Focal Length, Depth Compression and Camera Sensors

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Focal Length, Depth Compression and Camera Sensors by Mind Map: Focal Length, Depth Compression and Camera Sensors

1. Camera Sensors

1.1. What is the purpose of a camera sensor in a digital camera?

1.1.1. It’s job is to convert photons into a signal, which is then amplified to pixels to create a digital image. It dictates the size of the image, resolution, performance in low-light situations, depth of field, dynamic range, lenses, and even the camera's size.

1.1.2. What are the difference between the CCD & CMOS sensors?

1.1.2.1. CCD sensor cost lots more to produce than the cheaper CMOS sensors. Despite doing what is essentially the same job (converting photons into electrons) CCD sensors were long considered superior. They created higher quality images with a lot less noise than the CMOS sensors: the photons have to go through more transistors which decreases the sensors sensitivity to light.   For a long time the main draw to CMOS sensors was is low power consumption, with CCD sensors consuming upwards to 100x more power.

1.1.2.2. Over the past 5 years technology has allowed sensor manufacturers to improve the sensitivity of CMOS sensors to the point of surpassing the noise and quality performance of CCDs. It is predicted that camera manufacturers will cease to use CCD sensors completely if the construction price does not become more competitive.

1.1.3. How is a APS-H & APS-C sensor different from the above sensors?

1.1.3.1. The image sensor format is the shape and size of the image sensor.

1.1.3.2. APS-H & APS-C refer to different formats of a sensor. CMOS and CCD  refer to the science behind the sensor whereas APS-H and APS-C refer to the size of the camera sensor. This determines the angle of view of a particular lens when used with a any given camera body.

1.1.4. Dimensions of 5 different sensors

1.1.4.1. Micro Four Thirds: 17.3mm x 13mm ⅓”(iPhone 6): 4.8mm x 3.6mm Super 8mm: 5.79mm x 4.01mm Blackmagic Pocket Cinema Camera: 12.48mm x 7.02 16mm: 12.52mm x 7.41mm

1.2. What is the ‘Bayer Filter’ and what does it do?

1.2.1. The interesting part is that the light-sensitive element on a pixel cannot detect color. It can only detect the intensity of the light hitting it, which is why to calculate the RGB (red, green, and blue) color value of each pixel, the camera needs what's called a Bayer filter.

1.2.2. In a nutshell, today's cameras have sensors on which a grid of light-sensitive pixels is laid out. Put, let's say, 12 million of these together and you get a 12-megapixel camera. The light that hits these pixels when the shutter button is pressed is processed and turned into a digital image that ends up in your device's gallery.

1.2.3. A Bayer Filter mosaic is a color filter array also known as CFA and this is used for arranging RGB color filters on a square grid of photosensors. This helps you make different filters when taking a picture by editing how much blue,green and red is exposed.

1.2.4. Can you find out the sensors used & its dimensions in each of the following cameras?

1.2.4.1. Canon EOS 5D Mark IV: 30.4MP CMOS sensor- 61 point AF system with 41 cross-type sensors (24 × 36 mm) Sony RX100 IV: 20.1MP 1-type stacked CMOS sensor  (0.52 x 0.35)                                                                 Olympus Stylus Traveller: 16 MP CMOS-( 91 x 61 x 26 mm)                                                                                 Nikon COOLPIX L31: 5.1MP CCD-1/2.5 inch (5.8mm x 4.3mm)

1.3. What is crop factor?

1.3.1. When we use 35mm film as a standard, any camera with a sensor smaller than a frame of 35mm film will cover a smaller portion of the image circle produced by a given lens and will thereby change the field of view of that lens. This is the “crop” part of the crop factor. If you attach a 50mm lens to a camera with a smaller-than-35mm film sensor, you will have to multiply the focal length of that 50mm lens by a factor derived from the size differential of the sensor to calculate the 35mm equivalent focal length. This will then give you the means to figure out the lens’s field of view based on that new equivalent focal length. This is the “factor” part of crop factor. To create the crop factor of the camera.

1.3.1.1. Can be used to compare the Field of View and image quality of different cameras with the same lens

1.3.2. What effect does crop factor have on focal length?

1.3.2.1. The red frame is the view on Full frame. And green frame is the view of same focal length on a APS-C sensor.The angle of view of APS-C is more minimized than on a Full frame. A 50mm lens on a camera with a 1.5x crop factor APS-C sensor gives a field of view equivalent to that of a 75mm lens on a full-frame or 35mm film camera. Remember, the actual focal length of the lens is unchanged, as is its aperture.

1.4. How do you calculate the equivalent focal length of a lens?

1.4.1. Multiplying the actual focal length of the lens by the Crop Factor of the sensor gives the equivalent Focal Length of a lens, that would yield the same Angle of View if used on the reference format.

1.4.2. E.g.

1.4.2.1. Nikon D3000’s crop factor is around 1.5. A full-frame sensor is 36mm x 23.6mm Nikon D3000’s sensor 24mm x 15.8mm. 36mm / 23.6mm ≈ 1.52mm 24mm / 15.8mm ≈  1.52mm Thus the Nikon D3000 sensor is around 1.5x smaller than the full-frame sensor. 50*1.5 ≈ 75mm

1.4.3. Explain how the crop factor value of 1.2x was calculated, using this site http://www.abelcine.com/fov .  Use cameras: Super-35 film 16x9 & Canon 1D.

1.4.3.1. Sensor A A Super-35 Film sensor is 24.9 x 14mm Diagonal = 28.5mm Sensor B A Canon 1D sensor is 27.9 x 15.7mm Diagonal is 33.5mm  Sensor B/Sensor A = 33.5/28.5 = 1.17 ≈ 1.2

1.5. Alternative site for calculating equivalent focal length: https://www.digified.net/focallength/

2. Focal Length

2.1. What is Focal Length?

2.1.1. The Focal Length is the distance in millimeters, from the point where light rays converge in a lens to the sensor.

2.1.2. 6 Common Focal Lengths

2.1.2.1. Ultra-Wide: 10-18mm Wide-Angle: 18-35mm Normal: 35-70mm Short Telephoto: 70-100mm Medium Telephoto: 100-135mm Long Telephoto: 135-300mm

2.1.2.2. Changing the Focal Length on its own simply zoomig in/out of the image

2.1.2.2.1. 100mm

2.2. Does a wide angle lens have a short or long focal length?

2.2.1. The Focal Length tells us the Angle of View i.e. how much of the scene will be captured.

2.2.1.1. The longer the Focal Length, the narrower the Angle of View. The shorter the Focal Length, the wider the Angle of View.

2.2.2. Wider angles allow photographers to:

2.2.2.1. - Include more of a scene into the shot                       - Exaggerate the size of an object                               - Increase the distance between the foreground and background elements in a shot

2.2.3. 250mm

2.2.3.1. 200mm

2.2.3.1.1. 135mm

2.3. How does focal length affect perspective?

2.3.1. Perspective Distortion is actually the warping of objects based on the distance from the camera.

2.3.1.1. Distortion

2.3.1.1.1. Object Distortion

2.3.1.1.2. Facial Distortion

2.3.2. In order to achieve depth compression, the relative position of the camera to the subject must simultaneously change

2.3.3. For foreground elements to stay the same size, while background elements grow or shrink, the camera must either:

2.3.3.1. Zoom In+ Move Out

2.3.3.2. Zoom Out + Move In