Depth of Field

In earlier articles I mentioned depth of field, or DOF, and indicated that it is related to the f-number of a lens. That is, a lens with a smaller minimum f-number can produce an image with a more shallow depth of field than a lens with a higher minimum f-number. Since you want to achieve critical focus on your subject, you need to understand how DOF affects focus.

The depth of field defines the nearest and farthest points in the field of view that are reasonably in focus. When your lens is set to a higher f-number, the depth of field is increased and more of the image is in focus. This is usually what you want in landscape photography. When making a portrait or photographing a single flower, for example, a shallow depth of field can be used to emphasize the subject while most of the other elements in the scene are thrown out of focus. 

If your DOF is extremely shallow, you will find that only part of your subject can be in focus. For example, with a 50 mm lens capable of a maximum aperture of  f/1.2, the extremely narrow depth of field at f/1.2 will make focusing difficult. In model or portrait photography a good rule is to focus on the person's eyes. f/1.2 may not the best choice of aperture for most portrait photography.

In macro photography, you photograph small subjects such as insects. It is common to see that only one part of the subject is in focus. If the subject is stationary, you can take two or more shots at different f-numbers and combine them in a program such as Photoshop to produce an image in which the entire subject appears to be in focus. This differs from capturing images for High Dynamic Range (HDR) image processing: for HDR you vary the shutter speed, not the aperture. Very interesting effects might be achieved with a series of photos captured at varying f-numbers, combined with a series captured at varying shutter speeds. Needless to say, using a tripod would be essential.

Although very low f-number lenses have many uses, the cost for a wide aperture/low f-number lens can be very high. For example, the Nikkor AF-S 85mm f/1.8 lens sells for about US$500, while the Nikkor AF-S 85mm f/1.4 lens sells for over 3 times as much. Unless you have a very specific reason to need f/1.4 instead of f/1.8, it might be difficult to justify spending the extra US$1,000+.

An important thing to remember is that a narrow depth of field demands more attention to focus.

A good photograph has a clear subject, and its composition focuses attention on the subject while reducing distractions. Effectively using depth of field is an essential part of the process of drawing attention to the subject.

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.

Philip Wheeler Photography

Ice Plant

Exposure Basics: The f-number

My brief articles on exposure used an 'f-number' when discussing relative aperture and lens speed. The f-number is a very important notation when thinking about exposure in photography. As you may recall, an aperture with a smaller f-number admits more light over a given period of time than one with a larger f-number. Here are the most common full-stop f-numbers, called f stops:

                               f/1.4    f/2    f/2.8    f/4    f/5.6    f/8    f/11    f/16    f/22    f/32

Each of these represents a doubling, or halving, of light exposure from the adjacent number. It is worthwhile to memorize this short sequence of numbers. Here are a few practical examples. Each of these represents a change of one f stop:

        f/1.4 admits twice as much light as f/2
        f/11 admits twice as much light as f/16
        f/4 admits half as much light as f/2.8

f/2.8 admits four times as much light as f/5.6, because f/2.8 admits twice the light as f/4 and f/4 admits twice the light as f/5.6, and 2 times 2 equals 4, or an increase of two f stops. So you see, the f-number, or f stop, is a convenient system of notation in spite of its weird appearance. Stay with me now as this is important!

The concepts of aperture, shutter speed and ISO are combined for exposure as follows.

Consider a shutter speed of 1 second (shutter open for 1 second). It admits half as much light as a speed of 2 seconds. 1/120 second admits twice the light as 1/240 sec. So a halving or doubling of shutter speed equals a change of one f stop!

ISO follows a similar pattern: ISO 100 is half as light sensitive as ISO 200: 1 f stop decrease. ISO 400 is four times (2 X 100 = 200; 2 x 200 = 400) as sensitive as ISO 100, for a 2 f stop increase.

Aha! In spite of the non-linear appearance of the f-number sequence, we see that f-number (aperture), shutter speed and ISO are closely related through this doubling or halving of exposure.

Lets say you are considering a shot at ISO 100 at 1/60 sec. but you are concerned about hand-held camera shake. If you go from ISO 100 to ISO 200 and simultaneously increase the shutter speed from 1/60 to 1/120 second...presto! Your camera sensor's light sensitivity is doubled and your shutter-open time is halved, leaving your exposure essentially unchanged. And yet your camera shake is reduced (unless you move your camera about wildly, of course!)

Another example: You want to use ISO 100 to obtain a shot with the lowest sensor noise. At the same time, you want a fast shutter speed. An initial setting might be 1/500 second at f/11, but you could change that to 1/1000 second at f/8 and achieve the same exposure with a faster shutter speed.

It takes a while to get the hang of the relationship between f-number, shutter speed and ISO. Practice, and you will soon be tossing these numbers about like a pro!

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
Philip Wheeler Photography

M is for Manual exposure...do it!

Photographic Exposure Basics

Photographic exposure is a complex subject. Many books, courses, and lectures have been created solely on this subject. I will briefly review my current understanding of basic photographic exposure in this article.

The process of reproducing a scene as a photographic image requires film, a digital sensor, or some other material that reacts to the light that is allowed it strike it during a fixed period of time. One can think of this as capturing that light with the camera. The key to good exposure is to capture just enough light to achieve the desired image.

Available light is the light that exists in the scene. This is normally dominated by sunlight outdoors during daylight hours. Indoors, it might be light coming through a window. At night, available light could be moonlight, starlight, a campfire, artificial light sources, etc. At a music concert it could be the stage lights. Camera flash attachments as well as studio lights are not considered part of the available light since they are introduced by the photographer.

Here are the major factors that affect how much light strikes your film or sensor.

Lens: A lens is said to be fast if it can allow more light through in a given period of time. Lens speed is specified by an f-number. The maximum aperture is specified as the minimum f-number that a lens can achieve. A lens rated at f/1.4 can allow more light to pass through than a lens rated at f/4, for example. Faster lens speed generally comes at a higher cost.

Aperture: This is the opening inside the lens through which light travels. A fast lens allows a larger opening, allowing more light to enter in a given period of time. You control the aperture size, from the maximum allowed by the lens to the smallest allowed by the aperture mechanism. Any lens set at a very small aperture, such as f/22, allows very little light to enter, regardless of how 'fast' the lens may be.

Shutter: The shutter speed controls how long the film or sensor is exposed to the light admitted through the lens at the selected aperture.

ISO: Film is rated according to its sensitivity by an ISO number. Lower f-numbers indicate less sensitivity. ISO 100 is a good choice when there is bright available light. Higher ISO ratings, such as ISO 1000, are used to designate film that more sensitive to light. Higher ISO is good for low light situations and when shutter speed is set very fast to freeze motion, for example. Digital sensors can have their ISO sensitivity varied through the camera's electronics and software, providing you with another tool to help control exposure. However, higher ISO settings can result in more noise, or graininess, in your images.

Since your control over the available light is limited, it is important to measure it in order to help you choose appropriate exposure settings. Almost all cameras have a built-in reflected light meter. This in-camera meter often has options such as spot metering, center-weighted averaging, etc. Regardless of those options, the in-camera meter measures the light that is reflected from the subject and enters the lens through its aperture. A standalone light meter, separate from the camera, has an incident light metering mode, which indicates the proper exposure settings given the light that is actually striking the subject. Incident metering is often more accurate than reflected light metering but it requires that you invest in a quality light meter and take the time to learn how to use it effectively.

Whether you use a reflected light meter reading, incident light reading, or both, correct interpretation of the reading(s) is essential to achieving your vision of the image that you wish to capture. Auto exposure bracketing (AEB) can help by providing several alternate exposures of the same image with very little extra effort. This is extremely valuable when your subject would be difficult if not impossible to re-photograph at a later time.

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.

Philip Wheeler Photography

Manual Exposure, Part 1

Ahh, putting your DSLR on Manual...its not scary once you know the fundamentals. But instead of launching into theory and lots of technical details, I'll dive into this quick and dirty Get Started guide. Your goal is to learn to set the camera's exposure controls manually and obtain a photo with a reasonably good exposure. You should be outdoors in the daytime, cloudy or not, and choose a reasonably stationary subject to photograph. For some of the settings discussed, you will need to refer to your camera's manual to learn how to vary the settings. It is well worth your trouble to learn this stuff!

First a couple of brief definitions:
Over-exposed   -- your photo looks too bright, washed out. Too much light has been collected.
Under-exposed -- your photo is too dark. Not enough light has been collected.
Depth of Field -- a shallow depth of field means objects far away from your subject are blurry. A greater depth of field means that more of the objects in the scene are in focus, from near to far.

OK here we go in 360 words or less!

1. Set your camera into Manual mode, usually designated M on a selection dial.
2. Select your ISO. I generally start at ISO 100 since it introduces the least amount of noise.
3. Select your aperture. This is referred to as an f stop, designated as f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, etc.  A lower numbered f/stop allows more light to reach your camera's sensor. The smaller the f number, the shallower your depth of field. For a landscape shot, select a higher number. For a flower close-up, select a lower number.
4. Look at the exposure meter built into your camera. It will form a reading indicating the exposure based on the available light, your ISO setting, your f stop setting, and your shutter speed. If it shows over-exposure, increase your shutter speed. If it shows under-exposure, decrease your shutter speed. Note that your shutter speed needs to be faster than 1/60 second to help reduce camera shake. Otherwise, use a tripod.
5. Frame your subject, focus with care, and take the shot.

If you can't get a reasonable shutter speed setting, such as when there is not enough light available for your chosen f stop, increase the ISO and try again. Note that going much above ISO 800 will start to introduce some noise into your photo. You can also vary the aperture: lower f stops allow more light to reach the sensor. Watch your LCD display after the shot to get an indication as to whether the exposure was good. Moving clouds cause the light to change rapidly, so be ready to modify your shutter speed as that happens.

This method is not to be confused with aperture priority. It is similar, but when you switch your camera into aperture priority you are not only giving it control of your shutter speed, but also your ISO setting. You need to maintain control over all three of the main settings for exposure: ISO, aperture, and shutter speed.

That's it! Quick and dirty. In future posts I'll explain the details behind each setting, and talk about photographing non-stationary subjects. But for now -- practice!

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
Philip Wheeler Photography

Lens Optics Correction Revisited

Two days ago I posted an article called Lens Optics Distortion Correction. This is an update to that article.

After I installed the Photoshop and Lightroom updates, re-booted the computer, and restarted Photoshop and Lightroom, I found that no new camera or lens models had been installed. I searched the Adobe web site and found the Adobe Lens Profiler Downloader, which I installed. With that tool I found that the Canon 60D is not among the available camera models from Adobe. So my original comments on the distortion correction accomplished by these programs stands as written.

PTlens

I installed the trial version of PTlens, which allows you to correct 10 images before it expires. First you need to navigate to a folder that contains JPEG or TIFF images from your camera. It is unfortunate that it does not appear to work with camera RAW images. However, you can use either DPP (Canon), ViewNX 2 (Nikon), Photoshop, or another program to convert the RAW image into a TIFF, for example. I did that with the same test image and ran the PTlens default Barrel-Pincushion distortion correction. PTlens automatically saved the altered file under a new name that was easy to find.

PTlens detected the camera body model and lens right away, no downloads necessary. In a side-by-side set of before-and-after visual comparisons, the PTlens result was slightly different from the other 4 software packages previously tested. It was close to the DxO and DPP result, but still slightly different and quite possibly better. PTlens also includes perspective and chromatic aberration corrections, which I did not try. Photoshop has these as well. It appears that one must buy a separate DxO module to do perspective correction. If your lens is not already supported by PTlens, the developer will create calibration data from your images if specific criteria are met (http://epaperpress.com/ptlens/calOverview.html).

Of the 5 software packages I tested, DxO Optics and PTlens produced the best results, in my opinion. DxO Optics Pro is about $250 on amazon. PTlens is $25. PTlens doesn't have a super fancy user interface, but it gets the job done very well and I plan to purchase a license.

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.

Philip Wheeler Photography

Stuck Offshore

Critical Focus

Critical, or sharp, focus is one of the characteristics of a professional-quality photograph. A poorly focused image is a sure sign of an amateur.

First, check your camera's Diopter adjustment (see your camera's manual). This adjustment helps bring the focus points into focus within the viewfinder. The default adjustment on my Canon 60D was incorrect, and I could only focus properly if I removed my eyeglasses. This was not a problem on my old film camera. After adjusting the Diopter on the 60D, I can now focus through the viewfinder with my glasses on.

Auto-focus (AF) vs. Manual Focus (MF)

Auto-focus lenses typically have a very short range of motion in their focus adjustment. This means that once you have your subject in focus, it is very easy to knock the lens out of focus. The older lenses with the split-prism focus have a longer range of motion. A Katzeye screen can provide a split-prism type focus for many DSLRs (http://www.katzeyeoptics.com). Without such a screen, it is sometimes better to use auto-focus with AF lenses,taking care to select the proper focal point in the viewfinder before taking the shot. For information on selecting the focal point, see your manual. This is incredibly important with a narrow field-of-view shots, but also important with higher f-stops.

Some people have found that adding a 4x or 7x loupe behind the viewfinder helps them to focus better. Some manufacturers, such as Pentax, sell a magnifying eyepiece. There are also specialty focusing devices available for use in capturing astronomical images. Using Live View appeals to some people, especially for studio work, but be aware that the LCD screen only shows a low-resolution preview that uses a JPEG image.

Whether using AF of MF, take your time and get the focus exactly right on your subject. This will help set your photos apart from those taken with lack of attention to critical focus.

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
Philip Wheeler Photography

Lens Optics Distortion Correction

The optics in the lens on your camera create a unique distortion of the captured image, which is more pronounced with zoom lenses. You might not even notice the effect on your images until you see the results after using software to correct it. The camera body design can introduce some distortion as well. Taking the time to apply good distortion correction algorithms to your image is well worth the effort, in my opinion. Fortunately, with the proper software, it is also an easy process. There are a number of software packages available that perform fairly well. Here I will relate my first impressions of four popular programs. I am using a Canon 60D camera with an EF-S 18-135mm f/3.5-5.6 IS lens for this comparison. The image was saved by the camera in RAW mode at the highest resolution: 5184 x 3456 pixels.

Canon Digital Photo Professional (DPP) 3.13.10.0

DPP is provided free to Canon camera owners. DPP had the correct camera body and lens models available. Once the Lens fine tuning was selected, and distortion turned on (it is off by default), the correction was applied. The result was very good, and on a par with DxO Optics (see below). DPP does a good job and the price is right. However, the corrected image size grew to 5337 x 3558 pixels. When I reized this in Phoroshop to the original 5184 x 3456 size, there was an apparent difference from the result produced by DxO Optics.

Adobe Photoshop CC 14.1.1

Photoshop CC (Creative Cloud), approximately the equivalent of Photoshop CS6, has a filter called Lens Correction. After you select the filter, a window opens and you then select your camera model and lens. My exact camera model was not listed, but the lens was listed. I selected Canon 50D as the camera. (I'll explain the Photoshop update process in a later post, but suffice it to say it included a dreaded system restart.) The resulting image looked better than the original. Two camera models were available: the Canon 7D and the 50D. With the same lens model, selecting each of the two camera models produced slightly different results. With either setting, the result was not as pleasing as either DPP or DxO.

Adobe Lightroom 5.2

In Lightroom the proper lens model was available under Develop > Lens Corrections but only the Canon 7D body model was shown. It may be that I needed to restart the computer to let the latest update load. An interesting effect was noted: although the lens correction was apparently identical to that of Photoshop, Photoshop cropped the image slightly and resized it to its original size. Lightroom did not do this. This behavior was unexpected. I'd have to say the Lightroom result was better than the Photoshop result given this anomaly, leaving Photoshop as the least desirable optics correction software of these four software packages.

DxO Optics Pro 8.3.1

Unlike the Adobe programs, DxO Optics detected the camera and lens models from the RAW images and presented me with the option to download the appropriate plug-ins. I selected OK and they were painlessly installed. I say painlessly since I did not need to restart anything! There are ten possible corrections; all are selected by default except Color Enhancement and Contrast. But this is in First Steps...the Advanced mode includes many more options that I have yet to explore. The new plug-in models produced a much improved image, better than both the Photoshop and Lightroom results and, to my eye, slightly better than the DPP result. I highly recommend the DxO Optics software. DxO also has plug-ins for Photoshop and Lightroom.

PTlens is another software package that is popular for lens distortion correction, but I have not yet tried it. I'll post more information in the future.

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.

Philip Wheeler Photography

High Dynamic Range (HDR) Imaging

What is HDR? Back to basics: the human eye can see a much wider range of light intensity than most cameras. HDR is a way to expand the range of light intensities that the camera's sensor records. Here's how it works: first you must capture a set of images that are identical except for shutter speed. Next, with your computer, you process the images to create a single HDR image.

The Easy Way: With the camera mounted securely on a tripod, compose your shot. Set the exposure as you normally would and take the shot. Lower the shutter speed by 2 stops without changing anything else and take another shot. Now increase the shutter speed by two stops from the original shot, and take the third shot. Use specialized software such as PhotoMatix, Photoshop, FDRTools, Niksoft HDR Efex Pro, or Canon's Digital Photo Professional to combine the images into a single HDR image. In Photoshop CC with Adobe Bridge, for example, select the images to be merged in Bridge, then select Tools > Photoshop > Merge to HDR Pro...

The Harder Way: This is similar to the Easy Way except that you determine more precisely how much to vary your shutter speed. You take light meter readings of the areas from least well lit to brightest, and devise a set of exposures to cover the entire range. Once captured, process the images as previously mentioned.

Many DSLRs have a built-in function called Auto Exposure Bracketing (AEB). While not designed for HDR, it is very useful. You can typically set up your shots for -2, 0 and +2 stops. It is convenient to use a 2-second timer delay to further reduce camera vibrations. Push the shutter release and the camera will automatically capture the three images in succession. More advanced cameras can even capture a set of 5, 7 or 9 images in this way.

HDR has become more mainstream in the past few years.Some newer high-end DSLRs now have a built-in HDR function. HDR is here to stay. I recommend that you become familiar with its uses.

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.

Philip Wheeler Photography

Trey Ratcliff's Landscape Tutorial (use code SIC-6683 for 10% off!)

Finding Subjects to Photograph

Good subjects for photography are everywhere! Within walking distance of your house you should be able to find hundreds of potential subjects, dozens of interesting subjects, and maybe even a few really unusual ones. It comes down to developing your photographer's eye: looking at the world in a way such that you are constantly aware of interesting subjects.

Once you select a subject, take a few minutes to think about it. Observe the available light. Walk around the subject a bit to explore different possible angles. Watch out for annoying background distractions such as trash bins -- although you can edit out many things in post-processing, with a little care before taking the shot you won't have to.

I almost always take my camera with me. There is an old photographer's adage: the best camera is the one you have with you! You never know when an interesting subject will appear. As I left the fitness gym the other morning, I saw a nice green field nearby. I grabbed my camera and walked closer, and discovered the pond shown below. It was about 30 minutes past sunrise. In the distance you can see the Blue Ridge Mountains.

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
Philip Wheeler Photography

Should You Save your Images as JPEG, RAW or Both?

This is another question that have been a popular photo topic of late. For some cameras you don't have a choice, but with many DSLRs you have at least a choice between RAW, JPEG or both. Some allow saving in TIFF format as well.

First of all, lets talk about these three file formats.

RAW is the image produced by the camera's sensors and converted to a digital format from the analog signals recorded by the sensor. RAW is typically a proprietary format of the camera's manufacturer. Each manufacturer provides software for your computer that will convert their RAW images to another image format. From there, you can typically save them as JPEG, TIFF or whatever you require.

JPEG is a lossy compression format. The camera produces a JPEG after additional processing for white balance, contrast, sharpness, color space (such as sRGB or AdobeRGB), etc. If you don't do post-processing on the image, JPEG is often a good choice, and it saves memory card and disk space. Extensive post processing can result in degraded image quality when the file is re-saved as JPEG each time.

TIFF uses a lot of storage space. It is processed like a JPEG except a TIFF image is not compressed. Therefore it is valuable for use in post-processing, just as the RAW file is.

RAW preserves all of the information captured by your camera's sensor. This allows you to correct such things as white balance in post processing. If you only save to JPEG, accurate post processing is impossible.

Personally I save as RAW only, since all other formats can be created from RAW with no loss in quality. This is particularly useful in post processing. Photoshop, for example, can open a RAW image as a smart object. This helps prevent destructive editing. If you make mistakes, you can always revert to the original image.

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
Philip Wheeler Photography

Hand-Held vs. Tripod Mounted

Camera shake can severely degrade your focus. A sharp, or critical focus is one of the keys to achieving great photographs. A rule of thumb for taking a photo while holding the camera in your hands is 1/60 sec. exposure time, but I would extend that to at least 1/120 sec. to ensure better stability. Image Stabilizer (IS)/Vibration Reduction (VR) Lenses can extend this, but using a tripod is best in a low light situation. Using a very long focal length lens can also add to the problem, and a tripod is very important in this case.

When using a tripod you might need to switch off the Image Stabilization/Vibration Reduction on your lens. With no shake for which to compensate, some older IS/VR lenses will actually introduce shake of their own. Check your lens -- newer lenses can detect when they are tripod-mounted and their IS/VR can remain ON.

Once your camera is mounted on the tripod, there are two ways to correctly release the shutter: use a remote shutter release, or use the camera's built-in delay timer. If you manually press the shutter release button on the camera without using the delay timer, you might as well not be using a tripod at all! Pressing the shutter release introduces camera shake; the delay gives the system time to stabilize.

Some cameras such as the Canon 60D have the remote control sensor in the front of the camera, probably to facilitate group shots that include the photographer. Newer models have sensors in front and back. You need to know which side senses the remote command.

Of course, if your focusing skills are not spot-on, most of the above won't matter much. Be sure to focus on the most important part of the scene. For a portrait, it is the model's eyes. Generally it should be the main subject, the point in the photo where the eye is naturally drawn. If there is no clear subject, it might be best to reconsider your scene composition.

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
Philip Wheeler Photography

Megapixels and Aspect Ratio Considered Together

Let's say you have a 12 MP digital camera, and you are considering an upgrade to a camera with 18 MP. At first glance one might think that this is a 50% increase in image size: (18 - 12) / 12 = 0.50, or 50%, but that is incorrect. Let me show you why!

Now consider the ratio of 3:2, or 3 units of length by 2 units of height, which is the same aspect ratio of 35mm film. Here are some specifications taken from current models of Nikon and Canon digital SLRs. All of these share the same 3:2 aspect ratio.

12 MP   4256 x 2832 pixels
18 MP   5184 x 3456 pixels
24 MP   6016 x 4016 pixels
36 MP   7360 x 4912 pixels

Now let's compare the area increase among combinations of these sensor sizes:

12 MP -> 18 MP  22%
12 MP -> 24 MP  41%
12 MP -> 36 MP  73%
18 MP -> 24 MP  16%
18 MP -> 36 MP  42%
24 MP -> 36 MP  22%

So you see, the increase is based on the linear dimensions, not the total MP count. That is why a 24 MP image cannot be printed twice as large as a 12 MP image while maintaining the same pixels per inch (ppi) resolution. What does this mean in terms of print size? Here are a few examples using 300 ppi:

12 MP   14.2" x 9.4"
18 MP   17.3" x 11.5"
24 MP   20.1" x 13.4"
36 MP   24.5" x 16.4"

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
Philip Wheeler Photography

Sensor Size in DSLRs

What size is the sensor in your digital SLR camera? The first thing that comes to mind is megapixel (MP) count but that is not related. I am talking about the physical size of the camera's light sensor array. This is sometimes called the sensor format. Nikon has DX and FX sensors. Canon has APS-C and Full Frame. The Nikon FX is equivalent to the Canon Full Frame. The smaller APS-C sensor is also called a cropped sensor, since the image is smaller than the image a full-frame sensor would produce.

An FX/Full Frame sensor is approximately the size of one frame of 35mm film. The DX/APS-C sensors are smaller. This means that a 50mm lens on an FX/Full Frame sensor will allow about as much light to strike the sensor as it would on 35mm film.

On the other hand, a 50mm lens will cast less light on the smaller DX/APS-C sensors. This means the effective focal length of your 50mm lens becomes about equal to how a 75 to 80mm lens would expose 35mm film.

Here is an example. Suppose you have a Nikon D600 DSLR, which has an FX sensor. If you use an FX lens, you take advantage of the full 24 MP of the sensor. However, if you use a DX lens, you will only capture about 10.3 MP. This is about the same as the older Nikon D200, which has a DX format sensor. Bottom line: if you have an FX camera, use an FX lens. Using an FX lens on a DX camera gives you no advantage.

Nikon DX  1.5x focal length such as in the D7000
Nikon FX   35.9 x 24.0 mm in the D600   "Full Frame"
1.0x (Full Frame) such as in the Canon EOS 6D
1.6x (APS-C) such as in the Canon EOS 60D

"1.5x focal length" does not mean that a 200mm lens becomes the equivalent of a 300mm lens when used on a DX camera. It means that you get an angle of view on the sensor equivalent to that from a 300mm lens.

You can see the Nikon and Canon DSLR comparison charts here:

http://en.wikipedia.org/wiki/Comparison_of_Nikon_DSLR_cameras
http://en.wikipedia.org/wiki/Comparison_of_Canon_EOS_digital_cameras

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
Philip Wheeler Photography

Copyright © 2013 Philip N. Wheeler. All Rights Reserved

Aspect Ratio

This was a hot topic on one of the popular photography forums last weekend. Aspect ratio is the ratio of the length of a rectangular shape to its width. If the length is equal to the width, then the shape has a 1:1 aspect ratio. 5184 by 3456 pixels is 5184 / 3456 = 1.5, or expressed as an aspect ratio, 1.5:1. By convention, whole numbers are preferred, so 1.5:1 would be written as 3:2, Simple mathematics.

A digital camera's sensor aspect ratio is the width divided by the height, in pixels. For the Canon 60D, which has a RAW image size of 5184 x 3456 pixels (18.0 MP), this is 5184 / 3456, or 3/2. The accepted notation for aspect ratio is 3:2. Thus for the Canon 60D, 3:2 is the native aspect ratio. All RAW images are captured and saved with this aspect ratio by the 60D, preserving every possible pixel, regardless of the aspect ratio you might choose in the menus. 

Most DSLRs let you choose the quality of the image to be saved. Options typically include one or more RAW (the camera's native format) selections, and one or more JPEG selections.The Canon 60D allows you to save in RAW only, JPEG only, or RAW + JPEG. There are also settings for image quality: higher quality means more data saved. This means you use more storage space per image, and therefore your storage device cannot store as many images. I always save in RAW at maximum quality. You can always convert the RAW image to JPEG or another format with your computer. 

There are camera menu options that allow you to select among the aspect ratios 3:2, 4:3, 16:9 and 1:1, but these are only used in the Canon 60D if Live View mode is Enabled. Anything other than 3:2 will reduce your effective MP count for JPEGs only. You are trusting the camera to crop your JPEG images for you, but if you are also saving RAW you will still capture the whole image. If you leave Live View disabled, cropping is ignored. At maximum quality in Live View mode on the Canon 60D, your JPEG megapixel counts are as follows:

3:2 is 5184 x 3456, or 18.0 MP
4:3 is  4608 x 3456, or 16.0 MP.
16:9 is 5184 x 2912, or 15.1 MP.
1:1 is 3456 x 3456 pixels, or 11.9 MP.

The Canon 60D and other advanced DSLRs can do a lot of other in-camera image processing as well, but I prefer to do all post-processing on the computer. With good image processing software such as Photoshop, you can achieve any aspect ration that you require, but that is a topic for another day.

Here is a photo of a flower in the park. While it looks simple, getting the exposure just right was key: it was just after dawn under a totally overcast sky. A tripod was necessary to keep the camera steady during the exposure. 

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
Philip Wheeler Photography

Megapixels

I started serious film photography in 1985 with an Olympus SLR film camera. These days I use a DSLR (digital single-lens reflex) camera: a Canon 60D that I bought from Adorama with an 18-135mm zoom lens. The newer version is the Canon 70D. Unless you already have a compatible lens, you will probably want a kit that includes at least one lens. Nikon and Canon (among others) offer many excellent digital cameras and I will be comparing them in future blog entries. I've always experienced great customer service when purchasing through Adorama,  Amazon, and B&H Photo. 

The Canon 70D has 20.2 MP as opposed to the 18.0 MP of the 60D.  Let me take this opportunity to explain "MP" or megapixels.

A digital camera detects and records the light that falls on a sensor. The sensor is a rectangular grid of light sensitive elements called pixels. One million of these pixels is called one megapixel. The image size of your camera's digital sensor is measured in sensor array dimensions. For the Canon 60D this is 5184 x 3456 = 17,915,904 pixels, which is advertised as 18.0 MP. There is no visual reason to prefer 20.2 MP over 18.0 MP. A higher pixel count appeals to some consumers, but in fact many high-end professional digital cameras that sell for much more money than the Canon 70D have a lower megapixel count. So don't be tempted by a few extra MP -- save your money for a high-quality lens instead. I'll talk more about megapixels and sensor size in a later blog entry.

Here is a photo that I captured at 18 MP, then cropped to about 12 MP. I cropped the original image in order to have the child positioned in the right 1/3 of the image. She is running to the left, and the composition is improved by having more space in that direction. One advantage of using a high MP camera is the ability to crop and still maintain good image quality.

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
Philip Wheeler Photography

Making Photographs

Welcome to my photography blog! I am an electrical engineer seeking to improve my photography, to learn how to make photographs. Ansel Adams said, "You don't take a photograph, you make it." This blog will record some of my steps along the path toward making photographs. Hopefully you will learn something from my successes and failures along the way. I encourage your feedback and comments. And if I make a mistake, please correct me.

I'll start with this image I captured this morning: sunrise, 6:57AM, looking toward the Blue Ridge Mountains from Waynesboro's Constitution Park. Earlier the sky had a lot of reddish hues, but I missed that twilight marvel. I used a Canon 60D with 18-135mm lens -- a standard kit from Adorama that I bought a couple of years ago. The image was unremarkable, but with a little post-processing with Photoshop I think I added some visual interest or "pop" to the final image.

Copyright © 2013 Philip N. Wheeler. All Rights Reserved.
Philip Wheeler Photography