Aperture, Shutter Speed, ISO Sensitivity

Bulb Mode

COMPOSITION IN PHOTOGRAPHY

WEEK 3 - Digital Photography

Digital camera and it's controls

BOKEH

 

Bokeh describes the rendition of out-of-focus points of light.

• Bokeh is different from sharpness. Sharpness is what happens at the point of best focus. Bokeh is what happens away from the point of best focus.
• Bokeh describes the appearance, or "feel," of out-of-focus areas. Bokeh is not how far something is out-of-focus, bokeh is the character of whatever blur is there.

           Unfortunately good bokeh doesn't happen automatically in lens design. Perfect lenses render out-of-focus points of light as circles with sharp edges. Ideal bokeh would render each of these points as blurs, not hard-edged circles. Mathematicians would say the intensity distribution of the blur circles are rectangular in perfect lenses, and good bokeh would prefer a Gaussian distribution. This is one area in which physics doesn't mirror what we want artistically.

           Differing amounts of spherical aberration alter how lenses render out-of-focus points of light, and thus their bokeh. The word "bokeh" comes from the Japanese word "boke" (pronounced bo-keh) which literally means fuzziness or dizziness.

            A technically perfect lens has no spherical aberration. Therefore a perfect lens focuses all points of light as cones of light behind the lens. The image is in focus if the film is exactly where the cone reaches its finest point. The better the lens, the tinier this point gets.

           If the film is not exactly where that cone of light reaches its smallest point, then that point of the image is not in focus. Then that point is rendered on film as a disk of light, instead instead of as a point. This disc is also called the "blur circle," or "circle of confusion" by people calculating depth-of-field charts. In a lens with no spherical aberration this blur circle is an evenly illuminated disc. Out of focus points all look like perfect discs with sharp edges. (OK, at smaller apertures where the image is in pretty good focus you may see additional "Airy" rings around the circle, but that's a diffraction pattern we're not discussing here.) This isn't optimal for bokeh, since as you can imagine the sharp edge of these discs can start to give definition to things intended to be out-of-focus.

     There are no perfect lenses, so one usually does not see these perfect discs.

Real lenses have some degree of spherical aberration. This means that in practice, even though all the light coming through the lens from a point on the subject may meet at a nice, tiny point on the film, that the light distribution within the cone itself may be uneven. Yes, we are getting abstract here, which is why some denser photographers refuse to try understand bokeh.

Illustrations

Example of Bad Bokeh.

The blurs of the out-of-focus twigs still have sharp edges. Good bokeh would have soft-edged blurs.

Spherical aberration means that the discs made by out-of-focus points on the subject will not be evenly illuminated. Instead they tend to have more of the light collect in the middle of the disc or towards the edges. Here are some illustrations:

 

	Fig. 1. Poor Bokeh. This is a greatly magnified blur circle showing very poor bokeh. A blur circle is how an out-of-focus point of light is rendered. Note how the edge is sharply defined and even emphasized for a point that is supposed to be out-of-focus, and that the center is dim.
	Fig 2. Neutral Bokeh. This is a a technically perfect and evenly illuminated blur circle. This isn't good either for bokeh, because the edge is still well defined. Out-of-focus objects, either points of light or lines, can effectively create reasonably sharp lines in the image due to the edges of the sharp blur circle. This is the blur circle from most modern lenses designed to be "perfect."
	Fig. 3. Good Bokeh. Here is what we want. This is great for bokeh since the edge is completely undefined. This also is the result of the same spherical aberration, but in the opposite direction, of the poor example seen in Fig. 1. This is where art and engineering start to diverge, since the better looking image is the result of an imperfection. Perfect bokeh demands a Gaussian blur circle distribution, and lenses are designed for the neutral example shown in 2.) above.

DSLR vs Point and Shoot Digital Camera

what to consider??
http://www.digital-photography-school.com/should-you-buy-a-dslr-or-point-and-shoot-digital-camera

DSLR Strengths

• Image Quality - I’ve already covered this above in my discussion on megapixels and image sensors – but due to the larger size of image sensors in DSLRs which allows for larger pixel sizes – DSLRs are generally able to be used at a faster ISO which will lead to faster shutter speeds and less grain.
• Adaptability – DSLR’s ability to change lenses opens up a world of possibilities for photographers. While my point and shoot has a nice little 3x Optical Zoom (and many these days have longer ones) my DSLR can be fitted with many high quality lenses ranging from wide angle to super long focal lengths depending upon what I’m photographing (and of course my budget). Add to this a large range of other accessories (flashes, filters etc) and a DSLR can be adapted to many different situations. It should be noted that when it comes to lenses that the diversity in quality of lenses is great. Image quality is impacted greatly by the quality of the lens you use.
• Speed – DSLR’s are generally pretty fast pieces of machinery when it comes to things like start up, focussing and shutter lag.
• Optical Viewfinder – due to the reflex mirror DSLR’s are very much a what you see is what you get operation.
• large ISO range - this varies between cameras but generally DSLRs offer a wide array of ISO settings which lends itself to their flexibility in shooting in different conditions.
• Manual Controls – while many point and shoots come with the ability to shoot in manual mode, a DSLR is designed in such a way that it is assumed that the photographer using it will want to control their own settings. While they do come with good auto modes the manual controls are generally built in in such a way that they are at the photographers finger tips as they are shooting.
• Hold it’s value – some argue that a DSLR will hold it’s value longer than a point and shoot. There is probably some truth in this. DSLR models do not get updated quite as often as point and shoot models (which can be updated twice a year at times). The other factor in favor of DSLRs is that the lenses you buy for them are compatible with other camera bodies if you do choose to upgrade later on (as long as you stay with your brand). This means your investment in lenses is not a waste over the years.
• Depth of Field – one of the things I love about my DSLR is the versatility that it gives me in many areas, especially depth of field. I guess this is really an extension of it’s manual controls and ability to use a variety of lenses but a DSLR can give you depth of field that puts everything from forground to background in focus through to nice blurry backgrounds.
• Quality Optics – I hesitate to add this point as there is a large degree of difference in quality between DSLR lenses (and point and shoot cameras are always improving) but in general the lenses that you’ll find on a DSLR are superior to a point and shoot camera. DSLR lenses are larger (more glass can add to the quality) and many of them have many hours of time put into their manufacture (especially when you get into higher end lenses). I strongly advise DSLR buyers to buy the best quality lenses that they can afford. It it’s the difference between a high end lens on a medium range camera or a medium range lens on a high end camera I’d go for quality lenses every time as they add so much to photos.
•