I am sure this is a common question, but to find it easily, what is significant about 1/125 and 1/30? My teacher asked us and I have no idea. I can not find it anywhere. Why are these shutter speeds so important?

  • Voting to reopen on the the theory that the teacher may have had something specific in mind w.r.t these two given shutter speeds.
    – mattdm
    Nov 2, 2015 at 0:31

2 Answers 2


I understand that you mention those two specific speeds for some reason, and not as a general example.

My best guess on why your teacher is asking is:

Traditionally 1/125 was the maximum shutter speed to sync a flash, because higher velocities were achieved by starting to close the shutter before it has finished "opening", so a flash would only expose a fraction of the frame.

Now a common velocity for this is 1/180 - 1/250.

The 1/30 is probably considered the minimum velocity on which a photographer can hold a camera by hand and not take a shaky photo. This minimum speed depends on the photographer's skill, the focal length, the sensor size, and whether the camera or lens has a stabilizer integrated.

This 1/30 probably refers to a 50mm equivalent lens.


The amount of light hitting the light-sensitive material (film, digital sensor, collodion covered plate, etc) is measured in stops. Essentially, this is your exposure. One of the ways to control the amount of light reaching your light-sensitive material is with the speed of the shutter. Shutter speed is measured in seconds and fractions there of. The difference between your 1/125 (of a second) and 1/30 (of a second) is two full stops. With each stop you are doubling the amount of light, so with the shutter speeds you have given you will effectively quadruple the amount of light being let onto the material assuming you haven't changed your aperture (fstop), which is another way to change the amount of light coming in to the camera. Now, that being said, no shutter speed is any more or any less important than any other shutter speed. Some you will use more than others, but each one is important if it will give you the correct exposure for any particular shot.

  • 1
    "no shutter speed is any more or any less important than any other shutter speed." This isn't entirely true - the flash sync speed is pretty significant, and the fastest shutter speed your camera can manage can potentially be interesting (although the latter is almost always "faster than you ever really need").
    – Philip Kendall
    Mar 19, 2015 at 19:59
  • @Philip - that was my thinking too. The original question is "what is significant about 1/125 and 1/30?", not "how do these speeds relate to each other?". 1/30 was a fairly common sync speed for m-sync flashbulbs, whereas 1/125 was a fairly common x-sync speed for electronic flash units. Teach might be looking for a completely different answer but I'm not convinced it's purely about 1/125 being four times faster than 1/30 (or similar)...
    – Darkhausen
    Mar 19, 2015 at 23:03

Not the answer you're looking for? Browse other questions tagged or ask your own question.