Calendar Time

Buy, Buy, Buy!

Lost In the Toadstool Calendar Rack

It seems like everyone is publishing a calendar these days. There are some beautiful ones out there including a few from my friends in the New England Photography Guild. A visit to any bookstore will reveal hundreds of choices with themes ranging from local and global natural wonders to the artistically posed, but profoundly disturbing naked forms of members of the local Rotary Club. Please don't expect to see the "Men of the Chesterfield Conservation Commission" any time soon.

Of course this article is an unapologetic attempt to get you to support my "New England Reflections Calendar." With all the competition it can be a struggle to command the attention of the calendar buying public. I have no magic formula, but I can relate what has seemed to work for me over the last ten years.

Find a Cause
First and foremost, I feel that it has been the cause, to which all of the profits have been dedicated, that accounts for the popularity of my calendar.  For a number of years I struggled with the thought of producing a calendar. I felt uncomfortable with the idea of profiting by trying to market my work to all my unfortunate friends and family. Then a patient who is also a friend suggested that I sell the calendar to benefit a local charity. I knew exactly where I wanted the money to go, and over the last 10 years I've managed to send over $40k to support the work of the Pulmonary Rehabilitation Program at the Cheshire Medical Center in Keene, New Hampshire. The money has been used to help patients who would not have been able to afford the program and has made possible special events that have added to the experience for many needy participants. Getting no financial benefit from the sales has also made me much more comfortable when I shamelessly and obnoxiously hawk the calendar throughout the community. Of course, with the money going to such a worthy local cause, it has been easier to get a long list of wonderful stores to sell the calendar.

Quality Counts
All tricks aside, the quality of the images is most important for the long term popularity of the calendar. I've talked about the struggle

November

of selecting each year's images. Throughout the year I am looking for the perfect scenes, but in the end it is impossible to predict what will capture the eye of my audience. I really like this year's November image, but I was afraid that many would not enjoy a picture of frozen ground liter.  Happily the image has been one of the most popular in the 2015 calendar.  The large monthly pictures are important, but I think it is often the little additions, the thumbnail images, the banners, the choices of holidays, and the descriptions of the images, that make the calendar more attractive and complete. And of course the cover image is always a critical marketing choice.


 


2015 Gallery

 
Image Information and Links

 














Keep it Local
Of course the content of the calendar is very important. I know my customers and, as the "New England Reflections" title implies, I

Westmoreland, NH

have images that focus on my home region, trying to reflect a mix of landscapes from the Monadnock Region and Southern Vermont. I always like to add one Seacoast image and at least one of local wildlife. It is remarkable how many calendars get sent out of the region to those who have moved away or to explain to distant friends why we choose to live in this uniquely special corner of the world. I am told that there are folks in Germany, China and throughout the world for whom my calendar has become a holiday tradition, so it is important to select images that reflect the special character and feel of our region.

Get it Out
I have mentioned before the importance of getting the calendar out early. This has always been a problem for me, but in the last couple of years I have been able to start distribution in the late summer. The key is to get to people before they make their yearly calendar purchases and before the flood of free calendars start flowing in.

The real purpose of this blog is to remind everyone that it is calendar time. I, and the patients with chronic lung diseases in our community, would appreciate you considering buying one ( or ten ) New England Reflections Calendars. You can find the calendar at the Cheshire a Medical Center Gift Shop off of the main lobby or on-line at the hospital web site, and we will pay for the shipping.

Calendars are also available in many fine stores including:

Toadstool Bookstore in Keene and Peterborough, NH
Hanna Grimes, Keene, NH
Sharon Arts Center, Peterborough, NH
Harrisville General Store, Harrisville, NH
Monadnock Imaging, Keene, NH
Ingenuity Country Store, Keene, NH
Monadnock Food Co-op, Keene, NH
Heidis/Tildens Hallmark Store, Keene, NH
Nicole & Bonnie's Salon, Keene, NH
Leon's Auto Center, Keene, NH
Alyson's Orchard, Walpole, NH
J & J Discount Store, Chesterfield, NH
Westmoreland General Store, Westmoreland, NH
Gilsum General Store, Gilsum, NH
Walpole Grocery, Walpole, NH
Jingles Christmas Store, Westmoreland, NH
Harlow's Sugar House, Putney, Vt
Newfane Market, Newfane, Vt
Vermont Artisans Design, Brattleboro, Vt
South Woodstock Country Store, South Woodstock, Vt


 
This week's snow is a potent reminder that January is right around the corner, so get out there and buy calendars!

 

We thank you all for your wonderful support.


Jeffrey Newcomer
Partridgebrookreflections.com

Exposure - The Basics Part II

Everything in Balance

In my first exposure article I discussed how aperture, shutter speed and light sensitivity of the sensor work individually to affect 
proper exposure, but I 

Exposure Control with the Histogram

never explored what proper exposure actually is or how it is evaluated.  A simple definition might be that proper exposure is achieved when the recorded image matches the appearance of the original scene in brightness and tonal range. Simple enough, but no photographic media can fully reach this goal.  Pictures are always a compromise, but with the tools available in modern digital cameras, there is no longer any excuse for poor exposure. The challenge comes from the choices you make to get there.  

In previous articles I've talked about the use of the histogram to monitor  and  adjust exposure.  There is an infinite number of ways in which the three factors controlling exposure can be balanced to achieve an acceptable result, and although all can  appear the same on the histogram, the real challenge is to find the best balance among the secondary effects of these adjustments, so that the depth of field, motion control and image noise all conspire to achieve your vision.  This week I will suggest one, step by step,  approach to the balance of exposure control.


To briefly review from Part I, the camera controls of exposure include two which govern the amount of light and one which controls the sensor's sensitivity to the light which falls upon it. As the exposure triangle showed, each adjustment has a secondary effect that must be consider as the 3 factors are balanced.

Amount of Light:
1) Aperture: Effects Depth of Field
2) Shutter Speed: Effects the Ability to Stop Motion

Sensor Sensitivity
3) ISO: Increased Sensitivity Increases Image Noise

Taken Individually, the effects of these basic controls are easy to understand, but the challenge and the real art of photography comes from how these adjustments are balanced in different situations of light, composition, action and the purpose of the image.

A Matter of Priorities
 Ok, you are standing in front of the perfect vista. A glance at the Exposure Triangle would suggest that proper exposure is achieved through the simultaneous consideration of the effects of all three factors, aperture, shutter speed and ISO, but it can be unnecessarily complicated and confusing to try to balance the three components of exposure at the same time. Happily, most photographic situations inherently dictate which of these factors is most important and the resulting prioritization can provide a more reasonable step-wise approach to finding the best compromise among the factors contributing to exposure. The first step is to decide whether the control of aperture or shutter speed is the most important for the specific photographic situation.

This is usually referred to a Aperture or Shutter "Priority".  Happily most cameras provide modes that allow you to lock in your priority.

"Priority" Settings

Aperture & Shutter Priority
http://www.101-learn-dslr-photography-basics.com/

Most cameras have settings for aperture or shutter priority. In "Aperture Priority" the aperture is fixed and adjustments in exposure compensation affect only the shutter speed. In "Shutter Priority" it is the shutter speed which is fixed. Of course these same adjustments can be done in Manual mode, but in manual, the exposure does not automatically change when the meter detects a change in light. The Manual setting is great when you are learning about the functions on your camera, but many photographers shoot on Aperture or Shutter priority based on the requirements of the subject. On Canon cameras Aperture Priority is marked as "Av" and Shutter Priority "Tv" on Nikons it is "A" and "S".  
------------------------------------------------------------------------------

Baby Steps: A Systematic Approach
Ok, we start by considering the effects that changes in the aperture and shutter have on the final image, then step one is to study the scene and :

• 1) Decide whether aperture or shutter speed is most important to control for the desired effect.

Aperture Priority and Depth of Field

 

Broad Depth of Field

As I discussed in my first article on exposure, the camera aperture affects exposure based on the size of the opening allowing light to strike the sensor. I went into an involved discussion of why increasing aperture numbers (f/stops) resulted in smaller openings and less light. Happily, the aperture's secondary effect on depth of field follows a more intuitive progression with larger numbers resulting in larger bands of sharp focus. Small apertures with high f/stops, such as f/ 22 or f/32, lead to broad depth of field which is often preferred in landscape photography where sharp focus from
foreground to infinity is needed. With wide apertures, such as f/2 or

Shallow Depth of Field

f/4, the narrow depth of field can help to isolate and draw attention to a subject, de-emphasizing distracting elements in the foreground and/or background. Traditionally, narrow depth works well in portrait photography where the attention is usually centered on the eyes, but it can also be effective in many other situation to mute distractions such as in macro or wildlife photography. 




In these situations, control of the depth of field may be the most important factor and therefore the "priority". You can set your desired aperture in "aperture priority" mode and then achieve optimal exposure with changes in the shutter speed.  As predominately a landscape photographer I stay in aperture priority for about 90% of the time.

Stopping the Jump

Shutter Priority and Motion

Shutter speed controls exposure by governing the length of time that the sensor is exposed to the light and the shutter's secondary effect is on the ability to freeze motion. When capturing athletic events, running animals or birds in flight a fast shutter speed can keep the subject from becoming blurred, and in these situations the shutter speed adjustment may be the primary priority with the aperture allowed to drift to maintain the overall exposure. On occasions a

Slow Shutter

slow shutter speed might be preferred, such as when capturing a soft image of flowing water or when a blurring of motion can be used to imply movement. In many of these situations the specific depth of field may not be critical and setting the camera on Shutter Priority would be the best first step.






Considering the Side Effects
As we've seen, for any ISO, the Aperture and Shutter Speed settings are locked together to generate the exposure. Once aperture is fixed there is only one shutter speed which will result in proper exposure and the same fixed relationship is true when shutter speed is set as the fixed priority. In other words, once the priority setting is fixed the other  "secondary" factor, whether aperture or shutter is strictly dependent. So step two is :

• 2) Whether it is Aperture or Shutter that is the "Non-Priority" or dependent setting, you must decide whether the effect of that setting on the image is acceptable.




Deep Depth of Field

Consider an example that I frequently experience. I'm shooting a grand landscape and I want to get the maximum possible depth of field to record both the foreground flowers and the distant mountains in sharp detail. I set my camera to aperture priority and stop down to a small fixed aperture of f/22.  Great, everything from foreground to background looks sharp, but when I take the picture I find that the shutter speed that was required to maintain the desired exposure for that small fixed aperture had drifted to 1/4 second and, what seemed like a gentle breeze, had been enough to smear my beautiful flowers into a messy abstract blur. I could wait for a, usually nonexistent, lull in the wind or I could consider focus stacking (beyond the scope of our current discussion), but it is at this point that an ISO adjustment could save the day.

• 3) Apply the ISO Fudge Factor if Needed

As in my example, it often happens that the optimal adjustment of your priority setting leads to unacceptable side effects from the resulting secondary or dependent factor. In my landscape scenario I might be able to get by with a wider aperture, perhaps f/16 or f/18, which would allow a faster shutter, but these "compromises" too often yield unsatisfactory results in both DOF and shutter. A change in ISO is often a better solution. Adjustments in sensor sensitivity or "ISO" shift rather than break the aperture/shutter connection. In my example an increase of ISO from 100 to 800 (3 stops) will allow an increase of shutter speed to 1/30th of a second which may be fast enough to freeze the flowers without affecting my exposure, aperture or depth of field.


Adjustments in ISO is the new third control on exposure which digital photography has made practical. ISO has no effect on the amount of light hitting the sensor, but by managing the chip's sensitivity it can make possible a selection of aperture and shutter that does not force a compromise in either depth of field or control of motion. Of course the magic of ISO Adjustment is balanced by the effect of increasing ISO on the amount of digital noise in the image. As I discussed in Part One, digital noise can be muted in post processing, but in the end it must be balanced against all the factors that contribute to the quality of the final image.


Consider one more example. Assume you are set up to capture a

Pick-Off

baseball player streaking down the line to beat out a base hit. You set a fast shutter speed of 1/1000th of a second, in shutter priority, to freeze the motion. Your ISO is set to 100 and the resulting f/stop is at f/4. This wide aperture and resultant narrow DOF works well to isolate the runner against the blurred grandstands. A great choice, but if you want to see the faces of the screaming fans in the background you could increase the ISO to 1600 causing the f/stop to shift 4 stops to f/16. Both the runner and the fans would then be in dramatically sharp focus. The only question would be whether the increased image noise at ISO 1600 is acceptable.

I would love to show you an picture to fully illustrate this scenario, but, give me a break!, I'm a landscape photographer. Use your imagination! The best thing I could do was to show Youk (Kevin Youkilis, for non-Red Sox or, ick, Yankee fans) diving for first.

Light Modification

There are many schemes and techniques which work to control exposure by modifying the light.  Natural changes in light happen all the time, just wait for the sun to come out from behind that cloud, move from bright sunlight to the shadow of a tree or just come back when the light is better.  Natural light can also be modified with  filters, diffusers or reflectors and artificial light can be added with flash. These can all be effective, but the basic relationships between aperture, shutter and sensor sensitivity are always there and a system for balancing these fundamental adjustments makes achieving the perfect exposure much easier and sensible.


So to summarize this approach:

No triangle, but maybe a flow a diagram will help

1) Decide whether aperture or shutter speed is most important to control for the desired visual effect. It is usually easiest to use the Aperture or Shutter Priority setting on your camera to fix your desired priority.

2) Whether it is Aperture or Shutter that is the "Non-Priority" or dependent setting, your next step is to decide whether the effect of that setting on the image is acceptable.

3) If the resulting depth of field or motion effect is not what you want, it is time to consider applying the ISO Fudge Factor to shift the Aperture/Shutter relationship into a range that controls all of the important issues. Hopefully without an unacceptable level of noise in the image.

Simple !?

There are many other systemic approaches to achieving perfect exposure. The important thing is to pick one and start using it regularly. Happily with digital photography we get immediate feedback on the LCD screen, making the learning much easier. I hope that you will, quite quickly, find that the considerations, that I have so painfully presented, will become second nature.  Your camera will feel comfortable in your hands, like a familiar hammer. So go out and pound some nails.



Other Articles About Exposure

• Exposure, the Basics & More
• Using the Histogram
• Exposing to the Right
• ISO Control
• HDR: Bon Appetitt

Jeffrey Newcomer
Partridgebrookreflections.com

One Tree

 

After last week's exhaustive and exhausting article about exposure, I through it would nice for me, and a relief for my readers, to write about something simple. For a landscape photographer there may be few things as simple as a single tree, but even with that narrow focus there is much to explore and this is especially true amidst the restless changes of a New England Autumn.

By the beginning of last week I had largely given up on brilliant autumn color for this year. I knew that I had to be satisfied with the dull, but persistent orange of the oaks and the occasional splashes of yellow from the obstinate Beech trees, but then I stepped out of my door and saw our Japanese Maple.


 

Over the years I have planted many trees around our house. A Red Maple, and a Norway Maple along our stone wall, 9 Apple and two Pear Trees in the field across the street and a Birch that never really took off, but the little Japanese Maple was there when we moved in. Over 35 years it has thrived despite our general neglect and the fact that it is located in a shady north corner of our property which has been otherwise fit only for moss, moles and rotting firewood. The tree has survived these insults remarkably well, but I swear it hasn't grown an inch in over three decades. 

 
I assume that it is a dwarf variety, still standing only about 10 feet high, but this week, despite the general November devastation, the tree was aflame with color ranging from brilliant crimson to electric yellow. Obviously, I took a picture, but then I decided to capture the tree in more detail. Over this last week I tried to explore this brave little tree in a variety of ways. I followed the Maple's fantastically colorful show through to its remarkably sudden and inevitable surrender to the elements. What follows is a brief album celebrating that journey.




Full Color
At the beginning of the week the Japanese Maple was in full color and, despite the bare branches of trees all around, it was tenaciously clinging to its leaves. Seeing the brilliance of the reds in these images, it would be reasonable to think that I had leaned heavily on the saturation slider in Photoshop, but in most situations I actually reduced the red saturation to bring the color into a manageable gamut. The color was really that bright. As I mentioned this tree is tucked away in a back corner of our property and it was a challenge to find angles that would show the tree's full glory. Most view points had backgrounds complicated by our house to the side or the gazebo in front. To get a clear view, I had to take down our cloth lines and found a side view which showed how the tree was leaning to the south in a desperate attempt to get more light.

Variation in Leaves 

As I moved in closer I was struck by the wide variation in color and pattern of the leaves. This was probably related to the differences in the amount of light that struck various branches. Colors ranged from deep dark reds to bright yellows and some leaves had a stippled pattern of light and dark.

 

Variations in Light

  

Over the next few days I had the opportunity to catch the tree in a range intensities and angles of light. In the bright light the transilluminated  leaves became electric, while with soft overcast the full intensity of the color could be seen without being muted by reflections. As always, my polarizing filter help to bring out the colors even in softly diffused light.

 

Camera Motion

 The leaves were remarkable, but as I began to feel that my leaf exploration was coming to a close, I knew that it was time to put the vegetation in motion. I experimented with sweeps, circles and jiggles, but my favorite was zooming. I liked the effect created when I started with a pause for a fraction of a second and then zoomed out. By using ISO 100, a small aperture and the polarizer, the shutter was slow enough to create the exploding color effect. It all comes down to experimentation and the willingness to take enough pictures for luck to kick in.

 

  

 
Infrared 

Whenever I think about looking at things with different eyes infrared immediately comes to mind. Whether the leaves are deep red, yellow or mid-summer green, in the infrared spectrum they all come out ghostly white.

Leaf Drop 

 The late season color of our Japanese Maple was remarkable, but what was the most surprising was how suddenly the leaves all crashed to the ground. Essentially overnight the tree went from full bloom to nearly bare and without any unusual twist in the weather. No big storm or blustery winds to force the leaves to the ground. Apparently the tree just decided it was time. I was left with a few stragglers and a luxurious red carpet. 

Spending a week studying a single tree in its autumn glory and inevitable surrender provided a couple of important lessons. First, that with proper focus, even the largely barren November environment can still offer surprising splashes of autumn color and that color can be even more striking when contrasted with the somber melancholy of our "stick season". Secondly, given my tendency to frantically jump from one scene to another, it was good to be reminded that the exercise of restricting attention to one limited subject can refresh the eye and allow us to see in many new and surprising ways. 

 

Jeffrey Newcomer
partridgebrookreflections.com
603-363-8338

Exposure, the Basics & More

Shallow Depth : f/2.8

 One of the fundamental topics, key to the understanding of photography, is the  interaction of the factors which affect exposure. It is a short list, aperture, shutter speed and ISO, but it is in how these adjustments combine to control exposure and the effect that each has on the qualities of the image that is frequently the source of much confusion.

Easy for You to Say
Simply stated aperture and shutter speed control the amount of light that reaches the sensor and ISO controls the level of sensitivity of the sensor to the light falling upon it. In this article I want to discuss the nature of each of these adjustments, how they affect exposure and their impact on other aspects of the final image. In a future article I will suggest my approach to finding the optimal balance of these adjustments based on the special requirements of each photographic situation.

The relationship between aperture, shutter speed and ISO is often illustrated with the "exposure triangle". I have never felt that a triangle works geometrically to illustrate the interaction between these factors, but it does provide a structure to present the impact of each of these adjustments. So if you need a triangle, here you go:

Exposure Triangle : wildlife-photography-tips.com

Now lets talk.

Finding the perfect Exposure

 
Aperture

Deep DOF, f/22, 1/15", ISO 100

The aperture is the size of the opening through which light the passes to the sensor. The larger the opening, the more light gets through to expose the sensor and the brighter will be the image. Simple, but a stumbling block to understanding aperture has always been the apparently random and counter intuitive "f" numbers or "f stops" used to measure the size of the opening. The problem is two fold. First the numbers do not seem to follow any recognizable pattern and secondly, as the numbers increase in size the aperture opening actually gets smaller.







The standard progression of f stops, is:
1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 .......




Although it is rare to find a lens that can go this wide, F/1 would be the widest aperture in this sequence, letting the most amount of light to the sensor, and f/32 would be smallest. Each step increase in the f/stop is calculated to represent a halving of the size of the aperture and therefore a halving of the amount of light hitting the sensor.  These steps are referred to as "stops".  Of course there are f numbers which represent changes of  fractions of a stop, but for our discussion it is easier to focus on the one stop increments.  Great, but how does it make sense that f/5.6 admits twice the amount of light as f/8.? 


Shut Up.  It Just does! It's a Mystery!

Abby  f/3.5, Shallow DOF for Portraiture

At this point you have a choice. You can decide to happily agree to accept these numbers, not worry about where they come from, and go on to a joyful and worry-free exploration of the wonders of photography, or the annoying trouble-makers among you can insist on a needless dive into the source of the f/stops. I warn you. It involves math, but with a little effort it actually does make sense. The prudent will blissfully continue on to the discussion of the effects of changing aperture, but if you want to dive into the numbers, you can find my explanation neatly hidden at the bottom of this article. You have been warned!


Back to the Mystical f/stop
The aperture setting or f/stop controls the intensity of the light hitting the sensor by regulating the size of the aperture. As the f/stop gets smaller more light is admitted and we can shoot in darker locales, but nothing comes free in photography. As the aperture widens the depth of field is reduced. Depth of field (DOF) is the distance between the closet and farthest points that are in sharp focus  and that range is much larger at f/32 than at f/4. Varying the  DOF can be used in creative ways. Sharp focus from foreground to infinity is often preferred in landscape photography, but a narrow DOF, with a soft background can work well with portraits. When shooting in low light it can be difficult to use an aperture which is small enough to get the desired deep depth of field and that is when compensation with longer shutter speeds can be important.


So Aperture's primary effect is on exposure and its secondary effect is on the depth of field.
 

Shutter Speed

Catsbane Falls:
0.5 seconds, f/20, ISO 100

Shutter speed is the second of the two adjustments that control the amount of light hitting the sensor. After our struggle with the seemingly nonsensical number of f/stops, it is a pleasure to discuss shutter speed. No complicated math, but here again the standard intervals represent steps which double or halve the amount of light and therefore match or offset the effects of changes in the aperture. Of course, as with aperture adjustments we aren't restricted to full stop intervals, but for simplicity it is helpful to know that the standard, one stop, steps of shutter speed are:







... 2", 1", 1/2", 1/4", 1/8", 1/15", 1/30", 1/60", 1/125", 1/250", 1/500", 1/1000" ...
 

If you ventured to my f/stop explanation below you will be happy to note that there are no Pi or Squares, just straight ahead, good old non-metric, American doublings! With each doubling of the shutter time the exposure doubles. Now we can see how the aperture and shutter speed are locked together but can be shifted to produce a balance that can work the best for the perfect exposure in most photographic situations. Perhaps an example will help.

Example:
Assume that a scene is properly exposed with a relatively wide aperture of f/4 and a shutter speed of 1/125".  The wide aperture would lead to a shallow depth of field, but I could expand the depth of field by increasing the f/stop to f/16.  Since I would be reducing the light by 4 stops the image would be quite dark unless I offset this change by increasing the shutter duration by the same 4 stops to 1/8". The result would be the same exposure but a much wider depth of field.

But There is a Problem

Red Tail: 1/800th Second, f/9, ISO 400

Slower shutter speeds can allow for smaller apertures and wider DOF, but this is where shutter speed's secondary effect becomes important. Subjects that are in motion can become blurred with the longer shutter times. At 1/8" running animals or blowing leaves may not be sharply captured. On the other hand, fast shutter speeds are great for stopping action in sports or wildlife photography, but can require wider apertures resulting in a shallow depth of field. Nothing comes free in photography and that's where the compromises come into play.

Sprint : 1/13th Second, f/5.6, ISO 100

So Shutter Speed's primary effect is on exposure, but its secondary effect is on the ability to freeze motion.



ISO

A Bit of History / OK, I'm Old
With film photography, aperture and shutter speed were usually the only two adjustments available to balance exposure. For any amount of light, a specific aperture had only one shutter speed to which it was irrevocably linked to achieve proper exposure. Using film with a different sensitivity to light (ASA) could shift that link, but It was extremely awkward, to switch film.  I did it a few times. I had to carefully roll the film back into the canister trying to stop before the leader got disastrously sucked into the can. When it was time to put the original film back in the camera I had to remember how many pictures had been exposed and, to avoid double exposures, advance the roll beyond that point, wasting a few pictures in the process. It was a colossal pain, and was never a practical way to add media light sensitivity as a third adjustment for the control of exposure.

 
With digital photography that has all changed. Now sensor light sensitivity can be changed from shot to shot with the press of a button or the twist of a dial. On digital sensors, the light sensitivity is described by a scale established by the "International Standardization Organization", located in Geneva Switzerland,  hence "ISO Numbers".  Fortunately, ISO settings, like shutter speed, follow simple doublings to adjust exposure by one stop increments and higher numbers reflect greater sensitivity. God bless the Swiss!  A typical IS0 range, in one stop increments, might be :

... 50, 100, 200, 400, 800, 1600, 3200, 6400 ....
Many newer cameras go well beyond this range

Example
In the same example from above, Suppose I require a shutter speed of 1/8 " to get my desired DOF with f/16 at an ISO of 100. I left my tripod at home and my shaky old hands could never hold the camera still for the 1/8" exposure, but now I can break the chains connecting the aperture to a specific shutter speed and use what I like to call the ISO Fudge Factor. By increasing the ISO by three stops to 800, I can shift the aperture/shutter relationship to a more manageable speed of 1/60" while keeping the f stop and its resultant deep depth of field unchanged.

ISO Noise Test

As with both aperture and shutter speed, increase in ISO has its own disadvantage or secondary effect. With increasing ISO the trade-off comes from increased noise in the image. Newer cameras are getting better in terms of their image quality at higher ISO's and noise reduction protocols in post processing programs such as Lightroom and Photoshop do an amazing job, but image noise still has to be considered as we balance all the factors that contribute to perfect exposure. In a previous blog I discussed doing a test to see how your camera handles higher ISO noise. In the end your own acceptable maximum ISO will depend on the intended use of the image and your own taste. 

Digital Noise increases with increased ISO

Juggling Three Balls
That is really all there is to exposure control. Three adjustments, two which control the amount of light and one which controls the sensitivity of the sensor. As the exposure triangle shows each adjustment has a secondary effect that must be consider as the 3 factors are balanced.




Amount of Light:
1) Aperture : Affects Depth of Field
2) Shutter Speed: Affects the Ability to Stop Motion

Sensor Sensitivity
3) ISO : Increased Sensitivity Increases Image Noise

Simple, especially if you don't wander any further into the abyss below, but how do you decide what is the best balance of these controls for any particular photographic situation. It all depends on the light, the intended composition and the eventual use of image. There is no single right answer, but I will save that discussion for another article. A hint? It doesn't involve a triangle. 







--------------------------------------------------- 
The Source and Sense of F/stop Numbers :
 
"Here There Be Dragons"

 






















Here Goes,
If I have this wrong, keep it to yourself!

F number Ratio
The "f" in the term "f stop" comes from the fact that the number is a unit-less ratio (or fraction) where the

F number = Focal Length of the lens (mm) / Diameter of the Aperture (mm).

Rearranging the equation:
Diameter of the Aperture = focal length / f number

So a 50mm lens set at f/2 will have an aperture opening of 50/2 = 25mm, and
the aperture of a 100mm lens will be 50mm.


The key point is that, at any f/stop, the size of the opening is not the same on different lens, but varies based on the focal length.


Why Are Different Aperture Sizes Necessary
Longer lens' collect less light at any fixed aperture size and therefore they require larger openings than in shorter lens' to bring the same amount of light to the sensor. The f number ratio allows a particular f stop to provide the same amount of light to the sensor regardless of the focal length of the lens. At f/5.6 the camera sensor sees the same amount of light through a 400mm telephoto lens as it does through a 16mm wide angle, simply because the aperture on the 400mm lens is 25x larger than on the 16mm. This explains why fast telephoto lens' are so gigantic and expensive. The aperture of a f/2 400mm lens would have to be 200mm in diameter (400/2) and this requires much larger, heavier and expensive glass. As I discussed above, the large apertures on telephoto lens' also result in a shallower depth of field for any f/stop than at the same setting on a shorter lens.


Ok, so that explains where the f numbers come from and why they get larger as the openings get smaller.  The f number is inversely related to the aperture size and therefore to the amount of light striking the sensor.  As the standard f/stop numbers increase they reflect progressive halvings of the amount of light admitted to the sensor. Each time the exposure is doubled or halved we refer to the change as representing a one stop difference, but why these numbers?


1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 .......

 
The simple Answer:  They Work
If we consider a 100mm lens, at f/2 the aperture will be 50mm in diameter (25mm radius). The amount of light passing through the aperture is related to the area of the opening and high school geometry tells us that:

So, for our 100mm Lens
At f/2 the radius = 25mm
3.1416 x (25) ^2 =1963 mm^2

At the next stop smaller, f/2.8 : the radius = 17.86mm
3.1416 x (17.786)^2 = 1002mm^2

The aperture at f/2.8 is effectively half of that at f/2
It works!

Empiricism not enough for you? 
 
Give me a break ! This is photography, not higher math ! But if you must .....

Ok , what follows is mostly for me since I know, if I don't write it down, I will have no clue about the explanation tomorrow. The next time some dweeb asks me, it will be much easier to say, "Go read the blog". This is how I can understand it.  First remember that each stop represents a halving of the light on the sensor.  You MUST have that by now!

The Power of the Square
 Going back to the f/stop ratio :

Diameter = focal length / f number

It can be seen that doubling the f number will halve the diameter and therefore also halve the radius. Since the aperture area is  proportional to the radius squared, each doubling of the f number will actually reduce the aperture area by one quarter or two full stops.
If we go back to the f/stop numbers they no longer appear random, and it all comes back to simple doublings.

 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 .......

Starting with f/1, doubling to f/2 will drop the exposure by two stops. Then by successive doublings we drop by two stops for each step through f/4, f/8, f/16, and f/32. Great, but What about the single stops between the numbers in this f/1 sequence?

We can calculate that f/1.4 results in an aperture one half the size of that at f/1, and twice the area of f/2. That is f/1.4 is one stop smaller than f/1. Now all we need to do is follow the same doubling procedure to generate the f numbers that fill the single stop gaps between the numbers in the f/1 sequence.
 The f/1.4 sequence is : f/1.4, f/2.8, f/5.6, f/11(close enough), f/22 .....

By alternately doubling the numbers starting from f/1 and f/1.4 we get those previously mysterious numbers which are etched on your lens.

1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 .......

There you go. There are more complex formulas to describe these numbers, but this works for me and I'm more than ready to get back to actual photography.
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West River, Jamaica, Vermont

Jeffrey Newcomer
Partridgebrookreflections.com