Memo from the third meeting at 12.12.2011

Topic : Aperture and Focal length

Aperture

To balance amount of light that your camera is taking for the picture, you can use mainly two things: speed (as we talked last meeting) and aperture.

In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. (wikipedia)

[ See this here: http://www.whatsoever.hk/my.photo.album/aperture.gif ]

If  you will open your aperture, you will get more light, so you can use higher speed. This can help in taking not moved pictures. From the other side, if you will close the aperture, you will get less light, so you should use lower speed.

[Focal-length differs : http://cdn-7.nikon-cdn.com/en_US/IMG/Images/Learn-And-Explore/2009/Photography-Techniques/Focal-Length/Media/red-barn-sequence.jpg ]

Also aperture is “responsible” for the focus on your pictures. If you will open a lot your aperture, you will get more or less same sharpness in whole picture area. This is good for example for landscape pictures. Opposite, if you will close your aperture, you will have sharp just part of your picture. This is good for the portraits- you can let the eyes sharp and focused and the background blur.

You can express aperture in 'f' number. The higher f number, the smaller the aperture (small hole, less light). And of course, the lower f number, the bigger aperture (big hole and a lot of light)

 [ See it here: http://cdn-7.nikon-cdn.com/en_US/IMG/Images/Learn-And-Explore/2009/Photography-Techniques/Focal-Length/Media/focal-length-graphic.jpg ]

You can think that f around 1 is usually same amount of light that our eyes are getting. So the best lenses should be able to reach f number around (or even less than) 1. Extreme values of f number can give a bit worst quality, for example with f around 30 or more, you can see light diffraction (less sharp pictures).

The aperture can be close or open with different number of plates you have in lens. The good lenses have more petals, so while closing they create better circle (which is the perfect shape). This also effects the Flare and ghosts in your picture.

Tip:

If you want to get nice star's shaped lights during night pictures, you need to have in account the number of petals and f number that you are using. Your start will have as many arms as many petals your lens has. (You can check this effect in some pictures from our last week homework).

Focal length

Is a measure of how strongly the system converges (focuses) or diverges (defocuses) light.  (wikipedia) Camera lens focal lengths are usually specified in millimeters for example lenses 50 mm or 150 mm and so on.

Focal length is the distance between the center of the lens and focused image produced on the sensor. Is telling you which angle you can see with your lens (the wide or narrow).

See the table here: http://static.photo.net/attachments/bboard/00K/00KpA6-36104884.jpg

Effect here: http://www.warehouseexpress.com/webcontent/images/guides/exposure-guide/f-stop-chart.jpg

For example:

You will keep same amount of light in your picture using the values of each row of the shutter speed combined with corresponding column of the f number. (like with f=1,4 and speed 250 you will have same light amount as with f= 2,8 and speed 60).

See the difference here:  http://media.the-digital-picture.com/Images/Other/Focal-Length-Background-Blur.jpg

If you are interested, you can also try making your own bokeh :http://www.diyphotography.net/diy_create_your_own_bokeh

Homework:

Take two interesting pictures:

- First picture which has the highest 'f' value from your camera(ie, focus is not specific to any object in picture but everywhere in the picture, more things are sharp)

- second picture which has very small 'f' value (very focused, trying to get blur background)

(How does this going to work: http://www.abc.net.au/science/askanexpert/img/aperture.jpg )

It really does not matter what kind of objectives or camera you have, the point is to learn how to set those things in your camera. [ You can read these values in your camera like in this picture:

http://images.cambridgeincolour.com/tutorials/lenses_maxaperture2.jpg ]

Send it to us at joemul.photo@gmail.com before next Monday and we will look at your pictures and give talk about it in next meeting.

Information:

• We are going to have probably 2 exhibitions. The main theme of the exhibition is 'Life in Joensuu/ Finland”. Please keep it in your mind while doing your homeworks. Also try to take picture with higher resolution, since we would need printed pictures in size of A3. (Resolution as big as possible, more than 12 Mpx)
• In one of the mails you got the list of subjects that we probably will discuss during our meetings. If you are interested in preparing some information please, send us the e-mail. For now Heikki will prepare HDR photography, Lai- Microphotography and Victor (??)- Night and Bulb pictures. We can think about the dates, and you can also prepare in groups :)
• If you are not getting the news from us in your email (or if you know someone who is not getting the news from us) please send us mail, so we can add it to the mailing list.
• Here is a link to our public albums, where you can see previously published homework and also you can check the album later if you cannot come.
  • https://picasaweb.google.com/117111564646533836628