Understanding High Speed Sync

It isn't about stopping motion

A few days ago I was having a conversation with another photographer and they brought up the idea of using high speed sync flash to stop motion. If I remember correctly, it was in regards to photographing liquid pouring out of a bottle into a glass. That got me thinking that the concept of hight speed sync (HSS) sounds like it might help, but that really isn't true.

Let's start with what HSS is. It allows you to sync your flash with shutter speeds above your normal sync speed so that you can use larger apertures for shallower depth of field or so that you can control the exposure on your background when working outdoors in full sunlight. A big minus is that HSS eats a lot of power and lowers the output of the flash and it eats through batteries (not an issue if you have an a/c powered flash).

What HSS does not do it help freeze motion. The two things that can help freeze motion are a fast shutter speed and/or a flash with a very short flash duration. High speed sync does let you use a faster shutter speed. But you no longer have a single fast flash burst. Instead, when your flash is in HSS mode it fires a number of times in rapid succession in sync with your camera’s shutter. The flashes are too close together for your eye to register them separately, so to your eye it looks like one flash, but it is actually strobing. At full power your speed light might take 1 to 3 or more seconds to recycle between flashes. In order to flash that many times in the short timespan of your shutter speed the flashes are relatively weak to allow the immediate recycling of the flash. 

To show this, I’ve set up a couple of very basic experiments with a speed light and a Paul C. Buff Einstein studio flash (which offers an “action” mode with a very fast flash duration). Nothing very fancy, it is just an ordinary personal size desk fan, a camera, and a light. As a control, the first image is taken without any flash. It is lit by window light with the ISO cranked way up (256,000) to allow for a shutter speed of 1/4000 second. You can clearly see that 1/4000 of a second was not fast enough to freeze the blades on the fan.

Next is a series of images lit by a Canon 430 EXII speed light, off camera, connected by a remote cable. The first two images are taken at 1/5 of a second and 1/200 of a second (normal sync mode) and you can see that the flash did a fairly decent job of freezing the blades of the fan, but not quite good enough to make the label on one of the blades readable. 

The next image is at 1/400 second, putting the flash into high speed sync mode. As you can see, it did a much worse job at freezing the blades of the fan. The next image moves the shutter speed up to 1/1250 of a second in HSS mode, and still a big blur. Even at 1/4000 of a second in HSS mode the label is a blur.

Compare the images at 1/4000 of a second with and without flash.

Very little difference in stopping action with or without a flash at 1/4000 of a second.

Very little difference in stopping action with or without a flash at 1/4000 of a second.

Now switch to the Einstein flash. The first two images have the Einstein in “color” mode which is intended to provide consistent color between flashes at the expense of a longer flash duration. You can see that at 1/2 second and at 1/160 of a second the label on the fan blade is not readily readable. 

Changing the Einstein to “Action” mode to provide a shorter flash duration gives us the last two images, made at 1/2 and 1/160 second. Even these have a blurred label, but much sharper than the images made with high speed sync at 1/4000 of a second. 

Now, I’m sure that most of us don’t have much occasion to photograph spinning fans. But we do sometimes get called on to photograph a liquid being poured. Does HSS help in this situation? I hope that you have already guessed the answer based on what you have read here so far. But let’s look at some images.

This time I will start with two using the Einstein. Each of these is at 1/2 second in “color” mode and in “action” mode. Both do a decent job of freezing the action of the pour and the bubbles.

Compare the above to the following images made with a speed light. The first one is at 1/60th second (normal sync) with good motion stopping. Next is at 1/500th second and we see that it is underexposed by a stop or two. Even with the flash being about 18-inches from the glass, it doesn’t have enough power to give me f/11. So, for the next image I bumped the ISO up from 100 to 400 to get a better exposure. Note that the action stopping is pretty much the same as at 1/60th of a second, at the cost of more noise due to the higher ISO (or you could give up depth of field and use a wider aperture—another tradeoff). Next I go to 1/2000 of a second, losing more power, but not gaining much, if anything, in the ability to stop action. 

Here are two pour photos side by side. One is lit with a speed light in high speed sync mode at a shutter speed of 1/2000th of a second. The other is lit by an Einstein flash in normal sync mode at 1/60th of a second. Can you see much difference in them? Can you tell which one is at 1/2000th of a second?

One of these pours is lit with a flash in normal sync at 1/60 of a second. The other is lit with a flash in High Speed Sync mode at 1/2000 of a second. Can you tell which is which?

One of these pours is lit with a flash in normal sync at 1/60 of a second. The other is lit with a flash in High Speed Sync mode at 1/2000 of a second. Can you tell which is which?

So, there you have it. High Speed Sync is not helping you freeze motion. It is mainly used for outdoor photos where you want fill flash at wide open apertures for limited depth of field and/or to control the ambient exposure. For example, let's say your are making a portrait outdoors and you want to use an aperture of f/2.8 and on that particular day the shutter speed would need to be 1/2000. Without HSS or the use of neutral density filters you can't use your flash to fill in shadows. You would have to lower your shutter speed to 1/200 to sync, and that would need an aperture of f/9 (3-1/3 stops difference). Using HSS would allow you to photograph at 1/2000 @ f/2.8 and use your flash (in pretty close to the subject, as it won't be a very powerful flash). It will also allow you to go to 1/4000 @ f/2.8 to darken the ambient exposure while still giving the subject the correct flash exposure.

What about HSS in the studio. Is HSS valuable in a studio situation? That depends on the lights you are using. Personally, I can’t think of a reason to use HSS indoors with speed lights. In ETTL mode you can set the aperture you want and a low ISO to be able to take photos at wide open apertures. With more powerful studio flash units it will depend on how low you can set the power on the flashes. If you find yourself with your flash at minimum power and it is still giving you a smaller aperture than you want, then you can  go into HSS mode and set your shutter speed above 1/250 and this will lower the power of the flash. Again, this is to control exposure, not to stop motion.

I hope this helps clarify things a bit. And, by the way, in the last image, A is 1/2000th of a second, B is 1/60th of a second.

 

 

 

LED Light Sticks

I've had a few emails today about a set of LED light sticks I made a few years ago.  Since then the light sticks I used became unavailable, so I removed the blog post. I basically took two LED stick fluorescent tube replacements and soldered an extension cord to them.

Also since then, there are commercially made sticks, like this one https://www.bhphotovideo.com/c/product/1300752-REG/yongnuo_yn360w_handheld_led_video_light.html that are not too expensive, are battery powered, have a way to mount on a light stand, have better color consistency, and are dimmable. And they are safer, too, as you don't have to worry about figuring out the A/C wiring on the commercially available models.

Thanks for your interest!
John Cornicello

Andrew Scrivani at CreativeLive

Tripod Side Arm and Counter Weight

Andrew Scrivani just finished up a 2-day class on the business of food photography at CreativeLive. For one of the class segments we did make some photographs to show what it is like to interact with a client, chefs, a prop stylist, and a photo assistant (played by yours truly). 

Because this was a business class, not a class on studio equipment or lighting, we didn't talk too much about the photography. But after the class I had a few of the students approach me to ask about the equipment, hence this blog post.

The most repeated questions were about the tripod, the cross-arm, and the counter weight I added to help with stability. The tripod was a large Gitzo carbon fibre tripod, the current model is the 5542, with a rapid column. On top of the tripod I added a cross-arm so we could boom the camera out over the set to photograph straight down on the plates. For this I used a Manfrotto side-arm or cross-arm (they call it a reproduction arm) along with a pan & tilt tripod head, such as this Manfrotto head (both Andrew and I prefer a 3-wawy head over a ball head when the camera is used over the set like this) and because the camera was going to be hanging out there I added a small Manfrotto counter weight to the cross arm. I also added a 20lb. sand bag to the tripod for even more stability. I didn't want Andrew, the tripod and camera, or me to go crashing into the set because of the uneven weight distribution. If your studio space and budget can handle it, a better solution for this would be a dedicated camera stand, such as those from Foba.

Manfrotto side arm to extend the camera out over the set to photograph straight down

Manfrotto side arm to extend the camera out over the set to photograph straight down

Manfrotto counter weight added to the cross arm to balance the camera

Manfrotto counter weight added to the cross arm to balance the camera

All of the above, except for the counter weight (which I supplied) and the sand bag were rented locally from Glazer's Camera here in Seattle. If you are in the Seattle area and are looking to purchase any of these items please consider buying locally. If your local dealer cannot supply these items. I have also provided a list of the items at Amazon at the end of this post (these are affiliate links, if you purchase via these links I will get credit and possibly a few cents on the purchases).

The camera we used was a Canon 5D mkIII with a Zeiss 50mm Makro-Planar T* 2/50 ZE  lens and a Canon 100mm macro lens. If you watched, you might have heard Andrew and I comment about the autofocus not working with the 100mm lens (the 50 is manual focus only). Full disclosure, the camera belongs to CreativeLive and they had it set to back-button focus. Neither Andrew or I use back-button focus, so we never even thought of that being the issue until the very end of the segment.

The lighting for the set was a foam-core V-flat (made from 2 4x8 sheets of white foam-core taped together along a long edge to form a hinged "V" with a diffuser clamped to the open end of the V-flat. Inside the v-flat we had two Profoto D1 strobe heads (Profoto now has a D2 version) pointed into the V so the light would bounce back from the V-flats through the diffusion silk and onto the set. We used two strobe heads because a single head didn't give quite as much power as we wanted to photograph at f/8 and a relatively low ISO. Here is an overhead diagram of the lighting...

The Incredible Shrinking Space Needle

A lesson in perspective

My friend Rebekah recently posted this on Facebook

I’m kind of obsessed with this optical illusion from the window of my new floor at work. When I first get off the elevator the Space Needle looks ginormous, and as I walk towards the window it gets tiny. My teams might be questioning my sanity as I keep walking back and forth going “whooaaah…

My response to her was, "May I borrow these to use when discussing perspective? It is all relative. The closer you are to your subject, the smaller the background elements will appear. The further you are from your subject, the larger the background elements will appear. In this case, the 'subject' is actually the window. While at the elevator, the window and the space needle are relatively closer to each other than to you. But as you approach the window the window gets progressively closer and larger, while the space needle remains the same distance and size.
"I am assuming that in the first photo, with the large needle you had to crop in quite a bit on the photo or that you had to use a longer focal length lens to fill the frame
.”

Her response, "You're welcome to use this John! You can even come by my office for a better quality version sometime if you want . You're right that I had to zoom in on the first one... and I was just using my iPhone so the quality isn't as good as if you used a lens for it."

So, thank you, Rebekah. Here are my photos after taking her up on her offer to have me visit her office.

All three images were made with a 24mm lens, but from three different distances from the window. The first one, as you enter the office is around 20 meters from the window and the Space Needle fills the window frame. The second image is taken from about 5 meters away from the window and we see that the Space Needle seems smaller. The third image is taken right at the window, so the window frame doesn’t appear in the photograph. 

However, if you look more closely, you will see that the Space Needle is actually the same size in all three images. It is the window frame that has gotten larger as I got physically closer to it.

As you walk out of the elevator into the hallway you see the space needle and your mind “zooms” in on it, with the rest of the office falling off into the periphery. We take for granted what we see. The Space Needle looms large, filling the window. Our brain conveniently dismisses the rest of the office.

Our camera, on the other hand, doesn’t have a brain. It just records what is actually in front of it. When we look at the first photograph we do notice all the periphery. But we also have the ability to “zoom in” on the photograph taken near the elevator and concentrate on the Space Needle via one of two ways. First, we can take the photo made with the shorter focal length lens into Photoshop and crop in to eliminate the distracting peripheral elements. Or we can take another photo using a longer focal length lens to come in closer by magnifying the scene. Notice that either way, cropping or using a longer lens, the relationship between the elements of the scene (the perspective) remains the same. The cropped version has greater depth of field, but at a tremendous loss of quality as a result of the center portion of the image having to be enlarged. The telephoto version has less depth of field (look at the lamps and furniture inside the office), but has greater image quality. The same “compression” of the scene is recognizable in the area of the scene common to both the 24mm and the 105mm images, showing that it is not the lens that causes the compression, but rather the distance between the camera and the subjects. 
In the case of the first set of images above, the Space Needle remained relatively the same distance from the camera while the camera to window distance changed. Let’s say that in the first photograph the Space Needle was 800 meters away and the window was 20 meters away from the camera. In the second photograph the window was now 5 meters from the camera and thereby four times as large as when 20 meters away. But the Space Needle is now 785 meters instead of 800 meters away, an insignificant change in the distance. So while the window grew dramatically in size as we approached it, the Space Needle remained the same size.
In this case, with the camera remaining at a stationary distance from the window and space needle we actually zoomed in, which has the same effect as cropping. In a zoom, the relationship between the elements in the scene remain the same, they all get larger (zooming in) or all get smaller (zooming out) at the same rate. This is not a natural way to look at things. And this brings me to the the saying that photographers often here, “you should zoom with your feet, not with your lens.” 
I have a problem with this statement. I totally agree with the concept that you should move around your subject—get closer, move back, go higher or lower, move left or right—to give a different perspective. But you cannot zoom with your feet. Zooming assumes a static camera position and the same rate of change in the size of all the elements in the scene. As soon as you move your feet the relationship between elements in the scene starts changing. You are no longer zooming, but, to borrow a term from the film industry, you are making a dolly move. This is a much more natural movement. When you move in closer to your subject the items behind your subject will get smaller. And consequently when you move back away from your subject the items behind your subject will get larger. 
This may sound counter-intuitive at first, so let’s go over that again. Basically, the closer you are to your main subject when making a photograph, the smaller the background elements are going to appear. As you move back, away from your main subject, the background elements will look larger (scene compression). It does not matter what focal length lens you use. People throw around the term “telephoto compression” because this is more noticeable in photos made with long lenses. But the reason is not the lens itself, but the situations when longer lenses are used. We tend to use long lenses to magnify a part of a scene when we photograph at longer distances from our subjects.
As illustrated in the third set of images above, if you crop in or if you use a longer lens from the same camera position the compression in the area of the scene that is common to both the cropped short lens photo and the uncropped long lens photo will be exactly the same. Quality of the image will be very different, but the perspective will be the same.
In these particular photographs the subject is actually the window in the office. Let’s look at them again, in reverse. 

Now we are starting at the window. The window is too close and too large to be in the frame of the photograph. By stepping back about 5 meters we can now see the window as well as the Space Needle. Notice that the window got smaller, but the needle remained the same size. Then we move back to 20 meters and now the window is even smaller in the frame and now about the same size as the Space Needle (which is still the same size it was in the first photo). By moving back, away from our subject (the window), we have made the background element (the Space Needle) look larger.

Somewhere up above I mentioned the film term "dolly." There is a move in film called a dolly/zoom, sometimes also called the Hitchcock Effect. Here the camera is moved towards or away from the subject while the lens is simultaneously zoomed at the same speed. The effect can be shocking or subtle. One of the more subtle uses of a Dolly Zoom is in the film Goodfellas with Robert Deniro and Ray Liotta sitting across a table in a diner. As they are talking to each other the camera is rolled (dollied) back away from the actors and the lens is zoomed in so that the actors remain the same size but the scene going on in the background across the street from the diner gets larger. You can find this clip on YouTube .

Comparing sensors

How much does size matter in today's digital cameras (Feb 2017)

Curious about the differences between a crop frame and a full frame sensor? Are you worried that you are missing out on something by using a crop frame sensor instead of a full frame?

I am probably in the minority, but I think that the latest "crop" of crop frame sensors, such as the Canon EOS 80D or even the Canon EOS M5 mirrorless camera compare favorably with full frame sensors, such as in the Canon EOS 6D, especially for studio work.

Here is a pair of images made with a 6D and an M5. The subject and the lens (Canon 70-200L f/4 IS) remained stationary between the images, but the lens was zoomed to approximate the same angle of view/framing. The lens was attached to the tripod via its tripod color and then I simply switched out camera bodies to make the two exposures. The image with the 6D was taken at 200mm and the image with the M5 was taken at 121mm to account for the 1.6x crop factor (yes, it should have been 125mm, but the lens doesn't have a marking between 100mm and 135mm, so I had to guess at mark, and came up a few mm short). Lighting is a single Einstein head with a 35" octabank about 20" from the subject with no fill card.

In creating this, I noticed a slight change in the shape of the mannequin's face between the two images. My best guess on this is that there is a different amount of distortion (barrel vs pincusion) at the 121mm and 200mm focal length settings on this lens. Additionally, this is an internal focus/zoom lens that doesn't change physical size when focusing or zooming, so the magnification math (1.6x between the two cameras) might not be exact when the lens is focused closer than infinity. 

Anyway, I think you will see that the two images are very similar in quality. As expected, the depth of field is slightly shallower in the full frame (6D) image because the image is magnified more vs the small sensor. You can see this around the hair and the earring hole in the ear of the mannequin. But other than that, I think that you would be hard pressed to be able to see a difference between these two images if they were printed side by side in a magazine.

If you are just getting started in digital photography, or if you are sitting on the fence trying to decide if you should trade in your crop frame camera to buy a new full frame, I think I would opt for keeping the crop frame and using the savings on better glass or on lighting gear in the studio.

I have not made a comparison of images made in low light situations, such as stage performances. There might be, and probably is, a small advantage to the full frame sensors in those situations. I will see if I can do a comparison at the next event I photograph. 

Until then, keep enjoying the camera that you have now. 

Another New Year Fireworks Show at the Space Needle

Things going BOOM in the night

For the last 6 years I've spent part of my New Years Eve a few blocks away from Seattle's iconic Space Needle waiting for the midnight fireworks show. Here is a compilation of some of my favorite images from each show (2014 was a very foggy night). 

needle_fireworks

In preparation for the fireworks I presented a class at Glazer's Camera (which will be repeated in June in time for 4th of July fireworks shows) and had a short segment on KING5 TV's New Day show with Margaret Larson. 

I am also going to be presenting workshops at Glazer's in February and April on studio lighting and on corporate headshots. Look for them on the Glazer's class schedule page.

Happy New Year! 
John Cornicello

 

Another Perspective on Photography

Perspective -- The effect of viewpoint

Objects appear to shrink in size according to the distance from our eye.

Perspective comes from a Latin word, perspicere, “to look through.”

If you have a grouping of subjects in front of you (a scene) and you draw straight lines from all the points of the objects to a fixed point and then you take a plane surface (tracing paper, glass, etc.) and have those lines pass through that surface, the image formed on that surface is the perspective of that scene. 

In the case of our cameras and lenses, the lines will pass through the lens and be projected reversed left to right and inverted onto a surface (our image sensor or a piece of film). Either way, the projections are exactly the same. What you see are the relationships in sizes between the items in the scene. And this is how I will define perspective for this article. I will also take liberties with the word “distortion” in this article. Technically, distortion is one of the aberrations that can occur in a lens design. You can have barrel distortion where the corners of the image pull inward or pincushion distortion where the corners of the image pull outward. But for the sake of this article, I will use the word distort (distortion, distorted) to describe things that just don’t look quite right in the image. 

 
lens-distortion
 
Perspective projected between the objects and the viewer

Perspective projected between the objects and the viewer

Perspective projected through a lens

Perspective projected through a lens

If all we are to photograph are flat/2D objects on a single plane (such as a painting), we need to set up the camera parallel to the object and evenly centered on the object and we are probably done with the lesson on perspective. But we are often called on to photograph 3D scenes where we want to show the relationship between the objects in the scene. In doing so, we often want to keep parallel lines in the scene parallel in our photographs. So, we will start there. If the camera is held parallel to the lines in the subject they will be parallel on the sensor. But if the camera is tilted up or down (or left or right) from parallel we have the familiar situation of a building that looks like it is falling backward (by tilting the camera up) or we see parallel train tracks appearing to converge in the distance, or rectangular building appears to be a trapezoidal shape with one side being shorter than the other. These effects are also known as “keystoning” because the distortion resembles the shape of the keystone in a stone archway.  The closer you are to your subject(s) the more pronounced the effect will be.

This is because of relative distances. In the case of the building falling backwards, the effect indicates that the photographer is too close to the building and not able to get up high enough to photograph straight on. In order to frame the entire building the photographer points the camera upward to capture the top of the building and while the base of the building might be 10 units away, the top of the building might now be 20 or 30 (or more) units away. Objects closer to the lens (the base of the building) appear larger than objects farther away (the top of the building). So the building takes on a trapezoidal shape and looks like it is falling backwards. It does this when viewed with the naked eye or with a camera. However, with our eye our brain kicks in and compensates because it knows that the building isn’t falling. We expect that the top of the building is farther away and smaller. In a photograph, our brain doesn’t engage that process and we see the distortion.

There are a few solutions to this situation that we can see in this illustration.  

Camera A is in our basic situation. On the ground in front of and near to a building. Even with a wide angle lens, the camera cannot capture the entire height of the building while maintaining a parallel relationship to the building (red lines in the upper diagram). The first solution is to use a tilt-shift or perspective control lens. Using the shift function of the lens the photographer can set up the camera parallel to the building and shift the lens upward to move the image on the sensor to encompass the building (blue lines). Now the perspective on the building is actually wrong in the photo, but appears closer to what we want or expect to see. Personally, I often find these “corrected” photographs to be more disconcerting than the falling building in an uncorrected photograph. It is subtlety “just not right.” And a tilt/shift lens is usually an expensive option and not always readily available.

The next option is to raise the camera (B) up to a higher position, about midpoint on the height of the building so that the base and the top are the same distance from the camera.

The third option is the best, but usually not an option, and that is to move back a few hundred units so that the distance from camera to the base of the building and the distance from the camera to the top of the building are relatively the same. At this longer distance the camera can be parallel to the building or even off a little bit from parallel, and the lines will appear parallel.

The bottom diagram above will help understand what is happening. With camera A the top of the building is twice as far from the camera as the base of the building. So the top will be half as big as the bottom, leading to the “falling backwards” feeling in the photograph. With camera C, the base and the top of the building are virtually the same distance away, so will be the same size in the photograph. 

There is also a fourth option, that is to “correct” the image in post-processing. For this you will need to use a wide angle lens and be back far enough from the building to capture the building top to bottom (with the camera tilted up) so you can stretch out the top of the building to make it similar in size to the base.

Up until the last paragraph I have not mentioned the type of lens (wide angle, normal, telephoto) involved because all of the effects mentioned are determined by the camera to subject distance. When forced to be in close you are forced to use a shorter lens and this causes many people to think that the lens is the cause of the distortion. It is not. All lenses when used from the same position have the same perspective. Camera A or camera C are forced to use a wide angle lens because the field of view of a longer lens will only take in a small part of the building. As you back up to the position of camera C you can use a short, normal, or telephoto lens and the choice of lens will determine the magnification of the building and how much of the surrounding landscape will be included in the frame, but the perspective will be the same with any of the lenses.

This doesn’t only apply to buildings or other tall objects. The same thing happens if you are looking down on a subject. For example, if you are at the top of the grand canyon and photograph down into the canyon from the rim, the bottom of the canyon appears much smaller than the top. But if you were flying over and photographed the canyon from a very high altitude the effect would be much less extreme.

So far, we’ve dealt with one object in the scene and its relationship to itself. Perspective is also about the relationship of various objects in a scene. It can be a landscape with a barn, some trees, and mountain range in the background. Or it could be players on a sports field. Or it can be two wine glasses on a table. 

As with the building, the relationship between the glasses in the following examples is determined by the camera to subject distance. The focal length of the lens just determines what fits into the frame at that distance. The basic set up here is a white seamless paper backdrop with two wine glasses about 46” in front of the backdrop. The glasses are identical in size with one glass six inches in front of the other. There is also a snooted light on the backdrop simulating a spot light. All of that will remain the same and we will examine what happens when the camera is moved closer or farther from the glasses. 

We will start out with the camera in close, about 12” from the front wine glass. To fit the glasses into the frame I have selected a 24mm lens. At this close distance the front glass appears to be almost twice the size of the rear glass, even though they are physically the exact same height. The spotlight on the background is small and tight. The front glass is in focus, but the rear glass is soft and out of the range of the depth of field at the aperture used for the photo (f/10). 

24mm lens 12 inches from the front wine glass

24mm lens 12 inches from the front wine glass

Next, I will keep the 24mm lens on the camera but I am going to back up the camera to be 85 inches from the front glass. Obviously everything in the frame is a lot smaller because we are 7x farther away from the glasses. But now both glasses appear at almost the same size and the spot light on the background has grown larger (even though the light was not moved or changed in any way between shots.

24mm lens at 85 inches from the front wine glass

24mm lens at 85 inches from the front wine glass

Keeping the camera at the new 85 inch distance, let’s change to a 135mm lens and get this image. 

Again the glasses are almost the same size and the background spot is larger than in the first image above. People often call this look “telephoto compression,” but is it? In the next set of images I have taken the photo with the 24mm lens and cropped it to match the framing of the image taken with the 135mm lens. Remember what I said earlier, all lenses have the same perspective from the same camera position.

Here are the images with both lenses taken from the same camera position 85 inches from the glasses and cropped the same compared with the 24mm image that was taken at 12 inches from the glasses.

There are a few things to take notice of here. First, of course, is that even though the photos were taken by radically different focal length lenses (24mm and 135mm), the area of the images common to both images have the exact same perspective. Changing the focal length of the lens did not change perspective. But it did change the field of view and hence the size of the objects in the scene. And what about the spotlight on the background? Why did it change in size between the close in shot with the 24mm lens and the more distant shots with the 24mm and 135mm lenses? It is all back to relative distances. When in close (12”) with the 24mm lens the background is 46” away, about 4 times as far away as the glasses. When the camera is backed up to 85” the background is still 46” behind the glasses, but now the background is only about 1/3 farther away from the camera instead of 4 times as far away, making the background appear larger in the image.

The thing to remember here is that the closer you are to your subject, the smaller items behind the subject will appear. The farther you are from your subject, the larger the items behind your subject will appear. At first this might sound a bit backwards. Shouldn’t items in the photo get smaller as you move back away from them? Yes, they do. But foreground items get smaller much faster than background items as you move back. Then the usual option is to use a longer lens to "zoom" in on the subject and make it larger (along with the background). As you move back the scene compresses. This compression is NOT caused by the lens you use, but it is most noticeable in photos taken with longer lenses because they crop in on the scene and only show you a smaller area than you would see with a shorter lens. The area of the scene that is common to both photos will have the same compressed look. I will come back to this once more a bit later.

Next look at the depth of field in the images. The left image (24mm) has much more depth of field. Both glasses are reasonably in focus, though overall quality of the left image is lower because it has been enlarged so much. In the photo taken with the 135mm lens the front glass is reasonably sharp, but the back glass is beyond the depth of field at f/10 and has gone soft. Does that sound familiar? Go back to the 24mm full frame image above and see that the depth of field is about the same as in the 135mm full frame. Let that sink in. The depth of field with the 24mm and the 135mm lenses is the same when the size of the subject is the same in the frame. The focal length of the lens on its own is not a factor in determining the depth of field in a photograph. It is the magnification of the subject (focal length plus camera to subject distance) that determines the depth of field at any given aperture (f/10 in the case of these examples).

I hope that at this point you are starting to take on the mantra, “it is all about the distance.” Take a look at some of my lighting articles, where you will see a similar situation. The closer your light (camera) is to your subject, the darker (smaller) the background will be. The farther your light (camera) is from your subject, the lighter (larger) your background will be. We can even extend this to depth of field. The closer your camera is to your subject (with the same focal length lens), the less depth of field you have and the further you are from your subject (with the same focal length lens) the more depth of field you have. It is all about the distance.

OK. One more time through this to drive home what happens as you move in closer or move back farther from your subject. This time a landscape scene where we have a house with a mountain range in the distance behind it. Start with the camera 1000 feet away from the house and 5000 feet from the mountains. Now move in closer to be 500 feet from the house. The house is now twice as close and consequently twice as large as it was before. But the mountains in the background went from 5000 feet away to 4500 feet away, hardly any change at all. So while the house doubled in size, the mountains stayed the same size and now appear much smaller in relation to the house than they were originally at 1000 feet from the house.

We can turn that around if that makes it easier to understand. Same house and mountains. We set up the camera 500 feet in front of the house, which is 4500 feet in front of the mountain. Next we back up the camera to be 1000 feet from the house and 5000 feet from the mountain. The house became half the size it was before, but the mountains remained the same size, making the mountains appear that much larger in relation to the house.

Again notice that no mention was made of the focal length of the lens used for these photos. These changes in proportions are independent of the lens used. There is a famous quote from Robert Capa stating that, "if your photos are not good enough, you are not close enough."  There are multiple ways to get closer to your subjects. Your lenses are like a set of tools, you select the right size for the job. The camera to subject distance determines the perspective and then you chose the lens with the field of view that frames the scene the way you want. As a journalist you might be working on an intimate story and want to be in physically close to your subjects. A short/wide angle lens allows you to get in closer, making a stronger impact, giving a feeling that the viewer is right there next to the subject of the photograph. But at other times or in other situations you might want to back away from the subject to increase density, then a longer lens is the choice to bring things closer. It depends on the story you want to tell in your photograph. 

I hope that helps clear up some misunderstandings about lenses and perspective. But there is still more to it. How you view the photographs. But that's fodder for another article about viewing distances and enlargements. For now, please go out and make some meaningful photographs!

Thanks!
JohnC

 

Light Depth

Inverse what?

In our last exciting episode, I wrote about adding diffusion to your lights. In that article I made a few references to the depth of your light and why you want to have various size light modifiers instead of moving your lights closer or farther from your subject. I promised that I would write more about this in a follow-up article, so here we are.

As noted previously, the quality of light (hard or soft), is determined by the size of the light as seen by the subject. When first starting out, you might only have one light modifier, such as a 24x30 softbox. So the temptation there is to move the light in closer or move it back farther from your subject to control the size of the light, and thereby the quality of the light. This does work. However, it has a secondary effect on your image. Moving the light changes the depth of the light.

Depth is one of the four main things I think about when designing my lighting for a portrait. The others are the depth of field that I want (how much is in focus), the size of the light (the shadow edge quality), and the amount of power I need (to get the aperture I want for the depth of field I want).

The depth of the light is based on a law of physics called the Inverse Square Law. This law states that a specified intensity (in our case, light) is inversely proportional to the square of the distance from the source of that light. As an example, if you double the distance between the light and your subject the amount of light falling on the subject will be 1/4 (at twice the distance the light has to spread out to cover 4x the area, see the illustration below). If you move the light back to 3 times the distance, the amount of light will be 1/9th the power, and so on.  

inverse-square-1
inverse-square-simplified

Another part of this law, that seems to be often forgotten or ignored, is that it applies to a point source of light, something we rarely, if ever, actually use. As you put modifiers on your lights, such as softboxes, umbrellas, or add a lens, such as in a spot light, we start drifting away from the law. So don’t get hung up on the inverse square law or on measuring the distance between your light and subject. You only need to remember one simple rule: The closer your lights are to your subject, the darker the background will be.  

OK, sounds simple enough. But it is also very powerful knowledge. With this knowledge you can take a simple white seamless paper background and make it appear white, black, or any shade of gray between them. It also allows you to light your background separately from the subject to control the apparent depth of the scene. More on that later.

So, let’s look at some examples. In this series of images the subject is 65” in front of a white seamless paper background. The single light is a 24x30 softbox. The only changes between the images is the distance from the softbox to the subject and the power setting on the light to maintain the same f/4.0 exposure. As indicated in the images, the distances are 12”, 24”, 48”, and 96”. The first thing I think you will notice is how the tone of the backdrop changes. 

light-depth

You will also want to take a look at highlights on the subject. Look at the cheek. Specular highlights are mirror-like and at first seem to not follow the inverse square law. In actuality they do follow the law, but in a reverse way. Specular highlights maintain the same brightness, no matter what the light to subject distance is, but they change in size inversely proportional to the distance. As your light is moved farther from your subject that specular highlights get smaller and appear brighter because the rest of the image is getting darker while the highlight stays the same brightness.

specular-highlights

Now, about lighting your background separately from the subject. This involves adding more lights. In this case I added one light on my white background, a flash with a 7” silver dish reflector with a red gel. With the main light (the light on the subject) 96” away from the subject you can make out a pinkish glow on the background. But when I move the light in to 12” away from the subject the white background goes to a dark gray (as shown above) and the red gel on the background light can now be seen. If I had used a dark gray or a black background paper the red would be a richer tone than the pink that you see here. The background light was on its lowest setting. If I could have lowered the power more, it would have been more red, too.

background color

A practical application: Group Photos

So far, I’ve been talking about light falloff from subject to background. We can also think about group photos and fall off from subjects different distances from the light. By combining our knowledge of light falloff with a lighting technique called feathering we can learn to light a group of people. Feathering is when instead of pointing the light directly at our subject(s) we point it a bit off so that the light skims across our subjects. A fill card (white foamcore or a pop-up white disc) helps fill in the shadows from the right side.

group-lighting-1

As an example, if our light is on the left side of our camera we would point the softbox or umbrella at the person on the right side of the group. The main intensity of the light will now be aimed at the person farthest from the light and the lower intensities from the edges of the light will be lighting the person closer to the light, helping to even out the light across the group. If the light is still too uneven, we use our knowledge of inverse square to tell us to move the light back, farther away from the group to even out the illumination across the group.

group-lighting-2

Here is a group photo of my friends at CreativeLive posing for me. This image was lit with one studio flash in a 60" Photek Softlighter on camera left and a fill card on the right. The Softlighter was backed up a bit to help even out the exposure across the four individuals.

softlighter-group-photo

That's all for today. Thank you for following along.

JohnC