that is a great explanation but i will never remember it all. is there a simple way to look at it to get a quick summary? such as the black line for a general indicator and how tight the lines are together? do these mtf charts generally translate into what is found in testing of real lenses?
You can't really narrow it down. That's the fundamental fallacy everyone falls into, and why a lot of the stuff DXO, DPR, and the whole host of other "lens testers" produce is largely useless.
If you want to eliminate anything, eliminate the set of curves that don't fit with the apertures you will most use. If you will mostly shoot wide open, then you can ignore the blue curves. If you will mostly shoot stopped down, then you can ignore the black curves. You could ignore dashed curves, and just use the solid curves, but then your not really getting the whole picture.
There is no "one number tells all". That's just a fallacy. The attempt to utterly simplify everything is really what gets you into trouble.
When it comes to the difference between an MTF and a lens test, lens tests all ultimately run into the "sensor bound" problem. Sensors have a fixed resolving power...it's the same across the entire area of the sensor. Lenses, on the other hand, have a non-linear resolving power that falls off as you stop down. At apertures wider than f/8, the potential for a lens to resolve much finer detail than the sensor becomes very real. The problem is, final "output" resolution has an asymptotic relationship with the lowest common denominator. Since the sensor usually IS that lowest common denominator, at faster apertures, where lenses have the potential to resolve a LOT of detail, may all end up looking the same in the end. Why? Well, let's say your sensor can resolve 50lp/mm, and you have four lenses capable of resolving, at f/4, 100lp/mm, 130lp/mm, 150lp/mm, and 173lp/mm (the latter is the maximum diffraction-limited resolving power of an f/4 lens.) The problem is that all of these lenses will all appear to resolve somewhere between 45-49lp/mm with a "real world" lens test, like the kind that DXO does. They are all SENSOR BOUND! The SENSOR cannot resolve more than 50lp/mm, so that is your absolute limit on final output resolution (the resolution measured in the RAW images by computer algorithms.)
So, first off, your standard lens test that tests lenses attached to cameras are largely useless for any apertures above f/8, however from f/8 and narrower, the vast majority of lenses are diffraction limited, so they will all perform the same anyway.
Second, MTFs really don't have any relationship with artificial lens test results, because they are either performed algorithmically based on fairly accurate computer models that account for overall lens construction and design, as well as material traits; or they are performed with optical lens bench testing, which uses a special apparatus to test JUST the lens. Synthetic MTFs will usually indicate just a little bit better performance than Real MTFs generated with a optical test bench, however both will be largely similar, and neither will bear any resemblance to your "standard lens+camera" tests.
If you want to keep it simple: Pick one set of solid lines, for max aperture or f/8 (depending on whichever you use most), and go with that.