Step 1: Don’t point it at anything other than the sky.
Step 2: Under no circumstance attach a tele-converter to it.
Step 3: In the event that you failed to follow Step 2, please revisit Step 1.
Disclaimer: If you are Law Enforcement (involved in a lawful investigation) and are trying to observe someone from far away but don’t need clear photographs, disregard what I’ve said.
Instead of explaining the following, I’ll just post the pictures and let your eyes do the explanations by comparing it to my 18-200mm Sony lens. Since I’m using an APS-C sensor, and tele-converters I will post the effective length with each. These images are cropped to about 1000×800 at 1:1 pixel ratio; so while they are cropped, these are not re-sized at all. Also note, some of the ‘wavy’ distortion is due to atmospheric issues. I’m going to be making a post regarding that later on this week.
18mm (effective 28mm)
200mm (effective 300mm)
200mm with internal 2x tele-converter (effective 600mm)
200mm with external 2x tele-converter (effective 600mm)
200mm with internal and external 2x tele-converter (effective 1200mm)
800mm (effective 1200mm)
800mm with internal 2x tele-converter (effective 2400mm)
800mm with external 2x tele-converter (effective 2400mm)
And just to be stupid for no good reason…
800mm with internal and external 2x tele-converter (effective 4800mm)