Was asked by Owen Brazell if I had an image of planetary Nebula Abell 5. The big dob boys had been unable to see it - they generally use an Oxygen OIII filter on PN. I now know why it is difficult (impossible) to see as it has the faintest OIII signal I have ever recorded. Below is 4 hours worth of OIII (12 x 20 mins) and after 4 x log stretches -no other processing yet though. There is just the faintest of rings.

The H-alpha signal on the other hand shows the nebula well but this wavelength is not visible to those who look through telescopes - our eyes don't see the deep red at night.