaging, DSO imaging too. Another good‘un is the 6.3 Reducer for my SCT - better for photography and eyepieces work better too. Not many mentions of eyepieces but the pick for me would be my ES 6.7 82 degree.
  17. Mars is always very small as its diameter is only twice the Moon’s in absolute terms and of course it is much further away. Despite that, on a good night you can still pick out dark regions like Syrtis Major, the bright spot of a polar cap and even hints of clouds at the limb. It does take patience and careful observing though. I also have a 150 mm SCT and one accessory has been very good for me - a 6.3 reducer that reduces focal length to 945 mm and lets the scope show much wider fields. I used to have a Celestron 25 mm plossl and it was a very pleasing eyepiece.
  18. Ags

    The Great SLV Hunt

    Still looking... Also looking for a 2.5 and 5.
  19. @vlaiv That's the best equation I have seen this decade! Does it have a name?
  20. I think I simply remounted the shoe on the other side - are there no screws on your tube to move the finder over? The way you have it mounted will confuse the tracking I think - but you can download firmware for EQ mode and right arm mode.
  21. Ags

    The Great SLV Hunt

    I have decided the path to astronomical Nirvana lies in 4 SLVs mounted in a Baader turret. I have an SLV 6, so going with 1.5x steps in focal length, I need the SLV 4, SLV 9 (or 10) and SLV 20. Do you have an SLV spare in any of these lengths? As long as they are optically in order and the eyecup still works I don't care about exterior condition. I will pay postage to Holland of course.
  22. By the way, the Fi C6 weights 3.3 kgs without diagonal and eyepiece.
  23. That's right - my RDF is at best 0.5 degrees out of alignment with the scope. I am used to the issue now which i treat as a feature. I simply mentally correct for the offset
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