easy question about canon 50mm

[tomsphotography1664882219]

<p><em>On a 40D body can anyone tell me what the aperture increments are on a 50mm 1.8 lens? This question is posed purely so that I can decide if it is worth buying for low light portrait photography.</em><br>

<em>Thanks</em> </p>

[bueh]

<p>⅓ stops. All lenses have the same increments, as it is a function of the camera (which can be set to ½ or ⅓).</p>

[derek_linney]

<p>If you set camera to 1/2 stop increments you'll get f1.8, f2, f2.5, f2.8, f3.5, f4 etc<br>

If you set camera to 1/3 stop increments you'll get f1.8, f2, f2.2, f2.5, f2.8, f3.2, f3.5, f4 etc</p>

<p>Derek<br>

<a href="http://www.takebetterpictures.co.uk">www.takebetterpictures.co.uk</a></p>

[tomsphotography1664882219]

<p>Thanks, as I currently have a max of 3.5 on all my lenses that really is a big jump and must make a massive difference to low light shoots.</p>

[mendel_leisk]

<p>The full aperture stops are 1.4, 2.0, 2.8, 4.0, 5.6 and so on.</p>

<p>Just rounding your 3.5 to 4.0 for expedience, from 4.0 to 1.4 is 3 full stops. So for example, if you were shooting with f4.0 and 1/30 sec, you could use f1.4 and 1/125 sec.</p>

<p>For each full stop change in aperture value, you can change shutter speed by a corresponding full stop. Shutter speed full stops are each double (or half) of their neighbours, ie: 1/30, 1/60, 1/125( I know), slight adjustment), 1/250, and so on.</p>

[tomsphotography1664882219]

<p>I thought I had two simple and straight forward answers until Mendel joined in! Without any disrespect at all your knowledge has far exceeded mine and managed to baffle me somewhat. If I currently take a picture at f3.5 @ 1/60 what would my shutter speed be if I selected f1.8? </p>

[bueh]

<blockquote>

<p>If I currently take a picture at f3.5 @ 1/60 what would my shutter speed be if I selected f1.8?</p>

</blockquote>

<p>1/250 sec.</p>

[neill_farmer2]

<p>Hi Tom. Aperture and Shutter speed are a trade off, For any given value of light there are many aperture and shutter speed combinations that will admit the right amount of light onto your camera sensor. Be aware that it's not a free ride, go wide on the aperture (1.4- 1.8) and your depth of field becomes very thin and only a thin plane through your image will be in focus (the eyes could be in but the tip of the nose and the ears out). Got too slow and the image will be blurred by camera shake and subject motion. One of the basic skills of the photographer is to choose the right combination for the image ( I often get it wrong). By all means get a 50mm lens, it is basic kit for low light photography, but also be aware of the limitations you will be working with. The lens is worth it just for the sharpness alone. Neill</p>

[mendel_leisk]

<p>"If I currently take a picture at f3.5 @ 1/60 what would my shutter speed be if I selected f1.8?"</p>

<p>Just to avoid confusion, why don't we stick to <em>full stop</em> examples. With apertures, recapping, the full stops are:</p>

<p>1.4, 2.0, 2.8, 4.0, 5.6, 8, 11, 16, 22</p>

<p>And shutter speeds:</p>

<p>1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000</p>

<p>The lists carry on, at both ends, but this is enough to play with. Bottom line, shift either of the two values to the right by one, and you need to shift the other to the left by one. That's why the apertures go up in such odd numbers: each stop represents a halfing or doubling of light.</p>

<p>So taking a full stop example similar to yours, say:</p>

<p><strong>f4.0 @ 1/60</strong></p>

<p>if you change your aperture to <strong>f2.0</strong> (2 fold increase in light gathering), you can decrease your shutter open time to <strong>1/125</strong> (2 fold decrease in light gathering).</p>

[bueh]

<p>With all due respect, Mendel, you miscalculated in both of your postings. 2 stops advantage equals 2²=4 times faster shutter speed. So going from 1/60 @ f/3.5 to f/1.8 (which is exactly 2 full stops difference) means you get 1/250 sec shutter speed.</p>

[mendel_leisk]

<p>Bueh, you're right (both times): the shutter speed in my last paragraph (for instance) should be 1/250, my mistake, and sorry for confusion.</p>

[gabriel_l1]

<p>For the mathematically inclined, the aperture values are not "odd" but rather elegant. I don't want to confuse Tom - this information is purely theoretically interesting, not practical in the field, but in brief: increasing exposure one stop = doubling light = doubling the aperture's area = multiplying the original radius by square root of 2. Since apertures in photography are listed not absolutely but as a fraction of the focal length (f/x), that means the new "x" value needs to be *divided* by root 2 to increase exposure (or multiplied by root 2 to decrease exposure). Therefore aperture values are just ratios with powers of root 2 (1.41421) as the denominator - i.e., every other x value will be a power of 2:</p>

<p>f/{<strong>1</strong>, 1.4, <strong>2</strong>, 2.8, <strong>4</strong>, 5.6, <strong>8</strong>, 11, <strong>16</strong>, 22, <strong>32</strong>, 45, <strong>64</strong>, etc.}</p>

<p>Note that this means some of the intermediate values are really slight approximations. For instance, in reality we should have f/5.7 and f/23. Wonder who thought "5.6" was easier to remember than "5.7?"</p>

[gabriel_l1]

<p>PS - going back to Tom's original f/3.5 value, this means going to f/1.8 would result in an aperture of 3.7809 times as much area or light. So if your original shutter was 1/60th, the ideal new shutter would be 1/227, which the camera will round to 1/250 anyway.</p>

[paul_runnoe2]

<p>A good article here on pnet about the relation of shutter, aperture, and iso <a href="http://www.photo.net/learn/basic-photo-tips/aperture-shutterspeed-iso/">http://www.photo.net/learn/basic-photo-tips/aperture-shutterspeed-iso/</a><br>

Wiki f-stop to further the mathematical explanation <a href="http://en.wikipedia.org/wiki/F-number">http://en.wikipedia.org/wiki/F-number</a></p>