Questionnaire #4

Eleven Questions

1. What are the limitations of a Focal Plane shutter ?

it does not work well with artificial lighting (flash) due to how it exposes the film/sensor to light from top to bottom at higher shutted-speeds.

2. Should a Between The Lens of a leaf shutter be cocked during lens attachment/removal ?

no.

3. What is the maximum speed of a Between The Lens shutter ?

From what i could find, i believe it is only 1/400 second, because anything faster than this is actually faster than the mechanism itself and will result in a drop-off of light.

4. What is the definition of Depth of Field ?

Put simply - it is the amount of focus in a photograph.


Depth of field is a vital part of photography. It allows creative and technical control of the the photograph in order to achieve the desired result.


For example, in nature photography, if the photographer wants to capture the details of a pristine landscape, an almost-closed aperture is used. This gives a large depth of focus and produces detail throughout the entire image.

small aperture = focus throughout the image.

However, if the photographer wants to single out something from a scene, a wide-open aperture is used. This allows the photographer to acquire focus on the subject itself and blur 
out anything in front of or behind the point of interest. This gives a nice separation.

large aperture = focus on subject only.

So depth of focus (depth of field) is controlled by adjusting aperture.


Initially, aperture and f-stop numbers are confusing, but it is important to get your head around them. Put simply - a large f-number (22) is actually a small opening and a small f-number (2.8) is actually a large opening and both give a completely different result.


I like to think of it like this:
Small f-number = small depth of field.
Large f-number = large depth of field.


Below is a visual representation of depth of field (depth of focus).

5. How is depth of field increased ?

Depth of field is increased by opening up the aperture to increase the amount of light coming through the lens and hence increasing the circles of confusion effect. It can also be increased with lens choice and distance of subject from the camera.

6. Why is the automatic diaphragm fully open until until the shutter release is pressed ?

umm

7. What are the two types of sensor arrays ? and briefly describe the differences between the two.

CCD and CMOS are the two most common sensory arrays found in modern-day digital cameras. A sensory array consists of the following aspects.

• Total pixels.
• Effective pixels.
• Active pixels.
• Recording pixels.
• it is normal for a sensor to actually have a few DEAD pixels.

a common Bayer-filter elements and possible new sensor design.

Digital SLR cameras capture their images on a silicon semiconductor referred to as a digital sensor. This sensor is composed of an array of photosensitive diodes called photosites that capture photons (subatomic light particles) and converts them to electrons, much like solar panels convert light to energy. This build up of electrons in each photosite is converted to a voltage which in turn is converted to digital data as a picture element or ‘pixel’. These pixels are then relayed in consecutive order and stored as an image on the camera’s memory as a file. These files can then be viewed on the camera in the LCD screen, or uploaded to a computer where they can also be viewed or manipulated with imaging software.




Types of digital sensor.

CCD - Charged Coupling Device (CCD) sensors were invented by Dr. Willard Boyle and Dr. George Smith at Bell Labs in 1969. Today CCD sensors are used in a multitude of devices from scanners to telescopes.

CCD sensors derive their name from how the charge is read after an image is captured. Utilizing a special manufacturing process, the sensor is able to transport the built up charge across itself without compromising the image quality. The first row of the array is read into an output register, which in turn is fed into an amplifier and an analog to digital converter. After the first row has been read, it is dumped from the read out register and the next row of the array is read into the register. The charges of each row are ‘coupled’ so as each row moves down and out, the successive rows follow in turn. The digital data is then stored as a file that can be viewed and manipulated.

Until recently, CCD sensors have been predominant in digital SLR’s because of their high quality/ low noise images and their maturity, having been produced for over thirty years. But new manufacturing methods of an old technology have led to inroads for it to surpass CCD sensors.

breakdown of a CCD sensor.

CMOS - (Complimentary Metal Oxide Semiconductor) sensors or Active Pixel sensors were first discussed in length in a paper from Dr. Eric Fossum, a scientist at NASA’s Jet Propulsion Laboratory, in 1992. 1993 through to 1995, JPL developed much of the technology which would be implemented into the CMOS sensor. Fossum and other members of the JPL co-founded Photobit Corporation in 1995 to commercialize the technologies they had developed. In 2001, Micron Technology acquired Photobit and used its extensive knowledge of CMOS wafer manufacturing to enhance the development further.

CMOS sensors derive their name from the way they are manufactured. They are cut from a CMOS wafer which is cheaper to produce then a CCD wafer, provides less power consumption, and also allow for more involved circuitry along side of the photosite array. Each photosite in the CMOS sensor has three or more transistors which has its benefits and its draw backs. The transistors allow for processing to be done right at the photosite, and each pixel/photosite can be accessed independently. Because the transistors occupy space on the array, some of the incoming light hits the transistors and not the photosites, which leads to picture noise. CMOS sensors also function at a very low gain which may contribute to noise.

breakdown of a CMOS sensor.

The differences between the two sensor types are noticeable in a number of ways. Below is a comparison chart explaining them. Now that i know this, it makes sense why manufacturers push the CMOS SENSOR when advertising their cameras. Constant improvements appear to boost the CMOS sensor's capabilities and precision, but i feel the CCD still trumps it for now.

how each channel (RGB) combine to make an image.

Most of the above information has been referenced from - http://www.sensorcleaning.com/whatisasensor.php

8. What does a photo-site record ?

Light and then it is converted to an electronic signal and recoded by the camera's image processor. 

• 1 photo-site : 1 pixel.

9. What is interpolation ?

umm

10. Explain step by step the process of RAW file capture.

RAW data is the output from each of the original red, green and blue sensitive pixels of the image sensor, after being read out of the array by the array electronics and passing through an analog to digital converter. The readout electronics collect and amplify the sensor data and it's at this point that "ISO" (relative sensor speed) is set. As far as I know, RAW isn't an acronym, it doesn't stand for anything, it just means raw, unprocessed, data.

Now one of two things can be done with the RAW data. It can be stored on the memory card, or it can be further processed and compressed (lose information) to yield a JPEG image. The diagram below shows the processes involved:

If the data is stored as a JPEG file, it goes through the Bayer interpolation, is modified by in camera set parameters such as white balance, saturation, sharpness, contrast etc, is subject to JPEG compression and then stored. The advantage of saving JPEG data is that the file size is smaller and the file can be directly read by many programs or even sent directly to a printer. The disadvantage is that there is a quality loss, the amount of loss depending on how much compression is used. The more compression, the smaller the file but the lower the image quality. Lightly compressed JPEG files can save a significant amount of space and lose very little quality. For more on JPEG compression see http://www.photo.net/learn/jpeg/index.html

11. What is the difference between RAW and JPEG files ?

RAW - is an uncompressed recording of any light entering the camera.


JPEG - is a compressed recreation of the recorded light.

D.