NGC 3503 is a small emission nebula with a dim Blue reflection (seen in the middle of the frame).
It lies in a very large HII area (as can be seen by all the Red nebulae all around)
It is a VERY neglected nebula because it lies near the famous Eta Carina nebula.

At the upper left of the frame - a little surprise - the planetary nebula PK289-0.1 with a diameter of only 35".

Please see next image for an enlarged cropped view of this PN.

Imaged with the 16" f3.75 Dream Astrograph.
Apogee Alta U-16M camera.
L- Ha-RGB image

Lum- 60 min
Ha - 90 min
RGB 20 minutes each Bin 2x2

(Total of 3:30 Hrs )

Imaged from Tivoli farm in Namibia July 2013.