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MTF Curves: Theoretical Versus Actual

November 19, 2016

All camera companies (with the exception of Sigma and Leica) publish MTF curves for their lenses that are “theoretical” and not actually measured.  Should you care?

 

Personally, I believe in the old President Reagan saying “trust but verify”. What follows is a dose of reality, compared to theory.  I have chosen what most people would agree are among Nikon’s best pro lenses for this study, lest I get accused of measuring lenses that were manufactured using lesser standards.

 

The MTF curves I’m referring to are the traditional mix of MTF10 (contrast) and MTF30 (sharpness).  I used the “mtfmapper” software version 0.5.8 to create the following charts.  Personally, I place much more stock in the 2-dimensional MTF50 plots that measure the whole camera sensor.  Unfortunately, getting 2-D MTF50 plots is hard to come by outside of this site.

 

The MTF charts are traditionally generated for a wide-open aperture, so that’s how mine are measured.  It’s unknown what focus distance is used by Nikon; mine will be measured at the distance needed to photograph an “A0” resolution chart filling the frame.

 

I took the measurements in shade on a clear sunny day.  Light wavelengths can affect measurements; I like to test using the same lighting conditions that I normally shoot.

 

 

105mm f/2.8G ED‑IF AF‑S VR Micro Nikkor

 

This lens is supposed to be optimized for “close” distances, but I’m measuring it at a more conventional distance.

 

Nikon Theoretical Chart (from Nikon site) for 105mm

 

 

Measured MTF10 and MTF30 for 105mm at f/2.8

 

I don’t want to appear cynical, but I was 99% sure that my measurements would show less sweetness and light than the Nikon claims.  This is pretty much borne out by the measurements.

 

Take a look at the edge of the lens, though.  It actually performs better than theoretical!

 

 

 

 

 

 

Measured MTF10 and MTF30 for 85mm at f/1.4

 

Again, not quite as good as theoretical.  The edges have a few pleasant surprises, however.

 

 

85mm at f/4.0

 

Just for fun, I tried an f/4.0 test.  It really cranks up the quality, doesn’t it?

 

 


24-70mm f/2.8E ED VR AF-S Nikkor

 

 

The wide end of this lens looks dramatically different than theoretical.

 

 

 

Again, this lens at 70mm looks quite a bit different than the claims.

 

 

Conclusion

 

It appears that Reagan had some good advice.  Bear in mind that these lenses don’t represent the whole population; your mileage may vary.

 

My biggest surprise is that the FX frame edges fared better than expected.

 

Trust but verify.

 

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