What is the 500 rule in photography?

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    It is only a matter of time before you come across somebody talking about the "500 Rule," also known as the "rule of 500," if you are interested in night sky photography in any way. If you are interested in night sky photography in any way, then it is only a matter of time. When they are out shooting at night and want to capture one of those stunning images of the Milky Way that tend to blow audiences off their feet and keep the stars nice and sharp, most experienced photographers will commit this time-honored rule of thumb to memory so that they can use it.

    When first starting out in astrophotography, one of the most difficult tasks for novices is to capture a picture that is in focus and has stars that are round. If you take a picture of the night sky using a tripod and a long exposure, you might be able to see what is known as "star trailing." This is because it appears as though the night sky is moving from where we are standing on Earth.

    The 500 Rule is one of the most effective strategies for minimising the appearance of star trails in astrophotography images taken with a tripod mount that does not track the sky.

    If you have ever experimented with night photography, you are well aware of the many differences that exist between night landscape photography and traditional landscape photography. When the sun goes down and the stars take over the sky, you can forget all the rules and guidelines you know about the general settings for photography. The majority of these are likely to be more detrimental than beneficial to your photos.

    Instead, you will need to ignore everything you know about photography and crank up the ISO, widen the aperture, and use a slow shutter speed.

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    In spite of the fact that our beginner's guide to night photography goes into great detail about the various settings for night photography, there is one setting that has a tendency to be overlooked: the shutter speed. Yes, a slow shutter speed is required; however, wouldn't it be possible to keep the ISO at a low setting, keep the aperture at f/11, and then increase the exposure time to several minutes?

    Yes, we are able to do that; however, doing so will also add an effect to your photographs, which you may or may not want. The 500 Rule is the answer to this problem.

    What happens when we extend the shutter speed too much

    During the time that the shutter is open, the camera will record any motion that occurs. In other words, anything that moves within the frame while the shutter is open will be picked up by the camera; leaves blowing in the wind during an exposure time of five seconds will appear blurry due to the length of time the shutter was open.

    What repercussions does this have for photographing at night? When the shutter speed is faster than a certain period, the stars will have a blurry appearance because of the rotation of the Earth. These are what are commonly referred to as star trails.

    If you choose to keep your ISO at 100 and your aperture at f/11, then you might require a shutter speed of more than 20 minutes. Because of the long shutter speed, the resulting image file will be much cleaner (there will be less noise, and the sharpness from front to back will be improved), but it will also contain star trails.

    Now, experimenting with this method can be a lot of fun, but if you want your stars to be extremely sharp, what should you do? What is an appropriate speed for the shutter? Permit me to acquaint you with something called the 500 rule:

    What is the 500 Rule?

    The 500 rule is a measurement used to determine the maximum exposure time that can be used in a photograph before star trails appear or before the stars become blurry. If you set the shutter speed for a longer amount of time than what is permitted by this rule, the photographs you take will not have sharp stars.

    To calculate the correct exposure time and shutter speed when using a specific lens and either a full-frame or crop sensor camera, all you need is a straightforward formula. If you follow these steps exactly, your photographs of the Milky Way and pictures of the night sky will have stars that are pin-point sharp and razor-sharp, without any trailing.

    When photographing the night sky using a tripod and a fixed camera, the 500 rule can be of assistance. The method works on images with a wide range of focal lengths (up to about 200mm), but it is most useful when photographing the Milky Way with a wide-angle lens on a camera. Choosing the right wedding photographer in Melbourne to capture every moment on your wedding day. 

    Razor-Sharp Stars With the 500 Rule

    The challenge of night photography is that it requires you to take photographs with lower-quality settings than you would normally use. To capture crisp images of the night sky, your camera must have a high ISO and a wide open aperture. There is no way around this requirement.

    Even though star trails are occasionally a fun technique to use, there is one thing you should do everything in your power to prevent, and that is star blur. The shutter speed is only marginally too slow at this point, as evidenced by the stars' gradual deterioration into blurriness. At this point, it should be obvious that the star trail was not intentionally created; rather, it was created by accident. The 500 Rule is extremely helpful in situations like these.

    500 Rule for Night Photography

    The 500 rule is a straightforward guideline that can be utilised to determine the maximum exposure time that can be used in a photograph before the stars become blurry. Is it flawless? No. However, it provides a useful indication of the shutter speed that can be used with the equipment that is currently available to you.

    The 500 Rule for Full Frame Camera

    What is the 500 rule in photography?

    The 500 rule stipulates that you must set your full-frame camera's ISO to either 3200 or 6400, your aperture to f/2.8 (or as wide as it can go), and your shutter speed to 500 divided by the camera's focal length.

    When using a camera with a full-frame sensor, the calculation is made in the simplest way possible; however, you should be prepared for some reduction in exposure time. Because you do not need to multiply the focal length by a crop factor, the formula is simply 500 divided by your focal length. This is because you do not need to take into account any crop factors. If you were shooting with a lens that was 50 millimetres in focal length, for instance, your shutter speed would be 10 seconds (500 divided by 50 equals 10).

    If you are using a lens with a focal length of 24 millimetres, your shutter speed should be approximately 21 seconds (500 divided by 24 equals 21).

    Take into consideration that the response of the sensor in your camera to low light may dictate whether or not you need to lower the iso values. Some cameras have sensors that are perfect, allowing the user to take perfect photographs of stars at iso values close to 500.

    The 500 Rule for a Crop Sensor Canon Camera

    The crop factor of a Canon crop sensor camera is 1.6, so you need to account for that in your equation. Then it becomes this:

    500 / (focal length x 1.6)

    For example, with a 50mm lens it is 500 / (50 x 1.6) = 6 seconds (approximately).

    The 500 Rule for a Crop Sensor Nikon Camera

    The crop factor for a Nikon crop sensor camera is 1.5, so you account for that like this:

    500 / (focal length x 1.5)

    For example, with a 50mm lens, it is 500 / (50 x 1.5) = 7 seconds (approximately).

    Shutter Speed Settings for the 500 Rule

    It is essential to keep in mind that this guideline is not a foolproof method, and that some modifications, based on the specifics of the situation, may be required to be implemented. You need to make sure that you take into consideration things like the angle of the stars as well as things like light pollution and atmospheric haze.

    The following are the settings that you would use, depending on the camera and lens that you have. Just keep in mind that the 500 rule is not foolproof; you will most likely need to make some minor adjustments to account for the specifics of your situation, such as the amount of light pollution, the angle at which the stars are positioned, or even the amount of atmospheric haze.

    How to Calculate Shutter Speeds With the 500 Rule

    So what is this magic formula that calculates the maximum shutter speed? It's quite simple:


    You're photographing with a 14mm, a standard focal length for night photography. The slowest shutter speed you can use is then 500/14 = 35.7; anything below 35 seconds should give sharp stars.

    That's it? Finished? Not quite. The formula above isn't going to work for everyone reading this. If you use a crop sensor camera (APS-C or Micro Four Thirds), the calculated shutter speed above will result in blurry stars as it's intended for full-frame sensors.

    It would help if you multiplied the focal length with the crop factor to calculate the maximum shutter speed for an APS-C or Micro 4/3 sensor. Most APS-C sensors have a crop factor of 1.5, and Micro 4/3 have a crop factor of 2. Canon's APS-C sensors are slightly different and have a crop factor of 1.6




    Be careful when using the 500 rule for night photography.

    Even though the 500 rule is a great rule of thumb for night photography, it is absolutely necessary to exercise extreme caution. Even if you adhere to all of the recommendations presented above, there is a possibility that you will still notice some haziness in your stars. This is because the guideline is not flawless.

    We strongly advise that you take a test shot using the calculated shutter speed and zoom in on the preview to ensure that the stars come out clear in the final image. If they aren't, the amount of time they are exposed for should be shortened slightly. When photographing the night sky, the exposure time should never be longer than 30 seconds at any point.

    Why Photographers use The 500 Rule

    Even though the 500 rule is more of a suggestion, that does not mean that it cannot be put into practise. The application of this uncomplicated formula can have a significant impact on the quality of your photographs of the night sky. If all goes according to plan, you will be able to take pictures that include stars that are crisp all the way to the edges of the frame.

    The purpose of this is to determine the maximum exposure time that can be used before the stars become blurry or before star trails appear in the photograph. If you set the shutter speed for a longer amount of time than what is permitted by this rule, the resulting photograph will be unclear (the stars will appear as trails rather than dots).

    To use this formula, you need to have a basic understanding of mathematics, but you do not need to be a nuclear scientist to understand it and put it to use. It is simple, but frequently it is the inconsequential adjustments that result in the most noticeable shifts.

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    How it Works

    The rule is as follows:

    SS = 500 / (CF x FL)

    If you are perplexed by this formula, there is no need to worry; you just need to understand the abbreviations. SS stands for the shutter speed expressed in seconds, CF is the crop factor of your sensor (the ratio between your sensor and a full-frame one), while FL refers to the focal length in millimetres.

    500 / Crop-Factor x Focal Length = Ideal Shutter Speed

    According to the type of camera you own, you will have to use different crop-factor values. Here is the list you can refer to:

    1 X – Full-frame cameras

    1.5 (1.6) X – Nikon (Canon) APS-C cameras

    2 X- Micro 4/3 cameras

    2.7 X and higher – Compact cameras with a one-inch type sensor (or smaller)

    Even though it is widely accepted, the number "500" in this formula does not carry any particular meaning. This number is just something astrophotographers figured out works the best for this type of photos.

    This formula is effective because it automatically determines the ideal shutter speed for your camera, allowing you to take photographs with the highest possible degree of transparency. It completes the task in the least amount of time possible.

    Imagine for a moment that you had absolutely no idea how to prevent star trails from appearing in the photos you took of the night sky but still wanted to capture its beauty. For example, you use a remote shutter release cable on your micro 4/3 camera and set the shutter speed to 60 seconds with the expectation that the resulting photograph will be outstanding. You will, on the other hand, end up with a blurry photo that does not do justice to how lovely the sky actually appears in real life.

    The 500 Rule is a useful tool that can provide you with a point of reference for the amount of time that the image should be exposed for using your camera system. It cannot be considered an exact science.

    The Science Behind It

    The primary goal here is to devise a simple formula that can make an educated guess as to how much longer the exposure time can be before the motion of the stars is discernible.

    The sky rotates at a rate of 0.0042 arc degrees per second, or, to put that another way, it completes one full turn every 24 hours. When using a lens with a focal length of 24 millimetres and a full-frame camera, the horizontal field of view will be 73.7 degrees.

    Let's say that this camera has a sensor with 24 million pixels (6000 x 4000). The 73.7 degrees that were mentioned earlier are projected onto 6000 pixels, which results in 81.4 pixels per degree. According to the 500 rule, the exposure time will be approximately 21 seconds when using a lens of this type (500/24).

    Over the course of these 21 seconds, the sky will rotate by approximately 0.09 degrees (0.0042 degrees times 21 seconds). 0.1 degrees is equal to 7.3 pixels when using a camera of this type (81.4*0.1).

    The maximum acceptable amount of motion blur is exactly 7.3 pixels, and this is the exact number of pixels that must pass before the stars as we see them in the sky become star trails in the picture. However, are you able to see this movement in the pictures?

    The majority of the time, we look at images displayed on a computer screen. You will notice that the stars in your full-resolution photograph are not dots if you attempt to zoom in all the way to one hundred percent; however, this is irrelevant because you would never be able to see this with the naked eye.

    So, if you're planning on printing large-format versions of your photos, it's worth thinking about. If you generally share your photos online (Flickr, Instagram etc.), the fine details become much less critical. Looking for a Yarra Valley wedding photographer? Look no further! Wild Romantic Photography has you covered.

    Does the 500 Rule Work?

    How well do these shutter speeds perform in real life? The correct response is "sometimes."

    In response to the question of whether or not the 500 rules are accurate, there was a variety of opinions, but the general consensus was that it does an excellent job the majority of the time.

    An experienced photographer by the name of Craig Stocks pointed out that the resolution of the camera as well as the quality of the lens will determine whether or not an image taken with the 500 rule will be free of star trails. If the system has a higher resolution, then there is a greater possibility that you will observe star trailing.

    The effect is less pronounced in cameras with a lower pixel resolution, which is why the 500 rule produces a better result in those cameras.

    It is also important to mention that taking pictures close to the horizon will accentuate the effect, as the stars will appear to be moving slightly faster from your vantage point. This is something that should be mentioned because it is important.

    The bottom line is that the 500 rule should be considered a great starting point; however, it is not a precise measurement, and you will need to experiment using your particular camera and lens system in order to get the best results.

    Useful Tools

    What is the 500 rule in photography?

    Here are some of the many stacking software options available to you. I tend to use Adobe Photoshop to stack my untracked images or DeepSkyStacker. Adobe Photoshop has an image stacking script option to automate the process, and it is worth checking out. 

    • Senator – It is excellent to use if you are a Windows user because it is free. It makes the process of image stacking extremely easy, and you will end up with a beautiful photograph in no time. It also supports the RAW format, which is essential when trying to achieve the best quality.
    • Starry Landscape Stacker – This software is available only for Mac OS X users, and there is a free trial period. You won't have to worry that your pictures will turn out anything less than excellent when using this software. The only con about the software is that it doesn't support RAW files, so you have to convert them to TIFF using Adobe Camera RAW or similar software.
    • DeepSkyStacker – Another software that is supported on Windows. It simplifies stacking by doing registering, simple post stacking processes, and saving the final result to a TIFF file. We have an exclusive range of wedding photography Mornington Peninsula services. Check them out here.

    Star Trail Images

    What happens if you want to show the star trails at a certain time? The apparent motion of the stars in the night sky can be captured artistically through the practise of photography known as "star trailing." In order to complete the process, you will need to take pictures with exposure times that are significantly longer than those you would use for the 500 rule.

    In order to capture the most motion in the sky possible, photographers will use the longest exposure time possible (without blowing out the highlights). This is typically accomplished with a tripod and a fixed exposure time of thirty seconds. After that, the photographs are combined in Adobe Photoshop with the "lighten" blend mode in order to generate extremely long star trails over the course of time.


    The 500 Rule is not the ultimate solution to photographing the perfect image of the night sky, but it is a useful point of reference to keep in mind when doing so. Many novice photographers, including myself, begin their studies with a crop-sensor, entry-level DSLR camera and a kit lens (usually 18-55mm or similar).

    I think that the 500 Rule is a great formula for users in this scenario to try out the next time they set up their tripod, and I recommend that you do so. If you have a high-resolution sensor that has more than 30 megapixels, you might want to dial back the suggestion of the 500 Rule or look into the NPF Rule.

    You will have a better understanding of the process of taking photographs of the stars at night, which are essentially moving targets, if you simply understand how this formula works.

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    The 500 rule is a helpful benchmark that can be applied in many different situations, regardless of whether you are using a full-frame or a micro 4/3 camera. When combined with image stacking and various software tools, it is possible to take a stunning picture of the Milky Way or your favourite constellation in the night sky.

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