C27 Crescent Nebula-Ha-testing new spacers (Adel Kildeev)

Celestial hemisphere: Northern · Constellation: Cygnus (Cyg) · Contains: Crescent Nebula · NGC 6881 · NGC 6888 · PK074+02.1 · Sh2-105

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C27 Crescent Nebula-Ha-testing new spacers

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C27 Crescent Nebula-Ha-testing new spacers

I was listening the Devil's whispering to continue to increase back-focus to reduce curvature, so I made a radical change: instead adding thin spacers (it helped a bit) I added 10 mm extra length of back-focus, in total 66 mm. I expected horrible distorted stars but suprisely the image was fine.

The Orion flattener's manual states 55 mm required back-focus. But reading small print to found out interesting note:
“X”mm of additional spacing may be required to achieve 55mm, depending on make and model of camera." What does it mean? I have no idea.

I think that with 66 mm back-focus the image is pretty flat, all stars are round and sharp. Pixel scale has changed from 1.622 to 1.616 arcsec/pixel and focuser 's settings accordingly.

Narrowband imaging
ZWO ASI1600MM/QHY163M
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Status	Advanced success
Started	...
Astrometry.net job	5009679
PixInsight job	I6K67AC6M8JOOMUX0GTIQVYUXP0IMQNJ
PixInsight queue size	n/a
PixInsight stage	n/a

RA (center)	20h11m59s.29
RA (top/left)	20h13m32s.30
RA (top/right)	20h05m21s.31
RA (bottom/right)	20h10m29s.65
RA (bottom/left)	20h18m37s.82

Dec (center)	+38°22′39″.7
Dec (top/left)	+39°38′40″.1
Dec (top/right)	+38°18′30″.0
Dec (bottom/right)	+37°06′32″.9
Dec (bottom/left)	+38°25′21″.3

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C27 Crescent Nebula-Ha-testing new spacers

C27 Crescent Nebula-Ha-testing new spacers

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C27 Crescent Nebula-Ha-testing new spacers

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