Sunday, September 29, 2013

What is High Speed Sync?

1/3200th w/ High Speed Sync
1/3200th w/ High Speed Sync

High Speed Sync is a dedicated flash camera function that allows the photographer to use flash in situations where the lighting requires a shutter speed that would otherwise prohibit the use of flash. 

Ok that statement is a bit high on the techno speak, so lets look at it a bit differently. In most flash photography shutter speed is pretty irrelevant, the lighting situation is such that the ambient light leaves little or no impression on the sensor and the flash dictates both the exposure and acts to freeze the action. In photography without flash the aperture is used to control depth of field while the shutter acts to control action - a slow shutter shows motion blur and a fast shutter freezes objects in motion. With flash photography even in cases where you are blending with ambient light the flash will still have a tendency to freeze action. This happens because the short, high intensity burn of the flash acts as the effective shutter speed, usually somewhere around 1/1000th of a second depending on flash output.

I mention this because it can be easy to forget if you do not regularly shoot in situations where it is necessary to shoot outside of the cameras sync speed. When the flash is freezing your action for you it is easy to forget that the flash does not function with the camera at shutter speeds above the camera sync - for most cameras this will be 1/250th of a second, though for the EOS 6D that speed is 1/180th. To find your Camera’s sync speed you will need to check the camera's user manual.

Ok since we have established that flash freezes action and it is therefore not necessary to use the shutter to do that then why do you need to be able to use flash with a shutter set above the sync speed? Well sometimes the ambient light you are blending with is just too bright for your camera’s sync speed, this generally means you are shooting in sunlight. 

Second Curtain Closing
Second Curtain Closing
To understand this a little better it lets take a moment to look at how the shutter functions. At and below sync speed the first curtain of the shutter opens completely before the second curtain starts to close, this allows the entire sensor to be exposed at once. At speeds above the camera’s sync speed the second curtain starts to close before the first curtain has fully opened, at higher speeds only a partial strip of the sensor is being exposed at any given moment.

High Speed Sync changes the duration of the flash burn. Instead of the flash firing once the first curtain has cleared the shutter the flash fires a series of pulses and burns for the entire duration of the shutter action. This function allows the flash to be lit for every section of the sensor without the second curtain blocking part of the sensor which happens if the flash fires a single burst.

The Image at the top of the post was photographed using High Speed Sync. That image was taken at 1/3200th of a second, well out side of the camera’s normal sync speed. The next two images show the scene without flash, the first at 1/180th of a second which exposed the apple nicely but completely blew out the sky, the second at 1/3200th which was the speed needed to get proper exposure of the sky but it crushed the apple in shadow leaving it and the leaves quite dark. It would be possible to create an HDR of this scene, but for HDR you really need to be shooting still life. High Speed Sync can create the image in a single exposure and allows blend flash with sunlight, something the regular sync speed does not allow.

1/180th no flash
1/180th no flash

1/3200th no flash
1/3200th no flash

* Note not all flashes and cameras support High Speed Sync though it is available on Canon, Nikon, and Sony Alpha lines, as well as being supported by some third party flashes. You will need to consult both your camera and flash manuals to see if High Speed Sync is an option for you.



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Sunday, September 15, 2013

Photographing Sports


Photographing sports can be challenging for the beginning photographer. A couple of different approaches can be used to help get great images. In An 18% Grey World I wrote a bit about how the camera makes the decisions it makes, if you have not read that post yet it would be good to look over it now. When approaching sports photography there are three different approaches you can use.

Your first option is full automatic letting the camera make all the decisions on exposure. If your camera does not have a sports setting in its full auto array this tends to be the worst of the three options. Even in bright sun the camera will operate with lower shutter speeds so that it can keep the ISO low and the Aperture high giving the camera the biggest depth of field. In general full auto will always have motion blur, a lot of motion blur as it will keep your shutter between 1/60th and 1/250th of a second. The sports setting, if your camera has it, will help do a better job as it will tell the camera to try and keep the shutter at 1/250th or higher, greatly reducing the amount of motion blur. This will be your best option if you are using a point and shoot camera.

The next option is to use shutter priority or Time Value. Many photographers recommend this approach as the camera tries to maintain your preferred shutter while still judging exposure. It is important to remember that while you set the shutter this is still an automatic setting for the camera, many cameras will only give preference to the shutter speed you have selected. This means that while you may have told the camera you want a 1/500th shutter it may drop you to 1/60th if the meter tells the camera it is 3 stops under exposed, this can be very problematic especially if the camera is spot metering the scene, but even in evaluative metering the camera can still drag your shutter speed down to far for shooting sports. Some cameras allow you to turn off the Safety Shift or switch it to shifting the ISO to prevent the camera dragging the shutter.

My preferred option is shooting in full manual mode, this insures that I can keep the shutter speed high enough to capture the motion the way I want to show it. There is a bit more work associated with shooting this way if you are shooting in a changing light environment. However unless your subject is moving in and out of bright sun and extremely harsh shadows the change in exposure will only be a couple of stops. The other time you can see a big shift in light is when photographing a game that starts before sunset and continues into the night. In this latter case the exposure shift is much more gradual and is easy to compensate for as long as you pay attention to your shooting conditions. 

A brief run down of how I approach this shooting situation. If I am shooting sports in daylight I set the camera to f8 ISO 800. In bright sun this allows me a shutter speed of 1/1600th (Sunny 16) certainly fast enough for hand holding the camera at any focal length and freezing most action. Even if clouds are moving in and out from in front of the sun I can shift two stops in the shutter and still maintain a shutter speed of 1/400th Again this will allow me to hand hold a telephoto lens and still freeze most of the action. When shooting at night I set the camera (EOS 7D) to ISO 6400 and the shutter to 1/500th with the aperture set to the maximum aperture for the lens at its longest focal length. Many lenses have a variable aperture which will be something like f3.5-5.6. For this kind of lens I would set the Aperture to 5.6.

A few other things to keep in mind. 
  • Blur becomes much more apparent the longer the lens you use. If you are shooting with an 800mm lens then the motion blur of your subject will become more apparent and you will need a faster shutter to get tack sharp images. 
  • The same holds true for camera shake. As a general rule to eliminate camera shake the shutter speeds needs to be equal to or faster then your lens length. A 60mm lens can be hand held at 1/60th of a second, an 800mm lens can be hand held at 1/800th. An image stabilized lens will generally get you one stop of shutter speed, meaning an 800mm IS lens could be hand held at 1/400th.
  • Post production of RAW images can recover 3 or more stops in your image provided you don’t have blown highlights. What this means for shooting sports at night is you can recover a lot from what the camera considers under exposed. As long as you do not have an extreme amount of clipping in your shadows shoot the faster shutter speeds to eliminate blur and bring the images back in post.
  • If you can not shoot in RAW set the camera’s auto-light optimization to high and it will do the same thing for you by recovering shadows as it saves the image to Jpeg, allowing you to favor shutter over “correct” exposure.

* This post is written using the terms Canon uses, most manufactures have these options though sometimes under a different name. 


Sunday, September 8, 2013

Canon 580EX-II - Equipment Review

Canon 580EX-II
Canon 580EX-II

The 580EX-II was the top of the line Canon Speedlite until the release of the Canon 600EX-RT. For many shooters the release of new equipment opens opportunities for them that had not been practical before as older equipment re-enters the market at 1/3 or even 1/4 of original cost. For many shooters this will allow them the option of adding a powerful E-TTL II flash to their kit that can also function as a master controller for their existing 430EX-II or other Canon Speedlites. 

Many other shooters will be wondering if the 600EX-RT is a better option. Lets take a brief look at that first. Both the 580 and the 600 are capable as functioning as an optical master for the existing Speedlite lines, while the 600 is capable of controlling 5 flash groups and the 580 only controls 3 in optical mode the 600 is also limited to 3 flash groups. The rational behind this limit was probably limit of the older flashes to groups A thru C, however it would have been nice to have the option to use older units in those groups and use 600s in the D and E group in an optical controlled system. The short of it is to gain the added advantage of 600 series flashes at this point in time all flashes have to be 600 series making that set-up much more expensive then using a 580 master with other 580 and 430 units as slaves. Used 580s are now comparable in price to new 430s which makes adding a used 580 to the mix an attractive option.

For shooters that are already using cameras like the 60D and 7D which offer master controller function through the pop-up flash paying an additional $550 for a new 580EX-II was probably not an attractive option. Now you really should consider picking one up used in the $200 dollar range, this is why. The 60D and similar model cameras while capable as acting as a master controller were limited to flash groups A and B by using a 580 as your master controller you now have access to group C as well creating much greater freedom when using speedlites for 3-Point Lighting. For the higher end cameras that already supported all three flash groups the big advantage to having an on camera 580 is when you are controlling flash groups with the camera oriented to portrait format. The common problem the pop-up unit encounters in shooting in this fashion is putting some of the off camera flashes into the shadow of the lens which prevents them from firing. The larger surface of the 580 unit along with the ability to orient it in different directions can allow all of the flash units to easily see the master unit. 

If you are using a higher end camera like the 6D a pop-up option is not available and a 580 is a very affordable option. While it is true that ST-E2 units can be purchased new in the same price point as used 580s, the big advantage of a used 580 is that it gives you one more flash unit. Even with this unit mounted on camera it can provide fill light or be used as a Bounce Flash.

The 580EX-II is still a very relevant option for most shooters. It is a powerful reliable choice and when it comes to the use of other optical units it’s price point makes it a superior choice to the 600 Series.






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Sunday, September 1, 2013

Blending Flash with Ambient Light


Lighting Set-Up
Lighting Set-Up
Mixing strobes with existing light seems to be one of those things that confuses many photographers. This is most likely due to the fact that two sets of photographic rules are at play when blending flash and ambient light. The first set is what natural light shooters tend to live and die by, the “BIG 3”. If you have read my earlier blog post you know that I tend to look at this set of rules as being very malleable. The second set of rules come out of studio lighting, where light is controlled by light, or by aperture if you are working with a set of strobes that are not adjustable (but even in this case you can control flash power by distance to the subject or the use of neutral density gels and not need to use on camera settings).

So where does the confusion come in? When a photographer is shooting using all natural light where they have very little or no control over the light, such as landscapes, their only recourse is to adjust camera settings. If the scene is already properly exposed and the photographer wishes to adjust shutter, they then have to adjust aperture or ISO to get an equivalent exposure. In the days of film they were really stuck with adjusting aperture or wasting the rest of a roll of film to change ISO/ASA.

When shooting under studio strobes shutter speed is almost meaningless. A simple way to demonstrate this is to set a camera up in a room on manual setting. Set the ISO, shutter aperture and flash for the exposure you want when the lights are turned off. Turn the lights off take a picture with flash and then adjust your shutter - just your shutter - and take a second image. As long as both shutter speeds are within your cameras sync speed there will be no difference in the two images. This is because flash photography has an effective shutter speed which is the burn time of the flash, in most cases somewhere around 1/1000th of a second. This effective shutter is much much faster then even the cameras fastest sync speed (for most Canons 1/250th) As long as you understand this you understand how to mix flash with ambient light.

The how too blend flash and ambient is actually quite simple. Set your scene, set your camera for an ISO you are comfortable with and set your aperture to create the Depth of Field that you wish to have and set the shutter to your maximum sync speed. Once this is done set your flash output to properly expose your subject (depending on your flash this can either be done with output, neutral density gels, or distance to subject). At this point when you release the shutter you should have a properly exposed image. If you do not adjust your flash power accordingly. 

Once you have a properly exposed image you can then mix ambient light in simply by slowing your shutter speed. Remember from the lights turned off room exercise above that shutter speed does not effect flash exposure, so the Big 3 methodology does not apply to the exposure from the flash and you do not need to adjust aperture or ISO as you change the shutter(this is where people get confused). By slowing or “dragging” the shutter all you are doing is allowing more ambient light to balance the areas of the image that are not being exposed by the flash.

So why do we blend flash and ambient light? There are several situations which can call for this, the most common is when more light is needed then is available yet we do not wish to loose the ambience such as in a club. Another common place to use flash and ambient is when photographing a person at night and wishing to have a city scape behind them visible as well. This is similar to the first but the flash is needed because the person would not expose at all, they would simple be a shadow blotting out the city lights. Another case is to freeze action, such as bullet photography, the flash is used so the bullet can be frozen in the frame and the longer shutter allows the rest of the scene to also be exposed. Another reason to add flash is to create shadows, in the sequence below you can see that the room is very evenly lit and by adding flash I added shadows which creates depth in the images. In actuality blending flash will be used for multiply reasons in the same image.

So now we have covered the theory, lets look at the nuts and bolts of what I did for this exercise and how it affected the images. Photographed at the top you can see how I set the camera and flash in relation to the scene. I treated the piano as the subject of the image, I placed the 600EX-RT on 1/4 power, into a 24” softbox, 6 feet from the piano. The camera was the Canon 6D with the 24-105 f4 L set to 24mm. The ISO was 400 and the aperture was f4 for all of the images in the following sequence the only thing that changes is the shutter speed which is listed on the images.


1/180th

1/125th

1/60th

1/30th

1/15th

These last two images below show the scene, the first with the camera set to take a flash exposure but no power to the flash, and the second with the camera set to take the image just with ambient light. The Canon 6D sync speed maxes at 1/180th which is why there is a discrepancy between the first image in the sequence above and the image here for flash with the flash turned off. In situations where you need a faster sync speed Hi-Speed Sync can be used to get speeds above your cameras sync speed. (This will be covered in a later blog.) For this example I allowed the camera to set the default shutter sync for the 1st image. I also did not correct for Color Balance, the camera was set to Flash which is why the total ambient light image has a yellow cast. I did this deliberately, in the sequence the competing colors make it a little easier to spot how much ambient light is effecting exposure. If you use AWB it will set to flash when a flash unit is attached to the hot shoe so the area exposed by the flash is closer to white. If you use gels to match your environment you will need to set your cameras white balance accordingly with the camera’s custom white balance settings. The exception to this is when using Canon CTO gels with the 600EX-RT. The 600 has a sensor which allows it to correct white balance to the Canon CTO gel being used if the camera is set to AWB. I have not explored this function yet so I am not sure how well it works. It also only works if the flash is mounted in the hot shoe.

No Flash 1/250th

Ambient Only 1/15th


So that is the basics of mixing flash with ambient, like color balance the only way to really learn this skill is through practice. Depending on your set up it is possible that if you are mixing a lot of ambient light you would need to step the flash power down slightly. Do not be afraid to experiment once you have a good grasp on how the toe exposure models work and how well they blend.







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Sunday, August 25, 2013

Bounce Flash


So what is Bounce Flash? Specifically, bounce flash is any flash that is bounced off of a surface to illuminate the subject, so a mono-block firing into a reflective umbrella is a type of bounce flash. In more common usage bounce flash is the use of an on camera speedlite* which is being bounced off of a wall or ceiling to light the subject. 

A lot of the blog posts I have written on technic have been aimed towards the serious enthusiast or pro who has invested in a wider array of gear and has the option of shooting multiple light set ups or using other modifiers. Bounce flash is a technic which is available to any photographer using a camera that has a hot shoe supporting the use of a speedlite, who has also purchased a speedlite with a swivel head. The minimal need for equipment and the number of mid range cameras, like the SX-50, that offer a hot shoe as an option make this an ideal technic for anybody who wants to do photography on a budget, or who does a lot of photography on the go and wants to be able to travel light.

Apart from the relative in-expense of bounce flash it is also a relatively easy technic to get the hang of on most modern cameras. The majority of newer cameras offer some type of TTL metering. TTL stands for Through The Lens and the camera actually triggers a very brief pre-flash which lights the scene that the camera then uses to judge over all flash power for exposure of the image. This is the equivalent of setting the flash on automatic. This can be used in conjunction with the cameras automatic settings meaning that this technic is available even to very inexperienced photographers.

In general I recommend setting the camera to manual so that you have creative control over ISO, shutter, and aperture while leaving the flash to calculate the needed flash power. As a general rule bounce flash will be used in “Run and Gun” situations where the distance between the flash and the subject is changing and the flash output will have to be adjusted to match. This is what the TTL is designed to do, while it is possible to use this technic without TTL it then becomes more of a walk and gun situation and requires a lot more skill on the part of the photographer to be able to constantly adjust flash output to match the changing scene.

Bounce Flash is one of those technics where there is no specific “right” way to do it, however there is quite a lot of flexibility available to sculpt the light even when using TTL. What follows is a series of four images where the only change is the direction the bounce flash is being fired. All of these images where taken with the Canon 6D set to ISO 200, f8 and 1/180th with the 24-105 f4 L set to 85mm and the camera located 4 feet from the subject. The flash used was the Canon Speedlite 600 EX-RT set to ETTL. The E in ETTL stand for evaluative and refers to a Canon specific algorithm used to determine exposure. Nikon has a similar brand specific algorithm which is designated with an I in their ITTL flash units.

Flash bounced off Ceiling
Flash bounced off Ceiling 



Flash bounced off Wall Behind Camera
Flash bounced off Wall Behind Camera




















Flash bounced off Wall Camera Left
Flash bounced off Wall Camera Left




















Flash bounced off Wall Camera Right
Flash bounced off Wall Camera Right





















Looking at these four images you can see that there is a lot of flexibility in how the light falls on the subject. The primary thing to keep in mind when using this technic is where the light is coming from. In many situations your environment may dictate that by only providing one or two suitable surfaces to reflect the flash off of. It is important to remember that the flash will pick up the color of what ever surface it is reflected off of. In many cases this kind of color cast can be corrected in post as the flash will be lighting the subject and background both and the color cast will be applied to the entire scene. But when possible us a neutral surface like a white wall or ceiling.

If we look at this series a little more in depth, comparing the images where the light was bounced off of the ceiling with the image where the light was bounced off of the wall behind the camera we can see that both images are lit similarly but the light from behind the camera has a much softer quality. Similarly if we compare the images where the light was bounced from camera right and camera left we can again see that the light from camera left is softer. In both cases this is because the surface the light is reflecting off of is farther away allowing the light from the flash to spread out more. 

If you remember in this blog post we briefly looked at bounce flash in the discussion of on verses off camera light quality. In the second and third images on that post the hardness and softness of the bounced light was modified not by changing the distance of the light to the reflective surface but by changing the flash from wide angle (soft light) to telephoto (harder light). The wide angle - telephoto settings in the flash were originally designed so that when used in conjunction with different focal length lenses the flash would only light what was actually in the frame. This allowed the flashes to light subjects that were far away as the output was directed more to the front and not spread out. However for Bounce Flash it gives us more options for sculpting the light. another handy tool, particularly if you have an assistant is a piece of white foam core or other reflector. This allows you to position a reflective surface wherever you want. This is a very inexpensive way to overcome environmental obstacles.

So now you have an idea of what bounce flash is, but the way to really get an understanding of this technic is to just go out and shoot a lot, change the angles the flash is being bounced the distance to the subject, how much in front or behind the reflective surface is and you will quickly begin to understand all the potential this technic has for sculpting light. This method really opens up a lot of creative shooting options for events and parties. 


On Camera Flash for comparison
On Camera Flash for comparison

* In this post I am using the term speedlite as short hand for any on camera flash that is mounted in either a hot shoe or cold shoe and triggered by the cameras shutter.




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Sunday, August 18, 2013

What is Color Balance?


One of the more common mistakes beginning photographers make is not getting good color balance. In most situations, particularly with cameras introduced in the last 3 years the auto white balance function of the camera does a fairly good job most of the time, where it tends to fall flat are areas with mixed light temperatures, so after a brief intro to what color temperature is I am going to focus on ways to correct mixed light situations.

So what is Color Balance? To understand color balance (also commonly incorrectly called white balance) you need to first understand that all light has color. The Color of the light is referred to as color temperature and is measured in degrees kelvin. The warmer the light, that is the more yellow, orange or red the light is the lower the color temperature, as the light gets closer to white and then blue the temperature in degrees kelvin goes up. This seems backwards at first glance, but remember when iron is smelted it starts with a low red glow as it gets hot enough to forge it moves to letting off orange light and when it is hot enough to pour iron starts pushing into the yellow colors. Another way to remember that the high temperatures are the whites and blues is to think of arc welders or lighting. Electric arcs are one of the hottest things we can observe, with temperatures exceeding those of the surface of the sun, and they are in the white and blue color space. For a more complete run down of color temperature click here.

Now you have an idea of what color temperature is, how does it work with color balance? Color Balance is matching the light sources so they all of the same or very similar color temperatures so the camera can then shift the sensor to read white objects as white. It is a subtle but important difference between color balance, matching the light sources, and white balance, setting the camera to read the light sources correctly, but it is an important distinction. It is also why the auto white balance setting will always fail in mixed light. The other common mistake is having a camera set to daylight (essentially white light) and to take photos under artificial light, this is what gives photos that ugly yellow, yellow orange, or yellow/green cast. 

Modern artificial lights tend to be pretty close to 3000k without any green tint. As this gets more common, lower end cameras are tending to have one artificial light setting. High end cameras ,on the other hand, may have four or five artificial light settings (not counting flash, which is generally balanced for daylight). These multiple settings can more closely match the most common color temperatures of incandescent (orange/yellow to yellow) and florescent (yellow to yellow with a green tint) lights. Having these multiple presets can be a quick way to find a suitable white balance if you can not preform a custom white balance. I am not going to go into setting a custom white balance beyond mentioning it is a good idea to use a grey card, because different manufactures have different methods for achieving a custom white balance reading. Consualt the camera’s manual.

For this post I am going through a quick exercise of matching a 5600k Speedlite with modern florescent recessed canister lights. Here is a quick look at the equipment used. For the flash I used a Canon 580EX-II and to match the color of the ambient light I used LumiQuest gel holder. In the photo the gels on the left are used for color correction, The two at the top are a one stop and a two stop neutral density gels which can be used to cut flash intensity on flash units with a fixed power output. The gels on the right are used for Creative Lighting with Color (an upcoming post). For this entry I am only going to speak about the gels on the left. Starting at the top and moving counter clockwise we have a 1/2 stop (or cut) Color Temperature Green (CTG) followed by a 1/4 cut CTG, 1 cut Color Temperature Yellow (CTY), 1 cut Color Temperature Orange, 1/2 cut CTO, 1/4 cut CTO and finally a 1/2 cut Color Temperature Magenta. 

Speedlite with Gel Kit
Speedlite with Gel Kit

As a general rule the CTY and one of the CTGs will be used together to balance older florescent lights, newer florescent bulbs do not tend to have the green tint. The CTO,s will be used for incandescent, but actually look to see what color/s  are most prevalent. The CTM is used on your subject, usually used as fill, when the subject is placed in a green screen environment. In a green screen environment background light reflects off of the screen and will give the subject a green cast. By using a CTM on the subject the green tint is neutralized. If you use photo editing software in the white balance section you have probably noticed a slider that goes from yellow on the left to blue on the right and a second slider that goes from magenta on the left to green on the right. These colors are directly opposite each other on the color wheel and mixing them together neutralizes there impact. In effect your camera does this as its white balance function.

Ok, now you have the theory, lets look at it in practice. All four of these images are just a succession of photos of a white wall. The first image below is the color of the light in the room from the canisters lights when the camera is balanced for the color of the flash. The second images shows the flash firing and the ambient light being crushed out by the camera’s high shutter speed. When this is an option this is the best fix for the light. But it is not an option if you want a slower shutter speed to allow motion blur, or if you are shooting in an environment where blasting everything to white would not look natural, like a club for instance where doing so would destroy the ambience. I have included the histograms so you can better understand the differences in the light color that is causing the shift in the light. 

Image 1 and Image 2
Image 1 and Image 2

Looking at the first image you can see the light in this room has a definite orange cast to it, and looking at its histogram you can see how spread out the different colors of light are. Looking at the second image you can see how the light casts a gradient across the wall, even though the histogram covers a large part of the graph it is fairly uniformly grey as all of the colors are mixed fairly evenly giving us white light. 

The third and fourth images show blending and then correcting the light. In the third image the flash has not been adjusted but the shutter has been drastically reduced so that both the flash and the ambient light can expose the image. The gradient in this image from bottom right to top left clearly shows why the auto white balance in the camera can not adjust to this situation. There is not one uniform light color for it to adapt to and correct. You can also see how the histogram is all over the place even though this is just a photo of a white wall. The fourth image was taken with a 1/4 CTO placed over the flash and the white balance in the camera shifted from flash to florescent, this is because the flash is now pretty closely blended to the ambient light of the room which is pretty close to the florescent preset. 

Image 3 and Image 4
Image 3 and Image 4

Looking at the histogram we can tell it has not been perfectly balanced, but an exact balance is not possible with gels. At any rate it is much closer now the color is no longer painful to look at with only minor corrections needed in the computer. Corrections which can be applied across the whole image rather then trying to blend in different layers of correction, a much more difficult task. 

For these last two images I raised the flash to above the eye line as that is more typical for portraiture, as a result the gradient shift from the third images is seen here in the fifth images from top right to bottom left. The fifth image gives an idea of how difficult it would be to correct the color balance in the computer rather then only needing a minor adjustment to the over all white balance of the sixth photo taken in a close color balanced situation. The complete chaos in the histogram of the fifth image gives a clearer picture, even though the scene is very color neutral the histogram is all over the place.

Image 5 and Image 6
Image 5 and Image 6

All six of these images were shot on a the Canon EOS 6D camera with the 24-105 f4 L. The lens was set to 58mm the camera was set to ISO 400, f8 and a shutter of .4 seconds with the exception of the second image which had a shutter of 1/180th of a second to crush out the natural light. The flash was located 45 degrees camera right and was set to manual 1/32 power 14mm.


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Sunday, August 11, 2013

HDR


High Dynamic Range is a method of merging photographs to capture all of the visible scene in one image. HDR is only needed when the dynamic range, the difference from light to dark, is greater then the camera’s image sensor can capture. Many of todays cameras have a dynamic range of around 11 stops, the human eye has a dynamic range of around 14 stops. For this reason it is common to see photos where the landscape has a good exposure but the sky is blown out and has lost its blue color and all of the detail in the clouds, or the sky is in perfect exposure but the landscape is dark, lost in shadow. Using HDR to merge photos of differing exposures allows a person to create a photo that has detail visible in both the sky and the landscape.

Many of todays cameras have a built in HDR setting which removes the need to have software capable of merging the images for you, though software gives much greater flexibility in exactly how the images are blended. For instance on my Panasonic DMC-ZS10 point and shoot the HDR setting is a Scene function of the cameras automatic setting, as such I have no control over the aperture or shutter speed of the camera. On this camera when I use the HDR setting there is a slight lag to the shutter, the camera holds the shutter open creating an image out of the data captured. In this manner an image is created with a wider dynamic range then the camera would otherwise be capable of.

On the EOS Canon 6D the HDR functions more like it would if the photographer were to preform the image merging on computer in post production. The 6D has an HDR function that operates as part of the manual settings on the camera and can operate in M, P, Av, and Tv modes. On this camera when HDR is set you meter for the mid-tones and then select an exposure compensation value of either 1, 2 or 3 stops when the shutter release is pressed the camera quickly takes three images one exposed for the mid-tones one under exposed for the highlights and one over exposed for the shadows. The camera then creates a single image out of these three files.

In both of these cases software in the camera is attempting to mimic what can be done on computer in order to capture a wider range then the sensor normally would. Before digital HDR did not exist but other methods were employed to capture a wider dynamic range, HDR is an extension of those techniques. In the days of film when a photographer needed to capture a wide dynamic range a gradient filter would commonly be used to stop down the sky so that it was closer in exposure value to the landscape. If further correction was needed the developer of the film could selectively dodge and burn the film to lighten some areas and darken others. Gradient filters can also be purchased in blue or orange to better match the tint of the sky or sunset.

As photoshop and digital manipulation started to advance as a tool it became possible to capture a wider range of information then had been possible on film. Most film has a dynamic range of 4 or maybe 5 stops, this was particularly important in studio lighting and is where the 3/2 lighting ratio for subject and a background 2 stops brighter then subject (when you wanted a white background) come from. When you have a total of 4 stops it became critical to keep the lighting in a narrow band. The early digital sensors also had a very narrow band of sensitivity, however they had one distinct advantage over film. With digital it is possible to take several images at different exposure values stack them up and merge them into an image with a dynamic range of 10, 20 or even 100 stops if that were necessary. The spectacular images from Hubble are examples of HDR taken to extreme limits.

The other option that is available to digital is similar to the dodging and burning of the negatives during development. This is the use of RAW files, I mentioned above that many modern cameras have a dynamic range of 11 but there effective range when generating 8 bit Jpegs tends to be closer to 8 stops. By shooting in RAW and exposing for the highlights (this is key as anything lost in the highlights is lost) a photographer can then go into the file on computer and use RAW processing to pull up information that is being lost in the shadows. From this file an 8 bit Jpeg can then be produced that fully utilizes the 11 stops the camera has.

Now that we have spent a lot of time on what HDR is and where it comes from I am going to give a brief run down on how to do it. If you are about to ask why I am not spending more time on the how too, that is because it is about to be surpassed by technology, I mentioned that many cameras are already capturing 11 stops, they will soon be capturing more stops and in greater detail then the eye can see, as the greater demand for high definition moves forward the 8 bit format for Jpeg images, computer displays and printers will be surpassed by 16 or even 32 bit formats and the need for image stacking will again slip back into the realm of astronomy where it is being used to capture massive amounts of data that is not available in visible light. I have some confidence that this prediction is correct, in that, 8 years ago to get a good HDR image it required stacking 5, 7, or even 9 images to get a wide enough range of exposures. Now three images will allow you to use the 11 the camera captures plus 2 stops (or three if you use a 3 stop interval) below and above giving a rang of 15 (or even 17) stops.

So now we have an idea of what HDR is, how does it all work? I brushed over that above in that you take pictures with different exposures. The setup up is really quite simple though the blending on computer (the post) takes a bit more practice. To take the images you will need a camera and a tripod. It is possible to make an HDR with the camera set to auto (in some cases) by using the cameras exposure compensation settings to get the ver and under images, but it is best if you are comfortable shooting in full manual mode. Once the camera is on the tripod the image is framed and the focus has been set, turn the auto focus off (if you did not focus in manual) take your first images metered for the mid-tones then use the shutter speed to adjust down 2 stops, so if your mid-tones were shot at 1/125th then your shadows will be shot at 1/30th and then adjust up two stops above the first image to 1/500th to shoot your highlights. 

If you are using an older camera and need a wider range you could also shoot down an additional 2 stops at 1/7th and up two more at 1/2000th, but if you are using a fairly modern camera (made in the last 3 years or so) then you really wont need to. Once you have the 3 (or 5) images you will merge them in Aperture, Lightroom or Photoshop - depending on your software you may need to find an additional plugin to do this.

When is HDR used? HDR really is best used in situations where the dynamic range is too great for the camera and modifying the light is not practical, several examples are sunrise/sunset photos, landscapes, cityscapes, architectural photography, things that are too big to effectively light AND the dynamic range of the scene is greater then the camera can capture. If you are looking at a scene and the camera can capture the image without an clipping occurring in the histogram HDR is not needed.HDR is not really practical for subjects that move, portraits, pet photography - anything like that it is much better to correct the lighting before the image is taken then it is to try and get 3 or more images where everything but the exposure is the same.

Image created with HDR
Image created with HDR
This first image is an HDR composite.

















The three following images are the multiples used to create the HDR shot at 2 stop intervals 


2 stops underexposed to get highlights
2 stops underexposed to get highlights

Exposed for Mid-tones
Exposed for Mid-tones

2 stops over exposed to get shadow detail
2 stops over exposed to get shadow detail



This last image is the scene as the camera wanted to capture it using the auto setting














Comparing the first to the last it is possible to see how HDR both allows a photographer to capture a wider range and how close camera is getting to making HDR an unnecessary art. If you wish to explore HDR in more depth I suggest looking to the works of Colin Smith




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