By following these rules, RASC members will reduce the chance of an unfortunate incident involving laser pointers, and will demonstrate due diligence while leading public astronomical activities. To become a certified user/spotter, contact your Centre.

R.A. Rosenfeld, Chair (National Member) Chris Beckett (National Member) Dr. Roy L. Bishop, FRASC (Halifax Centre) Mike Hanes (London Centre) Dr. Paul Schumacher (Victoria Centre)

The f-stops work as inverse values, such that a small f/number (say f/2.8) corresponds to a larger or wider aperture size, which results in a shallow depth of field; conversely a large f/number (say f/16) results in a smaller or narrower aperture size and therefore a deeper depth of field.

Green laserfrom sky

Basically, when you change the aperture size one stop, you have to shift the shutter speed one stop in the opposite direction to maintain a consistent exposure… and this change in aperture alters the depth of field (DOF) accordingly.

It is the Centre's responsibility to ensure that all laser pointer users and spotters are trained according to RASC guidelines.

From a distance of 320 km (for example, from the ISS) my green laser will appear as bright as the planet Jupiter (neglecting atmospheric absorption). Thus, at "everyday" distances (several kilometres or less) a 5 mW green laser is going to be damn bright, and a major hazard to anyone whose attention is needed elsewhere, like a pilot or the driver of a car, especially at night.

Green laserpointer

Incidentally, to help you with this, every lens has a manual with a DOF chart for each f/stop and the major focusing distances. DOF is just a matter of physics, and it’s important to grasp this concept.

In this section we’re going to discuss several crucial elements for exercising greater creative control over your final photographic image.Other than lighting, composition and focus (which includes depth of field) are the main elements that you can exercise complete command over.Focus enables you to isolate a subject and specifically draw the viewer’s eye to exactly where you want it.The first thing to understand about focus is depth of field.1Depth of FieldThe depth of field (DOF) is the front-to-back zone of a photograph in which the image is razor sharp.As soon as an object (person, thing) falls out of this range, it begins to lose focus at an accelerating degree the farther out of the zone it falls; e.g., closer to the lens or deeper into the background. With any DOF zone, there is a Point of Optimum focus in which the object is most sharp.There are two ways to describe the qualities of depth of field – shallow DOF or deep DOF. Shallow is when the included focus range is very narrow, a few inches to several feet. Deep is when the included range is a couple of yards to infinity. In both cases DOF is measured in front of the focus point and behind the focus point.DOF is determined by three factors – aperture size, distance from the lens, and the focal length of the lens.Let’s look at how each one works.2ApertureThe aperture is the opening at the rear of the lens that determines how much light travels through the lens and falls on the image sensor.The size of the aperture’s opening is measured in f-stops – one of two sets of numbers on the lens barrel (the other being the focusing distance).The f-stops work as inverse values, such that a small f/number (say f/2.8) corresponds to a larger or wider aperture size, which results in a shallow depth of field; conversely a large f/number (say f/16) results in a smaller or narrower aperture size and therefore a deeper depth of field.3Small vs Large ApertureManipulating the aperture is the easiest and most often utilized means to adjust Depth of Field.To achieve a deep, rich and expansive DOF, you’ll want to set the f-stop to around f/11 or higher. You may have seen this principle demonstrated when you look at photos taken outside during the brightest time of the day. In such a case, the camera is typically set at f/16 or higher (that Sunny 16 Rule) and the Depth of Field is quite deep – perhaps several yards in front of and nearly to infinity beyond the exact focus point.Let’s take a look at these two photos as examples. The left side of the photo has an expansive DOF, most likely shot around noon (notice the short, but strong shadows), with an f/22 aperture. The right side of the photo has an extremely shallow DOF; probably an f/2.8 aperture setting.However, to achieve an identical proper exposure, the shutter speed is probably closer to 1/1000th to compensate for the increased amount of light entering the lens at f/2.8.4Aperture RangeThe aperture range identifies the widest to smallest range of lens openings, i.e., f/1.4 (on a super-fast lens) to f/32, with incremental “stops” in between (f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, and f/22).Each f-number is represents one “stop” of light, a stop is a mathematical equation (which is the focal length of the lens divided by the diameter of the aperture opening) that determines how much light that enters the lens regardless of the length of the lens. Such that an f/4 on a 50mm has smaller opening than an f/4 on a 200mm, but an equivalent amount of light travels through both lenses to reach the image sensor thus providing the same exposure.Each movement up the range (say f/2 to f.2.8) reduces the amount of light by one-half, and each movement down the range (say f/11 to f/8) doubles the amount of light passing through the lens.It’s important to understand this concept and how it affects exposure because it works in tandem with the shutter speed (we’ll discuss this in another section) to establish a given exposure value.Basically, when you change the aperture size one stop, you have to shift the shutter speed one stop in the opposite direction to maintain a consistent exposure… and this change in aperture alters the depth of field (DOF) accordingly.5Distance from the LensThe last element affecting depth of field is the distance of the subject from the lens – you can adjust the DOF by changing that distance.For example, the closer an object is to the lens (and the focus is set on that object) the shallower the DOF. Conversely, the reverse is true – the farther away an object is and focused on, the deeper the DOF. Changing the distance to subject is the least practical way to manipulate the depth of field, and by changing the distance from a subject to the lens, you immediately change your image’s composition. To maintain the compositional integrity of the shot, but still have the change in DOF from a distance, you can change the focal length (either by changing lenses or zooming in).Why does changing the focal length negate the effects on DOF? This is because the visual properties of a given lens either provide either greater DOF (shorter lenses) or shallower DOF (longer lenses). The physical properties of a lens at a given focal length also affect the depth of field. A shorter focal length lens (say 27mm) focused at 5 meters, set at f/4 has a deeper DOF (perhaps from 3 meters in front and 20 meters behind) than a longer focal length (say 300mm), also set at f/4 focused at 5 meters. The 300mm lens has a remarkably shallow depth of field.Incidentally, to help you with this, every lens has a manual with a DOF chart for each f/stop and the major focusing distances. DOF is just a matter of physics, and it’s important to grasp this concept.CConclusionManipulation of depth of field is a good way to modify the characteristics of your photo, and manipulating the aperture is the ideal way to do this because it has little or no effect on composition.You simply need to change the shutter speed (or change the light sensitivity – ISO) to compensate for the changes in the exposure from the adjustments to the f-number. Changes in distance and focal length also affect DOF, but these changes have trade-offs in terms of composition.Therefore, changes to aperture are the best way to manipulate DOF without affecting a photo’s composition.

Green LaserLevel

Under the Canadian Aeronautics Act, conviction for laser flashing an aircraft carries maximum penalties of a five-year prison term, and a $100,000 fine: https://tc.canada.ca/en/campaigns/aiming-laser-aircraft-not-bright-idea.

It’s important to understand this concept and how it affects exposure because it works in tandem with the shutter speed (we’ll discuss this in another section) to establish a given exposure value.

The aperture range identifies the widest to smallest range of lens openings, i.e., f/1.4 (on a super-fast lens) to f/32, with incremental “stops” in between (f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, and f/22).

Green Laserpointer 10000mw

Over the last decade, the striking ethereal glow of laser pointers (sometimes referred to as Green Laser Pointers, or GLPs) has become a familiar sight at astronomy education and public outreach (EPO) events, from star parties for beginners to sky-at-night tours around astronomical installations. With the beam of a laser pointer an astronomy educator can direct an audience unerringly to a specific object - planet, meteor-shower radiant, star, asterism, constellation, or nebula. The very light of the laser pointer itself can seem to confer an enhanced authority on the EPO instructor. The laser pointer remains one of the coolest tools in the amateur's instrument case - but only if used responsibly. Laser pointers are tools not toys, and their misuse can lead to serious harm.

Let’s take a look at these two photos as examples. The left side of the photo has an expansive DOF, most likely shot around noon (notice the short, but strong shadows), with an f/22 aperture. The right side of the photo has an extremely shallow DOF; probably an f/2.8 aperture setting.

You simply need to change the shutter speed (or change the light sensitivity – ISO) to compensate for the changes in the exposure from the adjustments to the f-number. Changes in distance and focal length also affect DOF, but these changes have trade-offs in terms of composition.

At the wavelength of the peak sensitivity for bright-adapted (photopic) vision (555 nm): 1 watt produces 683 lumens (p. 36 of the Observer's Handbook).

Green LaserDEWALT

The last element affecting depth of field is the distance of the subject from the lens – you can adjust the DOF by changing that distance.

The RASC provides training to its members on the safe usage of laser pointers for astronomical outreach. For details on the program and certification process, check out our Program Guide. Note that to access some items linked in the Program Guide, you must be certified as a Centre Trainer or National Instructor. More information about our Laser Pointer Certification Program is included below.

There are two ways to describe the qualities of depth of field – shallow DOF or deep DOF. Shallow is when the included focus range is very narrow, a few inches to several feet. Deep is when the included range is a couple of yards to infinity. In both cases DOF is measured in front of the focus point and behind the focus point.

Green LaserSight

The size of the aperture’s opening is measured in f-stops – one of two sets of numbers on the lens barrel (the other being the focusing distance).

As soon as an object (person, thing) falls out of this range, it begins to lose focus at an accelerating degree the farther out of the zone it falls; e.g., closer to the lens or deeper into the background. With any DOF zone, there is a Point of Optimum focus in which the object is most sharp.

The RASC has worked with Transport Canada to ensure laser pointer use for astronomical purposes is legal and safe. The RASC has authorisation from Transport Canada to train and certify our members to safely and legally use laser pointers for astronomy. Any individual, RASC member or otherwise, can use a laser pointer for astronomy provided they either:

In keeping with the RASC's commitment to informative, inspiring, and safe EPO, members are required to complete Laser Pointer User/Spotter training before using a laser pointer at an RASC event. Laser Pointer User/Spotter training goes over the basic rules a user/spotter must follow when using a laser pointer and tests future users/spotters' knowledge with an exam at the end of the course. The rules users/spotters must follow include, but are not limited to:

Certified Laser Pointer Users/Spotters must fill out this form after an event at which laser pointers were used. You must be logged into your member account to access the form.

As of May 2021, logging into the website is accomplished using the email address you have associated with your RASC membership and not the Username you may have created previously. If this is your first time logging in since this change, you will need to use the Forgot Password link after entering your email address so that you can be properly set up in the system. We appreciate your patience.

To put the latter number into perspective, the luminance of the surface of the Sun = 1.9 x 109 cd/m2, so my green laser has 2,600 times the luminance (surface brightness) of the Sun.

And mine is only a 5 mW laser. 600 mW (!) hand-held green lasers are being advertised for sale to the public, few of whom understand physical concepts like solid angles and luminance.

Each f-number is represents one “stop” of light, a stop is a mathematical equation (which is the focal length of the lens divided by the diameter of the aperture opening) that determines how much light that enters the lens regardless of the length of the lens. Such that an f/4 on a 50mm has smaller opening than an f/4 on a 200mm, but an equivalent amount of light travels through both lenses to reach the image sensor thus providing the same exposure.

Focus enables you to isolate a subject and specifically draw the viewer’s eye to exactly where you want it.The first thing to understand about focus is depth of field.1Depth of FieldThe depth of field (DOF) is the front-to-back zone of a photograph in which the image is razor sharp.As soon as an object (person, thing) falls out of this range, it begins to lose focus at an accelerating degree the farther out of the zone it falls; e.g., closer to the lens or deeper into the background. With any DOF zone, there is a Point of Optimum focus in which the object is most sharp.There are two ways to describe the qualities of depth of field – shallow DOF or deep DOF. Shallow is when the included focus range is very narrow, a few inches to several feet. Deep is when the included range is a couple of yards to infinity. In both cases DOF is measured in front of the focus point and behind the focus point.DOF is determined by three factors – aperture size, distance from the lens, and the focal length of the lens.Let’s look at how each one works.2ApertureThe aperture is the opening at the rear of the lens that determines how much light travels through the lens and falls on the image sensor.The size of the aperture’s opening is measured in f-stops – one of two sets of numbers on the lens barrel (the other being the focusing distance).The f-stops work as inverse values, such that a small f/number (say f/2.8) corresponds to a larger or wider aperture size, which results in a shallow depth of field; conversely a large f/number (say f/16) results in a smaller or narrower aperture size and therefore a deeper depth of field.3Small vs Large ApertureManipulating the aperture is the easiest and most often utilized means to adjust Depth of Field.To achieve a deep, rich and expansive DOF, you’ll want to set the f-stop to around f/11 or higher. You may have seen this principle demonstrated when you look at photos taken outside during the brightest time of the day. In such a case, the camera is typically set at f/16 or higher (that Sunny 16 Rule) and the Depth of Field is quite deep – perhaps several yards in front of and nearly to infinity beyond the exact focus point.Let’s take a look at these two photos as examples. The left side of the photo has an expansive DOF, most likely shot around noon (notice the short, but strong shadows), with an f/22 aperture. The right side of the photo has an extremely shallow DOF; probably an f/2.8 aperture setting.However, to achieve an identical proper exposure, the shutter speed is probably closer to 1/1000th to compensate for the increased amount of light entering the lens at f/2.8.4Aperture RangeThe aperture range identifies the widest to smallest range of lens openings, i.e., f/1.4 (on a super-fast lens) to f/32, with incremental “stops” in between (f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, and f/22).Each f-number is represents one “stop” of light, a stop is a mathematical equation (which is the focal length of the lens divided by the diameter of the aperture opening) that determines how much light that enters the lens regardless of the length of the lens. Such that an f/4 on a 50mm has smaller opening than an f/4 on a 200mm, but an equivalent amount of light travels through both lenses to reach the image sensor thus providing the same exposure.Each movement up the range (say f/2 to f.2.8) reduces the amount of light by one-half, and each movement down the range (say f/11 to f/8) doubles the amount of light passing through the lens.It’s important to understand this concept and how it affects exposure because it works in tandem with the shutter speed (we’ll discuss this in another section) to establish a given exposure value.Basically, when you change the aperture size one stop, you have to shift the shutter speed one stop in the opposite direction to maintain a consistent exposure… and this change in aperture alters the depth of field (DOF) accordingly.5Distance from the LensThe last element affecting depth of field is the distance of the subject from the lens – you can adjust the DOF by changing that distance.For example, the closer an object is to the lens (and the focus is set on that object) the shallower the DOF. Conversely, the reverse is true – the farther away an object is and focused on, the deeper the DOF. Changing the distance to subject is the least practical way to manipulate the depth of field, and by changing the distance from a subject to the lens, you immediately change your image’s composition. To maintain the compositional integrity of the shot, but still have the change in DOF from a distance, you can change the focal length (either by changing lenses or zooming in).Why does changing the focal length negate the effects on DOF? This is because the visual properties of a given lens either provide either greater DOF (shorter lenses) or shallower DOF (longer lenses). The physical properties of a lens at a given focal length also affect the depth of field. A shorter focal length lens (say 27mm) focused at 5 meters, set at f/4 has a deeper DOF (perhaps from 3 meters in front and 20 meters behind) than a longer focal length (say 300mm), also set at f/4 focused at 5 meters. The 300mm lens has a remarkably shallow depth of field.Incidentally, to help you with this, every lens has a manual with a DOF chart for each f/stop and the major focusing distances. DOF is just a matter of physics, and it’s important to grasp this concept.CConclusionManipulation of depth of field is a good way to modify the characteristics of your photo, and manipulating the aperture is the ideal way to do this because it has little or no effect on composition.You simply need to change the shutter speed (or change the light sensitivity – ISO) to compensate for the changes in the exposure from the adjustments to the f-number. Changes in distance and focal length also affect DOF, but these changes have trade-offs in terms of composition.Therefore, changes to aperture are the best way to manipulate DOF without affecting a photo’s composition.

Manipulation of depth of field is a good way to modify the characteristics of your photo, and manipulating the aperture is the ideal way to do this because it has little or no effect on composition.

I note in the recent flurry of emails on Green Laser Pointers, that some people seem to underestimate the hazard these devices pose if aimed at someone, particularly from a distance of several kilometres. I did some calculations for my 5 milliwatt green laser and arrived at these results:

Each movement up the range (say f/2 to f.2.8) reduces the amount of light by one-half, and each movement down the range (say f/11 to f/8) doubles the amount of light passing through the lens.

Lightgreen laser

Green laserfor sale

For example, the closer an object is to the lens (and the focus is set on that object) the shallower the DOF. Conversely, the reverse is true – the farther away an object is and focused on, the deeper the DOF. Changing the distance to subject is the least practical way to manipulate the depth of field, and by changing the distance from a subject to the lens, you immediately change your image’s composition. To maintain the compositional integrity of the shot, but still have the change in DOF from a distance, you can change the focal length (either by changing lenses or zooming in).

The aperture is the opening at the rear of the lens that determines how much light travels through the lens and falls on the image sensor.

To achieve a deep, rich and expansive DOF, you’ll want to set the f-stop to around f/11 or higher. You may have seen this principle demonstrated when you look at photos taken outside during the brightest time of the day. In such a case, the camera is typically set at f/16 or higher (that Sunny 16 Rule) and the Depth of Field is quite deep – perhaps several yards in front of and nearly to infinity beyond the exact focus point.

The power required to light an incandescent light bulb (sending light in all directions) that appears as bright as my green laser (when aimed at someone) = 3 megawatts (Three megawatts will power a sizeable town).

Why does changing the focal length negate the effects on DOF? This is because the visual properties of a given lens either provide either greater DOF (shorter lenses) or shallower DOF (longer lenses). The physical properties of a lens at a given focal length also affect the depth of field. A shorter focal length lens (say 27mm) focused at 5 meters, set at f/4 has a deeper DOF (perhaps from 3 meters in front and 20 meters behind) than a longer focal length (say 300mm), also set at f/4 focused at 5 meters. The 300mm lens has a remarkably shallow depth of field.

Other than lighting, composition and focus (which includes depth of field) are the main elements that you can exercise complete command over.Focus enables you to isolate a subject and specifically draw the viewer’s eye to exactly where you want it.The first thing to understand about focus is depth of field.1Depth of FieldThe depth of field (DOF) is the front-to-back zone of a photograph in which the image is razor sharp.As soon as an object (person, thing) falls out of this range, it begins to lose focus at an accelerating degree the farther out of the zone it falls; e.g., closer to the lens or deeper into the background. With any DOF zone, there is a Point of Optimum focus in which the object is most sharp.There are two ways to describe the qualities of depth of field – shallow DOF or deep DOF. Shallow is when the included focus range is very narrow, a few inches to several feet. Deep is when the included range is a couple of yards to infinity. In both cases DOF is measured in front of the focus point and behind the focus point.DOF is determined by three factors – aperture size, distance from the lens, and the focal length of the lens.Let’s look at how each one works.2ApertureThe aperture is the opening at the rear of the lens that determines how much light travels through the lens and falls on the image sensor.The size of the aperture’s opening is measured in f-stops – one of two sets of numbers on the lens barrel (the other being the focusing distance).The f-stops work as inverse values, such that a small f/number (say f/2.8) corresponds to a larger or wider aperture size, which results in a shallow depth of field; conversely a large f/number (say f/16) results in a smaller or narrower aperture size and therefore a deeper depth of field.3Small vs Large ApertureManipulating the aperture is the easiest and most often utilized means to adjust Depth of Field.To achieve a deep, rich and expansive DOF, you’ll want to set the f-stop to around f/11 or higher. You may have seen this principle demonstrated when you look at photos taken outside during the brightest time of the day. In such a case, the camera is typically set at f/16 or higher (that Sunny 16 Rule) and the Depth of Field is quite deep – perhaps several yards in front of and nearly to infinity beyond the exact focus point.Let’s take a look at these two photos as examples. The left side of the photo has an expansive DOF, most likely shot around noon (notice the short, but strong shadows), with an f/22 aperture. The right side of the photo has an extremely shallow DOF; probably an f/2.8 aperture setting.However, to achieve an identical proper exposure, the shutter speed is probably closer to 1/1000th to compensate for the increased amount of light entering the lens at f/2.8.4Aperture RangeThe aperture range identifies the widest to smallest range of lens openings, i.e., f/1.4 (on a super-fast lens) to f/32, with incremental “stops” in between (f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, and f/22).Each f-number is represents one “stop” of light, a stop is a mathematical equation (which is the focal length of the lens divided by the diameter of the aperture opening) that determines how much light that enters the lens regardless of the length of the lens. Such that an f/4 on a 50mm has smaller opening than an f/4 on a 200mm, but an equivalent amount of light travels through both lenses to reach the image sensor thus providing the same exposure.Each movement up the range (say f/2 to f.2.8) reduces the amount of light by one-half, and each movement down the range (say f/11 to f/8) doubles the amount of light passing through the lens.It’s important to understand this concept and how it affects exposure because it works in tandem with the shutter speed (we’ll discuss this in another section) to establish a given exposure value.Basically, when you change the aperture size one stop, you have to shift the shutter speed one stop in the opposite direction to maintain a consistent exposure… and this change in aperture alters the depth of field (DOF) accordingly.5Distance from the LensThe last element affecting depth of field is the distance of the subject from the lens – you can adjust the DOF by changing that distance.For example, the closer an object is to the lens (and the focus is set on that object) the shallower the DOF. Conversely, the reverse is true – the farther away an object is and focused on, the deeper the DOF. Changing the distance to subject is the least practical way to manipulate the depth of field, and by changing the distance from a subject to the lens, you immediately change your image’s composition. To maintain the compositional integrity of the shot, but still have the change in DOF from a distance, you can change the focal length (either by changing lenses or zooming in).Why does changing the focal length negate the effects on DOF? This is because the visual properties of a given lens either provide either greater DOF (shorter lenses) or shallower DOF (longer lenses). The physical properties of a lens at a given focal length also affect the depth of field. A shorter focal length lens (say 27mm) focused at 5 meters, set at f/4 has a deeper DOF (perhaps from 3 meters in front and 20 meters behind) than a longer focal length (say 300mm), also set at f/4 focused at 5 meters. The 300mm lens has a remarkably shallow depth of field.Incidentally, to help you with this, every lens has a manual with a DOF chart for each f/stop and the major focusing distances. DOF is just a matter of physics, and it’s important to grasp this concept.CConclusionManipulation of depth of field is a good way to modify the characteristics of your photo, and manipulating the aperture is the ideal way to do this because it has little or no effect on composition.You simply need to change the shutter speed (or change the light sensitivity – ISO) to compensate for the changes in the exposure from the adjustments to the f-number. Changes in distance and focal length also affect DOF, but these changes have trade-offs in terms of composition.Therefore, changes to aperture are the best way to manipulate DOF without affecting a photo’s composition.

© 2007 - 2024 ExposureGuide.com We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.

However, to achieve an identical proper exposure, the shutter speed is probably closer to 1/1000th to compensate for the increased amount of light entering the lens at f/2.8.