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BIt More Orion Nebulosity & Nice Eridanus Double


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7.15pm Thurs., some thin cloud (cleared soon after), Bresser Dob.

From Alnitak (Ori), it was an easy hop to some reflection nebulae - M78, NGC 2064, NGC 2067, all very close - they appeared as fuzziness around two close, faint stars, at x35, especially with AV.  The exit pupil was large, so I went up to x42 and managed more clarity, but (strangely) increasing the mag a bit more to x53, 64 did not help.  Neither did the Neodymium filter.  Perhaps what I saw was mainly the Messier object.  (There is another reflection nebula a little to the north (NGC 2071), but no fuzziness was detected there.)

Rigel was the next starting point.  Close by was a line of three bright stars in Eridanus, evenly spaced - SAO 131791, Sigma 649, and Lambda Eri.  The middle one is a double, with a spacing of 21.3", and the close, faint companion was clearly seen at x35.  It was clearer at x53, and then made a pleasing spectacle with the bright stars either side of the double in a 1.55deg FOV.

After an hour and a quarter, I finished the session.  New objects, very satisfying.

Doug.

 

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8 hours ago, cloudsweeper said:

but (strangely) increasing the mag a bit more to x53, 64 did not help.

Based on my total lack of visual work, doesn't increasing magnification without increasing the aperture just spreads the same light over a larger area and so make the object appear fainter? As such, wouldn't there be an "optimal" magnification, where the exit pupil matches your pupil dilation and anything on either side of that would diminish the view? [For diffuse objects, not stars]

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6 minutes ago, Demonperformer said:

Based on my total lack of visual work, doesn't increasing magnification without increasing the aperture just spreads the same light over a larger area and so make the object appear fainter? As such, wouldn't there be an "optimal" magnification, where the exit pupil matches your pupil dilation and anything on either side of that would diminish the view? [For diffuse objects, not stars]

Interesting topic, DP.  As I see it, decreasing the exit pupil helps with diffuse objects as it reduces the surface brightness of the background, but there is an optimal point after which the SB of the actual object then also falls.  x53, 64 were at the top end of the ideal range, so I had hoped for better contrast.  Perhaps the LP wasn't so bad, so the object's SB was dropping by then.

Doug.

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Nice report Neil!  It's been quite some time since I last observed M78.  I actually tried a couple of weeks ago with my 120ST but the transparency was no good at all.

For me, the optimal exit pupil for obtaining the maximum detail from a DSO is somewhere between 1.5mm and 2.5mm depending on the transparency of the sky.  Some objects will happily take even higher powers - M42 and some planetary nebulae for example will happily take an exit pupil of 1mm and show even more detail.

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31 minutes ago, Davesellars said:

Nice report Neil!  It's been quite some time since I last observed M78.  I actually tried a couple of weeks ago with my 120ST but the transparency was no good at all.

For me, the optimal exit pupil for obtaining the maximum detail from a DSO is somewhere between 1.5mm and 2.5mm depending on the transparency of the sky.  Some objects will happily take even higher powers - M42 and some planetary nebulae for example will happily take an exit pupil of 1mm and show even more detail.

Thanks Dave (but it's Doug, not Neil)!  M78 is fairly easy of course, but I'd just never got round viewing it.  And Yes, it's good to experiment to see how much mag (and thus low exit pupil) various objects can take.  Depends on conditions, and object brightness.

Doug.

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