Modulation Transfer Function Of Optical System Research Articles

Influence of spectral characteristics of light sources on measuring space camera modulation transfer function

Modulation transfer function (MTF) measurement is a major means to evaluate the imaging quality of a space camera. The influence caused by the spectral characteristic of light source on the MTF results is not negligible, because the transmittance and color aberration of optical systems, and quantum efficiency of the space camera detectors are all spectrally related. Thus, MTF results tested by different light sources are different from each other. To address this problem, we propose a method to analyze the influence of spectral characteristics of light sources on measuring the MTF of space cameras. In addition, the devices and methods are designed to calibrate the spectral response and monochrome point spread function (PSF) of space camera. A Sigma lens (focal length: 1000mm, F number: 5.6) and a Cannon EOS 5DSR camera (pixel size: 4.14 μm) are combined into an experimental space camera, whose spectral response is calibrated with a monochromator (Omno30300, NBeT) and a spectral radiometer (FieldSpec, ASD). We calibrate the monochrome PSF of the Sigma lens with the same monochromator and a CCD (PIXIS 1024, Princeton Instruments, pixel size: 13 μm) micro-measuring system (20X objective). During the calibration of spectral response and monochrome PSF, the same collimator (focus: 5000 mm, F number: 10) is used. With using the proposed method and those calibrating data, we compute the theoretical values of the MTF of a space camera measured separately with five different light sources. The results indicate that MTF measured by a xenon lamp is greatly different from those MTFs measured by the other four light sources. Comparisons of those theoretically calculated MTFs, separately, show that the MTF measured by a tungsten halogen lamp is greater than the MTF measured by a xenon lamp at each spatial frequency. The deviation between those two lamps reaches a maximum value of 0.075 in the medium-high frequency zone. Furthermore, in order to verify those theoretical conclusions, a platform including a collimator and the previous space camera is constructed. The MTFs measured by a tungsten halogen lamp and a xenon lamp are computed with the slanted-edge method respectively. The results demonstrate that the distributions and deviations of the MTFs tested by those two lamps are identical to those theoretical results at each spatial frequency, with the maximum deviation being 0.057. The theoretical and experimental results demonstrate that the suggested method can accurately calculate the influence of spectral characteristics of light sources on measuring MTF of space cameras. The proposed method can also be adopted to investigate the influence of spectral characteristics of light sources on MTF of optical systems in the design or test stages.

一种基于针孔像分析的光学系统调制传递函数测量的自适应背景校正方法

一种基于针孔像分析的光学系统调制传递函数测量的自适应背景校正方法

Visual quality evaluation on changes of MTF and wavefront aberration after laser in situ keratomileusis

To investigate the changes of the Modulation Transfer Function (MTF) and its effect on visual and optical quality with or without low and higher order wavefront aberration after conventional and wavefront guild laser in situ keratomileusis. It was a comparative case series. An aberrometer with Hartmann-shark sensor was used to measure the monochromatic aberration of eyes. One hundred and two cases entered the study; 38 cases were randomized to LASIK and 64 were randomized to WFG-LASIK. MTFs of optical system were calculated at various pupil size (3, 4, 5 and 6 mm) respectively and compared pre and 3 month postoperatively between conventional and wavefront guide ablation with or without higher order aberration. There was a significant increase in MTF positively compared with preoperative values at all spatial frequency (5-60 cycles per degree, c/d ), P < 0.05. MTF values got more improvement without spherical aberration than without coma aberration after LASIK surgery and there was significant different at a spatial frequency of 5 c/d. Higher MTFs were showed in the WFG-LASIK group although there were no significant difference between conventional LASIK group and WFG-LASIK group. However, there were apparently changed without high order aberration as compared to that with high order aberration at all spatial frequency (5-60 c/d. ) in WFG-LASIK group and higher MTFs were showed in the WFG-LASIK group compared with conventional LASIK group and there were significant different (P < 0.05) by calculation and evaluation. Spherical aberration have more negative role on visual quality than coma aberration after LASIK surgery. With the optical benefits expected from correcting higher aberration, wavefront guide ablation have shown a great benefit for low and high order aberration but it still leave a small amount of high order aberration and need further investigation. MTF is a sensitive and extensive in demonstrating the optical quality in refractive surgery.