So You Think You Know What An F-Number Is
By Brian Auer
Most of us have heard, and probably used, the term f-number. Most of us have also probably used the term interchangably with “f-stop” or “aperture”. What are all these things, really? Yes, they have to do with the size of the holeallowing light to pass through the lens, and they affect depth of field and light intensity. But I’m talking aboutwhat these things really are.
First, let’s start with a few definitions. An aperture is simply a hole which allows light to pass through it.A diaphragm is the mechanism inside your lens that forms an aperture, and most modern lenses have an iris diaphragm made up of several interlocking blades. An f-stop is a discrete step in the f-number, and it refers to the physical stops in the diaphragm adjustment. So how are all these things different from an f-number?
An f-number is a measure of lens speed and it is defined by the focal length of the lens divided by the diameter of the aperture — f/# = f/D where f = focal length and D = aperture diameter. So if the focal length of the lens is equal to the diameter of the aperture, you’d have an f/1. If the focal length of the lens is 8 times longer than the diameter of the aperture, you’d have an f/8.
F-Number = f/D = (Focal Length)/(Aperture Diameter)
Here’s an example with one of my fixed focal length lenses (zooms are a little more complicated so I’ll hit that in a moment). I have a 50mm f/1.4 lens. The f/1.4 designation means that it has a maximum f-number of 1.4 — so that’s as big as it gets. The minimum f-number on this lens is f/16, so it can vary from f/1.4 to f/16. So using the formula for f-number: at a 50mm focal length and an f-number of 1.4, the equation states 1.4(f/#) = 50mm(f)/(D). Do the algebra, and we get 50mm/1.4 = 35.7mm. That’s physically how big the aperture is at it’s maximum. If I had a f/1.2 lens, the max aperture would be 41.7mm. Now to the other end of the scale, the aperture on this lens has a minimum diameter of 50mm/16 = 3.1mm. Similarly, my 105mm f/2.8 lens has a maximum f-number of f/2.8, an aperture diameter of 37.5mm — which is about the same size as my 50mm lens at
f/1.4, which is two stops up from f/2.8.
On the 50mm lens, including the minimum and maximum f-numbers, there are a total of 8 full
f-stops: f/1.4, 2, 2.8, 4, 5.6, 8, 11, and 16, with half-stops between everything but 1.4 and 2
(things like f/1.7, f/6.7, and f/9.5 are half stops — f/1.8, f/3.5, and f/6.3 are third stops found
in most modern lenses). Each full stop lets half as much light in as the last full stop. This is
because the area of the aperture is reduced by half with each stop. The values in the table represent the f-numbers, aperture diameters, and aperture areas for this lens. Note the reduction of area as the f-numbers increase. Each full stop down lets half as much light into the camera, and you can see that the area of the aperture for each stop is also cut in half. This is where a lot of people end up confusing themselves over f-numbers. Higher f-numbers mean smaller apertures — just remember that. To help explain the numbers in the table a little better, the image below shows the 50mm lens at each full stop from f/1.4 to f/16 from left to right.
Zoom lenses are a bit more complicated, and they generally fall into two groups: constant f-number and variable f-number. Variable f-number zooms are most common because they are simpler and cheaper. You can spot these lenses by their markings — f/3.5-6.3 means that the lens has a maximum f-number of f/3.5 at the shorter focal length and f/6.3 at the longer focal length. This doesn’t mean that the aperture changes as you zoom; it actually means that it doesn’t change. Remember that f-number is the quotient of focal length and aperture diameter, so as you zoom to a higher focal length (and keep the aperture constant) you allow less light into the camera and the f-number changes. On the other hand, the really spendy zoom lenses can maintain a constant f-number at all focal lengths. To achieve this, they must increase the effective aperture diameter as the focal length increases to keep the same f-number ratio.
F-numbers in zoom lenses aren’t quite as simple as I’ve made them out to be. That’s basically how they work, but truthfully, I don’t know exactly how they work. If you run the numbers on a zoom lens, it turns out that you don’t get a constant aperture diameter as the focal length increases and the f-number changes. Physically, I’m pretty sure the aperture diameter stays the same. But when you zoom a lens, you shift the location of lens elements, the diaphragm, focal planes, inflection points, etc., and some of these things are factors for the effective aperture diameter. I’m not an optics expert, so I’ll leave it at that.
Basically, the major take-away from this should be that the f-number is a measure of lens speed — regardless of the camera, regardless of the lens, and regardless of the conditions. If you and a friend are out shooting, you should be able to get the same exposure of a particular subject if you shoot using the same f-number, shutter speed, and ISO value (assuming ISO’s between cameras is somewhat comparable). It takes the focal length and aperture diameter into account in order to give a value of how much light will be allowed into the camera.
source: http://blog.epicedits.com/2007/06/16/so-you-think-you-know-what-an-f-number-is/
So You Think You Know What An F-Number Is
Sony Digital Camera Cyber-shot DSC-T900
The Sony Digital Camera Cyber-shot DSC-T900 slim T line digital camera. This Sony digital camera has a 4x optical zoom lens, records 12-megapixel images, and HD video at 1280x720 resolution. It has 3.5-inch LCD with 920,000-dot touch-screen.
FEATURE
Easy Mode
FEATURE
Easy Mode
A picture paints a thousand words, so easy-to-understand screen icons are used to help you control the settings of your Cyber-shot. But for even greater simplicity, switch to Easy Mode and the camera will do all the thinking for you, and can even display just the bare essentials like remaining shots and battery life.
Touch screen simplicity
Shoot and share with greater ease than ever. With One Touch Thinking, simple onscreen graphics displayed on your clear, touch screen LCD will guide you easily to the best settings for the shooting environment.
Full High Definition 1080
Photos are meant to be shared. Now, with Full HD 1080 output, it’s easier than ever to show off your holiday shots or create an entertaining slideshow of party photos. Using an optional cable, just plug your Cyber-shot into any High Definition TV for crystal clear, vivid images that everyone can enjoy together. Not available on the DSCS730
Music Slideshow
Choose a music track, choose a presentation style, then sit back and relive your memories using Music Slideshow. It adds a whole new dimension to sharing your favourite shots.
BIONZ Image Processing Engine
The BIONZ Image Processing Engine suppresses colour and luminance noise, giving you enhanced colour reproduction, rich tonal graduations and an amazing clarity of detail that captures the instant the way it was meant to be.
Let the camera detect between the different types of scenes, automatically selecting the optimum settings for each situation. With this mode, shooting in varied situation is a breeze.
Carl Zeiss Vario-Tessar Lens
The world renowned Carl Zeiss Vario-Tessar lens is an exceptional optical solution that gives you the crisp imaging detail and vivid colour reproduction you have come to expect from an outstanding lens maker.
Double Anti-Blur Technologies
Sony's Double Anti-Blur combines two key technologies, High Sensitivity and Optical Steadyshot, to significantly reduce motion blurs and allow you to capture sharp images in any situation.
Scene Selection
Each of the Scene Selection mode has pre-set settings that allow you to select the optimal configurations for your image with just a touch of your finger. So no matter what the shooting condition, just switch to the most suitable mode and start snapping.
12.1 Mega Pixels
With 12.1 Mega Pixels, your picture offer amazing sharpness and clarity. Crop any part of an image that captured your imagination, its pin-sharp clarity will remain breathtaking. Should you require a larger print, the high resolution keeps quality impressively high.
source : http://www.sony.com.au
specification : http://www.sony.com.au/product/dsc-t900/sku/dsc-t900_s++au2
source : http://www.sony.com.au
specification : http://www.sony.com.au/product/dsc-t900/sku/dsc-t900_s++au2
FUJI Digital Camera FINEPIX Z300
Fujifilm announcing its first ever touch-screen digital compact camera, FinePixZ300. This camera features a 3” LCD Touch Screen panel which allows users to control and play around with the built-in features with just a simple finger touch. Users can touch configure the setting, snap photos and slide the images for replay conveniently using just their finger tips. With features such as Scene Recognition AUTO, a versatile 5x optical zoom, Group and Couple self-timer modes, plus its Touch Screen technology and iconic design, the Fujifilm FinePix Z300 is this year’s must have gadget.
Capable of recording VGA quality video at 30fps, the FinePix Z300 measures 92 x 56.5 x 18.5 mm and weighs 150g.
There’s also touch-focus control, automatic scene selection and face detection for up to 10 individual faces; the Z300 can even recognize faces when they’re in profile, oblique and upside-down. Onboard storage is 31MB, augmented by an SD/SDHC card slot.
SAMSUNG Digital Camera WB500/HZ10W
SAMSUNG WB500/HZ10W
Samsung digital camera WB500 comes with 10x optical zoom and 720p HD movie recording.
FEATURES:
* 10.2 Megapixels (effective pixels).
1/2.33 inch CCD sensor
* World famous Schneider Kreuznach 10x optical zoom.
F3.3-F5.8 approximately 24-240mm equvalent to 35 mm film.
* TFT 2.7 inch LCD ( 230.000 dots).
* ISO range up to 3200 (3MP)
* Dual Image Stabilization.
Using Optical Image Stablization + Digital Image Stabilization.
* HD 720p movie recording with H.264 codec and stereo microphone.
High quality video enabled optical zoom while recording.
* Perfect Portrait Technology.
Face detection, Smile shutter, Blink detection, Self Shoot, Beauty shot.
Specification :
http://www.samsungcamera.com/product/pro_view.asp?prol_uid=4584&step1=2&step2=1
source :
http://www.samsungcamera.com
SAMSUNG WB500/HZ10W review :
http://www.digitalartsonline.co.uk/reviews/index.cfm?ReviewID=1021
http://www.dpreview.com/reviews/q209grouplongzoom/page6.asp
FUJI Digital Camera FINEPIX F200 EXR
FUJI FINEPIX F200 EXR
New Digital camera from Fuji that offer wide dynamic range and low noise sensitivity.
* 12 Megapixels (effective pixels).
1/1.6 inch Super CCD EXR with CCD Shift image stabilization.
* New Super CCD EXR and EXR processor. EXR Priority optimized for fine detail HIGH RESOLUTION,
WIDE DYNAMIC RANGE, and HIGH SENSIVITY AND LOW NOISE.
* Fujinon 5x optical zoom.
F3.3-F32 approximately 28-140mm equvalent to 35 mm film.
* Bright TFT 3 inch colour display ( 230.000 dots) 100% coverage.
Provides high contrast to view the images, wide viewing angle from any angle,
and also detect available light to automatically adjust screen brightness.
* ISO range up to 12800.
* Film Simulation Mode.
PROVIA (normal), VELVIA (vivid), ASTIA (soft), BW, SEPHIA.
* Dual Image Stabilization.
Using CCD Shift Image and Finepix sensivity prevent image blur.
* Super Intelligent Flash
Next Generation Flash system make it easy to capture subjects and background on bright,
clear, and natural.
Specification :
http://www.fujifilmusa.com/products/digital_cameras/f/finepix_f200exr/specifications/index.html
source :
http://www.fujifilmusa.com/products/digital_cameras/f/finepix_f200exr/index.html
FUJI FINEPIX F200 EXR review :
http://www.dpreview.com/reviews/fujifilmf200exr/
http://www.infosyncworld.com/reviews/digital-cameras/fujifilm-finepix-f200exr/10269.html
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