Focal Lehgth

[valleyman]

What is the best focal lengths for differant subjects.

DSO, Luner, Planetry etc etc.

[brantuk]

Slow scopes of around f10 generally focus better with moon and planets - these tend to have long focal lengths. Faster scopes typically f5 are good for imaging dso's typically with wide fov and shorter focal length.

Don't forget that a barlow will extend the focal length and reducers will cut it down somewhat. It all depends if you're imaging or observing or both as to what scope you'd want to pick