ASb Back-up scam

It's christmas so I won't be spending long on thei spost but please be aware that the following e-mail is a scam designed to get your bank account details:

Dear ASB FastNet Customer,

We are currently performing a full customer database backup, to improve our security measures and reduce the number of inactive accounts. Please follow the link provided in this message and confirm your personal information.

https://.www.asb.co.nz/ 

Your account will be limited and eventually deleted if not confirmed within the next 24 hours. We apologize for any inconvenience this may have caused.

© 2011 ASB Bank Limited. All Rights Reserved.

The Magic Numbers of Photography - How Focus works

Lately I've been getting interested in the principles behind photography (think physics). One key part of this is focal length and the idea that focal length is the distance from the front of the lens to the image sensor (for digital cameras) or film (for film cameras). The focal length is also the point at which light passing through the lens becomes focussed. This should mean that lenses of a given focal length should only be able to focus on objects at a particular distance. To put it another way lenses of a given focal length should not be able to have variable focus.

Yet we know this isn't true. All of our lenses have a focus ring and they all allow us to control where focus is without changing the focal length...

Or do they?

I decided to test this out by slapping my 50mm prime lens onto my camera then setting my camera up on a tripod in my lounge. I then took two pictures, 1 with the focus ring set to the furthest distance possible (infinity), the second with it set to the closest distance possible (in this case 45cm). The results were surprsing and gratifying at the same time.

Photo taken with focus set to infinity

Photo taken with focus set to 45cm

As you can see in the images above the field of view has shifted between the 2 photos. In the first case with focus set to infinity we have a wider angle of view than the second case with focus set to 45cm. The changing focus has changed the focal length.

This is surprising because:

We expect fixed focal length lenses to maintain a constant focal length. Clearly this is not the case

This is not surprising/is gratifying because:

It fits with the basic physical principles of how light can be focussed on a surface

It fits with what you SEE happening when you adjust focus on a lens (the lens moves away from the sensor when focussing on close objects (increased focal length and a narrower angle of view) and towards the sensor when focussing on distant objects (decreased focal length and a wider angle of view)).

The Magic Numbers of Photography - Flash Sync Speed and the Consequences

The Magic Numbers of Photography - Calculating the F number

F numbers or F stops are an important concept to grasp in Photography. The F stop that you select will have important implications for your depth of field and the amount of light that enters the camera. But where does this value come from?

F numbers express the relationship between the focal length of a lens and the diameter of the opening through which light can pass (sometimes called a pupil or iris). The F number for any given lens is obtained by dividing the focal length by the diameter of the opening.

If they are equal the F number is 1.

If the focal length is smaller than the opening the F number is less than 1.

If the focal length is greater than the opening (the most common scenario) then the F number is greater than 1.

Now the truly interesting part about F numbers is the way that the relate to the amount of light that enters the lens. While doubling the shutter speed halves the amount of light that enters the camera doubling the f number more than halves the amount of light entering the camera. This is because the F number is related to the diameter of the opening while the amount of light that enters is determined by the area of the opening.

To illustrate this point we will compare the area and diameter of the opening for 3 F stop values in a 50mm lens: 1, 1.4, and 2.

F = 1

Diameter = 50/1 = 50mm

Area = 25 x 25 pi = 1964.29mm

F = 1.4

Diameter =  50/1.4 = 35.71...mm

Area = 17.86... x 17.86... x pi = 1002.19mm

F = 2

Diameter = 50/2 = 25mm

Area = 12.5 x 12.5 x pi = 491.07mm

NB:// This relationship holds for any focal length as F numbers take the focal length into account. 50mm simply used as a concrete example.

As it turns out in order to halve the amount of light that enters the camera you need to increase the f number by the sqaure root of 2 (1.4-ish). This is why the standard F stop scale goes:

1 - 1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22 - 32

Each value is an approximation to the preceding value multiplied by the square root of 2 (1.4-ish)

F = 1

Diameter = 50/1 = 50mm

Area = 25 x 25 pi = 1964.29mm

F= Square root of 2

Diameter = 35.53...

Area = 982.14

Now if you're super inquisitive you may be wondering why the square root of 2 is the magical number. If you're also super observant you may have noticed earlier that the change from an F number of 1 to an F number of 2 reduced the area by a factor of 4. If you extend that out to an F number of 4 the area is 16 times smaller than when you have an F number of 1.

F = 1

Diameter = 50/1 = 50mm

Area = 25 x 25 pi = 1964.29mm

F = 2

Diameter = 50/2 = 25mm

Area = 12.5 x 12.5 x pi = 491.07mm

F = 4

Diameter =  50/4 = 12.5.mm

Area = 6.25 x 6.25 x pi = 122.76mm

What's happening?

Every time you double the F number, by going from 1 to 2 or 2 to 4, the amount of light entering the camera reduces by 4 times (or 2 squared). 

If you quadruple the F number, by going from 1 to 4, the amount of light entering the camera reduces by 16 times (or 4 squared). Turning this around if you wanted to decrease the amount of light entering the lens by 16 times you could quadruple your f number (4 is the square root of 16). If you wanted to decrease the amount of light entering your camera by 4 times you could double your F number (2 is the square root of 4). Finally if you want to reduce the amount of light entering your camera by two times (i.e. if you wanted to halve the amount of light entering your camera) you could increase your F number by ~1.4 (~1.4 is the square root of 2).

In fact this concept pops up a lot in photography and is known as the inverse square law.

ASB Survey Scam

  1 minute for 5 Questions Survey . In return we will credit $40.00 to you !
       Please submit the survey form and allow 3 days in order to process it.

       To access the survey form, please download and complete survey              __    form attached to this email and open it in a web browser.
 

© 2009 ASB Bank Limited

Reasons to believe that this is a scam:

- Money for nothing

- The survey requires you to download a file, this file may contain malicious content. Normally if you were operating an online survey you would just provide a web link

- The credit will be designed as a legitimate reason to ask for your bank account details

- The survey isn't being promoted on any of ASB's web presences

Landscape Photography - Waiting for the light and capturing the luck

Today I got to put a couple of lessons I've learnt into practice with some landscape photography. These lessons were:

- Photographers Capture Luck

- Photographers Capture (and see) Light

- Photographers Capture these things with Cameras

The luck component, mentioned by David Oliver in a talk I attended earlier in the year, usually comes from being in the right place at the right time. Today's opportunity came about on a trip back to Auckland from a location scout in the Coromandel. Out of the corner of my eye, on the side of the road, I spotted something that I quite liked the look of, pulled over, and found the right spot for what I felt was the right shot.

The seeing and capturing has two parts to it. You have to be able to appreciate what light does and recognise when things are going to look pretty - this enables you to recognise the lucky combination of subject and lighting when it occurs. This sounds simple but is actually something of a stumbling block. I have included 2 images below to make the point that without the light the image isn't anywhere near as interesting. This image needs the contrast that the sun punching through the clouds to the left of the frame provides. When the sun is fully behind the clouds the light is flat, even, and uninteresting. To make things worse in order to compensate for the reduced light in the second image the exposure must be increased. Regardless of how you do it you end up blowing out the sky and losing some of the clouds and the blue of the sky.

Finally perhaps the most important component of the bunch is the fact that I actually had a camera on me. Having your camera on you as much as possible (preferably at all times) is a lesson worth learning. Think of all the photo opportunities you will be able to snag.

Fixing Chrome's \Device\Harddisk1\DR3 error

The Solution:
Ctrl + J
Press Clear all on the top right hand side of the screen

Why it works:
This error is due to google chrome being unable to find the last location that you saved a downloaded file to.
By performing the fix above you are clearing chrome's memory of what that last location was.

How this could be made clearer:
The error message the google chrome throws up is super vague.
It tells you that it can't find the hard disk which sounds like it's unable to find the internal hard drive.
This isn't what it means.
It would be clearer if it specified the path that it was unable to find rather than simply telling you it is unable to find something.

chrome.exe - No Disk
There is no disk in the drive.  Please insert a disk into drive
\Device\Harddisk1\DR3.
Cancel - Try Again - Continu