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F stop vs focal length vs shutter speed relationship

Sanford Edelstein , Jun 24, 2011; 10:30 a.m.

Is there a theory? For instance, can I hand hold a 28mm at F2.5 at a slower shutter speed as well as I can hand hold a 50mm at F1.8 at the higher shutter speed?

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Chris Waller , Jun 24, 2011; 10:47 a.m.

There is a rule of thumb which says that the slowest shutter-speed for hand-held shooting is equal to 1/focal length. E.g. for a 50mm lens the slowest hand-held speed would be 1/50, or 1/60, to the nearest actual setting available on the camera. So for a 200mm lens the slowest hand-held speed would be 1/200, or 1/250 to the nearest actual available shutter-speed.

Steve Levine , Jun 24, 2011; 10:47 a.m.

You are correct in theory. A wide angle can often be hand held at a slower SS that a longer lens. This has to do with magnification. The more magnified the view, the more shake will be a factor in your exposures.

Matt Laur , Jun 24, 2011; 10:52 a.m.

For a given focal length, the only thing that impacts your ability to hand-hold it for a given amount of blur tolerance is the shutter speed. Tp the the extent that you might need to use a wider aperture in order to bring in enough light to get you that fast-enough shutter speed, that's when aperture comes into play. But you could also achieve that by raising the ISO, making the camera more sensitive in the first place, and allowing a higher shutter speed that way, instead.

The issue here is that at longer focal lengths, you're dealing with greater magnification. Let's say you're in a dim room, and you're already raised your ISO and opened up your lens aperture to make the most of the light. The only other factor is shutter speed. Now let's say you're using a wide-ish lens, capturing the whole scene, and can get a satisying (to you, for the size of print you're making) motion-blur-free shot at 1/60th.

Now zoom in, or swap lenses, so that you're using a longer focal length. Focusing on a more detailed element in the scene ... say, a pencil on a table in that dim room. That small detail used to be very small indeed. Now, with the (let's say) 135mm lens on the camera, the pencil is occupying a much larger share of the frame. If you are moving the camera, that pencil's edges will, relative to the size of the frame, appear far more blurry than they would have when that pencil's edges were just a few pixels' worth of the image when you used a wide lens. So, you need a higher shutter speed to minimize that problem when you use the longer focal length. Where 1/60th was adequate before, you might now need 1/250th.

Essentially, you're camera-movement-blurring the pencil the same regardless of the focal length, but it doesn't matter as much with a wide lens, for a given size display of the results, because those blurred items occupy a much, much smal part of the resuls.

To get you those higher shutter speeds, you might need a wider aperture ... but that also means you lose depth of field, trading off motion-freezing for a more difficult focusing situation. Which is when very high ISO-capable cameras come in, or, adding more light. If you happen to be adding light by using a flash, and the flash is all or most of the light that makes up the exposure, then the flash pulse itself will do a good job of defining the edges of objects in the scene.

Stephen Penland , Jun 24, 2011; 11:13 a.m.

Because the previous responses have answered your question directly, I'll add a sidelight. I'm one of those who feels naked without a tripod. Not all of my lenses have IS, and even if they did I have a feeling (a prejudice, really) that I still can't get as sharp of a photo, especially if it is going to be printed large) without a tripod as I can with a tripod. A tripod may sometimes be inconvenient (carrying and setting up), and it may not work as well for rapidly changing compositions, but for me as a landscape photographer I'd still be using a tripod even with a wide-angle lens with IS. I consider it an indispensable piece of equipment, regardless of the existence of hand-holding guidelines for focal length and shutter speed.

Charles Stobbs , Jun 24, 2011; 12:46 p.m.

IMHO 1/200 was the shutter speed to use for a 50mm lens for consistently good results with projected 35mm slides.Anything less was a crap shoot. People raved about their results with an Olympus Trip 35 which I believe was mainly due to its fixed 1/200 hutter speed.

Frank Uhlig , Jun 24, 2011; 01:31 p.m.

The camera that you use also plays a HUGE role in accepatable shutter speed per focal length.

SLRs and DSLRs will suffer from mirror slap vibrations, even on a tripod ...; rangefinder and mirrorless cameras etc will not.

Scott Ferris , Jun 24, 2011; 01:35 p.m.

The rule of thumb really only worked on 35 mm sized cameras. As Matt says, the issue is magnification, because crop cameras magnify movement for the same print size, the rule of thumb breaks down.

For instance, if you can handhold a 50 mm on your ff camera at 1/50 sec and are happy with an 8" x12" print from it, you couldn't get the same result from the same print size with the same lens on a crop camera, you would have to be 1.5 (Nikon) or 1.6 (Canon) steadier, or instead of 1/50 sec you would probably need 1/80 sec to get the same result.

JDM von Weinberg , Jun 24, 2011; 01:39 p.m.

At a given speed, the amount of shake is going to be technically the same, actually. It's just that in a much wider field of view (say 100º) that shake will be so much smaller a percentage of the image size that it is either less noticeable or simply disappears into the acuity (lack of) of the image at that size.

When you have the same motion in a 15º telephoto image, the shake blur will be a larger percentage of the total image and much more noticeable.

With very sharp lenses/high-density sensors, you can see the motion blur in large magnifications of wide angle lenses too.

It's like depth of field; it's the limitation of human perception that lets unsharpness 'get by' at small scales.

Mukul Dube , Jun 24, 2011; 01:44 p.m.

The rule of thumb refers to an abstract thumb. It may not apply to you if your thumb is different. In this context, Thumb Improvement consists in practising those things that make hand-holding less shaky.


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