Most planetary nebulae visually are small. The few 'large' ones that we can actually see detail are not that many, and details are hard to make out and require not just aperture, but good seeing conditions.
An OIII filter is the greatest help with planetary nebulae.
In my humble opinion, chasing down the small and really small PN's is a good eye and mind tease,
. The technique I'll be describing below is not at all limited to sussing out small PN's, but also great for spotting larger one's too.
"Blinking" is an old visual trick where two images are quickly compared one after another to spot any differences - Pluto was discovered this way 'blinking' two photographic plates together. Pluto 'blinked' between the plates, its tiny movement between the time lapsed between the two photos was spotted by Clyde Tombaugh in 1930.
With PN's, we use an OIII filter to create the second visual image. The OIII filter is flicked between our eye and the eyepiece. The surrounding star field is toned down by the OIII filter, but the PN *POPS* out like a beacon through the OIII!
You can hold the OIII filter between your fingers, but this is clumsy, impractical and risky for the filter. An easier way is to use a
'blinking paddle' which is very easy to make. The paddle is very thin, thinner than one's fingers, so it is easy to flick it in and out of the FOV. My blinking paddle now stays in my eyepiece kit. Come to think of it, since I made my paddle, ALL my eyepieces have been changed over, but not the paddle that cost me squat!
