Understanding Exposure, Part 3: Shutter Speed


Shutter speed is a measurement of time that a camera's shutter is open—allowing light, usually after it has passed through a lens and through the aperture diaphragm, to strike a photosensitive surface, like film or a digital sensor.

This article is part of a multi-part series of about photographic Exposure.
1. Introduction: The Exposure Triangle
2. Aperture
3. Shutter Speed
4. ISO

Unlike the nuances of aperture and its relation to light and optics, shutter speed is much more of a straightforward affair. Because of this, permit me to take you off on a bit of a tangent so that we can talk about how camera shutters work.

Photographs © Todd Vorenkamp

Shutter speed values comparison

The challenge of the mechanics of the shutter is in designing a device that exposes the entire sensor or film plane to an equal number of photons so that exposure is consistent through the image. Many people think that the shutter works like a miniature garage door. If you can visualize a garage door opening and then closing in front of a photosensitive surface, you can see that the problem with that design is that the bottom of the image will be exposed to more photons of light as it is the first portion of the image to see light as the door begins to open and it is also the last part to be blocked by the door as the door closes. Therefore, a photo taken with a shutter that functions like a door will have an unbalanced exposure.

There have been several different designs of camera shutters over the years. The very first cameras had lens-cap-type shutters where the lens was exposed to light by removing the cap and then, after a calculated amount of time, the cover was placed back over the lens. Exposures back then took several minutes, and even hours, so the relatively slow opening and closing of the "shutter" was not problematic.

At the inexpensive end of the spectrum, the simple leaf shutter appears on many disposable and point-and-shoot cameras of yesterday. This is a mechanized version of the old lens cap "shutter" where a leaf, or two leaves, are mechanically pulled aside to let light through an opening. They generally only operate at one speed.

The leaf shutter, also known as a diaphragm shutter, functions very much like the aperture diaphragm of the lens in that a group of metal blades is mechanically opened and closed in rapid fashion. Unlike the blades of the aperture diaphragm that just constrict to a small opening, these blades close all the way until there is no light coming through the shutter. The shutters are designed to open and close extremely fast so that the center of the image does not see an appreciably greater amount of light than the edges. Because of their design, leaf shutters work very well when synchronized with flash strobes, but cannot operate at speeds as fast as the shutter type that we will discuss next.

Almost all modern SLR and DSLR cameras employ the focal-plane shutter. The focal-plane shutter works more like a garage door, but with a second door, called a curtain, that follows behind the first curtain to close the image sensor or film off from light after the first curtain opens. This two-curtain design allows a balance of light across the sensor or film so that exposure is even. This design allows for extremely fast operation, up to 1/8000 of a second, on today's SLR and DSLR cameras. However, focal-plane shutters, due to their complexity and exotic construction, are relatively expensive.

How a focal plane shutter works

Like most things, the shutter has gone digital. Many modern digital cameras operate an electronic shutter that simply powers the digital sensor on for a selected amount of time. Because there is no mechanical function, electronic shutter speeds can be extremely fast. A global shutter turns the entire sensor on and off at once, while a rolling shutter activates one row of pixels at a time across its width.

Both the focal-plane shutter and rolling electronic shutter, because of their design and function, can cause interesting distortion through an image when there is fast motion across the picture plane.

OK, back to shutter speeds. As I wrote earlier, shutter speed is simply a measure of time that the shutter is open, or, in the case of the electronic shutter, the sensor is powered. The longer the shutter is open, the more light comes through. No inverse square law here (thank goodness!); if you double the amount of time that the shutter is open, you will double the amount of light coming in. Shutter speed is simple, right?

How does this relate to exposure and the exposure values (EVs) that we discussed in the first lesson? Because of the linear nature of the relationship of photons entering the camera to shutter speed, we can use shutter speed to easily and precisely change the amount of light hitting our photosensitive surface. By slowing the shutter speed, from 1/30th of a second to 1/15th of a second, for instance, we will double the amount of light passing through the shutter. This doubling of light is identical to the doubling of light accomplished by opening aperture, albeit by a different mechanical function, and represents a +1 EV shift. Changing the shutter speed from 1/2000th of a second to 1/4000th of a second then halves the amount of light coming through the shutter and represents a -1 EV shift.

Shutter speed in 1-stop increments

Shutter speeds are listed as whole seconds or as fractions of a second. The maximum shutter speed for most SLR cameras is 30 seconds. If you want to take a photo longer than 30 seconds, you can use the bulb (B) or time (T) functions of the camera, if it is equipped with a specially built shutter release that includes a timer. The bulb function opens the shutter as long as the shutter release is depressed. The time function opens at the first press and closes the shutter at the second press of the shutter release.

Just like with aperture and ISO, there are some "side effects" of shutter speed.

Slow shutter speeds allow movement to be imaged across the photograph. This is not just movement of the subject or subjects, but also of the camera too. It is nearly impossible to hold a camera perfectly steady for any length of time, especially for a few seconds. Therefore, an image taken with a handheld camera that covers any length of time will have blur from camera shake. Definitely keep this in mind when shooting with slow(er) shutter speeds. The other motion the camera sees is movement in the frame. A slow shutter speed will allow moving cars, runners, animals, etc., to change position inside the duration of the image. This movement will show on the photograph as motion blur and can be a really great creative element in a photograph. Another creative technique for slow shutter speeds is intentional panning of the camera, or even random camera movements, while the shutter is open.

Low-light and nighttime photography dictate a slow shutter speed to allow enough photons to reach the sensor or film. The camera is usually stabilized by a tripod, and shutter speeds of great lengths can capture images in very dark places or even trace the stars streaking across the night sky as the Earth rotates.

Fast shutter speeds are used in the opposite fashion—to freeze action versus letting it blur across a photograph. Speeding cars, diving swimmers, racing animals, mischievous kids, and more can all be frozen in time with a fast shutter speed.

Ready for more math? The two biggest factors in how movement is "seen" by the camera are: speed and distance.

If you stand on a sidewalk and stare straight ahead and a car goes past you at 40 miles per hour, a few feet in front of you, it will go through your field of view in a very short amount of time—probably a fraction of a second. If you look out to the horizon and another car going 40 miles per hour is passing you, 4 miles into the distance, you will see that car, going the same speed as the one before it, for a much longer amount of time.

Shutter speeds for moving objects

The camera's limited field of view works the same way if the subject is moving or if the camera is moving. If you have ever taken a photo of a distant object from a speeding vehicle, you have seen the same type of effect in your image; the distant snow-capped mountain is clear and sharp, but the fences and fields and Armco next to the road are blurry from the motion. So, applying mathematics once again, we can crunch numbers to help us get the shutter speed effects we want in our images. When you double the distance from the camera to the moving subject, you will half its speed through the frame. Therefore, to get the same blur, you can use half the shutter speed. Conversely, if your moving subject is the same distance away each time you photograph it, but you double the speed of the subject, you will have to halve the speed of your shutter to get the same amount of blur.

Our discussion on shutter speed rounds out the physical camera adjustments that control the amount of light that gets to the sensor or film. In the final segment, Understanding ISO, we will discuss ISO and then bring all three adjustments together to show how they work interchangeably to control exposure.


fantastic explanation about aperture n shutter.Thanks a lot.

wow, your explanation here is fantastic. I havent been able to get my head aroun aperture, and no matter what i read the penny just didnt drop until i read this. Thanks so much for explaining it so well. Will now be following you. Have a great day.

Hey Toni,

I hope you meant "shutter speed" instead of "aperture" as this article is on shutter speed! :)

Thanks for the kind words and thanks for reading Explora!

You hear people talk about long exposures (night skylines, etc.) introducing noise. Can you explain? Thanks!

Hey Jason,

Great question! 

Heat causes digital noise and heat can get to your sensor in two basic ways.

1) Ambient heat. Taking photos on a hot day will show more sensor noise then the same photo on a colder day with the same exposure. When I was working on container ships, I was off the coast of Singapore and Thailand and in the Persian Gulf getting fairly noisy images with native ISO settings and reasonable shutter speeds.

2) Sensor heat. Regardless of the outside air temp, the longer the sensor is energized, the more heat is created by its electronic function. Therefore, the sensor worsens its own noise the longer the exposure is. 

With those two piece of info, you can see how noise can become a pretty big problem when doing nighttime images in hot climates.

I hope that explains it for you! I could probably get a more technical answer for you if you need...gotta go home to the reference library!

Thanks for stopping by!

[PS. As I was typing this, I had the hypothesis that using Live View, or a mirrorless camera, may actually be worse for noise as the sensor is energized in order to preview the image. Hmmmm.]

Film has a thing called reciprocity failure. Before film manufacturers went cheap, there used to be a paper insert in the box with the film describing the characteristics of the film.

But who reads that? Now  you have to go to the manufacturer's website to get the film's data sheet. 

Hi Ralph,

Yep! In the "early days" of night photography, photographers had to take detailed notes about exposure, ambient conditions, and processing to try to evaluate the reciprocity failure characteristics of different film stocks. How easy we have it today with digital ISO!

Thanks for reading!



Hi, on occasion I see a 404 website error when I browse this site. Just a heads up, best wishes

Very good explanation ...... I love this article with mathematical concepts..... well done 

I would like to know the advantages and disadvantages of the mechanical shutters & electronic shutters. Please explain how it works in Sony a6500.

Thank you.


Hi Asela,

Thanks for the kind words. In case you missed it, here is the section from the article:

Like most things, the shutter has gone digital. Many modern digital cameras operate an electronic shutter that simply powers the digital sensor on for a selected amount of time. Because there is no mechanical function, electronic shutter speeds can be extremely fast. A global shutter turns the entire sensor on and off at once, while a rolling shutter activates one row of pixels at a time across its width.

Both the focal-plane shutter and rolling electronic shutter, because of their design and function, can cause interesting distortion through an image when there is fast motion across the picture plane.

The advantage of the electronic shutter is that you can have much higher shutter speeds than you can achieve with a mechanical shutter. Interestingly, on the a6500, there is no electronic shutter speed advantage as you are restricted from 30sec-1/4000th second. Some cameras allow capture at up to 1/32,000th of a second with an electronic shutter.

The other advantage of the electronic shutter is that it can be completely silent. This allows you to take photos in scenarios where stealth is important and the loud click of the shutter may be distracting for the subject or others in your environment.

I hope this answers your questions.

Thanks for reading!

I very much like your articles and will share them with my photographer friends. I think this is a 3-part series, and I was wondering if you could please provide a link to your third article, please.  Thank you so much for sharing your knowlege in a very understandable and useful way!! 

Really nice description. Understood most of the concepts and its time to apply them :)

Thank you, Vishal! I am glad you liked the article! Thanks for reading!

Its nice subject especial when comes to ISO. Keep it up...!!

Thanks for reading, Alex! Be sure to check out the aperture and ISO articles, too!

hey this was quite helpful for my photography class and i like the examples they are quite helpful 

Hey jacob!

Thanks for your comments! I am glad this is going to help you in school. Study hard and let us know if you have other questions on homework or assignments!

Thanks for reading!

Thank you for such a clear explanation of this aspect of photography

Hey oliver! I am glad you enjoyed the article. Thanks for reading!

Hi Todd:

Thanks so much for your knowledgeable and well-written articles.

I've been a photo enthusiast (not a professional) for many years...since the days of film cameras. (I still treasure my Contax 139 Quartz SLR and Zeiss T* lenses.) But I'm gradually re-educating myself, learning about the wondrous potential of digital photography, and I'm greatly enjoying your articles. As a physicist, I commend your explanation of the inverse square law in the Understanding Aperture article. This piece on shutter speed is great too, and I'm looking forward to reading all of your other articles.

I did have to do a double take when I read, "The maximum shutter speed for most SLR cameras is 30 seconds." To be precise, if speed is the parameter you're measuring, then the "maximum speed" is the fastest shutter speed. Numerically, 30 seconds is a larger number than, say, 1/125 of a second, but it's not a faster shutter speed. So, while shutter speed is not an inverse square relationship (like light intensity), it's still an inverse (first power) relationship: The smaller the fraction, the faster (higher) the speed.

You already knew that, of course. But it might be confusing to some readers who are new to the subject to call a 30-second exposure the "maximum" shutter speed. For a camera whose longest (maximum) shutter opening duration is 30 seconds, that's actually the slowest (or minimum) shutter speed.

Thanks again for all your helpful and informative articles!

Hi Vito!

Keep on shooting your Contax!

My bad on the shutter speed verbiage. There is a definite linquistic issue with how we describe shutter speed. I try to talk about the duration as much as possible, but I may have slipped a few times. I almost wrote an article on this topic, but I got so confused when composing it in my head that I aborted the idea.

The problem stems from the fact that shutter speed is not a speed at all, so I need to figure out who coined the phrase way back when, buy a time machine from B&H, travel back in time, and hit them on the head when they decide to call the duration that the shutter is open a "speed."

Thanks for your compliments and comments. And, thank you for reading the B&H blog!

Both the lessons (aperature and shutter speed) are a great help to me.  They are well explained.  Adding the comparison to how the eye works add to the understanding.  I am new to using the manual settings, and experimenting with your information is giving me refined pictures.  I am looking forward to ISO so I can put it all together into the art I wish to create.  Thank you.

Hi Eileen! Thank you for your comments!

The ISO article is published here. Enjoy and keep shooting!

You´re great. I had never read such a clear explanation. Right  to the point  and very useful. Congratulations.

Thank you very much, Juan! I am glad you enjoyed it!

You are welcome, Dave! Thanks for reading!


        thank you ! .


You are very welcome, wenceslao! Thanks for reading!

Hi Todd....Thanks again for an insightful, easy to understand article on camera basics. I feel like I should be paying for this kind of tutorial. I'll continue to keep purchasing from B & H, that's for sure! The article did bring one question to light for me. I have read the word "native" in various articles about camera function including this one. No where in the manual for my D 90 nor in the in-camera menu is that word mentioned (maybe I missed it?). How do I know what my native ISO is and does the word apply to other camera or lens functions such as "native" aperture? Thanks, I'm moving on to the next article about understanding ISO.



Hi Tom,

Thanks for your kind words and question.

I am not sure who coined the word "native" when it comes to ISOs, but I have not heard it applied to aperture. If it is used in that way, it might be synonymous with the "sweet spot" that I described in the Aperture article.

For more clarity on "native" ISO, see the ISO article.

If you still have questions, please comment here or in one of the two other articles. Thanks for reading!

Mate, thanks for the information, sometimes you just need english to be english (or australian) and it will make sense, very much appreciate your articles

...or the Queen's English!

Thanks for reading and thanks for your comments, Steve!

Thank you so much for sharing information and your expertise. 

Thanks RALPH! I think "expertise" is generous, but I appreciate the kind words!

This article gives me a much clearer understanding of the effects of shutter speed on photo quality, and how to best use shutter speed to get the best shot. I'm not a pro, but this was a great synopsis of the subject. I look forward to reading more articles like this one.

Hey StevenD! Thanks! Be sure to check out the chapters on Aperture and ISO that accompany this article!

Thank you for the article I have been practiing doing ocean/wave breaking against rocks/waterfall shots and I have been experimenting to get the milky look but I still need to work on my ISO's. It seems to get really tricky keeping up with the setting sun and timing, any thoughts on that?


Hi Jen,

Thanks for your question. If you are trying to get the "milky" blur of moving water you need to set yourself up to get long shutter speeds to allow the action to happen while the shutter is open.

Therefore, you usually would have your ISO set at the native setting for your camera, as increasing the ISO would cause you to either shorten the shutter speed, or decrease your aperture, or both.

The pitfall of the long shutter speed is blur caused, not by breaking waves, but by the movement of the camera. If you can, work off a tripod or other support to help ensure the non-moving parts of the image are sharp. If you cannot use a support, then you will just need to experiment with how slowly you can shoot for a given camera/lens combination. The longer your focal length, the more camera movement will show up in the image.

You should also experiment to find out what shutter speeds give you the blur that you want. Feel free to research online and see if you can find out what speeds other photographers found to be good.

My suggestion for this type of shooting, especially around the changing light of dusk (or dawn), is to set your camera at the native ISO setting and change to Shutter Priority mode. Dial in the shutter speed that you want and let the camera adjust your aperture for you. If you are shooting at, for instance, 1/2 second and the camera has opened the lens's aperture to it its maximum, your images will start to get darker and darker. If you want to maintain that 1/2 second speed, you will then have to start increasing your ISO to compensate for the lack of light entering the camera as it gets darker.

Conversely, if you are shooting at dawn, the camera will close the aperture as the scene gets brighter to maintain that shutter speed. Your ISO should stay at the native setting. With 1/2 second shutter speed and your lens stopped down to its minimum aperture, the images will begin to get brighter and brighter. If your ISO is native, you may be able to knock it down one stop, but that will be the limit of that adjustment. If you want to maintain the 1/2 second shutter speed in bright daylight, you can add neutral density filters to your lens (basically sunglasses for your camera) to reduce the amount of light coming in.

Long answer, but I hope that helps you get started in the right direction. Feel free to follow up if I created more questions for you!

Hi Todd,

I appreciate the tips and have been trying to practice on my ceiling fan.  I use a bag of rice instead of a tripod because the rocks are so uneven.  and im usually at an angle.  

Thanks again and happy holidays!!





Hey Jen!

No worries at all! You will find, with moving water, there are very subtle differences in texture at the same location from one shutter speed to the next. My advice would be to keep changing your shutter speeds and aperture and shoot a lot of images to make sure you get the results you want.

However, be careful of spending hours in front of the computer trying to decide which shot you like best. Go with your gut response to the images and get back outside and make more photos!

The rice bag is a great idea! Portable and light. If you aren't using one now, I would encourage you to use a cable release as well to make sure you dont jiggle the camera when you release the shutter as no support can eliminate all movement.

Feel free to fire more questions my way! I live for this stuff!

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