I don't get the "your shutter speed should not be less than the focal length" rule.

[harmonica]

I have been at photography for a few years now, but there is one thing I recently was told in a tutorial, that I have never heard before. In this tutorial, at 3:20 into it:



He says that the rule of thumb is that the shutter speed should not be less than the focal length. But I do not understand why. For example, if you want to take a telephoto shot of some buildlings from far away at night, you have no choice but to put the camera on a tripod, and shoot at a much lower shutter speed, than the focal length. And what counts exactly as the focal length being more or less than the shutter speed? In the photograph he has an example, I don't think that the problem is is that you need to adjust the aperture or shutter speed to get the subject's eyes more in focus. You just have to turn the focus ring to a different notch, so that the focus is correct. What does shutter speed have to do with it, cause it seems that for pictures, especially pictures where you need a really slow shutter speed, such as at night, that the focal length does not matter, and should determine the framing of the picture, rather than the focus itself so much. Unless I am wrong?

Thanks.

 

[jjparson]

I think the advice you are referring to is for hand holding shots. The theory is that people cannot hand hold it steady to get a clear image at slower speeds.


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[JerryLove]

That rule of thumb is intended for hand-held shooting, not tripod shooting.
Also: when using IS, the rule of thumb is different.

If you aren't understanding why you would have such a rule hand-held: It's because is you zoom out the speed of movement caused by shake is higher. Faster shutters stop faster movement.

 

[JerryLove]

I think the advice you are referring to is for hand holding shots. The theory is that people cannot hand hold it steady to get a clear image at slower speeds.

I think it's less "cannot" and more "usually won't".

 

[Gavjenks]

The INVERSE of the focal length.

I.e. 300mm should be shot 1/300th second or faster.
50mm should be shot 1/50th second or faster.

The longer the focal length, the more you are magnifying your hand shaking, and thus the faster you need to shoot to not see blur.
As another more concrete example of the same concept, take a tape measure and pull it out 6 inches and hold it in front of you. See how much the end shakes. Now pull it out 4 feet and hold it out unsupported, and see how much the end shakes.

And it is only intended to apply to handheld shots without image stabilization technology.

 

[Gavjenks]

You just have to turn the focus ring to a different notch, so that the focus is correct. What does shutter speed have to do with it

You need to do both. Obviously the ring needs to be turned so that the subject is in focus. But no matter how close the subject is to being in focus, if your camera is moving (due to hand shake) enough furing exposure, it will be blurry from hand motion.

And yes, at night, you are forced to use long shutter speeds... thus this rule of thumb CORRECTLY tells you that it is essentially impossible to shoot a 300mm handheld image of inky darkness. You need to, as you say, resort to a tripod, or not take the photo at all.

 

[jjparson]

I think the advice you are referring to is for hand holding shots. The theory is that people cannot hand hold it steady to get a clear image at slower speeds.

I think it's less "cannot" and more "usually won't".

Agreed!



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[Overread14 2]

As said above this assumes that you are:

1) Hand holding the lens and camera

2) Holding a good posture whilst shooting

It is only a rough rule of thumb to give people a minimum shutter speed whilst handholding to work with. Some people will be able to hold for much slower shutter speeds and others might need to use faster speeds. Fatigue will also vary the amount as will the use of natural supports in the environment (eg crouching down or leaning on a wall/fence).

IT also doesn't factor in the use of IS/OS/VR.


It's only a rough guideline and not to be taken a gospel truth.

 

[harmonica]

Oh okay, thanks. But it seems in the video that the out of focus eyes, is a result of the aperture, rather than the shutter speed being too slow, so why would he bring up that rule, if the fault was the aperture?

All of my long lens shots have been mostly on tripods, of far away views. Why did the guy in the video say to bring your ISO to 400 and then open up the aperture to 3.2 then? The aperture is at 2.8, and isn't that good enough? I have been able to get eyes in focus at f2.8, and for daylight shots, I just leave the ISO at 100, and I turn down the shutter speed.

Another thing is, I did a photoshoot under low lighting once, and I was able to hold the camera steady while shooting at 1/15 with a 50mm, and most of the photos turned out good, so I guess it's about how much practice you have had with your hands as well. But now that I know that rule of thumb, perhaps I best stick to it.

 

[Gavjenks]

"Isn't 2.8 good enough?"

It's not all about eyes. It often looks goofy to have somebody's eyes in focus, but not their ears, for instance. So instead, you may want to close the aperture down a bit to get their whole face in focus, and then up the ISO (or slow the shutter) to compensate for the lower light.

That said, I didn't watch the video (can't right now), but 2.8 vs. 3.2 is negligible and nothing to get worked up over in general. It' also doesn't explain a difference between 100 and 400 ISO. So I don't really know what the hell was going on in that situation. Just explaining why you might want a smaller aperture sometimes.

 

[Overread14 2]

The rule of thumb is only a guideline to give people a starting point to work from. You'll oft find with a shorter lens shooting closer that you can go much slower whilst similarly with a heavier longer lens you might need to use a faster shutter speed.

I've not watched it yet but my impression is that its aimed at beginners and aiming to give them a starting point. A rough catch-all guideline for where to begin. Beginners can use that to get favourable results and from there evolve their method to suit their style and specific conditions.

 

[bribrius]

I do it the other way around and the blurry ones I just call art.

 

[glun]

I think the advice you are referring to is for hand holding shots. The theory is that people cannot hand hold it steady to get a clear image at slower speeds.

I think it's less "cannot" and more "usually won't".

Agreed!



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I agreed as well it's referring to people hand holding the camera.

 

[vimwiz]

That rule assumes handheld, and without IS.

Its usually fairly accurate. I.e. when handholding my 75-300mm lens (no IS), and im zoomed in, I struggle to get a clear image below 1/300.

 

[480sparky38 37]

That rule assumes handheld, and without IS.

Its usually fairly accurate. I.e. when handholding my 75-300mm lens (no IS), and im zoomed in, I struggle to get a clear image below 1/300.

OTOH, there's people who can hand-hold non-IS 1,000mm lenses and shoot at 1/100.........

....while in a canoe.