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  • Focal Length versus Shutter Speed

    There is a general rule of thumb about minimum shutter speed versus lens focal length, which goes something like this:

    Min Shutter Speed (secs) = 1/Focal Length (mm).

    So for a 50mm lens it is 1/50 sec.

    My question is, does the focal length for this "rule of thumb" relate to the specified, digital, focal length, or the equivalent film focal length? For example, I have a 70mm telephoto which has a 105mm equivalent film focal length - what would be the minimum, recommended shutter speed for this: 1/70 or 1/105?

    Second question (part of the first): does this limitation relate to the physical, constructed size of the lens? In other words, if my 70mm telephoto lens is a pancake design (physically only ~ 30mm long), can I rely on a slower shutter speed than a non-pancake telephoto design that is say, 100mm long (constructed length).

    Is the limitation therefore related to camera shake (the magnitude of the angle of rotation during shaking) multiplied by the distance from the sensor to the point of entry of light into the end of the lens.

    I hope I have described this question clearly; it seems a bit convoluted I know. Hopefully someone gets what I'm on about.
    Rhoufi -- Melbourne, Aust
    Pentax K-7; smc-DA, 18-55mm, f3.5-5.6, AL, WR zoom; smc-DA, 70mm, f2.4, LTD prime telephoto.
    Flickr:http://www.flickr.com/photos/47069987@N07/

  • #2
    You're asking for a lot of precision from a rule of thumb.

    It's mostly a matter of personal ability to handhold. Some folks throw in the crop factor, some don't. One DPS member multiplies by 3. Remember, too, that the rule of thumb also assumes you know how to hold your camera correctly.

    Personally, I don't use the crop factor with my dSLR, but I do with my P&S. My personal lower-bound for shutter speed without stabilization is around 1/30s.

    And part of the reason that camera shake registers more with longer lenses is the magnification. This is also why you need faster shutter speeds for macro work. So, my guess would be that the physical size of the lens doesn't actually matter as much as the focal length.

    Honestly, though, the only way to really know is to try it and see. It's a guideline, not a hard and fast rule.
    I shoot with a Canon 5DmkII, 50D, and S90, and Pansonic GX-7. flickr stream and equipment list

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    • #3
      Focal Length versus Shutter Speed

      Originally posted by inkista View Post
      You're asking for a lot of precision from a rule of thumb.

      It's mostly a matter of personal ability to handhold.

      Personally, I don't use the crop factor with my dSLR, but I do with my P&S. My personal lower-bound for shutter speed without stabilization is around 1/30s.

      And part of the reason that camera shake registers more with longer lenses is the magnification.

      So, my guess would be that the physical size of the lens doesn't actually matter as much as the focal length.
      Thanks, inkista.
      I know what you mean, a rule of thumb is only just that. All my experience has been with film camera with a 50mm lens and I have come to know that 1/60 was about as slow as I could go. I was using reference to the "thumb rule" to frame my real question: what are the real variables that affect the ability to hold it steady and what features of the lens make that more difficult?

      I took an image the other day that normally I should not have been able to take properly - indoor, no flash, focal length 70mm (prime lens), f2.4 and shutter speed 1/15. It was the first day I really got to use my new (and first) dSLR. Now I cannot normally hold any camera steady enough for such a slow shutter speed (nowhere near it), but the stationary subject at the focus point was sharp. This got me thinking about what really matters (hidden factors in any "thumb rule"). Hence my post - I want to know more exactly what factors really affect this area of possible error.

      You have contributed to the picture getting clearer. Thanks.

      BTW: using the term "crop factor" makes me think you work in irrigation - could that be a shrewd guess?
      Rhoufi -- Melbourne, Aust
      Pentax K-7; smc-DA, 18-55mm, f3.5-5.6, AL, WR zoom; smc-DA, 70mm, f2.4, LTD prime telephoto.
      Flickr:http://www.flickr.com/photos/47069987@N07/

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      • #4
        Crop factor is just the term thats been coined by the industry to explain the difference between full-frame and APS-C sensor sizes.

        I shot my grandfather's 80th birthday with a 50mm f/1.8. Shooting at f/2 i managed to handhold for 1/20 and 1/15 at times. It takes practice, but it *can* be done.
        I am responsible for what I say; not what you understand.
        adammontpetit.com
        Gear List
        500PX | Graphic Design

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        • #5
          Originally posted by Rhoufi View Post
          ... what are the real variables that affect the ability to hold it steady and what features of the lens make that more difficult?
          Ah. Yeah, it's kind of a mystery and a black art that gets condensed down to that rule of thumb. Mostly, I'd say it's physical length and weight, too, make it harder to hold a lens steady. But that more than that, the knowledge/experience the shooter has at stabilizing themselves can create a wide variance. Standing/sitting/lying down makes a difference. Leaning against something, supporting or stabilizing your elbows on something makes a difference, etc. Different holds on the camera can make a difference.

          Obviously, the biggest factor in helping you out with a lens is going to be built-in stabilization (IS/VR/etc.)

          I took an image the other day that normally I should not have been able to take properly - indoor, no flash, focal length 70mm (prime lens), f2.4 and shutter speed 1/15. It was the first day I really got to use my new (and first) dSLR. Now I cannot normally hold any camera steady enough for such a slow shutter speed (nowhere near it), but the stationary subject at the focus point was sharp.
          Sounds like your technique is better than you've been assuming.

          BTW: using the term "crop factor" makes me think you work in irrigation - could that be a shrewd guess?
          No. I'm a city girl. I earn my wage as a technical writer, so I'm very picky about terminology. The effect that a smaller sensor has on the field of view of a given focal length, to me, has more to do with cropping off the edges of an image than changing the focal length of the lens, so I use "crop factor" instead of "equivalent focal length" or "focal length multiplier." A 50mm lens is still a 50mm lens, regardless of whether it's mounted on a full-frame or a crop body.
          I shoot with a Canon 5DmkII, 50D, and S90, and Pansonic GX-7. flickr stream and equipment list

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          • #6
            Focal Length versus Shutter Speed

            Originally posted by OsmosisStudios View Post
            Crop factor is just the term thats been coined by the industry to explain the difference between full-frame and APS-C sensor sizes.

            I shot my grandfather's 80th birthday with a 50mm f/1.8. Shooting at f/2 i managed to handhold for 1/20 and 1/15 at times. It takes practice, but it *can* be done.
            Yes, my camera has an APS-C Sensor (23.4x15.6) and in-built stabilization, and I suppose I might have fluked it, but I am still curious about the physical length of the lens (and weight) versus the focal length being the primary controlling factor. I'll just have to practise more and observe the differences between longer zooms and pancake telephotos.

            Thanks for your help.

            Originally posted by inkista View Post
            Mostly, I'd say it's physical length and weight, too, make it harder to hold a lens steady.

            Obviously, the biggest factor in helping you out with a lens is going to be built-in stabilization (IS/VR/etc.)

            Sounds like your technique is better than you've been assuming.
            I didn't have time to brace myself for the shot, and this was what struck me. The built in stabilization works on steadying the sensor against the rotation of the camera. Also the shorter and lighter the lens, the less likelihood of rotation. So the shortness of the 70mm pancake lens makes the whole package short, light and easier to hold. This is where my thinking is going. But I will test this theory out with the 18-55mm zoom and compare.

            No. I'm a city girl. I use "crop factor" instead of "equivalent focal length" or "focal length multiplier."
            Well, isn't the argot of a particular passion interesting? You both have different definitions. In irrigation "crop factor" is the multiplier given to a particular 'crop' (maize, lucerne, rye grass) to apply to the Class A Pan evaporation loss for the day, to establish how much water to apply to a field. So there you go - too much knowledge can mislead you!

            Regards to you both for the discussion. Every day is a school day.
            Rhoufi -- Melbourne, Aust
            Pentax K-7; smc-DA, 18-55mm, f3.5-5.6, AL, WR zoom; smc-DA, 70mm, f2.4, LTD prime telephoto.
            Flickr:http://www.flickr.com/photos/47069987@N07/

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            • #7
              Originally posted by Rhoufi View Post
              Well, isn't the argot of a particular passion interesting? You both have different definitions. In irrigation "crop factor" is the multiplier given to a particular 'crop' (maize, lucerne, rye grass) to apply to the Class A Pan evaporation loss for the day, to establish how much water to apply to a field. So there you go - too much knowledge can mislead you!...
              That's totally cool! I like knowing that different plants are differently thirsty/abled at holding onto their water. Plus y'know, I never knew alfalfa was also called lucerne.
              I shoot with a Canon 5DmkII, 50D, and S90, and Pansonic GX-7. flickr stream and equipment list

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              • #8
                Originally posted by Rhoufi View Post
                Yes, my camera has an APS-C Sensor (23.4x15.6) and in-built stabilization, and I suppose I might have fluked it, but I am still curious about the physical length of the lens (and weight) versus the focal length being the primary controlling factor. I'll just have to practise more and observe the differences between longer zooms and pancake telephotos.
                Physical length and weight have very little to do with focal length. "Focal length" refers to the distance from the front of the lens to the nodal point of the lens (where the light beams converge and flip). 24, 35 and 50mm lenses are all about the same actual size, but the focal length varies.

                longer zooms / pancake telephotos is an interesting juxtaposition of terms. "Longer" usually refers to focal length, and a zoom referring to a vari-focal lens. That's fine. A pancake telephoto however is a complete oxymoron: pancake lenses are usually less than an inch long and are, for the most part, in the 45mm range simply as a factor of their design. Telephoto just indicates a focal length above "normal", so greater than 70mm.

                Focal length doesnt actually change with crop factor. Think of it like matting a print in a big frame. If you have a 16x20 frame and an 11x14 print, for instance, the 11x14 print represents your sensor whereas the 16x20 frame represents the image circle that's projected by the lens. If you had a 16x20 print and simply added a 16x20->11x14 matte to it, you'd only see the centre section. Your camera does the same thing: you only get the centre part of an image (the camera "crops" the rest). It just so happens that this factor is 1.5 (Nikon, sony, pentax), 1.6 (Canon) or 2 (olympus) of what the original size.

                The "equivalent" focal length just indicates the difference in what is apparent to the sensor. The better term would be "apparent focal length", as it appears youre using a longer lens, but arent.
                I am responsible for what I say; not what you understand.
                adammontpetit.com
                Gear List
                500PX | Graphic Design

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                • #9
                  Originally posted by OsmosisStudios View Post
                  Physical length and weight have very little to do with focal length. "Focal length" refers to the distance from the front of the lens to the nodal point of the lens (where the light beams converge and flip). 24, 35 and 50mm lenses are all about the same actual size, but the focal length varies.
                  I think the OP was not relating them to eachother, but trying to see if the size and weight of the lens has more effect on camera shake than the focal length.

                  If I have a P&S camera that weighs 1lbs with a 300mm zoom that fits in the palm of my hand and I have a dSLR that weighs 9lbs with a 300mm zoom that's a foot long, would the average person be able to hold the P&S camera with less camera shake than the dSLR due to its size and weight?

                  If I can hold the P&S with less camera shake, then I could "break the rule of thumb" and go to 1/100s and get a picture that is equally as "still" (not shaken) as if I took the shot with the dSLR at 1/300s.

                  The correct answer to all of this is to buy a freakin' tripod!

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                  • #10
                    Originally posted by Naois View Post
                    ...If I have a P&S camera that weighs 1lbs with a 300mm zoom...
                    Actually, if you look closely at what's printed on the lens, it's probably really only a 50mm zoom. The crop factor on a P&S with a 1/2.3" sensor is 6x. So, yeah, theoretically, the average person would be able to hold it with less shake, because it's a shorter lens.
                    Last edited by inkista; 02-12-2010, 10:03 PM.
                    I shoot with a Canon 5DmkII, 50D, and S90, and Pansonic GX-7. flickr stream and equipment list

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                    • #11
                      Originally posted by inkista View Post
                      Actually, if you look closely at what's printed on the lens, it's probably really only a 50mm zoom.
                      Isn't the end result the same?

                      What if they were both 50mm lenses? Would the extra weight and size of the DSLR make it harder to hold steady than the little camera?

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                      • #12
                        Originally posted by Bob529 View Post
                        Isn't the end result the same?
                        No. Depth of field and "compression" are vastly different between a 50mm lens and a 300mm lens. This is one of the main reasons that blurring the background with a P&S camera is incredibly difficult. The small sensor size requires tiny focal lengths, which have very deep DoF.

                        What if they were both 50mm lenses? Would the extra weight and size of the DSLR make it harder to hold steady than the little camera?
                        Yes. Actually, it would. You wouldn't believe the number of people I see who can't hold their dSLRs properly, and a constant complaint among newbie dSLR shooters is lack of sharpness and the awkwardness of the camera grip because they haven't got a clue how to support the additional weight on the palm of their left hand.

                        The problem with P&S cameras is that handholding technique is equally horrific. The LCD prompts people to hold the camera at arm's length, rather than pressed against the face, which can help stabilize the camera overall.
                        I shoot with a Canon 5DmkII, 50D, and S90, and Pansonic GX-7. flickr stream and equipment list

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                        • #13
                          Originally posted by Naois View Post
                          I think the OP was not relating them to each other, but trying to see if the size and weight of the lens has more effect on camera shake than the focal length.

                          If I can hold the P&S with less camera shake, then I could "break the rule of thumb" and go to 1/100s and get a picture that is equally as "still" (not shaken) as if I took the shot with the dSLR at 1/300s.

                          The correct answer to all of this is to buy a freakin' tripod!
                          Well yes, but….. I’ll try to clear this up. Naois is correct: “trying to see if the size and weight of the lens has more effect on camera shake than the focal length”, is what I’m on about. The reason is, I like Street Photography and therefore I do not want to carry a tripod (I have one but no way will I take into the street) and I do not want a huge barrel of a lens poking out from my stomach. You need to be quick on your feet, discrete, and have a camera that feels like it’s a part of you.

                          So after many, many years shooting with an Olympus OM1 (yes, an OM1, still works) fitted with a 50mm prime and a Rollei 35B (don’t laugh – some of the best images I captured were with this nano, 35mm film rangefinder), I finally bought the smallest most compact DSLR I could – Pentax K-7 fitted with a DA, 70mm, f2.4, LTD prime telephoto (105mm apparent focal length). Although this pancake lens may be a oxymoron, it works OK, and so far I am having a great deal of fun with it. The whole package is compact, discrete and a joy to hold, and it gets me closer to my subjects than my old 50mm prime, and yet it is only physically 26mm long (Pentax DA 70mm | Pentax.com.au). Now what I seem to be finding is that I can hold this combination steady at much slower shutter speeds than my old OM1 with the 50mm lens or the 18-55mm (75mm long) kit zoom that came with the Pentax.

                          So I started to think that I did not understand what were the real controlling factors over blur caused by camera shake. Is it all about the size, weight, cantilever effect of a physically long lens OR is it about focal length. Even small angles of rotation at the hand end, cause huge displacements at the end of a long telephoto lens. Now the 70mm, f2.4, LTD prime telephoto is a very weird lens , granted, because it has a focal length of 70mm/105mm but is really short and light. And, due to my observations so far (and because I have been using a dSLR for only 6 weeks) I posted my question. I want to understand this stuff, so I can understand and my limitations in the field.

                          I have been delighted with all the generous advice so far. But I’m not sure I have a conclusive answer yet.

                          Originally posted by inkista View Post
                          No. Depth of field and "compression" are vastly different between a 50mm lens and a 300mm lens. This is one of the main reasons that blurring the background with a P&S camera is incredibly difficult. The small sensor size requires tiny focal lengths, which have very deep DoF.

                          Yes. Actually, it would. You wouldn't believe the number of people I see who can't hold their dSLRs properly, and a constant complaint among newbie dSLR shooters is lack of sharpness and the awkwardness of the camera grip because they haven't got a clue how to support the additional weight on the palm of their left hand.

                          The problem with P&S cameras is that handholding technique is equally horrific. The LCD prompts people to hold the camera at arm's length, rather than pressed against the face, which can help stabilize the camera overall.
                          Inkista, I think you are on the money, and I don’t think the “effective focal length” (thanks OsmosisStudios for the term) has as much to do with it as I originally thought. It’s just that most big telephoto, or long zoom, lenses are actually very long physically, very heavy, move around a lot due to camera rotation and are therefore too hard to hold steady at slow shutter speeds.

                          I hope I am not driving you all nuts with this. I don’t want to wear you all out. And now I hope I have explained it as clearly as I can.
                          Rhoufi -- Melbourne, Aust
                          Pentax K-7; smc-DA, 18-55mm, f3.5-5.6, AL, WR zoom; smc-DA, 70mm, f2.4, LTD prime telephoto.
                          Flickr:http://www.flickr.com/photos/47069987@N07/

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                          • #14
                            Here's what I think. For a fixed rate of rotation, the amount of motion blur due to camera rotation depends only on the magnification level of the lens.

                            Beyond that, the physical properties of the camera and lens could have an effect on how well you are able to hold it steady, thus changing the rate of rotation. But the crop-factor-adjusted focal length is the only one that inherently affects the amount of blur.

                            So the question is really just how much different lenses affect one's ability to hold the camera steady. Now, I can count on one hand the times I have held a DSLR, but here's my take on it:

                            A heavier, longer-built lens should actually make it easier to hold the camera steady because it increases the moment of inertia of the camera. The moment of inertia is a quantity describing the tendency for an object to resist changes in rotational motion. When you have more mass out farther from the rotation axis, you get a higher moment of inertia. It makes sense too - it's much easier to rotate a p&s with all of its weight in the body of the camera than it is to rotate a heavy camera with a big lens on it.

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                            • #15
                              Focal Length versus Shutter Speed - Inertia

                              Originally posted by Suleyman View Post
                              For a fixed rate of rotation, the amount of motion blur due to camera rotation depends only on the magnification level of the lens.

                              A heavier, longer-built lens should actually make it easier to hold the camera steady because it increases the moment of inertia of the camera. The moment of inertia is a quantity describing the tendency for an object to resist changes in rotational motion. When you have more mass out farther from the rotation axis, you get a higher moment of inertia. It makes sense too - it's much easier to rotate a p&s with all of its weight in the body of the camera than it is to rotate a heavy camera with a big lens on it.
                              Interesting take. The trouble is, inertia is a stabilizing effect only if you are starting from dead still in the first place. If the camera is moving slightly during set up, then the extra inertia of a heavy camera/lens package makes it harder to stop the movement, stabilize and bring it to rest for the shot. I've held both - heavy cameras with long lenses and light cameras with short compact lenses - and it is much easier to stabilize the lighter more compact unit. The closer everything is to your body the easier it is to hold steady. The further out you need to extend your arm for the barrel, the harder it becomes (why live view shooting is hopeless).

                              It's another angle, but I think your first point holds most of the essence:
                              motion blur due to camera rotation depends only on the magnification level of the lens.
                              Rhoufi -- Melbourne, Aust
                              Pentax K-7; smc-DA, 18-55mm, f3.5-5.6, AL, WR zoom; smc-DA, 70mm, f2.4, LTD prime telephoto.
                              Flickr:http://www.flickr.com/photos/47069987@N07/

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