Objective accurately determine lens quality: the MTF imaging graph
In many considerations lens quality factors, the two have been the most objective: optical structure and the MTF curve.
The former is the basis of the difference between each lens imaging, the latter is by far the most accurate and scientific test methods.
Although all kinds of lens imaging quality testing methods emerge in endlessly, but due to the different test conditions, so can't very accurate reflection of the lens of real quality.
And MTF curve, is by the lens manufacturer in extremely objective and rigorous testing environment measured and made public, about the lens imaging quality is the most authoritative, the most objective lens MTF curve is technical reference for what?
MTF full name is the Modulation Transfer Function, as the Modulation Transfer Function, the unit represented by the line/mm.
Comprehensive reflects the contrast and resolution of lens MTF characteristics of MTF is measured with instrument, thus it can be completely ruled out film and other objective factors and artificial interpretation of subjective factors, is currently the most objective accurately judging method of industrial camera quality.
1 1 minute to quickly understand MTF curve.
The MTF values as close to 1 as possible, that is, the MTF line jumped over higher. 2.
The higher the thick line, explains the contrast of lens performance, the better.
The higher the fine line, illustrates the lens, the better the resolution of 4.
The MTF curve is smooth, edge and center of the smaller imaging gap 5.
The closer the solid line and dotted line, the better the lens bokeh 6.
The blue line shows the lens imaging level on f / 8, similar to the best imaging lens level 7.
Black line that the lens aperture imaging level, large aperture more than the value of the curve, for example: the lens in the low frequency contrast curve A represent is moderate, but with the improvement of spatial frequency, its slow attenuation process, its quality is still good curve B represents the lens did very well in the low frequency, shows the contrast of the lens is very good, but with the improvement of spatial frequency, its attenuation curve soon, explain the resolution of the camera is not very good.
The lens in the low frequency curve C represent quickly decay, overall quality is low.
A picture about the MTF curve, matters need to pay attention to the summary is as follows: 1, the bigger the area below contains the MTF curve, the better.
MTF curve as straight as possible, flat laymen edge and uniformity of the central part of the imaging lens.
2, the S curve and the closer the better 3 M curve, (
10 lines to/mm)
Curve representing lens contrast feature.
High frequency (
30 line to/mm)
Curve representing the camera resolution features.
4, do not use different focal length, different class, different specifications (
The whole picture, APS -
And fixed focus and zoom lens, because their characteristics by the design specifications, the optical properties and aberration and the influence of cost, with makings is very big, is not comparable.
Only the same, with specifications of the lens has more significance.
Don't compare the lens MTF curve of different manufacturers, because each manufacturer MTF curve are announced by the income measures in their respective test environment, test environment.
In short, the MTF curve is not everything, it can only interpretation contrast and resolution characteristic of lens, unable to distinguish features such as anti glare, distortion, everyone in a reasonable interpretation of MTF curve at the same time, to be rational and objective attitude.