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Best refractor in the 3,000 to 4,000 USD (visual and DSLR photo)

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#51 SimonIRE

SimonIRE

    Apollo

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  • Posts: 1,163
  • Joined: 16 Dec 2018
  • Loc: South East England

Posted 07 April 2021 - 12:56 PM

Yeah... if you mean zero light falloff, I suspect there are none, but my NP101is has only minor falloff to a full frame easily corrected by flats.

If you mean perfect round stars at center and corner... well, it's a work in progress for me, I did something stupid and did not design my imaging train so I could adjust backfocus (I just ordered parts to hit the number they said). I think I'm a mm or so short (or long) and so get a tiny bit of coma in the far corners. But I don't think it is the optics, I think it was stupidity's cost. But I cannot prove it.

And of course there's just "how flat is flat". Does that mean zero measurable variation in PSF or eccentricity measures? Or "not noticeable to a human". I'm after the latter, and even with what I can see is wrong, I think the NP101is meets that. When I look at a final wide image nothing says "not flat". Example (very large image, bandwidth warning): https://photos.smugm..._Narrowband.jpg

There's some "shape" to the corner stars, but at any reasonable viewing distance I do not think you can see it.


Visually no star elongation. I think it’s pushing it to have measurably no star elongation.

As for the FSQ106, it’s possible I have a problem with mine but even looking at the spot diagrams for the FSQ106, with small pixels across a full frame sensor, I think it’s questionable whether “visually” a flat frame is possible.

I’d be delighted to be wrong so I’m not looking for a bust up!


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