Clarifying Terminology with Lenses

<p>So after reading and studying books from the library and various sources online it has come to my attention that certain terms or phrases, particularly concerning lenses, can become confusing. I'm writing in hopes that someone can simply clarify a couple of things.</p>

<p>Closing down the lense = creating a smaller aperture<br /> i.e. close down from f/2.8 to f/16 literally closes the leaf, allowing less light and,</p>

<p>choosing a smaller aperture = increasing depth of field<br /> i.e. one would wish to increase depth of field to blur the surroundings of a subject</p>

<p>increasing aperture = using smaller f/stop values<br /> i.e. to allow more light into the lense, one would go from f/16 to f/2.8 or open up the lense aka decreasing f/stop values</p>

<p>decreasing f/stop = going to a higher number<br /> i.e. larger apertures mean lower f/stop values, for example f/2.8 is a larger aperture than f/16</p>

<p>Thanks in advance--already getting confusing here, lol. I can essentially do these things when the equipment is in my hands, but understanding the correlation would definitely help especially when discussing such issues</p>

<p>Close yet this link might help : http://en.wikipedia.org/wiki/Stopping_down<br /> One needs to be clear when talking about aperture number e.g. f/16 vs just aperture size. So saying increasing aperture is a little ambiguous because increasing aperture number is decreasing aperture size and decreasing aperture number is increasing the aperture size. So best not to just say increasing/decreasing aperture without a clarifying word in my opinion.<br /> Hope that helps.</p>

<blockquote>

<p>i.e. one would wish to increase depth of field to blur the surroundings of a subject</p>

</blockquote>

<p>Backwards on that one. Closing down the lens (say, from f/2.8 to f/16) does make for more depth of field, and that means that MORE will be in focus (in front of, and behind your focused-upon subject). The wider the aperture (the lower that f-stop number), the more <em>shallow</em> that depth of field becomes, thus making focus more selective (and throwing that background more out of focus). Obviously, changing the aperture also impacts exposure - which means compensating for that change by also adjusting either or both shutter speed and ISO sensitivity.</p>

<p>I think more common than "closing down" is "stopping down". Lens aperture rings used to be set by stops, metal tangs limitting rotation, at the various "f-stops".</p>

<p>Also for clarification, please note the spelling: 'lens' (singular); 'lenses' (plural). </p>

"choosing a smaller aperture = increasing depth of field

i.e. one would wish to increase depth of field to blur the surroundings of a subject"

 

The opposite in fact. Stopping down , increasing the depth of field increases the apparent sharpness of the areas around

the plane you have focused on.

 

Something else to keep in mind the difference in whole stops - stopping down from f/5.6 to f/8 for example- decreases the

amount of light coming through the lens by half.

<blockquote>increasing aperture = using smaller f/stop values<br />

decreasing f/stop = going to a higher number</blockquote>

 

<p>The trick to avoiding confusion here is to realise that "f/2" and "f/4", etc., are fractions. "f" in this case is the focal length of the lens - the effective size of hole that's letting light in scales with how long the lens is, but - because it's correspendingly farther from the sensor - the length of the lens cancels out when you're trying to work out how much light is reaching the sensor. That's why people work in f-stops.<br />

<br />

Because it's a fraction, "f/2" is bigger than "f/4", for example (just as 1/2 is bigger than 1/4). The amount of light coming in depends on the area of the aperture, whereas the f-stop describes the diameter of the aperture - f/2 lets in four times as much light as f/4 (twice as big, but squared). That's why we have the sequence "f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8..." - they're approximately what you get if you keep dividing the aperture by the square root of two, which halves the amount of light that can get in each time.<br />

<br />

A bigger aperture means that you're gathering light from a wider angle, as seen by the thing you're shooting - that's why it lets in more light. If you look at an f/2 lens, the front looks twice as wide as an f/4 lens (give or take the details of the optics). Anything you're not focussing on gets spread out according to this angle, so a bigger aperture means you get more blur away from the plane of focus. The details of how much depend on how far away the lens is from what you're shooting, and how far things are from the focal plane, but if you're standing in one place and shooting one scene, a bigger aperture (f/smaller number) will blur the background (and foreground) more.<br />

<br />

On some lenses, you can see the aperture iris closing down if you fiddle with the aperture settings and look through the lens. You might need to use "depth of field preview" to see it when attached to a camera, depending on what you're using.<br />

<br />

I hope that helps.</p>

<p>One of the many DSLR simulator apps might help you get your head round apertures e.g. <a href="http://www.kamerasimulator.se/eng/">http://www.kamerasimulator.se/eng/</a></p>

<p>Try adjusting the aperture from large (small f number) to small (large f number) to see a simulation of what happens to the depth of field.</p>

<p>Of course you will need to adjust the shutter speed and/or ISO value to get the exposure right!</p>

 

<p><strong>Lower</strong> f-number = <strong>larger</strong> opening = <strong>more light</strong> = <strong>less</strong> depth of field = more blur beyond and before the plane of focus</p>

<p><strong>Higher</strong> f-number =<strong> smaller</strong> opening = <strong>less light</strong> = <strong>greater</strong> depth of field = less blur beyond and before the plane of focus</p>

<p>Here are some examples of lower f-numbers (larger aperture relative to focal length): 1.4, 2, 2.8, 4, 5.6</p>

<p>Here are some examples of higher f-numbers (smaller aperture relative to focal length): 8, 11, 16, 22, 32</p>