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Digital SLR Guide News, Dec. 2006 - How to Find the Best SLR Lens
December 28, 2006
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Digital SLR Q & A
Question: What are f-stops?
AnswerIn last month's newsletter I talked about aperture and noted that by changing the aperture you can alter the amount of light that passes through the lens and enters the camera.
I also mentioned that the aperture numbers that appear on your digital SLR camera are the inverse of what you'd expect: a small number like 3.5 is a wide aperture and a large number like 16 is a narrow aperture.
In this month's Q & A, I'm going to dig a bit deeper into what these numbers really mean.
To answer the question above directly, an f-stop is simply a unit of measurement like a mile, meter, gram or ounce. Since the f-stop is the unit of measurement for aperture settings, this explains why all aperture references are preceded by an f (f/2.8, f/8, f/16).
Aperture numbers aren't all over the map and aren't just any number you can think up in your head (there is no f/4.9). Instead, there's a common set of aperture numbers that are used by digital SLR lenses:
Important point #1: as the aperture number increases to the next value in the scale, half the amount of light enters the camera.
Changing from an aperture of f/2.8 to f/4.0 (1 full f-stop) HALVES the amount of light passing through the lens and into the camera. Conversely, switching from f/4.0 to f/2.8 DOUBLES the amount of light passing through the lens.
Important point #2: you don't always have to make aperture changes in full stops.
Think of the aperture values that I presented in the table above like measurements on a ruler. Whether you measure things in inches or millimeters, the same reasoning applies: in between each one of the primary numbers on the ruler, there are finer measurements that you can make. You can wind up with a measurement of 3.25 inches or 5.5 millimeters.
The same sort of fractional measurements can be used with f-stops, and there are two different ways that digital SLR cameras handle this: some are able to change aperture in half-stops, while others are set to make changes in third-stops.
The following table shows you an aperture f-stop scale with half-stops (the whole stops appear in bold):
And this table shows you aperture f-stops in third-stops (again, whole stops appear in bold):
So there you have it - f-stops are a unit of measurement that can be measured in whole, half and thirds increments. Understanding this scale becomes especially important when you switch your SLR out of AUTO mode and start using more manual controls.
But we'll get into that next month.
This irreverent attitude permeates the content of the site, where you'll find such interesting (and odd) photo tidbits as these:
It's almost impossible to verbally describe the WIDE variety of information that pops up on this site, so I'll just give you the link here and let you go have a look for yourself: Photojojo.com
How and WhenThis month's How and When section is going to delve into something that's a bit counter-intuitive...
When to Turn Off Anti-Shake
I can already hear the cries of protest.
Why in the world would you spend money on an advanced digital SLR camera that includes built-in anti-shake, and then go and turn it off?
There's a perfectly good reason for doing so, and here's the key: it all depends on how fast your SUBJECT is moving.
I think anti-shake is a fantastic tool for the average snapshot photographer, and that's why it's no surprise that many more SLR and compact digital cameras are including this helpful technology.
The big deal here is that anti-shake reduces camera vibration when you hold your SLR in your hands, which in turn leads to clearer photos. That's the simple definition.
The more complex one is that anti-shake helps you take clear photos when your camera selects a slow shutter speed to get a correct exposure. The slower the shutter speed your camera uses, the higher your chance of getting a blurry photo due to camera shake.
Let's put this into table form to illustrate your changes of getting a blurry photo at different shutter speeds:
See what's happening here? Anti-shake just reduces the probability of blurry photos, since you can use very slow shutter speeds and still get clear images (without anti-shake those same slow shutter speeds result in blur).
Key point: anti-shake only applies when you're not using the flash.
The minute you activate your camera's flash, anti-shake's ability to counteract slow shutter speed no longer applies. The reason is that the camera wants to activate the flash when it senses that there isn't enough light. As soon as the flash is active, the camera will set a shutter speed (typically around 1/60th of a second) so that you won't get a blurry photo.
Your flash must be turned off in order for anti-shake to work its magic at shutter speeds slower than 1/60th of a second.
This is why anti-shake is an incredibly useful feature for anyone who takes photos indoors without a flash: specifically, the interior of houses, museums and aquariums. If you want to take some photos of your relatives standing in front of an ancient artifact, anti-shake will ensure that your photo turns out crisp and clear.
But if those same relatives are romping all over the museum, your trusty anti-shake isn't going to do a bit of good.
The problem here is that even though the anti-shake is working to reduce the camera's vibration, the only thing that will freeze the motion of a fast-moving subject is a fast shutter speed. Since the use of anti-shake doesn't necessarily increase your shutter speed, it won't help you get clear shots of fast-moving subjects.
Let's talk about some concrete examples that will help clarify what's going on here.
In scenario number two anti-shake isn't going to help you get the clear photo that you're looking for - might as well turn it off. Instead, use two other techniques that WILL increase your shutter speed:
Doing these two things (and not relying on your anti-shake system) will ensure that you get a clear photo in dim lighting (without the flash), even though your subject is moving all over the place.
Cameras and Accessories
Latest Digital SLRThe latest digital SLR camera that will be hitting the shelves in February of 2007 is the FujiFilm S5Pro.
Fuji-wha? Yes, I realize that Fuji is not a name that is synonymous with digital SLR camera technology (unlike Canon and Nikon) but they have been a player in the SLR market for some time now.
The real reason you don't hear all that much about Fuji is because they don't release the same number of cameras as the other companies (1 every other year vs. 2 or even 3 per year for the big players) and their cameras are aimed more at the professional photography crowd rather than consumers.
However, Fuji cameras have two very interesting advantages: first, they are compatible with all Nikon lenses. This is probably more tempting to the person who already has a collection of Nikon lenses lying about, since a digital SLR newcomer is probably more likely just to go with a Nikon SLR camera.
Fuji's second advantage is unique: the Fuji digital SLR cameras are the only ones that have wide dynamic range sensors.
Put into non-technical terms, this sensor is able to capture more detail from highlight to shadow, resulting in photos that are more similar to what your eyes are able to see. Every other SLR on the market has a fairly limited dynamic range, which means that in high-contrast situations highlights in your photograph become pure white and shadows become pure black.
The S5Pro also introduces Fuji's face-detection technology, which allows you to quickly zero in on people's faces when you're reviewing photos on the camera's LCD. This quickly shows you that Grandma had her eyes closed for the last shot and that you need to re-take that family portrait.
More information and specifications will be added to the Digital SLR Guide once the camera is available.
Digital SLR Camera of the Month
Anyone who's been out there comparison shopping will know that the Rebel xTi is one of the most inexpensive 10 megapixel digital SLR cameras you can buy (the Sony ALPHA A100 is the other). This makes the xTi a good deal for photographers who want to make enormous prints but are on a limited budget.
The xTi also features a new dust-resistant sensor, but this is not really an innovative feature since the very first Olympus SLR released in early 2005 had a similar system. The dust-repellent sensor is new to the Rebel line of cameras, and the xTi is the only Canon SLR that includes it.
The strengths of the xTi are its compatibility with all of the available Canon and third party lenses, small size and weight (it measures 4.98 x 3.71 x 2.56 inches / 126.5 x 94.2 x 65mm and weighs 18 oz / 510g without a lens) and the addition of the 9-point autofocus system used by the semi-professional Canon 20D and 30D cameras.
The xTi also features what Canon calls "Picture Styles", a feature that they are beginning to include in all of their latest cameras (the 30D has these as well). Think of picture styles like buying different film for your camera. Some films excelled at portraits (producing natural-looking flesh tones) while others were ideal for landscapes (creating rich saturated colors).
The nice part about picture styles is that you can customize them (there are 3 user-defined picture styles) so that you can set the camera up to capture color and detail differently depending on your subject. While this is certainly a more advanced use of the camera, it's a feature that you can grow into over time once you're comfortable manipulating the other camera controls like aperture and shutter speed.
Bottom line? The Rebel xTi is a great option for photographers who want:
Accessory of the Month
Since many of you are probably using your cameras right now to photograph holiday gatherings, you're probably using your camera's flash a lot more than you normally would.
It's not that I'm opposed to flash photography, I'm just not overly fond of the direct frontal lighting and harsh shadows that it produces.
One easy way to improve photos taken with a flash is to use a diffuser: a device that takes the light of the flash and spreads it out over a wider area. This cuts back on the harshness of the flash and creates more appealing images (especially of people).
While flash diffusers come in all shapes and sizes, the LumiQuest Soft Screen is one of the smallest and easiest to use that I have found, AND it work with your camera's built-in flash. You don't have to go out and spend a lot of money on an external flash unit for this to work.
Most important of all - diffusing your flash virtually eliminates red-eye, which is the result of light from the flash bouncing off your subject's retina and back into the camera. Yes, there are plenty of image editing programs out there that quickly remove red-eye, but isn't it easier just to not capture it in the first place?
In ConclusionIt's been a great year for the Digital SLR Guide, and I certainly hope that it's been a good one for you too.
Digital SLR development does not seem to be slowing down in any way, so it looks like I'll have a lot to chatter about for a long time to come.
Thanks for reading, Happy Holidays, best wishes for the New Year and most of all...happy picture-taking!
--Chris Roberts, Your Digital SLR Guide
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