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DSLR Talk

April 15

The novice photographer often feels as though the most important thing about taking pictures is the camera they get. This often starts with a budget and, once this is established, the most expensive body is then acquired. The lens(es) that will come as part of a kit are… well. They’re bundled for super cheap for a reason. They’re super cheap, at least compared to other lenses that are available. Upgrading a lens will make a newbie realise how important good lenses are. They can often make you feel like you just bought a new body.

The cameras and the kit lenses with which they are bundled work. They take very nice pictures. But they’re subject to very notable limitations. After learning some things the hard way, and after having done quite a bit of reading, I decided to share what I’ve learned in one post.

A quick note about acquiring a body. Firstly, if the intent is to leave the camera on full auto all the time, perhaps an SLR is not the camera for you. Yet. A very advanced point-and-shoot  might make more sense. The Canon G-series comes to mind (note, I talk a lot about Canon as it’s what I have. Nikon make super mega excellent cameras). There are tons of manual controls, but they’re built to do most the thinking for you. They’re designed to be in full auto mode most of the time. Before you balk at me, yes,  DSLR (for Digital Single Lens Reflex, and yes, there are Twin Lens Reflex cameras) can be used in full auto mode all of the time. Just as an 18-year-old single malt scotch can be used to make whisky sours. My unsolicited recommendation? if you don’t understand the ISO-Aperture-Shutter Speed relationship at all, an SLR will be overkill for you at this point in time. Based on that, you decide what you do with your money.

I started with an advanced point-and-shoot (Canon S3) about four years ago. At first, I was enthralled by it and its capability. Two and a half years after obtaining it, I found myself increasingly limited by it. I hunted for manual features that, although present, were tricky to get to (though never thought of approaching these settings for the first year I had the camera). More than once, as I tried  to change a setting, I’d lost my shot. Something had moved, lighting changed, etc. I think that camera had about 3,000 shutter actuations. Nothing astronomical, but I got some decent use out of it.

A year and a half ago I upgraded to the Canon T2i. It came with the 18-55mm and 55-200mm zoom lenses. This move threw me into the world of manual settings, different lenses, sensor types and body categories. All pictures on this blog taken before December 2011 were taken with the T2i and these lenses (though I added a 50mm lens in the spring of 2011 and a 100mm macro late in the summer).

Cropped vs. Full-Frame Sensor Bodies

I’ll start from the sensor. What does the sensor size mean? What does it change? Well, a lot if you know precisely what you’re after. If you’re still learning the ropes, a little less.

A full-frame sensor is a digital image sensor that is the same size as a 35mm film frame (think of a 35mm negative). They are larger and therefore more expensive. Often a lot more expensive.  They are also more unforgiving. These sensors push lenses to their limits and often amplify a lens’s shortcomings. More on that later.

A cropped sensor is a digital image sensor that is smaller than a 35mm film frame. There are various sizes. Cropped sensors offer many advantages and make a lot more practical sense to most photographers.

Because cropped sensors are physically smaller, their size affect their interaction with the lenses they wear. You might have read terms such as crop factor. This term is related to the fact that because the digital image sensor is smaller than a 35mm film frame, it doesn’t use the full extent of a lens and creates a magnification factor. Some cropped sensors cause a lens to be 1.3, 1.5 or 1.6 times the focal length of a lens (so a 100mm lens becomes, in essence, a 130mm, 150mm or 160mm lens, respectively).

This can be great because with my T2i (which has a Canon APS-C sensor), has a sensor with a crop factor of 1.6, the 55-200mm lens became a 88-320mm lens. This means I could “reach out” further with the lens. To get the same effect on a full-frame sensor, I would have had to spend a lot more money for a lens that went to 300+mm.

MTF Charts

Another advantage of the cropped sensor camera is that it doesn’t use the full breadth of a traditional lens. In the Canon world, there are the traditional “EF” lenses. These are the way they’ve been making lenses for many years now, and these lenses work on all their SLR cameras in recent memory. Canon also has a series of “EF-S” lenses, which are for cropped sensor cameras. They cannot be used with full-frame digital SLRs or traditional film SLRs because (typically) the rear element (or lens/grouping of lens, moving bit closest to the camera) would hit the mirror or just screw things up.

When looking at lenses, websites will often show an MTF chart. MTF, or Modular Transfer Function, is the typical way a lens’s performance is conveyed to conusmers. There are articles fully explaining why this chart is important so won’t spend too much time on this. In short, this chart shows how well a lens transfers the subject to the image. Black lines is the lens wide open (so if it’s an ƒ1.4 lens, it’s at ƒ1.4, if it’s an ƒ4.0 lens, it’s at ƒ4.0) and the blue lines the lens at ƒ8.0 (my understanding is that this is because at this aperture, lenses are in their sweet spot, where they handle light at their best, so black lines never do as well as the blue lines, but the gap between the colours shows you how much your image changes when you stop down).  Ideally, you want nice, straight lines near the top all the way across like this:

Some of the lines represent the contrast reproduction (thick lines), some represent how sharp the detail will be (thin lines). Again, you want the lines straight and near the top for a faithful reproduction of a subject on the image. The chart above is for a 135mm Canon lens.  With zoom lenses, there tends to be a notable drop off in performance, at least in one portion of the zoom range. Below are the MTF charts for the Canon 28mm-200mm lens.  This lens is very versatile as it goes from wide angle to a strong telephoto in one lens. But here’s the price you’re paying for that flexibility:

In this one, at 28mm, the lines are… not straight and, as you go towards the right, are not near the top. When you zoom in to 200mm, however, there is an improvement. This graph suggests that you’ll get nicer images at 200mm than at 28mm. Why am I rambling on about all of this? Well, if the crop factor for a cropped sensor is 1.6, then when you look at the MTF charts, you stop reading the X-axis at 16. It doesn’t matter what the lines do further right of that number, the sensor doesn’t go that far and you won’t experience it. This means that the camera will typically take advantage of a lens’s “sweet spot” and ignore the troublesome area, the edge of the image. With a full-frame sensor, the entire chart is important. This means that with a full-frame sensor you need to spend money on higher quality lenses to get the performance you come to expect.

All technical talk aside, though what matters is that you get what you want out of it. This means that when you take pictures, you like the results. If you’re happy, that’s all there is to it. A better lens will provide a more faithful representation of your subject, but it won’t help you with composition, timing, opportunity and creativity.

To recap, cropped sensor means the lens acts like a more powerful telephoto lens, and you get to disregard the troublesome performance areas of lenses. So if cropped sensors have all of these advantages, why would anyone get a full-frame sensor? The richness of the colour. The depth of the colour. The… yeah. There’s a quality difference.  But it’s more challenging, more expensive, more more more.

 Aperture

When looking at the name of a lens, there’s one number for the focal length (50mm, 70-200mm, 800mm) and the aperture (ƒ3.5, ƒ2.8,ƒf1.4). The focal length is a calculation of the distance from the lens to the sensor when the lens is focused to infinity (though often if you look at a lens that says 400mm and measure it, it’s far less than 40cm, this is because of the interplay of the lenses within the unit allowing for a shorter physical size, these lenses are telephoto lenses). The aperture tells you how wide the lens will go and therefore how much light it will let in. What does it matter? Well… a heck of a lot.

First, most zoom lenses have an aperture range. Above I mention the EF 28-200mm, its range is ƒ3.5-5.6 (the ƒ is for Factorial System). This means that at 28mm, it opens up to ƒ3.5. At 200mm, it only opens up to ƒ5.6. At ƒ5.6, you’ll need a sunny day. Using this indoors or in the evenings is likely to be challenging. There just won’t be enough light coming in. The shutter speed will have to be slow (and if hand held, will show how much your hand shook) or the ISO increased (grainy picture). The other lens I mention up there is the Canon EF 135mm f/2.0L (some say L stands for Luxury, some say it doesn’t mean anything; it’s Canon’s pro lens series). This opens up to f2, a lot more light comes in. If you like taking pictures with available light (no flash or additional artificial light sources), the “slowest” most people want is ƒ2.8. So ƒ2, ƒ1.4, etc. lenses are even better for available light photography. Leica makes one 50mm lens that opens up to ƒ0.95. But that will set you back CAD$11,000.

Depth of Field

It’s not just as simple as just getting an expensive lens that lets lots of light in, however. The “faster” (or smaller ƒ number, which means it lets in more light) a lens, the more you have to be conscious of which f-stop the camera is using when you’re composing your shot. I word it this way as most people use the automatic modes and seldom look at what aperture and shutter setting it’s selected for you. The smaller the ƒ-stop number, the shallower the depth of field. This means that less of the subject is in focus.

Depth of field is how much is in focus. When a lens focuses, assuming there’s not much distortion, is a plane. Think of is as a rectangular box. Everything within the box is in focus, everything without is out of focus. A lens at ƒ13.0 will have a lot in focus. So if you wanted your subject and the building in the background to be in focus, this is what you’d want to use. If you wanted the subject in focus, but the background blurry, you’d want to open up the lens. The wider the lens, the shallower the depth of field, or the thinner the rectangle. At ƒ2.8 I can usually still make out what the object behind my subject is, though the details are very fuzzy. At ƒ1.4, the background is a total blur, only faint shapes and melted colours are seen.

When I use the Canon 50mm ƒ1.4 at ƒ1.4, the depth of field is so shallow that only half of someone’s head can be in focus. If I want more of the subject in focus, I need to stop down to, say, ƒ2.8. By doing this, less light hits the sensor. That leads to me needing a slower shutter speed (risk of my hand shaking affecting the shot) or higher ISO (grainier image). So if the camera does the thinking for me and, because of the low light situation, it selects ƒ1.4, I might not have my entire subject in focus. If I want to change that, I need to know how to alter the settings to achieve a workable compromise.

So if you’re buying a lens because it’s a super telephoto zoom, but it’s an ƒ5.6 lens, AND you expected to use it for indoor sports photography in low-lit areas, you’ll be very disappointed. Your pictures will all be blurry from your hand shaking. Conversely, if you buy a lens because it’s super fast (say ƒ1.2) but then find that your pictures are all out of focus, it’s because you’ve yet to master your camera’s controls.

There’s also focus shift in very fast lenses (typically ƒ1.4 and faster). This is when the camera is on automatic mode and you focus on a subject, take the picture and… the focus is elsewhere! To prevent this from happening you need to manually control the settings and/or stop the lens down to ƒ2.8 or smaller. Fast lenses are great, but demanding. A lot of people complain (e.g. the Canon 50mm ƒ1.4 is superior to the 50mm ƒ1.2) but it’s often more the operator than the equipment, also known as an “ID-10-T” error. Companies like Canon and Nikon won’t make a $1300 lens that’s absolute crap. But they will make precision instruments that requires that the user is trained to operate them.

Zooms vs. Primes

Primes are not for everyone. That being said, right now, I do not own a zoom lens. Like I mentioned above, a zoom lens is a technical compromise but a practical marvel. If you get the right zoom lens, you don’t need to move to get the perfect framing. You just twist a ring on the lens.You can get the equivalent of two, three, even four lenses in one package. Some are very specialised (the 8-15mm fisheye wide angle comes to mind). Some very broad (100-400mm lens comes to mind).

So what about primes? Well, you need to zoom with your feet. This is very restricting to most people. You want a different focal length? You have to change lens. So for me, right now, I have three lenses. a 50mm ƒ1.4, a 100mm f2.8 macro and a 135mm f2.0. The macro is a special lens (and its Auto Focus is too slow for street/action photography). So for most applications I have the 50mm and 135mm lenses. If the 135mm is too narrow an angle, then I have to switch it for the 50mm. If I want wider angle… I either have to step back of buy/rent a lens for that application.

Defining Camera Use

My message, don’t start by reading bulletin boards, articles or reviews. Start by thinking about how you want to use this camera you’re dreaming of obtaining.

So, what will be he intended use for your SLR? Everything? Good luck. Indoor sports? Portraits? Weddings? Travel? What are the typical lighting conditions? Will you take it out in the rain/sand/dust (and therefore need weather sealing for the body and lenses)? How heartbroken would you be if you or someone dropped it, or it got stolen? How often will you use it?

Well, first, are you depending on the camera’s computer and the zoom capability of a lens to take the thinking out of the photography? Then hand your money to Canon or Nikon. Thousands of dollars of it. 61 Auto Focus points, crazy zoom range, in-camera image processing… or learn to shoot. Capture everything you want on a 50mm lens (like Cartier-Bresson does). Take it out of full-auto. Learn how to use Aperture Priority (Av), Shutter Priority (Tv) for quick snaps and full manual for meaningful ones. That might make me sound like a snob and, well…  I am.

 

Posted by on April 15, 2012 in Photography

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