I’ve been wondering...

[MarkInSpace]

If I am doing narrow band imaging - is there any value in buying an APO? As long as I use very narrow narrow band filters and refocus between filters, does APO help me? If so, how?

[DavidTrap]

I contemplated the same thing when shooting LRGB with a doublet scope.

In my experience, you still get a bit of colour fringing.

Ultimately, an APO will usually be a higher quality scope, so there is an “overall” improvement in image quality.

DT

[gregbradley]

APOs are usually corrected for other aberrations besides false colour.

Also higher quality APOs have a larger corrected circle so you can use large sensors.

Greg.