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Focal Length and Shutter Speed
I recently posted a photo in the Nikon Dxx forum. One of four leaves was out of focus due to the effect of wind on the one leaf. I was given a kind explanation as follows:.

"Looks a bit blurry to me. This may be why:.

D80, 18-135mm @ 98mm ~ 1/40 ~ f/5.3 ~ ISO: 200.

You might want to up your ISO rather than use a lower shutter speed. I believe the "golden rule" is 1/fl (or maybe 1/efl). [fl=focal length; efl=effective focal length (fl*1.5)]".

The above explanation is quite obviously understood to most, except to me, a beginner. Can anyone explain the 'rule of thumb' that someone as dumb as I can understand it? Thanks..

Rick.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

'You can please some of the people all of the time and all of the people some of the time, but you cant please all of the people all of the time.'..

Comments (7)

It basically means you need to have your shutter speed = your focal length also know as zoom. So if your are shooting at 200mm you need at least the very least 1/200 of a second shutter speed to help stop motion and help you with camera shake/lens shake. 1.5 times is better 1/300th of a second for a zoom of 200mm (I rounded numbers for easy understanding).

You took a photo at 98mm at 1/40th of a second which is too slow to stop movement a shutter speed of 1/125 would of helped stop the motion though you can not always use faster shutter speeds in dark places so you have to turn the ISO up. You will need at least a speed of 1/60th to freeze slight movements, like a person sitting still this will work, but if you are photographing sports in low light you will need a much higher shutter speed and a higher ISO.

Try an ISO of 400 or 800 on your next attempt in the same lighting conditions..

Sparky_caI have a photographic memory, but I always seem to have the lens cap on. Current Camera Canon 30D..

Comment #1

The rule of thumb is, for example, a 200mm focal length you should not use a slower shutter speed than 1/200th of a second without a tripod, for a 50 mm lens, 1/50th of a second, etc. The rule is about eliminating blur due to camera shake. Some people are rock solid at much slower shutter speeds and some shake at any speed. Image stabilizer lenses or cameras usually improve this by 3-4 stops. It depends on how much coffee you drink and how you hold your camera. Elbows in tight and propping up the lens with one hand is usually best..

There is also blur due to subject movement which can only be solved by faster shutter speeds and blur due to depth of field which is improved by a smaller aperture...

Comment #2

It isn't as complicated as it might first appear! They were simply saying that the leaf was blurred because it moved during the exposure. 1/40 second is relatively slow; a lot of things can move significantly during that period of time. If they move they will be blurred, which can look similar to (but is not the same as) being out of focus..

The advice was to increase the ISO speed setting on the camera. The ISO setting is effectively the sensitivity of the sensor; if you increase the sensitivity you shorten the period of time that the sutter needs to be open to achieve a proper exposure. Every time you double the ISO you cut the needed shutter speed in half (assuming you don't change the f stop.) So if you were to set the ISO to 400, the shutter speed would be 1/80 sec; ISO 800 would give you a shutter speed of 1/160, etc. Those shorter shutter speeds would have a better chance of minimizing the movement of the leaf during the shorter time period, and thus minimizing the motion blur..

You could also reduce the time the shutter is open by increasing the aperture (using a larger f stop, which would be a smaller "f number".) In this case increasing the aperature by one "stop" (to approximately f3.5) would give the the same reduction in shutter speed from 1/40 to 1/80. They propbably didn't recommend that because your aperture is already fairly wide. But you could also do both: increase the aperture to f3.5 (or closest equivalent on your camera) AND increase ISO to 400. That would gain you 2 stops you could shoot at 1/160 sec..

Note that there are other effects on the image and other considerations in changing the aperture and the ISO sensitivity, but I hope that this serves to answer your basic question..

Davehttp://www.pbase.com/dsjtecserv..

Comment #3

Thank you for an easy to understand explanation regarding my question. I appreciate your time in answering.Rick.

Sparky_ca wrote:.

It basically means you need to have your shutter speed = your focallength also know as zoom. So if your are shooting at 200mm you needat least the very least 1/200 of a second shutter speed to help stopmotion and help you with camera shake/lens shake. 1.5 times is better1/300th of a second for a zoom of 200mm (I rounded numbers for easyunderstanding).

You took a photo at 98mm at 1/40th of a second which is too slow tostop movement a shutter speed of 1/125 would of helped stop themotion though you can not always use faster shutter speeds in darkplaces so you have to turn the ISO up. You will need at least a speedof 1/60th to freeze slight movements, like a person sitting stillthis will work, but if you are photographing sports in low light youwill need a much higher shutter speed and a higher ISO.

Try an ISO of 400 or 800 on your next attempt in the same lightingconditions..

Sparky_caI have a photographic memory, but I always seem to have the lens cap on. Current Camera Canon 30D.

Rick.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

'You can please some of the people all of the time and all of the people some of the time, but you cant please all of the people all of the time.'..

Comment #4

Hi,.

Just a couple of points; IS ain't as wonderfull as some say and can screw up especially if you think it will cure everything. I have it on a camera and it works best if you forget it's there and work as though it isn't. And a tripod and cable release are even better (and no batteries required)..

Better is to use the old technique which involves holding the camera with both hands and squeezing the shutter gently. You also need to watch how you are breathing as in:- breath in, pause, squeeze shutter, pause and then breath out. Some people, I have noticed, swap around the "in" and "out" in that explanation and it works for them..

Regards, David..

Comment #5

One must use the EFFECTIVE focal length not the actual focal length of a lens. *.

If you use a 200mm lens on a 1.6x crop body your shutter speed should not be below 1.6 x 200, in other words a 1/320 of a second. This is a rule for hand-held photography. If you take a picture of a moving object you will need even a higher shutter-speed..

(* Yes, this does matter. If it did not I could get away with 1/72 of a second shutter speed at full zoom on my wife's S2-IS as the lens real focal length is 72. The effective focal length is of course 432mm and the minimum shutter speed 1/432th)..

Comment #6

That is all very well, but how many of use (beginners) actually note down the focal length of the picture. Unless i'm mistaken, that is not displayed on the lCD and the only way is to check on the zoom marking..

And if you have to apply the crop factor, I'll have to use a small calculator al the time...

Comment #7

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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