how to test camera lens quality


how to test camera lens quality插图

Mount and dismount the lens several times on the cameras and ask yourself the following questions:Does it go on easily but firmly?When seated is it firm with no looseness?Does the locking pin catch properly and then release easily when you push the camera’s dismount button?

How do you evaluate the quality of your lenses?

With an interchangeable lens camera, we always use the highest-quality lens we have available to evaluate noise and detail, at its best f-stop. We use an SFRplus test chart to check lens resolution and distortion, and shoot a flat gray image to to see how much a lens will vignette.

How to determine lens quality of cell phone camera?

To determine lens quality, you really need to take a photo with the cell phone to see what the quality is. Most cell phones cameras are fixed lens cameras. 3. CCD Quality

Why is lens quality important?

Lens quality is more important now than ever, due to the ever-increasing number of megapixels found in today's digital cameras. Frequently, the resolution of your digital photos is actually limited by the camera's lens — and not by the resolution of the camera itself.

How do we test digital cameras and lenses?

We take a dual approach to testing digital cameras and lenses at PCMag. Work is split between standardized lab tests, performed in a controlled environment, and time spent making photos outside in the real world. This allows us to evaluate image quality in a predictable way, and challenge modern autofocus systems with various types of subjects.

What happens if you stick a bad lens on a camera?

If you stick a horrible lens onto a high-megapixel camera, your photographs may pop out with a large megapixel “size”, but the sharpness of the photo may be equivalent to the sharpness of a photo taken with a much smaller sensor and a “perfect” lens.

What is a P-MPix?

Perceptual Megapixels , (P-MPix), can be described as the “equivalent” number of megapixels when using a particular lens. Just as lenses offer different equivalent focal lengths when paired with different sensor sizes, sensors can have different equivalent megapixels when paired with lenses of various optical qualities.

What is the degree to which a lens cannot render straight lines in a scene as straight lines in the final image?

Camera lens distortion is the degree to which a lens cannot render straight lines in a scene as straight lines in the final image. Vignetting (or light shading) consists of the attenuation of light as you move away from the image centre.

What is the lens test?

Well the standard lens test is based on what’s know as ‘optical metric scores’ which are standard measurements used to rate the performance of a camera lens , such as its sharpness, distortion, vignetting, transmission and chromatic aberration (see image above).

What is transmission in photography?

Transmission or Light Transmission. Transmission of a photographic lens describes its ability to transmit light from the photographic scene to the sensor surface. Lenses consists of many glass elements, each reflecting or absorbing a portion of the light; therefore the more elements, the lower the transmission.

What is the meaning of sharpness?

Sharpness. Sharpness while subjective, is considered to be the quality attribute of an image. Sharpness indicates the visually perceived quality of detail in an image and is associated with both resolution and contrast. The score for Sharpness is based on something called the Modulation Transfer Function (MTF) of the lens, ...

What does refraction mean in photography?

Lens refraction depends on the wavelength. This means that magnification not only depends on the image field position but also on the light wavelength. A perfectly sharp edge going from white to black yields a smooth transition showing the decomposition of the light spectrum.

Why are large apertures important?

Large apertures are where high quality lenses really stand out, because the materials and engineering of the lens are much more important . In fact, a perfect lens would not even have a "sweet spot"; the optimal aperture would just be wide open.

What does MTF of 1.0 mean?

An MTF of 1.0 represents perfect contrast preservation, whereas values less than this mean that more and more contrast is being lost — until an MTF of 0, where line pairs can no longer be distinguished at all. This resolution limit is an unavoidable barrier with any lens; it only depends on the camera lens aperture and is unrelated to the number of megapixels. The figure below compares a perfect lens to two real-world examples:

How many different types of lines are there in the MTF chart?

Since a given line can have any combination of thickness, color and type, the above MTF chart has a total of eight different types of lines. For example, a curve that is bold, blue and dashed would describe the MTF of meridional 10 LP/mm lines at an aperture of f/8.0.

What is MTF in photography?

A Modulation Transfer Function (MTF) quantifies how well a subject's regional brightness variations are preserved when they pass through a camera lens. The example below illustrates an MTF curve for a perfect* lens:

What does resolution mean in photography?

Resolution only describes how much detail a lens is capable of capturing — and not necessarily the quality of the detail that is captured. Other factors therefore often contribute much more to our perception of the quality and sharpness of a digital image.

Why are M lines better than S lines?

Technical Note: With wide angle lenses, M lines are much more likely to have a lower MTF than S lines, partly because these try to preserve a rectilinear image projection. Therefore, as the angle of view becomes wider, subjects near the periphery become progressively more stretched/distorted in directions leading away from the center of the image. A wide angle lens with significant barrel distortion can therefore achieve a better MTF since objects at the periphery are stretched much less than they would be otherwise. However, this is usually an unacceptable trade-off with architectural photography.

How to measure MTF?

The MTF is usually measured along a line leading out from the center of the image and into a far corner, for a fixed line frequency (usually 10 -30 LP/mm). These lines can either be parallel to the direction leading away from the center (sagittal) or perpendicular to this direction (meridional). The example below shows how these lines might be measured and shown on an MTF chart for a full frame 35mm camera:

How many pixels are in a 100mm line?

You can also measure the length of the 100mm line on the chart in pixels. Let's say you find the line is 670 pixels long. With an EOS 40D we know the sensor is 22.2mm wide and contains 3888 pixels across the width. Therefore the image of the 100mm line on the sensor must be (670/3888) * 22.2mm = 3.825mm. The magnification factor is therefore 100/3.825 = 26.14x

How to calculate magnification factor of EOS 40D?

If you count 22.5, the image is of an area 22.5" wide, which is 571.5mm. Divide this by the actual width of your image sensor. For an EOS 40D this is 22.2mm. So you divide 571.5 by 22.2 to get the magnification factor, which in this case would be 25.75x

What is the magnification of a 15x22 frame?

If you have the corners of the 15"x22" area at the corners of the frame, the magnification will be around 26x . This is approximate, but probably good enough!

What makes a good lens better than a poor lens?

What makes a good lens better than a poor lens then, if the digital images they produce all have similar center resolution? The answer is contrast, or more specifically MTF (modulation transfer function) at resolutions less then the theoretical limit. For an explanation of MTF see the MTF and SQF article on this website. Higher contrast (MTF) will result in images which look sharper, and will in fact contain more information. That's why these charts have a high and low contrast set of patterns. Better lenses will better show finer detail in the low contrast patterns than poor lenses will and so may give a better indication of a better lens.

What are the resolution patterns on the NBS 1010A test chart?

In the center is a checkerboard pattern which is used for focusing. Within the resolution patterns on each side is a Siemens star pattern. Below the test patterns is a line which is exactly 100mm long that can be used for calibration as described later. There are also a small texture patches and text blocks on the left and right at the foot of the chart which can be used for visual assessment of image quality. A black border is used to look for chromatic aberration as will also be described later.

How to find resolution of a sensor?

To find the resolution on the sensor we need to know the magnification. For example if the magnification is 1/26 (1:26) and the line set at 2.5 lp/mm is resolved in the image , that really corresponds to a resolution of 26x that on the sensor, i.e. 2.5 x 26 = 65 lp/mm. There are three ways to determine the magnification. Note that resolution can only be determined in steps of about 12%. If the 2.5 lp/mm group is resolved the resulting calculated resolution is 65 lp/mm. The next group (2.8 lp/mm) corresponds to 73 lp/mm. So you get 65 or 73 lp/mm. You can't really get anything in between from this chart.

What is Siemens star pattern?

This is a pattern consisting of alternating black and white thin "pie shaped" segments. As you move towards the center of the star the lines get closer and closer together. The higher the resolution of the system generating the star pattern, the closer to the center of the star they will appear to merge. Below are actual siemens star images taken using an EOS 40D and an EF 50/1.8 lens at apertures of f16 (left) and f5.6 (right).

How to calculate magnification factor of EOS 40D?

If you count 22.5, the image is of an area 22.5" wide, which is 571.5mm. Divide this by the actual width of your image sensor. For an EOS 40D this is 22.2mm. So you divide 571.5 by 22.2 to get the magnification factor, which in this case would be 25.75x

What is the magnification of a 15x22 frame?

If you have the corners of the 15"x22" area at the corners of the frame, the magnification will be around 26x . This is approximate, but probably good enough!

What makes a good lens better than a poor lens?

What makes a good lens better than a poor lens then, if the digital images they produce all have similar center resolution? The answer is contrast, or more specifically MTF (modulation transfer function) at resolutions less then the theoretical limit. For an explanation of MTF see the MTF and SQF article on this website. Higher contrast (MTF) will result in images which look sharper, and will in fact contain more information. That's why these charts have a high and low contrast set of patterns. Better lenses will better show finer detail in the low contrast patterns than poor lenses will and so may give a better indication of a better lens.

What are the resolution patterns on the NBS 1010A test chart?

In the center is a checkerboard pattern which is used for focusing. Within the resolution patterns on each side is a Siemens star pattern. Below the test patterns is a line which is exactly 100mm long that can be used for calibration as described later. There are also a small texture patches and text blocks on the left and right at the foot of the chart which can be used for visual assessment of image quality. A black border is used to look for chromatic aberration as will also be described later.

How to find resolution of a sensor?

To find the resolution on the sensor we need to know the magnification. For example if the magnification is 1/26 (1:26) and the line set at 2.5 lp/mm is resolved in the image , that really corresponds to a resolution of 26x that on the sensor, i.e. 2.5 x 26 = 65 lp/mm. There are three ways to determine the magnification. Note that resolution can only be determined in steps of about 12%. If the 2.5 lp/mm group is resolved the resulting calculated resolution is 65 lp/mm. The next group (2.8 lp/mm) corresponds to 73 lp/mm. So you get 65 or 73 lp/mm. You can't really get anything in between from this chart.

How to use AF on a camera?

If you know your AF is good, you can use AF. If you're not sure, compare a few manual focus shots with autofocus, or do an autofocus test as described HERE. Select the "one shot" AF mode and use the center AF zone only. If you want to make absolutely certain that all the shots use the exact same focus setting, you can focus the lens using AF, the switch to manual focus. If your camera has a "Live View" option, use it. For manual focus it will show you exactly when the image is in best focus with no ambiguity. A viewfinder screen has to be perfectly aligned to show best focus, but the same sensor is used for Live View manual focus as for the actual image, so if one is in focus, so will the other be in focus. Most cameras provide for a magnified live view image for even better focus accuracy.

How to use a tripod for a chart?

Set the height of the tripod so that the center of the lens is level with the center of the chart. The move the camera away from the chart until the 15" x 22" area just fits in the viewfinder. Now make sure your camera is square on to the chart. Set up your lighting (if you're doing this indoors), adjust your white balance and take an exposure reading from a gray card. If you don't have a gray card and you're using a white background as in the example above, just set your exposure compensation to about +1.5 stops. That should make the whites white rather than a mid gray.

Why is lens quality important?

Lens quality is more important than zoom when you are buying a cell phone camera. To determine lens quality, you really need to take a photo with the cell phone to see what the quality is. Most cell phones cameras are fixed lens cameras.

How many megapixels should a camera have?

The more pixels, the better your photos will be. You should only look at cell phone cameras that have at least 3 megapixels if you want to take high quality photos.

Can a cell phone camera have multiple CCD sensors?

Most cell phone cameras will feature CCD sensors. In terms of quality, you should be okay with a single CCD sensor. If you can afford a cell phone camera that has multiple CCD sensors, then by all means, go for it. Cheaper cell phone cameras will have a CMOS sensor, which produces low quality images.