Evaluation of Lightweight and Soft Pentax 100mm Macro Lens

Budweiser? Lenses, that is, macro lenses with a focal length of 100mm (sometimes including 100mm or so), are very frequently used in macro photography. Because of the long focal length of this lens, a large proportion of images can be obtained from a long distance, which reserves flexible space for lighting and composition. At the same time, a longer focal length is also conducive to creating a soft Jiao Wai effect.

Pentax D FA 1:2.8 100mm macro lens (click here to view larger image.

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Compared with similar lenses of other brands, Pentax's D FA 1:2.8 100mm macro lens is very lightweight? Budweiser? The lens supports the imaging format of 35mm Quan Huafu. D FA 1:2.8 100mm macro can get the same picture reproduction ratio (1: 1) at the nearest focus distance while having a large aperture of f/2.8. On the eve of the unveiling of Pentax K-series SLR, let's review this classic macro lens, which is also a little warm-up for the new SLR. However, our test still uses K20D in APS-C format as the platform.

Macro photo of Pentax D FA 1:2.8 100mm with soft background.

"Product advantages:

1, light lens, comfortable control experience.

2, the lens comes with a hood effect

3. The imaging Jiao Wai effect is soft.

"Product disadvantages:

1, autofocus is noisy.

2. The image definition is not high.

Specification analysis

The lightness of D FA 1:2.8 100mm macro comes from its simple lens structure, and a total of 9 lenses are used. When used in digital SLR cameras with APS-C format (such as K20D), the shooting angle is 16 degrees. The following are the detailed technical specifications of D FA 1:2.8 100mm macro:

"Angle of view [degree]

24.5 (16 when installed on a digital SLR camera)

"Number of components [group * pieces]

8? nine

"Minimum aperture [F]

32

"Minimum photographic distance [m]

0.303m (working distance 0.130m)

"Filter diameter [mm]

Forty nine

"The largest diameter? Length [mm]

67.5? 80.5

"mass (weight) [g]

345

Appearance and sense of operation

From the appearance, the D FA 1:2.8 100mm macro lens is not as delicate as those of the gold ring and limited lens, and the appearance is made of more plastic materials, which is one of the reasons for keeping the lens body light and thin. However, due to the wide manual focusing ring and the uniform feedback of operating resistance, the manual focusing operation experience is still good.

Pentax D FA 1:2.8 100mm macro (click here to view larger image.

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Pentax D FA 1:2.8 100mm macro (click here to view larger image.

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The front aperture of this lens is small, the filter size is only 49 mm, and the front lens barrel has a cavity about 2 cm deep. On the one hand, it can play the role of a hood when shooting, and on the other hand, it can protect the front lens from being touched so easily.

Pentax D FA 1:2.8 100mm macro (click here to view larger image.

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D FA 1:2.8 100mm Macro In the latest focusing state, the front lens barrel will stretch about 5 cm, which looks awkward. Slim? In my mind. However, due to the small total weight of the lens, the center of gravity of the whole system is slightly shifted during use, which will not have a significant impact on the grip.

Pentax D FA 1:2.8 100mm macro (click here to view larger image.

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In order to facilitate accurate manual focus control, D FA 1:2.8 100mm macro lens provides a focus lock switch, which can lock the focus state of the lens at any time, and the auto-focus function of the system will also fail after locking. In addition, the macro of D FA 1:2.8 100mm also supports full-time manual focusing in the auto-focusing state of the system; Auto focus is noisy when it works, which is the only deficiency in the experience.

Imaging resolution test

In the imaging test, according to the method provided in the Imatest software reference, we use the test prototype to shoot the test target for many times under the illumination of 5000K standard color temperature lamp (the color rendering index is greater than 95%), and then use Imatest software to analyze and get the numerical value, and select the numerical value that can represent the average level or the average value of many tests to be listed in this paper.

Enhanced ISO 12233 Resolution Test Target

When testing the imaging resolution, we use the aperture priority mode of the test prototype and use the sensitivity of ISO 100 to shoot the test target that enhances the resolution of ISO 12233. The photos are stored in 16-bit RAW format, then converted to TIFF format without compression and sharpening, and then the local objects in the center and edge areas of the image are numerically analyzed by Imatest. The above is the resolution test target of D FA 1:2.8 100mm macro shooting, and the red marked area is the test sample area. We use the MTF50 value obtained by Imatest analysis as a reference to examine the imaging resolution of the camera. The MTF50 value of the test results (unit: LW/PH, line width/image height) indicates the maximum number of black and white lines that the camera can distinguish per imaging height (contrast is 50%). The higher the numerical value, the higher the imaging resolution of the camera (lens).

The test results show that the overall image clarity of D FA 1:2.8 100mm macro is not high. After all, the total number of pixels of K20D has exceeded14 million, and the highest MTF50 of this lens is only 2000 lw/h. From the overall distribution, after the aperture of the macro of D FA 1:2.8 100mm is slightly reduced, excellent imaging sharpness can be obtained until F/7./kl. In addition, from the test results of the edge area, the image clarity of the edge area has not obviously decreased, after all, it is a lens suitable for Quan Huafu models.

Imaging dispersion test

Imaging dispersion: When analyzing imaging dispersion, we use the same analysis object as in the resolution test. This value has a great relationship with lens quality, and the lower the value, the better.

According to the test results, the macro lens of D FA 1:2.8 100mm controls the dispersion in the whole picture very well, which is also an important reason to ensure that the macro edge imaging clarity of D FA 1:2.8 100mm does not decrease obviously.

Imaging shape distortion test

When testing the shape distortion of imaging, we use the test prototype to shoot the square on the plane, and then use Imatest to test the distortion of imaging. The values in the list are SMIA TV distortion, and the closer to zero, the better. A positive value indicates that the imaging produces pincushion distortion, while a negative value is the opposite.

Test results of shape distortion of D FA 1:2.8 100mm macro imaging.

The test results of about -0.0 1% show that there is almost no shape distortion when D FA 1:2.8 100mm macro is imaged by K20D, which will not affect the image quality. That is, using D FA 1:2.8 100mm macro to shoot some subjects in the field of scientific research, its rigor can also be guaranteed.

Imaging opacity test

We use the wide-angle end of the test prototype to shoot an unfocused white object with uniform illumination, and then use software to test the loss of brightness, and get the ratio of the brightness of the corners to the highest brightness of the imaging center. This value can show the light loss at the corner of the lens and reflect the uniformity of the lens. Below 100%, the bigger the better.

Loss of light test results of D FA 1:2.8 100mm macro full aperture.

Due to the low exposure of matrix photometry of D FA 1:2.8 100mm macro Pentax K20D, the overall brightness of the test screen is not high. However, from the angle contrast, the dark angle of D FA 1:2.8 100mm macro lens is not obvious even with K20D full aperture.

Imaging color test

When analyzing and testing the imaging color of the prototype, we use it to shoot the X-rite ColorChecker SG color test target at the sensitivity of ISO 100, and then analyze the color, and we can get the data such as imaging color error and white balance error. The value of the white balance error in the list is the color temperature error of the medium gray block, and the closer this value is to zero, the better. If this value is positive, it means that the imaging tone is cold, and if it is negative, it is the opposite. In the color error diagram, the squares in the Lab color gamut coordinates represent the ideal color (standard color) of the subject, and the circles represent the imaging color of the camera under test. In the color error diagram below, the upper left corner of the square represents the ideal color (standard color) of the subject, and the lower right corner represents the imaging color of the camera under test.

Color test results of D FA 1:2.8 100mm macro

Judging from the color test results, the imaging style of D FA 1:2.8 100mm macro lens conforms to Pentax's consistent characteristics, most of which are bright and bright, and blue is particularly rich. However, its cyan tone is warmer.

Test sample (1)

The focal length and large aperture of D FA 1:2.8 100mm macro determine that it can shoot extremely shallow depth of field and soft Jiao Wai images. Even if the aperture is reduced to f/ 10, the imaging depth of field is still very small. In fact, due to the extremely shallow depth of field, it is difficult to accurately grasp the focus state at close range when the aperture is fully open, but this is also the fun of macro photography. Sharp imaging is not the performance advantage of D FA 1:2.8 100mm macro lens, but its soft and delicate Jiao Wai effect is the most attractive place as a macro lens. The following are some test samples of D FA 1:2.8 100mm macros, most of which were converted from RAW files without sharpening, and finally saved as JPG with the largest size and highest quality:

Test sample (2)

The focal length and large aperture of D FA 1:2.8 100mm macro determine that it can shoot extremely shallow depth of field and soft Jiao Wai images. Even if the aperture is reduced to f/ 10, the imaging depth of field is still very small. In fact, due to the extremely shallow depth of field, it is difficult to accurately grasp the focus state at close range when the aperture is fully open, but this is also the fun of macro photography. Sharp imaging is not the performance advantage of D FA 1:2.8 100mm macro lens, but its soft and delicate Jiao Wai effect is the most attractive place as a macro lens. The following are some test samples of D FA 1:2.8 100mm macros, most of which were converted from RAW files without sharpening, and finally saved as JPG with the largest size and highest quality:

"IT 168 assessment center view

D FA 1:2.8 100mm macro is not impressive in appearance design and technical identification, and it is not a gold ring lens, nor does it use too many advanced technologies. However, the light and thin volume and good operating experience of D FA 1:2.8 100mm macro left a good impression on the author. In fact, as a macro lens that can be applied to full-frame models, its focal length and aperture determine that it is still the backbone of macro photography for Pentax users.

Pentax D FA 1:2.8 100mm macro lens (click here to view larger image.

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Judging from the imaging performance test, the advantage of D FA 1:2.8 100mm macro is to create an image effect with extremely shallow depth of field and soft Jiao Wai, and to take macro photos with rich layering by combining reality with reality. However, the overall sharpness of imaging is not too high, which still makes people feel unsatisfactory. In other aspects, D FA 1:2.8 100mm macro controls all kinds of distortions at a very low level, and the fidelity of the shooting effect is trustworthy.

"Disclaimer: The evaluation content of this article is based on the samples provided by Pentax Company (product number: 6 1 17892). Our evaluation conclusion is only responsible for the individual who sent the samples for testing, and there is no guarantee that this individual can represent the overall level of products on the market.