Effect of focal Length of your lens/camera

Hi Guys,

Every now and then friends ask technical Q’s on photography, and one popular question is “how do I get the shots with a blurry background and nothing else”.

An easy and difficult question to answer. I know what I need to do for all scenarios so it’s quite easy “for me”, but I don’t know what settings or scenarios the people whom ask me are dealing with so quite difficult as there are a few aspects that need to be taken into consideration. Sadly it’s all scientific, Optics actually.

(A)perture, (D)istance from subjects, Sensor size, lens (F)ocal length all need to be considered.

For portraits small A number, big D number, big F number all lead to blurry compact portraits. Or set A –  say 5.6 – 7? , small D, small L might work for you’re composition – Can be confusing.

I have found something to help understand lens focal length (Zooming in or out will change this-  this only applies to a  lens changing its physical state ie longer or shorter. It wont apply to Digital zooming  ie. phones) BUT! there is the issue of optical distortion that comes with altering focal length.

Click on the pic to go to the Photshelter blog post and see the article – Very informative and shows the effect of changing lens focal length on perspective, distortion and depth of field – watch the background go from uncluttered to more back ground detail.


Hope it helps.



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