Which of the two photographs appears to be the sharpest to your eyes? The image on the left has relatively low resolution with high contrast, while the image on the right has high resolution but low contrast.About 80% of what you see as sharpness comes from contrast rendition, not resolution.

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Flare is non-image forming light. It comes in two varieties, one is represented by the dots we see when we include a light source in (or very near) our image.

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The other, more insidious type of flare is a veiling flare that desaturates color and contrast across the entire scene.Certain photographers, in the film era, under-exposed their photos to obtain richer saturation. What they did not realize was that their lousy lens was stealing the saturation through flare.Lenses are often still lousy, however, we can get past some lens shortcomings by simply boosting saturation or vibrance in post-production.

One Hundred-twelve point five nanometers (billionths of a meter)* is the thickness of a single layer of anti-reflection coating. There are six, or seven on every modern lens. The anti-reflection coating layer addresses flare for each of the major components of the visible spectrum. Each layer is 1/4 of that wavelength of light thick. The violet layer is 112.5 nanometers thick. Plus or minus nothing.

Red Orange Yellow GreenBlueIndigo Violet

*(One nanometer is approximately seven hydrogen atoms placed side-by-side.)

A yellow photon

A yellow photon comes streaming to the lens. It passes through the violet, indigo, blue and green coating layers and as it passes through the yellow layer it gets phase shifted 90 degrees. Unfortunately, this photon will bounce off one of the glass elements as flare and come back through the yellow coating layer again. As it passes through the yellow coating layer again, it gets phase shifted again another 90 degrees, and since it is now 180 degrees out of phase, it vanishes.

A Practical DemonstrationThis is a practical demonstration of how a phase shift works. The viewer is welcome to be skeptical of the efficiency of such a crazy scheme. The problem is - it works - very well.

Direction of Light

Normal Light (Unpolarized)

Horizontal Polarizer 1

Vertical Polarizer 2

Horizontally Polarized Light

Light Completely Blocked

Horizontal Polarizer 1

Vertical Polarizer 2

Sensor Size and Magnification

35mm Film Size (Full-frame DSLR)

Image as Projected

APS-C Image Size

Crop Factor is usually arrived at by a ratio of the diagonal of a camera’s sensor to the reference format. Most often the reference is 35mm film (43.3mm). 43.3mm / 27mm = 1.603

43.3mm27mm

When using a lens designed for full-frame on a smaller sensor sized camera depth of field may change.Shooting from the same location at the same f/stop but enlarging the image to the same size will reduce depth of field.

Sensor Size and Magnification (Continued)

35mm Film Size (Full-frame DSLR)

Image as Projected

APS-C Image Size

However, similar framing of the image will provide more depth of field with the smaller sensor.Perspective depends only on the camera position. But if you move the lens to a smaller sensor-sized camera and adjust your position to achieve the same image size then perspective will be affected.

Distortion

Distortion is probably a more limited term than you might suspect. It is only two things:Barrel Distortion and Pin-cushion DistortionIn your image of these two lines, if the centers of both lines bend away from each other, you have barrel distortion. If they bend towards each other, you have an example of pin-cushion distortion.If the bend goes in the same direction, there is an out of center lens element .

Aberrations consist of a family of problems such as:

• Chromatic Aberrations

• Spherical Aberration

• Coma

• Astigmatism