- High level explanation of basic photography terminology as well as optics and imaging in general
- References to give a non-mathematical, intuitive understanding of optics and imaging
- Corrections/Additions are welcome
- We can assume the complex lens assembly is replaced by an equivalent thin-lens of same focal length.
- https://www.khanacademy.org/science/physics/geometric-optics/lenses/v/convex-lens-examples
- http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/lenseq.html
- Complex lens assembly is required since thin-lens are only theoretical
- Complex assembly prevent spherical aberration and chromatic abberation.
- https://en.wikipedia.org/wiki/Optical_aberration
- https://en.wikipedia.org/wiki/Spherical_aberration
- https://en.wikipedia.org/wiki/Chromatic_aberration
- For normal lenses, object is beyond 2f and real image is formed on sensor between f and 2f
- When you focus a camera, you move the sensor between f and 2f to get a sharp image.
- For macro lenses, object is between f and 2f, and real image is formed on sensor beyond 2f. Hence, the magnification.
- Focus length of lens has nothing to do with where the camera is focused at.
- Focus length limits if a close object can be focused or not/
- For normal lenses: Objects should be stay beyond 2f
- For macro lenses: Objects should NOT be farther than 2f
- Focal length also defines how big the lens assembly is - assembly will be approximately 2f in length.
- https://en.wikipedia.org/wiki/Aperture
- Fast aperture: Large opening, more light, faster capture.
- Slow aperture: Small opening, less light, longer exposure time or higher ISO needed.
- f-stop numbers increase like: f/1.4, f/2, f/2.8, f/4...
- Radius increase by sqrt(2), Open area increases by 2x. Therefore, image brightness increases by 2x
- Point and shoot cameras have smaller absolute size of apertures. Therefore slower f-stops are not useful.
- Typically, point and shoot cameras have only one or two options for aperture, typically f2.8/f5.6/f8
- In most cameras, step size increase brightness by (1/3) to match changes with ISO scale.
- As a result, we have intermediate f-numbers like f/1.8, f/2.2, etc
- Ref: https://en.wikipedia.org/wiki/F-number
- Sensor size are given in terms of its diagonal size
- Full-frame sensors have a sizeof 35mm and are considered standard (Originates from 35mm film used in movies)
- Entry level DSLRs are 1.6x smaller - APS-C - (crop-factor = 1.6x)
- Point and shoot camera's are significantly smaller - 1/2.3"
- How much area is captured depends on the sensor size and focal length of the lens
- Area capture on 24mm lens on Full-Frame SLR is considered as 1x Zoom
- Zoom factor scale approximately linearly with focal length. eg: 48mm lens will have 2x zoom.
- Smaller cameras need smaller focal length for same field of view
- Since crop factor of APS-C is 1.6x, 24/1.6 = 15mm lens will give 1x zoom on APS-C sensor
- So a 15mm lens on APS-C is said to be full-frame equivalent to 24mm.
- To enable easy comparison, several camera manufactures specify focal lengths in terms of equivalent full frame length
- eg: https://www.canon.com.mt/for_home/product_finder/cameras/digital_camera/powershot/powershot_sx60_hs/specification.html
- Above camera has full-frame-equivalent focal length range of 21mm to 1365mm - approximately 1365/21 = 65x Zoom range
- The actual focal length range is just 3.8 to 247.0 mm
- Since smaller cameras need smaller focal length for same field of view - it has following advantages:
- Lens assemblies are smaller allowing for larger full-frame equivalent focal lengths.
- Zoom ranges in point and shoot cameras are ,therfore, typically larger as compared to DSLR.
- https://en.wikipedia.org/wiki/Film_speed
- Defines sensitivity of the sensor.
- Original defined based on photo sensitivity of chemicals used on the films.
- Higher ISO means higher sensitivity.
- ISO Step sizes are defined similar to aperture: 100/200/400/800 - each step indicates 2x increase in brightness.
- Higher ISO means higher sensitivity - but also means higher noise.
- Higher ISO images are typically noisy
- Example of why ISO change is useful
- If a scene is bright, increasing ISO would not result in much visible noise.
- This will allow shutter speed to be lower resulting in lower shaking movement.
- https://en.wikipedia.org/wiki/Shutter_speed
- Defines how long the camera shutter is open to allow light.
- Shutter step sizes are also standardized to that each step results in approximately 2x increase in brightness.
- Camera keeps aperture fixed as specified by user.
- It changes shutter speed and ISO appropriately to get overall brightness to a defined level.
- Camera keeps shutter speed fixed as specified by user.
- It changes aperture and ISO appropriately to get overall brightness to a defined level.
- Camera sets aperture, shutter speed and ISO to get an optimal picture.
- All parameters are specified by user
- Try out DSLR manual mode online: http://www.canonoutsideofauto.ca/play/
- This is the background blurring which occurs in fast lenses on larger frame-size cameras.
- https://en.wikipedia.org/wiki/Bokeh
- In case of point and shoot camera, since absolute aperture sizes very small, bokeh effects are not prominent.
- In point and shoot cameras, some bokeh effect can be observed at very high zoom values - typically in cases like wildlife and bird photogrpahy
- This is the distance at which if you focus a camera, all objects beyond that distance appear to be in focus.
- https://en.wikipedia.org/wiki/Hyperfocal_distance
- This is related to circle of confusion as well.
- This is small in case of smaller focal lengths and smaller apertures.
- As a result, Smartphone and point and shoot cameras have very short hyperfocal distance
- Therefore most images taken with these have all objects in focus.
- Boundary case for hyperfocal distance is a pinhole camera.
- https://en.wikipedia.org/wiki/Pinhole_camera
- Hyperfocal distance is zero
- Hyperfocal distance can be reduced by reducing aperture - which causes reduction in circle of confusion.
- eg: For taking landscape photos in DSLR, to get faraway mountains and trees is sharp focus, you need to ensure higher f-stop value
- Typically f-7.1 or higher.
- https://en.wikipedia.org/wiki/High-dynamic-range_imaging
- https://en.wikipedia.org/wiki/Tone_mapping
- These are traditionally generated by merging images taken at multiple exposures
- Newer cameras (esp: smartphone cameras) do this processing at sensor level on-the-fly.
- This is possible by storing digital data with higher precision.
- Free tools for HDR:
- https://en.wikipedia.org/wiki/Light_painting
- Typically done with exposures larger than 1sec (typically larger than 15sec)
- Requirements
- Camera with tripod
- Turn image stablization off when on tripod. Stablization system give wrong outputs on tripod causing shake when there isn't any.
- Turn off auto-white-balance.
- Dark area - very little should be visible when using shutter speed of 15 sec.
- Bright light source like LED torches.
- Camera in manual mode. Use viewfinder/display to manual focus by shining light on some objects.
- In DSLR, use slightly higher f-stop values to avoid background blurring - typically f6.3/f7.1
- Some examples:
- Requirements
- Camera with tripod
- Turn image stablization off when on tripod. Stablization system give wrong outputs on tripod causing shake when there isn't any.
- Turn off auto-white-balance.
- Focus on bright stars first like Venus/Sirius/Jupiter first and lock the focus.
- For star trails:
- Take multiple photos with long exposure and merge them using available softwares like https://www.startrails.de/
- https://earthsky.org/astronomy-essentials/what-are-star-trails
- For astronomical deep-sky objects:
- Needs tracking mounts like these:
- Skyguider Pro: https://www.ioptron.com/product-p/3550a.htm
- CEM25P tracking mount - https://www.ioptron.com/product-p/7100p.htm
- Telescope + mounts: https://www.ioptron.com/product-p/12150.htm
- Needs tracking mounts like these:
- For purchasing guides and setting expectations on what you will get out of your telescopes/binoculars, read the sticky articles on following subreddits