Can someone please interpret the MTF charts for me please? What is the f1.4 chart showing in comparison to the to the f1.8 chart? Does the sloping solid red line on the 1.4 chart mean poorer corner performance, or? Thanks.
The perhaps non-technical explanation...
The gist of Nikon MTFs is the closer the dotted and solid red lines are to eachother, the better the contrast. The closer the solid blue and dotted blue lines are to eachother, the better sharpness, although you also want to look at the curve of these lines too.
The gap between the dotted and solid colored lines will indicate where you will start to lose contrast and resolution/sharpness (there is an official term for that but for simplicity I will stick to common terms). The larger the gap, the more "loss" you will incur although this does not always translate in a linear fashion I guess we'll say but it will indicate that if you have a progressively widen gap in contrast or sharpness over the viewable area you will be losing contrast and/or sharpness the farther out from the center you go.
Ideally, from the center, the straighter or shallower the curve, the better although you do want to watch out for "waves" in the curve, particularly where it might spike say mid-frame as that can indicate some optical deficiencies like filed curvature (areas that may not be as sharp as others).
Ideally you want the least amout of curve (a straight line for both colors would indicate a "perfect" lens that transmits 100% of the light with no optical deficiencies but these don't eixst so my general "rule" is you want the solid and dotted lines to be as close to each other and the least amount of slope). I also feel that how sharp the lens starts out being (From the center) is less important than how sharp it is across the frame IMO. (so by this I mean I'd rather have a lens that starts around 8 or 80% according to their charts, but only drops to about 6 / 60% at the edges with no field curvature, versus a lens that starts out very sharp say 9 or 90% at the center but falls off at the edges, say going to 5/ 50%).
But that's just my personal preference and is based on me doing landscape photography where even sharpness to me is a bit more important than having a lens that starts out very strong but falls off [perhaps sharply] towards t he mid frame or edges.
PhotographyLife had a good article on how to read MTFs for various brands. I would Google it and read it. It's very informative and they basically explain what I just did in more detail. Unfrotunately I feel NIkon's MTFs are a bit more limiting when comparing to ones from say Canon or Sony.
A few things to keep in mind...
Keep in mind that MTFs only give us an idea of how a lens behaves, but you may find that a lens performs to your liking even though the MTFs may not relay that, so in the end, how it looks to you is what matters, not so much the MTF. So take them with a grain of salt. My 40mm f/2 Z lens is not terribly sharp according to the MTF< but it's sharp enough for me and I love that lens. So sharpness is only part of what makes a "good" lens in my opinion. Character (such as how it render bokeh) is also something you may want to consider if that matters to you, so don't make your decisions based just on MTFs or you will go crazy or you may end up with a lens you actually don't like, even though it's sharp on paper.
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