M20

[Ivan Maly]

The drawing is mainly the view at 140x without a filter, although 45 and 230x and an OIII filter were also used. 16", Cherry Springs dark sky park, July new moon.

1316

[Don Pensack]

One of the interesting things about the H-emission part is the multiple star in the center, not in your drawing.
I wonder if it's substantially dimmed by your O-III filter. You don't use a Baader O-III filter, by any chance?

[Ivan Maly]

The filters were Orion, and they dimmed the star relative to the central nebulosity. What can be said about the Baader OIII in this connection?

[Don Pensack]

The orion O-III has a FWHM bandwidth of about 15nm.
The Baader has (depending on version) an 8.5nm or 10nm bandwidth.
Unlike the Orion, it transmits only 1 of the 2 O-III lines with a high percentage (501nm).
Not the best for visual use unless you know that nebula emits all of its energy at 501nm, but it significantly dims the stars (so does the Orion, but just not to as great a degree).
That's why I thought that, perhaps, you were using a Baader O-III.

[hajuem]

Hi Ivan
Puhh! Very good observation and sketch . Many many Details!!
Respect!!!

Lg Hajü