Why spend a fortune on lenses?
I have a very natty little superzoom Nikkor 28-300mm, nice and light to carry, does everything you want in one lens from landscapes to portraits and everything in between. No messy lens changes in difficult conditions. Great for travel and very tempting to use for other things too. Retails at about £700 and most people will be very pleased with the results it produces.
I also have a very big heavy Nikkor prime, 300mm, f2.8. Needs a case all of its own to carry it, and I hate to carry it more than a few hundred yards from the car. My arms ache after using it for an hour or so. And it costs quite a lot more than my trusty little superzoom. It rarely sees the light of day.
This wasn’t meant to be a direct comparison of two very different lenses, but I took both to the woods with Coco last Saturday, and took the same image from the same distance with each lens. Nikon D810 and on a gloomy overcast day the ISO was bumped to 1600 for the superzoom, which is not ideal on this camera; I was able to use a much cleaner 400 ISO for the prime. Both lenses produced results which looked very pretty on the back of the camera. For example see the image below which was taken with the prime at f2.8, ISO400, 1/320s.
Zoom in close on a large computer screen and the results are very different. Below are 100% crops of the image with (top image) prime at f2.8, ISO 400, 1/320s and (bottom image) superzoom at f5.6, ISO 1600, 1/320s (you’ll need to click through to Flickr to see the image uncompressed and really appreciate the differences). Not a very scientific comparison, but that, in a nutshell, is why it pays to invest in good glass.