The teaser post of Fred and Tanya’s Wedding.
Wedding Photography by : Robert Hall Photography
Wedding Ceremony Location : Home Ceremony Brighton, MI
Romantics Location : Oak Pointe Country Club
Wedding Reception Location : Oak Pointe Country Club
A blend of my daily and professional life.
Check out www.robhallphoto.com for more
When making the jump to manual photography, one of the most confusing topics can be that of the f-stop. Even after learning that the aperture controls your depth of field, you can still be very confused by why the numbers change the way they do. It’s no surprise, as circle geometry isn’t something you use in your daily life.
However, understanding the mathematics can give you an excellent grip on the f stop scale, especially if you’re the left-brain type. Let’s assume that you are already familiar with the full f-stop scale (1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 etc.). Why is it that only increasing .6 from 1.4 to 2 is the same time of adjustment as moving 5 from 11 to 16?
The reason is that the f/stop number is actually a ratio between the diameter and focal length of the lens. The inverse relation of light stems from the diameter becoming smaller as the f/stop number increases. For instance, an 85mm lens at f/2 will yield a diameter of 42.5mm (85 / 2), If you stop down (increase the f/stop and reducing the light 1 stop) to f/2.8, the diameter is now 30.3 (85 / 2.8). Now I know what you are thinking, 30 isn’t half of 43, so how did we halve the light if the diameter didn’t get cut in half?
This brings us back to circle geometry. We need to look at the area of light that passes through the opening. The area of a circle is found by πx radius^2. The radius is half of the diameter, and pi is a constant that represents the circumference divided by the diameter. So, lets do the area math for the example above with the 85mm lens.
At F/2 we have a diameter of 42.5, and F/2.8 is 30.3. This gives us a radius of 21.25 and 15.15 respectively.
So for f/2 we have π x 21.25^2 = 3.14 x 451.5 = 1418 square mm (rounded)
For f/2.8, its π x 15.15^2 = 3.14 x 229.5 = 720 square mm (rounded)
As you can see (while looking past some rounding), we have cut the area of light in half. This is why when you stop down, you are actually cutting the strength of light by 2. The ratio also explains while the numbers start to have bigger intervals as you move up the scale.
Hope this helps and please feel free to keep asking questions so I can provide you with more educational content!
Robert Hall is a professional photographer in Southeast Michigan. His work primarily consists of weddings, commercial and editorial. He is constantly improving his skills through discussion of techniques and critique with fellow photographers. Robert is always looking for new connections on social networks!
Wedding Date: January 4th, 2014
Wedding Ceremony Location: The Inn at St. John’s - Chapel - Plymouth, MI
Wedding Reception Location: The Inn at St. John’s - Grande Ballroom - Plymouth, MI
Wedding Photographer: Robert Hall Photography
Flowers: Viviano Flower Shop
Here’s the resulting beauty when a couple bravely chooses January as their wedding month in Michigan. The Inn at St. John’s was the perfect backdrop with their excellent chapel, courtyard, and grande ballroom. The timeless color palette and lively dispositions brought warmth to an otherwise chilly day. The grande ballroom was elegantly decorated with subtle hints of a concluding holiday season. While the day went without a flake, the night brought on a massive flurry. The adventurous couple capitalized on the moment by capping the night with an outdoor kiss.
Do you avoid the TTL system on your speedlite because you never know what you are going to get as a result? It’s an extremely complex system that intends to figure out the flash output for you, yet constantly photographers are frustrated by the seemingly random nature of it’s results. Well I’m here to give you a few tips on how to increase the accuracy of your TTL system.
First, a little background on how TTL works. TTL (Through-the-lens) metering determines the value of flash output by sending out a pre-flash to expose the subject, and then uses that data to determine the final power to use during the exposure. This all happens extremely flash, which is why you and your subject may not even see a gap in between flashes. There is some variety to the process, based on models, however this is the current standard of TTL for major companies. Much like the ambient light meter in your camera that you use to determine your exposure settings, the flash aims to expose your subject at an 18% gray value. Some systems also incorporate the subject distance based on the autofocus information to determine where the subject is in the scene.
It sounds like there is plenty of information for the TTL to create an accurate flash, so why are the results all over the place? There are a number of things to consider, and thankfully most are controllable by the photographer.
The most important thing to realize, is that the TTL system is always aiming for an 18% gray midtone result. To combat this, you use the same technique as when compensating for light and dark subjects in natural light. When you have a subject that is darker than the 18% gray, you must tell the camera to reduce the TTL output (essentially the EV of a speedlite). Conversely for brighter subjects you want to increase the power.
Next, you have to consider the metering mode. If you are in matrix metering, realize that the camera is trying to light the entire scene evenly through the use of the flash. This is where I see a lot of photographers getting overexposed results on their subjects, especially when they are in a dark environment. The speedlite is selecting a power amount to get the subject and background to it’s desired exposure. By the time the background is properly illuminated, the much closer subjects are overexposed or completely blown out. Partial metering will give you a variety of results depending on what is in the center area of your image. This generally works well, until you are creating a composition where the subject is off-center. This goes for re-composing a shot after locking focus. While you retain focus on the subject, your meter is now making a completely different calculation. I will address this more later. Finally, spot metering chooses the smallest area to determine flash power. Based on the autofocus selection, the speedlite will aim to properly expose only 1-5% of the viewfinder area. As with Partial metering, re-composing an image will also change the flash value.
There is hope however, to still get accurate flash results when re-composing an image after achieving focus. When shooting in an automated mode (such as Aperture priority), the camera has an option called AE-L to lock in the exposure information on a particular subject, prior to changing the position of the camera. There is also a flash version of that called FV-Lock. This enables you to focus on the subject, hold the FV Lock button to lock in that information, and then adjust the composition. This works perfectly in scenarios where your subject is off-center or out of the focusing grid area.
The last thing to consider is strong ambient light or reflections. Back lit situations will force the speedlite to be under powered, sometimes to the point where maxing out the increased flash compensation still won’t be enough. This happens similarly when the flash hits a highly reflective surface such as a mirror. When the flash bounces off the mirror and into the lens, it thinks it has achieved a proper exposure much sooner. It is best to keep your flash from being visible in a mirror or reflective surface to ensure a proper exposure. Even after being fully aware of all this information, TTL may still be ineffective in certain scenarios. If this is the case, simply swap to manual. I hope this gives a greater understanding of how you can make TTL work for you in a more consistent manner.
Robert Hall is a freelance photographer in Southeast Michigan. His work primarily consists of weddings, commercial and editorial. He is constantly improving his skills through trading of techniques and critique with fellow photographers. Robert is always looking for new connections on social networks!