Meter this.

We’ve all seen the portrait photographer holding a white-domed object next to the subject’s face to take a light reading. So why is that being done? Why not just let the camera do its automatic exposure thing and take the picture?



 

It’s a good question in this digital age, where we can instantly review our shots to see if we need to re-shoot with a little exposure compensation. After all, the histogram in the camera tells us just about everything we need to know about the exposure in the shot – is it under- or over-exposed and is the exposure evenly distributed over the entire tonal range?

The short answer is that the handheld meter is mostly used to measure the light falling on the subject from studio strobes or flashes mounted off-camera.  In this scenario, the camera doesn’t typically have the ability to control the flash output, as it does in ETTL mode when the flash is mounted on the camera’s hot shoe.  Hence, studio photographers usually work with the camera in manual exposure mode, where they manually set the shutter speed to a value that will synchronize with the flash and the aperture to a value that gives the correct exposure. Alternatively, they can use the  meter reading to set the brightness of each flash in a multi-light setup to give a particular effect while ensuring a proper exposure.

Here, I’ve used the words ‘light falling on the subject’, meaning incident light. Hence, the incident light handheld meter measures the ambient light and ignores how much light the subject is likely to reflect.  The metering system in our camera, on the other hand, does rely on the light reflected from the subject to determine exposure.

Which is more accurate? The incident meter is, because it is calibrated so that it will give camera settings to make an 18% grey card look like 18% grey (middle mark on the histogram) when photographed.  The reflected meter, however, relies on the subject's tone averaging out to 18% grey in order for the exposure to be accurate. If the subject is overly dark or bright (such as a snow scene), the reflected meter gets fooled because it tells the camera to expose as if the subject is mid-grey. The incident meter would read the light falling on the snow rather than the light reflected from it, thereby resulting in the snow looking like bright white snow rather than grey slush.

I started out stating that the incident meter is used in the studio to measure the light from strobes or flashes, but obviously it has a function in outdoor ambient (continuous) light photography as well. Some photographers work in manual exposure mode all the time and therefore rely on an incident meter for camera settings.

So why bother? Part of the answer may be a throwback to the film days, where you never knew until it was developed whether you got the exposure right or not. An incident meter (and a little exposure  bracketing) gave you the confidence that you got the shot. That way of working may still influence the photographer who has made the transition to digital, partly because it’s good practice.

The bottom line, though, is that anyone seriously considering turning pro using studio lighting setups should consider working with a combination flash/continuous incident meter, if for no other reason than to save time. The alternative is to shoot, tweak, shoot and then tweak some more.

Combination meters can be a bit of an investment, so they’re not for everyone.  If you’ve got the spare change, though, a meter can help you understand the exposure mystery a little better and hit the bullseye every time.

Lenses for the DSLR: Crop Factor and Image Circles

(Not to be confused with crop circles)

 

A few months ago, I wrote about how sensor size affects the way different cameras capture an image when using the same lens. To refine the topic a bit further, I’m going to introduce two terms: crop factor and image circles.

Why bother with this techno-babble? Well, as stated in the earlier article, if you now own a consumer DSLR with an APS-C sized sensor, chances are that when you want to replace it down the road, your next camera will have a full frame sensor. This means that the lenses you have now are going to behave differently on your future camera, or, worst case, will force you to buy at least one new lens.

Now for my definitions:

Crop Factor – The ratio of apparent magnification provided by the same lens when switching between two different-sized camera sensors.

For example, a lens on an APS-C sized sensor will produce an image that appears magnified by a factor of 1.6 times over the image captured by that same lens on a full frame sensor. The actual image projected by the lens is the same in both cases (note that the focal length of the lens is assumed to be fixed), but the smaller APS-C sensor sees fractionally less of the projected image than the full frame sensor. In effect, the APS-C sensor is ‘cropping’ the image, thereby giving the impression that it is magnifying part of the image.

Image Circle – The diameter of a circular image projected by a lens when focused on a surface. It is usually expressed in millimetres.

In this context, the lens is projecting the image from a scene in front of the camera onto the back of the camera. At the back of the camera is the sensor. In order for the image to fully cover the sensor, the image circle must be at least as large as the diagonal measurement of the sensor. Otherwise, we would see a darkening in the corners of the resulting image where the projected image didn’t fully cover the sensor. This is called vignetting.

One important fact to note is that lens manufacturers make two different types of lenses for DSLRs: full frame and digital-only. For example, Canon full frame lenses are designated EF and digital-only are designated EF-S. They may have exactly the same focal length, but the difference is that the full frame version projects a bigger image circle, more than sufficient to cover the full frame sensor. The full frame version works fine on both full frame and APS-C cameras, whereas the digital-only version would cause vignetting on the full frame camera. Note: while the mounts look the same on the EF and EF-S lenses, there is a protruding 'shoulder' on the EF-S lenses that prevents you from mounting them on full frame cameras.

Now, you would be tempted to think that using a full frame lens on an APS-C sensor when compared with the digital-only lens would result in apparent magnification, just like the crop factor, because the smaller sensor is only capturing part of the full frame lens image circle. An important difference, however, is that if you looked at the projected images from the full frame and digital-only lenses (with the same focal length) under the exact same conditions, an object in the scene would be projected at exactly the same size. Why? - because the full frame lens actually captures a wider field of view. In other words, putting the full frame lens on an APS-C camera will project peripheral information outside of the sensor, while the digital-only lens will not project that peripheral information but will adequately cover the sensor.

If that didn’t do it for you, here’s a scenario that might explain the difference between crop factor and image circle. Hopefully, the accompanying graphics will help:

1.  I have an APS-C sensor DSLR in front of me. I also have two lenses – both are 50 mm focal length, but one is designed for full frame and one is designed for digital-only. I have the camera set up on a tripod aimed at an object (X) which sits in the middle of the viewfinder. I try each of the lenses in turn and focus on the X. I notice that the X appears to be the same size in each case, and fills the frame from top to bottom. As long as the focal length on both lenses is the same, there is no change to the size of the image or the apparent angle of view in the captured image. The only difference is that the full frame lens is projecting a bigger image circle with more peripheral information (the dots) that the sensor doesn’t see anyway.

 

2.  I now take the full frame 50 mm lens and put it on a full frame sensor DSLR. The angle of view now appears wider than it did on the APS-C camera and the X is smaller (doesn’t fill the frame from top to bottom) by a factor of 1/1.6 (62.5%) because of crop factor in reverse. Saying it another way, the full frame lens now just covers the full frame sensor as opposed to the APS-C sensor which cropped the full frame lens image circle and caused apparent magnification. Again, focal length remained the same, but sensor size changed. Note that the full frame sensor captures some of the peripheral image (dots) that the APS-C sensor didn't.

 

3.  If I put the digital-only 50mm lens on the full frame camera (not generally possible as explained above), the object size is the same as in 2., but I see severe vignetting in the corners. This is because the image circle of the digital-only lens is too small for the full frame sensor.

To tie this discussion up with a nice ribbon, we can summarize where crop factor and image circle come into play as follows:

 

• Crop factor is a consideration when using the same lens on two different cameras with different sensor sizes.
• Image circle is a consideration when using two different lenses with the same focal length but different image circle sizes on the same camera.

Taking this one step further, what if you had a full frame DSLR, but you wanted to use a lens of the same focal length (ie. 50 mm) but with a bigger image circle than the full frame lens provided? Those of us geezers who used to use medium format film know that the lenses for those old cameras projected an even bigger image circle than full frame DSLR lenses because medium format film sizes were larger than a full frame sensor. So, as long as you were comfortable shooting in manual mode, you can adapt your medium format film lenses to your DSLR for reasonable cost. Why would you need a bigger image circle if the full frame lens covered your sensor? Well, with a bigger image circle, you can (with the right adapter) use tilt and shift functions over a wider range than you could with a full frame lens.

But tilting and shifting is another subject for another blog post….



Fill Flash: Balancing Ambient Background and Subject

I've often ranted in my courses about how horrible mid-day light is for photography. Apart from the colour temperature concerns - an overly bluish, cold tinge to the light - harsh shadows cast from overhead are unflattering, particularly on human subjects.

The flash, either the built-in pop-up variety or the accessory hot shoe type, can assist if you are forced to shoot in the daytime outdoors. Weddings fit this scenario. Turning on your flash to shoot outdoors may seem absurd, but pros use it all the time as 'fill flash'. The word fill refers to the fact that the flash illuminates the face to fill in shadows in the eye sockets and under the nose and chin. Photographic Botox®, as it were.

The modern digital SLR does its best to balance the ambient outdoor light and the fill flash through ETTL (evaluative through-the-lens) metering. ETTL uses a number of different points on the image to determine what the correct exposure setting (ie. aperture and shutter speed) should be, and controls the output from the flash to properly illuminate the subject.

As brilliant as the microcomputer in the camera is at doing this, results can sometimes be other than expected. Let's say the background looks properly exposed but the subject looks a little dark. If you have a strong backlight, this may mean re-positioning your subject. If that's not possible, you can adjust the flash output, independently from the camera's exposure setting, by using flash exposure compensation.

Accessory Flash Exposure Compensation

There are two ways you can change flash output. The accessory hot shoe flash will allow you to adjust output using either the buttons on the flash itself OR through the flash exposure compensation setting in the camera. Depending on the camera, either the camera's flash exposure compensation will be used or the setting dialled into the accessory flash will be used: they cannot be used in combination. For the built-in pop-up flash, you can (obviously) only use the camera's flash exposure compensation setting. So, for the underexposed subject, set the compensation for, say, +2/3 stop and try again. The subject should brighten and balance with the background. 

Exposure Compensation button on camera

For the opposite scenario - the subject is properly lit by the flash but the background is too dark, you can use exposure compensation to control the background exposure. This is different from flash exposure compensation in that it controls the choice of aperture and/or shutter speed but not flash output. For a dark background, dial in a positive number, and for an overly bright background, dial in a negative number. You may have to tweak the flash exposure combination again to get the best result.



Negative Exposure Compensation plus
positive Flash Exposure Compensation

So, by setting flash exposure compensation and exposure compensation independently, you can achieve a balanced image.

Let's leave the mid-day scenario and think about doing a portrait just after sunset ('magic hour'). Using aperture priority or shutter priority modes, the camera's metering system will try to expose the twilight sky properly before lighting your subject with the flash. If the subject looks overly bright and unnatural against the sky, you can balance them by using negative flash exposure compensation or a bit of positive exposure compensation, or both.

The results from doing so will amaze you. After all, the pros adjust their light sources to balance them against the ambient light.

A Little Off-Topic

Although this is a photography blog, I feel it is important to mention something a little more pressing in this post.

A neighbour became quite ill during 2012, and is now unable to work. Apart from the stress of waiting for an organ transplant as his health declines, finances are becoming a concern.

As a stopgap to remove the money worries, I have started a campaign on Indiegogo to raise some funds to help cover living expenses for the next 6 months. While it has only been going a few days, it is a disappointment that more people who have been notified of the campaign have not made even a small donation. Perhaps if a lot of people make even a small donation (ie. $1 to $5), momentum will be created.

Please take a moment to read the listing at http://www.indiegogo.com/ivorohan

Many thanks!

NEW LIGHTING COURSE IN 2013

Many people have taken my Digital Photography for Beginners course to overcome their reluctance to take their camera out of Auto mode and take control of exposure and depth of field.

For those who are starting to feel comfortable with their camera's creative modes and now want to take portraits or product shots aided by low cost lighting equipment, this 3-hour course should fit the bill.

Dubbed 'Lighting for the Beginner Photographer', the course provides plenty of hands-on practice using equipment the student may not yet own. All that is required is to bring along a digital SLR and to have an understanding of the basic concepts in the Digital Photography for Beginners course. You can also bring a hot-shoe flash if you have one.This is taught in my home in London, Ontario.

To register for the course, please visit http://filmscapes.ca/html/photography_courses.html

Here is an outline of the course (subject to change):

1.       The Camera’s Creative Modes

a.       Review of Aperture Priority, Shutter Priority, Program and Manual Modes

b.      When to use these modes in available light

c.       When to use these modes with fill flash (built in to the camera or external)

d.      Taking control of light and depth of field in the studio with Manual mode

e.      Flash sync and its relationship to maximum shutter speed

PRACTICE: Using fill flash in various creative modes. Observing shutter speed limitations with flash.

2.       Light Sources and Exposure

a.       The meaning of colour temperature and its relationship to outdoor and artificial light

b.      Selecting white balance for the light source (outdoor light/flash/indoor lighting)

                                                               i.      Preset vs. auto white balance

                                                             ii.      Custom white balance: when to use and how to set it

c.       The hot-shoe flash vs. the built-in flash

d.      Strobes (optional)

e.      Continuous (hot) lights

f.        Guide Numbers and Watt-Seconds

g.       Use of the light/flash meter (optional)

h.      Camera metering modes

i.         The histogram as an exposure tool and the meaning of 18% grey

PRACTICE: Experimenting with White Balance presets. Setting a custom white balance. Shooting without flash using various metering modes and comparing results in the histograms.

3.       Remote Triggering of Flash/Strobe

a.       Radio triggers and adapters for flash mounted on light stand

b.      Optical triggering

c.       Controlling the flash in manual mode

d.      Controlling the strobe output (optional)

PRACTICE: Setting remote flash output. Triggering from camera with radio trigger or optically from camera’s flash.

4.       Introduction to Light Diffusers and Reflectors

a.       Umbrellas

b.      Soft Boxes for strobes and hot-shoe flash

c.       Reflectors and Absorbers: outdoors with/without flash; in the studio

d.      Diffusers for harsh daylight

PRACTICE: Take a portrait shot/object shot with remote flash, with and without umbrella Repeat using available light and reflector, then diffuser.

5.       Basic Portraiture Methods

a.       Background stands

b.      Choice of material and colour for the type of shoot (including green screen)

c.       The role of depth of field and lens choice

d.      Using natural light

e.      The single light setup

f.        The two light setup

g.       Balancing sources for intensity

h.      Mixed light sources and the importance of custom white balance

PRACTICE:

-          Portraiture/object shoot using window light and choice of background (try black then white)

-          Portraiture/object shoot using window light, reflector and/or absorber and choice of background

-          Portraiture/object shoot using window light and single hair light (custom white balance)

-          Portraiture/object shoot using single light in studio setting (custom white balance)

-          Portraiture/object shoot using two lights with umbrellas/soft boxes in studio setting (custom white balance)

-          Experiments with other combinations

Size matters – in sensors, that is.

When digital SLRs started to come into the market, they essentially replaced the 35mm film camera. In most cases, the lenses that fit your 35mm camera could now be used on the new digitals (from the same manufacturer, of course) without the need for any adapters. Sweet.

Those who made this transition noticed something right away. The 50mm focal length lens that gave a ‘normal’ angle of view on their film camera now acted like an 80mm lens, or slight telephoto, when attached to the digital SLR. In other words, the image was now magnified compared to using the same lens on the 35mm camera.

In some ways this was a benefit, because it meant that the telephoto lens you bought for your 35mm camera now reached a bit further on the digital SLR– about 1.6 times further. The downside was that the wide angle lens that used to work beautifully for landscapes on your 35mm wasn’t so wide anymore on the digital.

This difference is attributable to the size of the sensor in the digital camera. Most consumer SLRs use an APS-C size sensor, which is 22mm x 15mm. Compare that to 35mm film at 36mm x 24mm. Given the same lens projecting the same ‘image circle’ on the digital sensor  and the 35mm negative, the digital sensor only captures part of what the negative captures. Essentially, the digital image is magnified (by 1.6 times) since it’s like zooming in on a small part of the image circle.

For years now, professionals who could afford it have been using full frame digital SLRs (example – the Canon 5D) which use a 36mm x 24mm sensor, just like the 35mm negative size. While the manufacturers could have stuffed more pixels into this bigger sensor (and did so to an extent), the big benefit is that they can now make the pixels bigger.

Why? The bigger the pixel, the more light it can gather, meaning the camera will yield less ‘noise’ in the image in low light situations. Overall, the image is cleaner and yes, at a somewhat higher resolution. In fact, Nikon recently introduced the full frame D800 with an astonishing 36 megapixel sensor. Compare that to the Canon 5D’s 22 megapixel resolution or 18 megapixels on most consumer SLRs. Of course, file sizes bloom with higher resolution.

All of this is significant because the prices of full frame camera bodies are starting to slide below the $2000 price point. While APS-C and other similar size sensors kick-started the digital photography revolution, affordable full frames will eventually bring it full circle. The smaller sensors won’t disappear for a while yet, but those of us who came up through the film world will once again be able to shoot the way we used to – only with the immediacy of digital and a moderate size hole in our pocket.

Depth of Field: Choosing the Right Focus Point

Most of the time, when we want to get everything in our shot in focus from our feet out to infinity, the tendency is to dial in as high an aperture number, or f/stop, as possible. In doing so, we hope to increase the depth of field in the image, or the range from our near in-focus point to our distant in-focus point.

But there are two other parameters that have a dramatic effect on depth of field: focus point and focal length of the lens. Two rules of thumb for increasing depth of field are

·         Manually focus as far away as you can from your subject while still keeping them in focus at the aperture you are using, and

·         Use as short a focal length as you can to compose the shot.

Take the second point. We’ve all seen wildlife and sports shots that are taken with a very long focal length lens. The subject is very sharp while the background and foreground are very much out of focus (shallow depth of field). So, conversely, using a short focal length (or wide angle setting) results in a deeper depth of field.

Choosing the focus point, however, is probably the most critical parameter in achieving the shot you want. The first point above implies that the further away from the camera that you focus, eventually you will have everything in focus from a point close to the camera out to the horizon (infinity). To put a label on it, when this happens, you are focused at the hyperfocal distance. This term is mostly of interest to landscape photographers but the point is that, counter-intuitively, we need to focus beyond our subject to get it and the background appearing sharp.

The best graphical demonstration of this is the Online Depth of Field Calculator at www.dofmaster.com. Choose your camera model, focal length, aperture and subject distance. Assuming you focus on your subject, the calculator tells you the near focus and distant focus points. The difference between these is the depth of field.

Hyperfocal distance is also illustrated. If you focused at this distance, everything would be in focus from the distance shown in the illustration out to the horizon. Note that sometimes hyperfocal distance won’t get your subject in focus because the near focus limit is further out than your subject. In this case, you would have to use a higher f/number, shorten your focal length or resign yourself to not having the horizon in perfect focus.

The following images were shot using highly sophisticated dollar store markers at 5 foot intervals. The closest was 5 feet from the camera’s sensor. The camera was a Canon Digital Rebel using a fixed focal length of 35mm in all examples. Each image has been cropped from the originals.

In the first image, aperture was set to f/22 and focus was manually set to the calculated hyperfocal distance of 9.5 feet (just in front of the second marker).  Notice that the 5 foot marker is still in focus, as well as the tree top a couple of  hundred feet away (See insert). This is because the near focus limit is calculated to be 4.7 feet. (Note that the insert looks a little soft because the sensor resolution is starting to come into play.)

 

The second image was also at f/22, but the camera was now focused at our subject, the 5 foot marker. The calculator tells us that if we focus at 5 feet rather than the hyperfocal distance, our focus range now covers 3.3 feet to 7.2 feet. So our depth of field has now decreased from infinite to 3.9 feet just by focusing at 5 feet rather than 9.5 feet from the camera. Note that the markers at 10 feet and beyond are a little softer, and the tree top is no longer in focus (slightly softer).

 

At f/10, our next image was focused at the calculated hyperfocal distance of 21.1 feet (just past the lowest 'lollipop'). The near focus limit is calculated at 10.5 feet, and indeed the second marker at 10 feet is very slightly soft. The tree top, while not perfectly sharp, is close to being in focus. I chalk this discrepancy up to difficulty in getting the focus exactly at 21.1 feet. Note that our subject at 5 feet is badly out of focus, so f/10 is clearly not a good choice if we want focus from 5 feet to the horizon.

 

 

Still at f/10 in the last image, the subject at 5 feet was once again our focus point. Calculated near and far focus limits are 4.1 feet and 6.5 feet, giving a depth of field of only 2.4 feet.

 

The conclusion? Decide whether you want to shoot like a landscape photographer or whether a little bit of in-focus background will suffice for your shot. Even if you don’t use hyperfocal distance, the calculator will help you choose a manual focus point beyond your subject that will keep it in focus but still give you a decent background focus.