WildWolf,
It is very difficult to qualify lenses without some type of controlled environment. The following is a method I have used with good results.
Make a test pattern. This can be an 8.5X11 sheet of paper placed in landscape with some words in the middle. The letters should be about 1/4 inch high, black, bold and printed with a good printer. Mark each corner with a black brush pen so they are very obvious.
Mount this target on a board at the same height as your tripod mounted camera and give it good lighting.
Mount the first lens on the camera and adjust for lowest number focal length.
Adjust the distance between the camera and target so the target just fills the frame. Take your first picture. (should be high resolution)
Increase focal length to the highest for that lens or some intermediate point on a zoom lens with longer range. Repeat the above step and take your second picture. Continue for as many test shots you may want.
View the text on each picture at 100% and note the sharpness. For example, this test will very often indicate if a lens is soft at full zoom and can be used to compare two lenses. Text can also be placed along the edge of the target to determine edge sharpness.
If the lens(es) produce sharp text under these conditions, pictures in the field should be sharp as well if adjusted properly.
This is by no means the most accurate method although, with the minimal time and material required, fairly reliable results can be obtained.
Good luck
Arvid