You can get acquainted with the reviews of the technical characteristics of the objects of the equipment manufacturers themselves, read the reviews of the happy owners of this or that "glass" on the forums. All this information should be treated critically, because the best test is practical use. Independent testing of the object at the time of purchase will allow you to visually verify the quality of its assembly and functioning.

1. Why are you buying a new object?

The choice of one or another "glass" directly depends on your creative goals. If you are buying a portrait object, then the best test for it will be a portrait photographed at different focal lengths and apertures. You will be able to evaluate the following parameters:

  • focus accuracy
  • how beautifully the object "draws"
  • are you satisfied with the minimum sharpness zone
  • smooth transition from sharpness to non-sharpness
  • bokeh

In the case when an object is needed for landscape or interior photography, take several pictures of nature or interior at different scales and look:

  • how well does the object convey small details
  • what is its minimum focus distance
  • are you satisfied with spatial distortions at a wide shooting angle

It is better to take test photos in good light conditions and view them on a calibrated monitor at 100% scale - then all the details of the frame are best visible. Accordingly, you can easily notice all the defects of the picture.

2. Mechanical characteristics of the object

All mechanical elements of the object must work properly:

  • The zoom ring should rotate smoothly, quietly and not jam.
  • The focus ring should also move smoothly and quietly, but not too easily, so that the focus does not get lost.
  • A moving group of lenses (in some objects it "moves out" when zooming, in some it is inside) should not shift from gravity when you lift the object vertically up or lower it down.
  • Focus should happen quickly: to control this parameter, focus on infinity, and then on a closely located object.
  • The object must be firmly attached to the camera – backlash in the bayonet area is unacceptable.
  • If the object has an optical image stabilizer, check at how long exposures it allows you to take clear photos.

3. Front-focus and back-focus test (front-focus, back-focus)

Front-focus is the displacement of the object's sharpness zone forward, closer to the camera, and back-focus is the displacement of the sharpness zone backward, behind the photographed object. To check the location of the sharpness zone, there is a special scale with a target that can be downloaded on the Internet and printed out. In addition, you can use a regular ruler:

  • position the scale or ruler at an angle of 45% from the optical axis of the object.
  • in the scale, the focus area should be located perpendicular to the optical axis of the object – this will allow you to adjust the sharpness more accurately.
  • mark one of the divisions ("0" is already marked on the scale, mark any one in the middle on the ruler)
  • set the shooting mode to the priority of the diaphragm (Av, A) and open it as much as possible
  • set the frame-by-frame shooting mode (One Shot)
  • turn off the stabilizer, if there is one (IS)
  • select the focus on the centre point in the camera
  • set the exposure adjustment +1 – +1,5 stages (EV +1, +1.5)
  • focus on the marked division and take several takes in autofocus (AF) mode
  • then switch to manual mode (M)
  • on the computer monitor (not on the camera screen!) check the test result

The sharpness zone should be located where you were aiming. The blur should be evenly distributed both in front and behind the marked division. There are some acceptable values of error when focus – they are 1-1.3 grips (the depth of the sharply depicted space), depending on the camera model. If the autofocus "misses" in most shots and the focus point goes beyond the GRIP, then you should look for another object.

 
 

4. Optical characteristics

The optical characteristics of objects include their sharpness and uniformity of its distribution. And also such defects: vignetting - a drop in the brightness of the image at the edges of the frame distortion - an asymmetric curvature of the proportions of objects in the frame – there is a "pillow-shaped" when the edges of the photo seem to fall into the frame, and "barrel-shaped" when the centre of the image protrudes from the frame stronger than the edges. To check the uniform distribution of sharpness and the absence of distortion in the frame, take a picture with a special sharpness check table, a sheet of paper with a similar pattern or an ordinary newspaper. It should be clearly opposite the camera, parallel to the front lens. Pay attention to whether there are any distortions, vignetting or distortion, whether sharpness disappears at the edges of the frame. However, remember that on wide-angle objects, blurring at the edges of the frame at an open aperture and slight distortion are the norm.

5. Chromatic aberrations

Another optical defect of objects is chromatic aberrations (artifacts in the form of coloured stripes around objects). They are most clearly manifested on contrasting objects and in contour lighting. Take a picture of a black font on a white background or tree branches against the sky and look at the photos in large magnification. You can see blue and red stripes along the edges of the branches. They appear because rays of different lengths are focused at different distances passing through the lenses. Many objects use special achromatic lenses to minimize this effect. This defect may be slightly manifested even in expensive series of professional objects.

6. What to pay attention to when buying a used object

If you decide to purchase previously used optics, then you should pay special attention to the degree of its deterioration and the absence of breakdowns. Need to check:

  • Damage to the object body may indicate that it was dropped.
  • The abrasion and the number of scratches on the bayonet terminals will show how often the object was used.
  • The worn-out zoom and autofocus rings also show the degree of operation of the object.
  • If the autofocus ring moves too freely, the aiming may be lost when focus.
  • Scratches and warps on the screws of the object show that it has already been repaired.
  • Turn the object at an angle to the light and check the amount of dust inside it on the front and back lens. Remember that the dust under the front lens affects the image much less than under the back. Because the rear lens of the object is much closer to the matrix.

7. What filters affect

Complete with objects, light filters are often purchased. A protective filter is needed in order to protect the front lens of the object from chemical exposure and mechanical damage. The filter also affects the image quality, so it is worth testing it: First, you should not buy the cheapest filters: they can significantly lower the light intensity of your object. Secondly, they can create glare. To check this defect, take several photos of a light source (for example, a regular desk lamp) from different angles. Then view the received images. If the camera "catches a hare" in a certain position, then it is worth checking whether this is a defect of the object itself. Just remove the filter and take the same photo without it.

Conclusion

Conduct these tests for several objects, and you will immediately see the advantages and disadvantages of each, you will be able to feel the difference between them and decide on the choice much more consciously.