Camera and lens combinations.
I will be testing different cameras on the current system that I have, keeping fixed the focal length at 1000mm.
Now I am using a 5 megapixels IP camera with sensor size of 1/2.5" or 7.1mm, this give at full frame(2952x1920) 140x optical magnification, in HD resolution 1920x1080 gives 280x optical magnification. The "image quality" is not very good but the optical magnification is really great.
Today or tomorrow I will replace that IP camera with a Nikon D3300 24 megapixels, the image quality will be far superior, but and a big but, its image sensor is 27mm, with 1000mm focal length that give just 36x optical magnification at full frame 6000x4000, at HD frame 1920x1080 just 130x optical magnification.
This give an idea that sometimes higher image quality not always is better if we want to get more details by "resolution". This is essentially the same argument used to critique the systems used by nighttime observers that have low optical magnification.