Aperture setting

[victor_ng2]

<p>Generally, in order to get a clear picture, as many of us know the rule-of-thump for setting the speed: 1/focal length of the lens. This works quite well with me especially when I use speed priority mode. However, in a not well lit area, if I want to take a fast moving subject with my long prime lens Canon F4 400mm lens, for example, if I use this setting, I won't get any good sharp picture at all. I tried to switch to aperture priority & set it to F21, for example, I have a few good pictures.</p>

<p>So my question is that is there a rule of thump for setting aperture in association with the focal length of the lens like what we have for speed setting? Thanks!</p>

[SCL]

<p>Each lens is optimized for use at a particular aperture, and performance usually falls off either side of this value. Performance is usually a combination of resolution, chromatic abberation, flare, and distortion characteristics. Most consumer grade lenses are optimized at apertures about 2 stops closed down from wide open. Some high end telephoto lenses were optimized for use wide open....the older ones I'm most familiar with are the Canon FD 300 f/4.0 L; the Leitz Telyt-R APO 180mm f/3.4, which was designed for the U.S.Navy for surveillance work; and the Leitz Tele-Elmar (M) 135mm f/4.0. No matter what the focal length, whenever I get a lens, I test it out for optimal aperture. Thankfully, Zeiss often includes graphs of their tests with each new lens.</p>

<p>When a lens is stopped down too far beyond its optimal aperture, diffraction enters the picture as a type of distortion, reducing the sharpness of the image.</p>

[craig_shearman1]

<p>"is that is there a rule of thump for setting aperture in association with the focal length of the lens like what we have for speed setting?"<br /><br />No. The 1/focal length rule is intended to prevent blur from camera shake. It has nothing to do with sharpness of the lens as such.<br /><br />When you're in low light, you need to open the lens up far enough to get to the 1/focal length speed, even if that means shooting wide open (aka f/4 on your 400 f/4). If that's not enough you can crank up the ISO depending on how high your camera can go without digital noise. Putting the camera on a tripod/monopod also minimizes or eliminates camera shake, so you can go to a slower shutter speed. VR/IS can also help considerably.<br /><br />Shooting wide open gives you little depth of field so you have to focus very accurately. If you're not getting as much depth of field as you want and need to close down, then you need to compromise with a slower shutter speed. As mentioned, a tripod/monopod will take care of the camera shake but can't do anything about motion blur if the subject is moving quickly.<br /><br /></p>

[parv]

<p>Highlighting is all mine of Victor N's words...

<blockquote>

in a <b>not well lit</b> area, if I want to take a <b>fast moving subject</b> with my long prime lens Canon <b>F4 400mm</b> lens, for example, if I use [1/400 s shutter speed], I won't get any good sharp picture at all. I tried to switch to aperture priority & set it to <b>F21</b>, for example, I have a few <b>good pictures</b>.

</blockquote>

 

<p> Victor, what shutter speed do you get while using aperture of f/21? What aperture do you get at shutter speed of 1/400 s (going by 1/focal-length-in-mm guide)?

 

<p>Either the subject is not moving fast enough (for the presumably slower shutter speed) or subject is damn well lit for you get usable images at f/21. Else, please explain how you are able to get usable images.

[Matt Laur]

<p>Indeed, f/21 is a small enough aperture that it's going to be letting in very little light - causing you to either need a very high ISO setting (noisy images!) or a very slow shutter speed (motion blur of the subject, and motion blur from the camera's movement if you're hand-holding!) or both ... unless you're in very bright light. But you said LOW light. So I'm confused as to what you're actually experiencing.<br /><br />If you want a fast enough shutter speed to freeze the motion of your subjects and to minimize the appearance of an unsteady camera (let's say that should be at least 1/400th, but more like 1/800th with a long lens), the you'll need to open up that lens all the way to f/4 (for the most light gathering it can do) and crank up the ISO to something high enough (making the camera sensitive enough to support that high shutter speed you're after). But in a "low light" scenario, I'm betting that you'll have to go to ISO 3200 or ISO 6400 to get anything even close to a fast shutter speed, even with the lens opened up all the way to f/4. It depends on how one defines "low" light.</p>

[JDMvW]

<p>I like "rule of thump" - but the usual usage, for future reference, is "rule of thum<strong>b</strong>" :)<br>

An ancestor, of German heritage, thought the long-eared creatures in his garden were "rapids" - makes sense to me. <br>

NTIM</p>

[jcuknz]

<p>Since the guide dates from 'film days' I have always taken it to mean that based as it is on the angle of the lens that one should use the effective focal length ... So if you have a full frame camera than you use the lens focal length but APS-C then it is fx1.6 or in my case with MFT it is fx2 .... I only normally have a 140mm lens which means I use 1/280 if in a situation where I can carefully make the exposure ... in less than ideal situations a higher shutter speed is indicated.</p>

<p>After all the correspindence in recent years about diffraction I would be reluctant to use f/21 and am suprised, and pleased for you, that your results were good. Thoiugh some say that other factors come into play before diffraction makes much difference.</p>

[charles_stobbs3]

IMHO 1/focal length is totally inadequate for anything larger than 4X6" prints. For slide film I found 1/250

was a safe choice with a 50mm lens. Sometimes I got lucky with a slower shutter speed, but it was just

luck.

[sarah_fox]

<p>The 1/fl rule of thumb is only that -- a rule of thumb. It's subject to modification for any individual, any purpose, and any particular set of circumstances. It works pretty well as a starting point for most people and most purposes. Some people have very solid holds, and some do not. Some people shake with their morning caffeine, and some people don't. Some people are stronger than others. Some people have less tolerance for camera shake than others. These factors are so highly variable that Charles and I are about three stops apart from each other in our personal "rules." Perhaps I'm steadier than he is? Perhaps I tolerate more shake in my photos? Perhaps some combination?</p>

<p>And the rule also requires modification the second you switch on an image stabilizer.</p>

<p>This "rule" should really be restated that if you double your focal length, you half your shutter speed to arrive at the same level of stability/shake. And this rule falls short when the camera lens combo starts getting heavy/clumsy/awkward. In that case it's wise to add a bit more correction.</p>

<p>As it pertains to this thread, the rule must be violated in small measure under certain circumstances. Photography usually involves competing factors that are traded off. To use a faster shutter speed, you have to open up your lens, but that introduces some softness from spherical aberration -- or perhaps you can find yourself lacking in the depth of field you desire. Or you can adjust ISO, but that comes at a cost too. So you strike compromises. You maybe shoot just a bit slower than you'd like, with a slightly larger aperture than you'd like and a slightly higher ISO than you'd like. (I've not even mentioned the possibility of adding more light, which introduces a forth or even fifth variable -- interaction of shutter speed with flash speed and ambient light levels.) That's the reality of photography. Generally speaking, I make these compromises in equal measure. However, sometimes I HAVE to limit compromises to one factor, which forces greater compromises to the other factors. This is where photography becomes more of an art than a science.</p>

[jcuknz]

<p>Life was so much simpler when usually one only had a 50mm lens for one's camera [ or 80mm on my MF TLR ] ... I realise that I didn't hear about the rule until I started blogging and that parralleled my entry to the digital world.<br>

Perhaps the sixth and seventh factors are the size of the image you are producing and seventh the balance of your rig .... put a long heavy lens on the camera , particularly the smaller versions, and you have a very unstable rig ... compensated for by holding camera with one hand and lens with other or else perhap organising things to support the rig under the nodel point of the lens with a pistol grip .... as Sarah wrote "So many compromises" </p>