Hi Dave and welcome.
Very crudely, you will probably find that astro-imaging can be classified into a few major groups:
- Individual DSO’s (Deep Sky Objects). e.g. galaxies, clusters, nebulae, etc. as the dominant subject matter.
- Wide field. As above but in a wider field – a pretty setting where the object is generally not dominant (not including the large area nebulae, etc).
- Lunar and Planetary (high resolution)
- Lunar and Planetary (wider, pretty pictures).
The 80mm is probably more optimised for 2 and 4 which IMO do not require a barlow.
1 and 3 require more aperture.
1 requires a solid, accurate (= expensive) mount for tracking and auto-guiding purposes.
Based upon the above, I would probably not recommend spending money on a Barlow at this stage, as this places far too great a demand on the mount (long exposures required) and allied skills such as finding objects, focusing, etc.
Anyhow, that’s a brief brain dump to try and cover what I think may be some main topics for consideration.
Cheers
Dennis