A guide in finding the slowest usable shutter speed

A short guide on how to find the minimum shutter speed for any focal length

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1) Minimum Shutter Speeds to use for a set focal length.

  • The old question: “What is the lowest (longest) shutter speed I can use with my lens, and not get camera shake causing an out of focus image?
    • The old and still valid answer is: “Use the shutter speed that is the reciprocal of the “Focal Length”
    • If the focal length is 50mm, then, the minimum shutter speed would 1/50s (1/60s). (not the corrected focal length for the sensor size)
    • For the focal length of 250mm, then, the minimum shutter speed would be 1/250s.
  • Adapting this guide to modern DSLRs with sensors that are smaller than full frame sensors.
    • Here is where there is a small division among photographers.
      • 1) Some say to “Stick to the old guide” because the lens’s focal length has not changed. And that group is  right so far.  They say that a 100mm lens is still a 100mm lens,  regardless of the sensor size of the camera. And that fact is correct too. So you would use 1/100sminimum shutter speed that will cancel camera shake and get a sharp image.  And this about it as far as how to pick a usable lower speed. But, in #2 next, adds a bit more to the old equation that worked when “ONLY” full frame was the standard. This is one train of thought
        • In Sum: If I had a 100mm lens on a 1.5, 1.6x or 2x crop camera, I would use a 1/100s shutter speed for all the camera types.
      • 2) Others say to “Adjust the shutter speed for the adjusted focal length from the crop ratio of the sensor“. For example 1:5, or 1:6, or 2:1 (4/3rds). That would translate to using different shutter speeds for the same focal length on different sensor sizes.
      • On a 1:5 sensor:  Pentax, Nikon, Sony/Minolta. With a 100mm lens, the Field of  View (FOV) is like a 150mm lens on a full frame sensor. So, the corrected shutter speed would be 1/150s, not 1/100s. This is because that the sensor is reading a smaller area of the full frame. So, it acts like a 150mm lens on your camera. that’s why many would say to use the shutter speed that corresponds to the cropped field of view. The thing is, it is still a 100mm lens on the crop sensor camera.  And the camera is not really magnifying the image. It is only cropping the image of the 100mm lens. Now, the other issue is that it “is” acting like a 150mm lens, so, camera movement is magnified. Many photographers say to use the shutter speed for the corrected FOV of the original focal length, because the camera movement is like a 150mm lens, so you would use a 1/150s.
        • In Sum: If I had  100mm lens on a 1.5x crop, I would use 1/150s shutter speed. On a 1.6x crop camera, I would use 1/160s shutter speed, if I used a 2x crop camera, I would use 1/200s shutter speed.
      • I opt for the later #2 explanation as more sensible usage in todays DSLR cameras.
  • What about the new crop of camera’s and lenses that have an in camera “Shake Reduction“, or an in lens “Image Stabilization” and “Vibration Reduction“. How does this affect the lowest usable shutter speed with any lens?
    • This adds yet another variable to the “old guide” to incorporate in the equation.
      • The old timers photographer dream came true with the invention of Image Stabilization built in the body or lens. What this new technology does, is either correct the camera movement by shifting the sensor to compensate for the camera shake (In-Body control). Or, In the lens is a group of elements that shift to compensate for camera movement.
      • So, now you don’t need to follow the “old guide” anymore. But, something to think about now, you can probably safely use up to 3 f/stops slower shutter speed with most lenses. This has opened up a whole world of available light photography to many of us. And for the Wildlife photographers, it has opened up the possibility of not using a tripod with long telephoto lenses.
      • How much is enough? I have linked two website tests. One is for “In-Body” Stabilization, the other is “In-Lens” Stabilization.  Link: “IN BODY”.   “IN-LENS/KIT“.  “IN-LENS/MULTI-PURPOSE”.  Links to the Digital Camera Review web reviews.  dpreviewPlease scroll down each page to the graphs. The lens graphs have an area to hover over to see the on/off differences at the bottom.
        • Please note that as the focal length gets longer, the available slower f/stops diminishes. This is pretty much across the board. your wide-angle zooms benefit about 2/stops with a 90% sharpness ratio. so the “old guide” still holds somewhat true. The best sharpness is still obtained at the shutter speed in number, equal to the focal length. (100mm = 1/100s). But, with a proper stance you should be able to use a shutter speed of 1/2 the focal. (100mm = 1/100s for the normal rule, 100mm = 1/50s using some kind of image stabilization). With shorter focal lengths, in the 10mm to 25mm range, you may get up to 3-f/stops, but, once you start getting in the normal range and above, maybe 1-or 1.1/2-f/stops slower is all you get for the sharpest results. BUT, how well you can brace yourself plays an important part too. Somethings never change with technology. Proper body stance and camera/lens bracing is still an important ingredient for sharp images.