1. What is the maximum lens aperture?
How wide the diaphragm opens.
2. If a 50mm lens has an aperture diameter of 25mm what f stop is it set at?
Focal length/ aperture diameter = 2
3. What is a lens aberration? And why do they exist?
Problems with the lens. No lens is perfect and have some compromises.
4. What is spherical aberration? How can it be reduced?
Where light passing through the centre of the lens has a different focal point to that traversing the edge. It can be reduced by stopping down the lens.
5. What are chromatic aberrations?
Light of different colours is not focused at the same point. Causes colour fringes.
6. What do these lenses do?
a) achromatic – lens corrected for two different wavelengths
b) apochromatic – lens corrected for three different wavelengths
c) superachromatic – lens corrected for four different wavelengths
7. What is coma?
Cannot produce a sharp point away from the lens axis – looks like a comet
8. What is astigmatism?
An inability to focus sharply horizontal and vertical lines near the edge of the sensor/film
9. What is distortion? And geometric distortion?
A lens being in front of or behind the aperture causes barrel or pincushion distortion. Geometric distortion covers both of these.
10. What is curvature of field?
A lens that cannot produce a flat image of a flat subject.
11. What is a sweet spot on your lens?
Where the lens performs at its best for sharpness.
Sunday, April 29, 2012
Sunday, April 15, 2012
First folio photos...
The first person I've started photographing is Danny. He works at the local tip but also runs the Bungendore music and poetry evenings. The contrast between what he does as a job and what his true passions are is what I'm documenting.
The photos above are all of Danny at work.
Danny has been involved with music all of his life and is an accomplished guitar player. Once a month he runs the music and poetry evenings in Bungendore. He has been doing this for the last seventeen years!
I had a few technical issues taking the photos at the venue. I had to push my camera to its maximum ISO (3200) so the photos were very noisy. Also, I had to shoot at 1/40th at f4. I've converted them to black and whit to try and hide some of the noise.
The photos above are all of Danny at work.
Danny has been involved with music all of his life and is an accomplished guitar player. Once a month he runs the music and poetry evenings in Bungendore. He has been doing this for the last seventeen years!
I had a few technical issues taking the photos at the venue. I had to push my camera to its maximum ISO (3200) so the photos were very noisy. Also, I had to shoot at 1/40th at f4. I've converted them to black and whit to try and hide some of the noise.
Danny's mate - they were playing together
Sunday, April 1, 2012
Week 7 - 15 Questions
Light and Lenses
1. The speed of light is medium dependant. Which means it changes speed depending on what it
is travelling through. Does it get slower or faster travelling through denser mediums. Yes or
no?
It travels slower and can be calculated by the refractive index of a material. Glass is about 1.5
so the speed light travels is c/1.5
2. If light enters glass at an angle other than 90 degrees what happens to it? Explain.
It bends due to refraction. As light slows entering glass it changes direction. At 90 degrees it
is still refracted but does not change direction.
3. Light travels in waves. What is the measurement for this?
Wavelength – visible light is within the range of 350-790 nm
4. What is the degree of the refraction of light dependant on? And which colour is refracted the
most?
The degree of refraction is dependant on the refractive medium and its wavelength. Violet is
refracted the most.
5. What is the angle of incidence?
The angle at which a light ray approaches a medium.
6. What is the refractive index of material?
A number that is used to calculate the speed that light traverses a medium. Glass is about 1.5
so the speed light is traversing it is c/1.5
7. What is the difference between a convergent and divergent lens?
In a convergent lens the light rays are bent inwards and cross at the focal point. In a divergent
lens the light rays are bent outwards.
8. What is the focal length of an optical system?
The distance from the front of the first lens through to the focal point.
9. What are circles of confusion?
A lens that is focused on an object does not render everything sharp. Depth of field will show
some things as sharp and some things as blurred. The circle of confusion are those parts of the
image that are no longer sharp as perceived by the human eye or the largest blur spot that the
human eye would still see as a point.
10. What is the angle of view of a lens?
The angle of the scene that the lens will include in an image.
11. What is the covering power of a lens?
The usable area of the image circle a lens makes.
12. Do lenses alter perspective?
Yes – long lenses shorten perspective and wide angle increase perspective.
13. What is geometric distortion?
When lines appear to be bent. Common forms are barrel distortion or pincushion distortion.
14. What is the equation to calculate correct viewing distance?
And, PROBLEM to solve:
You need to make a vertical portrait using 24x36mm format which will be used on a roadside billboard
where the photo will be 5m high and it will be ideally seen from 50m. What lens focal length should
you use to maintain ‘correct’ seen perspective?
Given: image height = 36mm
print height = 5000mm (5m)
viewing distance (VD) = 50,000mm (50m)
Unknown: magnification (M) = print / image
= 5000 / 36 = 139x
focal length (f) = ?
15. For the following lens types, write a description of each
using no more than 10 words for each lens.
Wide angle – field of view greater than what a human eye sees
Zoom – a lens with variable focal lengths
Long focus – focal length greater than the diagonal of the sensor
Telephoto – lens is shorter than the focal length
Retro focus – regular focal length with wide angle attachment
Quasi fish eye – image covers the entire sensor
Fish eye – field of vie greater than 100 degrees
Catadioptric - mirror used to increase focal length but maintain small overall length
Macro - produces images sizes greater than 1:1
Teleconverter – increases focal length of lens with a 1 stop drop normally
Supplementary or close up lens – accessory attached to front of lens to alter focal length
PC or tilt shift lens – perspective correction lens
1. The speed of light is medium dependant. Which means it changes speed depending on what it
is travelling through. Does it get slower or faster travelling through denser mediums. Yes or
no?
It travels slower and can be calculated by the refractive index of a material. Glass is about 1.5
so the speed light travels is c/1.5
2. If light enters glass at an angle other than 90 degrees what happens to it? Explain.
It bends due to refraction. As light slows entering glass it changes direction. At 90 degrees it
is still refracted but does not change direction.
3. Light travels in waves. What is the measurement for this?
Wavelength – visible light is within the range of 350-790 nm
4. What is the degree of the refraction of light dependant on? And which colour is refracted the
most?
The degree of refraction is dependant on the refractive medium and its wavelength. Violet is
refracted the most.
5. What is the angle of incidence?
The angle at which a light ray approaches a medium.
6. What is the refractive index of material?
A number that is used to calculate the speed that light traverses a medium. Glass is about 1.5
so the speed light is traversing it is c/1.5
7. What is the difference between a convergent and divergent lens?
In a convergent lens the light rays are bent inwards and cross at the focal point. In a divergent
lens the light rays are bent outwards.
8. What is the focal length of an optical system?
The distance from the front of the first lens through to the focal point.
9. What are circles of confusion?
A lens that is focused on an object does not render everything sharp. Depth of field will show
some things as sharp and some things as blurred. The circle of confusion are those parts of the
image that are no longer sharp as perceived by the human eye or the largest blur spot that the
human eye would still see as a point.
10. What is the angle of view of a lens?
The angle of the scene that the lens will include in an image.
11. What is the covering power of a lens?
The usable area of the image circle a lens makes.
12. Do lenses alter perspective?
Yes – long lenses shorten perspective and wide angle increase perspective.
13. What is geometric distortion?
When lines appear to be bent. Common forms are barrel distortion or pincushion distortion.
14. What is the equation to calculate correct viewing distance?
And, PROBLEM to solve:
You need to make a vertical portrait using 24x36mm format which will be used on a roadside billboard
where the photo will be 5m high and it will be ideally seen from 50m. What lens focal length should
you use to maintain ‘correct’ seen perspective?
Given: image height = 36mm
print height = 5000mm (5m)
viewing distance (VD) = 50,000mm (50m)
Unknown: magnification (M) = print / image
= 5000 / 36 = 139x
focal length (f) = ?
15. For the following lens types, write a description of each
using no more than 10 words for each lens.
Wide angle – field of view greater than what a human eye sees
Zoom – a lens with variable focal lengths
Long focus – focal length greater than the diagonal of the sensor
Telephoto – lens is shorter than the focal length
Retro focus – regular focal length with wide angle attachment
Quasi fish eye – image covers the entire sensor
Fish eye – field of vie greater than 100 degrees
Catadioptric - mirror used to increase focal length but maintain small overall length
Macro - produces images sizes greater than 1:1
Teleconverter – increases focal length of lens with a 1 stop drop normally
Supplementary or close up lens – accessory attached to front of lens to alter focal length
PC or tilt shift lens – perspective correction lens
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