JPS58218632A - Driving controlling method of solid state image pickup element on modulation transfer function measuring device - Google Patents

Abstract

PURPOSE:To make a transfer time shorter than an exposure time at all times, and to execute exactly an MTF measurement, by varying the exposure time and driving frequency of a solid state image pickup element in accordance with brightness of a lens to be inspected. CONSTITUTION:Irradiance is calculated by a computer 24 basing on an F-number and a projection magnification, and when a necessary storage time is set, an address signal for selecting a clock pulse phii corresponding to this storage time is sent out, and a switching circuit 27 gives phii to a phase difference pulse generating circuit 28. Also, clock pulses phiR, phiX and phiT generated in accordance with an output of the generating circuit 28 are given to a solid state image pickup element 10, and its storage time is controlled. A video signal from the element 10 is stored in an RAM36, and thereafter, is inputted to the computer 24, and MTF is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device drive control method that uses a self-scanning solid-state imaging device and is blind to an MTF measuring device.

The MTF measurement device is a device that measures the contrast of the image by receiving the original scleral distribution of an optical image with a photoelectric conversion element and performing Fourier transformation electrically or optically. This device has used a photovoltaic multiplier tube or a photodiode that covers a single light-receiving surface as a photoelectric conversion element, but when using these photoelectric conversion elements, a mechanical scanning mechanism is required. This has the disadvantage that the measurement is complicated and the measurement time is long.

Therefore, by using one-dimensional self-scanning type image carriers as high-quality photoelectric conversion elements for charge transfer elements, photodiode arrays, packet pre-gated devices, etc. used in facsimiles, -%g character reading devices, etc. An MTF measuring device with a significantly simplified configuration and shortening the fixed time by two orders of magnitude compared to the conventional device is conceivable.

To explain briefly, a solid-state image sensor has a plurality of light-receiving elements arranged in a planar line, and a photoelectric conversion signal corresponding to the optical distribution irradiated onto each light-receiving element is sequentially set by an electronic pulse. Extracted as a time series signal.

FIG. 1 is a diagram showing an example of the configuration of an optical system in an MTF measurement lifting device using a solid-state image sensor. , ]
03 is distributed. Similarly, the chart provided in the Nayat frame 1 includes the spatial frequency components to be measured and is formed corresponding to the measurement points, and the chart provided in the Nayat frame
2 through the optical fiber 13. The image of this chart is captured by each solid-state image sensor 10 by the lens 14 to be tested. .about.103 via an imaging mirror 15.1.6. The imaging mirrors 15 and J6 can be moved up and down according to the projection magnification, and the solid-state imaging device installed off the optical axis can also be moved according to the projection magnification. The mount on which the test lens 14 is installed can be arbitrarily rotated with a υ blower, and the MTF relative to the rotation angle of the test lens can be measured.

By the way, in the MTF measuring device having such an optical system, assuming that the chart surface is uniformly irradiated, the irradiance is EO%, the F number of the test lens 14 is F1, and the F1 projection magnification is m, then the solid state is Radiant heat #E on the surface of the image sensor is expressed by the following equation.

T: Transmittance θ of the test lens 14: Half angle of view of the measurement point AE (θ): Aperture efficiency R: Imaging mirror For reflective non-photographic lenses of ]5 and ]6, the F number is 12 to 16 and the projection magnification is 20
Since it is necessary to measure the MTF at a magnification of ~50 (times), the minimum and maximum irradiance of the solid-state image sensor surface will differ by about three orders of magnitude. When using a solid-state image sensor, the radiant heat # is usually controlled by controlling the accumulation time (exposure time).
Even if E is different, a uniform exposure amount can be obtained, but when the radiant heat 17E is significantly different between the minimum and maximum, as is the case when measuring the MTF of a photographic lens, controlling the accumulation time alone is not perfect. In other words, when using a solid-state image sensor, it is essential that the transfer time is always shorter than the storage time, but even if the storage time is set to be approximately equal to the transfer time when both the projection magnification and the F-number are small, the If only the time is controlled, the exposure amount may reach saturation, making it impossible to measure the correct MTF.

In order to eliminate this, it is necessary to lower the voltage of the lamp 2 or install an ND filter in the optical path, resulting in poor operability. 1. An object of the present invention is to provide a method for controlling the driving of a solid-state image pickup device of an MTF measuring device, which improves the above-mentioned drawbacks and makes it possible to measure MTF correctly with simple operations.

The present invention will be described with reference to examples.

FIG. 2 shows a timing chart when charge-coupled devices are used as the solid-state image sensors 101 to 1.03.

ΦTΦR represents a transport clock and a reset clock, respectively. The transport clock ΦT transfers the charge signal from the photoelement to the output amplifier, the reset clock, and ΦR represent the transport clock Φr.
It functions to charge the charge detector voltage of the charge detector connected to the output amplifier to the reference level before the next charge signal is input from Vc. Here, when the transport clock ΦT has a logical value of 1, it transfers the charge signals of the even numbered bits of the photo element, and when it has a logical value of 0, it transfers the charge signals of the odd numbered bits and bits of the photo element. These charge signals are combined in series by an output amplifier and output. Therefore, in a solid-state image sensor with such characteristics, the transport clock ΦTttl
The clock pulse needs to have a data ratio of 50%, and the driving frequency of the solid-state image sensor is expressed as twice the frequency of the transport clock ΦT.

Now the number of photo elements (7) of the solid-state image sensor 'i N
.

If the drive period is TD, the transfer time Ttra is Ttra
> TDX N −・= −(represented by 21, the period (accumulation time) of the transfer clock ΦX Ti
It must always be true for nt K. Also, the output of the solid-state image sensor is Tint.
Since it is proportional to K, as mentioned above, when the projection magnification is small or the F number is small, Tint must be shortened, and then TD must also be shortened within a range that satisfies equation (3). In other words, in such a field, it is necessary to use a TD that increases the drive frequency (=-) of the solid-state image sensor, and the dynamics and
It turns out that it is necessary to change the driving frequency of the solid-state image sensor.

Figure 4 is a diagram showing an example of an apparatus for implementing the present invention, and Figure 4 is a timing chart thereof.

Clock pulse φ from oscillator 21. is divided into n stages by the frequency dividing circuit 22 to become clock pulses φ1 to φn. The F number and projection magnification of the lens to be tested 14 are sent in advance from the input/output device #23 to the computer 24 at the input/output port 2.
5, and the F of the computer 24
Based on the number and the projection magnification, an instruction signal for selecting the accumulation time and 7 pulses φ, .about.φn is calculated and sent to the output port 26. The command signal from this output port 26 is applied to the switching circuit 27, and the switching circuit 2
7 is the clock signal 1.7 from the frequency dividing circuit 22. φ1 (i=], 2, . . . , or n) is selected and outputted to the phase difference pulse generation circuit 28.

The switching circuit is, for example, a multiplexer consisting of m address lines satisfying 2m>n with n inputs, and these address lines are connected to output ports of the computer.

Therefore, when the radiation illumination corresponding to formula 90 is calculated using the F number and projection magnification, and the required accumulation time is set, the clock pulse φ1 corresponding to this accumulation time is calculated.
An address signal for selecting the phase difference pulse circuit 28 is sent out from the computer through the output bus, and the switching circuit (multiplexer) outputs the phase difference pulse circuit 28 VCφI.

The phase difference pulse generation circuit 28 is, for example, a circuit composed of a several-bit binary counter and a decoder,
The clock pulse φi from the switching circuit 27 is divided into lock pulses φi and IR as shown in FIG.
make. Of these, the clock pulse φ'r is frequency-divided by the -y rip-off clock 29 and the transport clock φT
Then, the clock pulse TR (l-j: inverter 30
is inverted and becomes the reset clock φR. The transport clock φT, the reset clock, and the clock φR are given as clock pulses with different phases, and the one-dimensional self-scanning body image sensor 10 made of the charge coupled device
Applied to (]0+ to 103). After the accumulation time setting counter 3 counts M clock pulses JR, the gate circuit 32 outputs the transfer clock φX. Here, M is preset in the accumulation time setting counter 3 according to a command signal input from the output port 26 to the register 33 in advance.

The clock φR1φX1 φT generated in this manner is input to the solid-state image sensor 10, and the video signal is sampled and held by the sample-and-hold circuit 34, and then transferred to the analog/digital converter 35 and stored in the random access memory 36. Memorized temporarily. When all the video signals are stored in the memory 36, this memory 3
6 is input into the computer 24 through the input port 37 and the MTF is calculated. This result is output to the input/output device 23 through the entire input/output boat 25.

In this embodiment, the storage time of the solid-state image sensor is controlled according to the brightness and projection magnification of the lens under test, and the switching circuit selects the clock pulse of the optimum frequency, so the transfer time is always υ shorter than the storage time. I can do it. Therefore, even if the F/S of the lens to be tested is small or the projection magnification is small, the exposure amount will not be saturated and the correct M
TF measurement can be performed.

As described above, according to the present invention, in an MTF measuring device using a self-scanning solid-state image sensor, the exposure time and drive frequency of the solid-state image sensor are changed in accordance with the brightness of the test lens, so the transfer time is always By making the exposure time υ shorter, the exposure amount will not be saturated and the correct M
TF measurements can be performed. Moreover, since no means for optically or mechanically reducing the exposure amount is required, the operability and reliability of the apparatus are significantly improved.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an example of an optical system in an MTF measuring device, Fig. 2 is a timing chart of a charge coupled device, Fig. 3 is a block diagram showing an example of an apparatus for implementing the present invention, and Fig. 4 is an apparatus for implementing the same. This is an example timing chart. 10... Solid-state image sensor, 21... Oscillator, 22...
- Frequency dividing circuit, 23... Input/output device, 24... Computer, 27... Switching circuit, 31... Accumulation time setting counter, 33... Register. -1]-

Claims (1)

[Claims] An MTF measuring device using a self-scanning solid-state image sensor, characterized in that the driving frequency and exposure time of the self-scanning solid-state image sensor are changed in accordance with the brightness of a lens to be tested. solid-state image sensor drive control method.