Perhaps one of the more confusing subjects in the world of digital cameras is lens length. We hear terms like “telephoto”, “wide angle”, “field of view”, “5X” and a host of others to describe our lenses. Then once we get all of that business sorted out we crank in other arcane phrases like “crop factor” and “35mm equivalent”. Is it any wonder that it’s tough to make a decision on a lens?

While it is easy to grasp that a longer lens length offers more magnification and a short lens length provides a wider view, it helps to understand what a standard lens length is before we begin making comparisons.
There is a way to use math to determine what constitutes a standard lens length for any camera and I’ll add that bit of mathematical fun at the end of this discussion. That kind of mental gymnastics is interesting stuff to us photo geeks but the remaining 98% of the world I believe would rather have root canal.

That said we are going to make an assumption: On average, digital cameras using an APS-sized image sensor will have a standard (sometimes called normal) lens length of 28mm.

OK, big deal, what does it mean? What this little bit of information tells us is that if we mount a lens on a DSLR and set it to a length of 28mm the view through the camera shows the world in the same perspective as we might see it through one open eye. In other words this is a “normal” or “standard” lens length. We have our benchmark length that can be used to compare lenses.

Let’s do some mental housekeeping first. I would like to encourage you to disregard a few terms. We can forget “crop factor” and “35mm equivalent” for now. Since the majority of new DSLR camera buyers never owned a film camera with interchangeable lenses these terms simply add needless layers of numbers and confuse the subject.

Another term to set aside for the moment is the “X Factor”. Compact camera lenses are described with phrases like “5X zoom lens” which frankly is kind of meaningless. Expressing lens length this way is handy but ineffective and here’s why. A lens that is 20-100mm is a 5X lens, but then so is a 50-250mm lens. The “X Factor” is ad-speak and only superficially useful in the world of compact cameras.

So we are left with wide angle, telephoto and field of view. These are three good terms we can sink our teeth in and here’s how: As we have just discussed, a DSLR with a 28mm lens has a field of view similar to that of one open eye. Any lens length shorter than 28mm will have a wider field of view (wide angle), a longer lens a narrower field of view (telephoto).

There is some easy, do-it-in-your-head math that we can now use to compare lenses. If 28mm is a normal view then a lens that is 14mm will have a view twice wider. A lens of 50mm will provide a view almost twice closer. Do we really care what the 35mm film camera equivalent or the crop factor is? Nope.

So in the real world we can now make some well informed judgments when we compare digital camera lenses. If we are offered a lens that is 18-55mm we now know that we have a lens of slight wide angle and a telephoto length that will make the world look twice closer. Another kit offers a lens of 28-80mm and we understand that we are getting a lens with zero wide angle capability and a telephoto view about three times closer than our eye sees it.

We’ve added just a little bit of new knowledge and our confidence in making a decision between digital camera lenses has increased.

In conclusion I’d like to offer a bit of advice. With every manufacturer in the world trumpeting their high magnification telephoto lenses it’s easy to overlook the wide angle side of the equation. If you ever shoot pictures in your own living room you will be better served if your digital camera lens offers wide angle coverage below 28mm.

The difference between 28mm and 17mm we know from this discussion offers a wider view with the shorter lens, but how much wider? At 28mm we can capture three people scrunched together on the couch. At 17mm we are now getting the whole couch and the end tables too.

Photo Geeks Corner: The Math behind Normal Lenses
As we did earlier, there are a few assumptions I’d like to offer up as a way of cutting to the chase:
1) We are discussing digital single lens reflex cameras collectively using APS-sized image sensors.
2) There is a lot of difference between the major manufacturers of image sensors in the actual size of their sensors. However the real impact of these size differences is minimal.
3) The terms “Normal” and “Standard” refer to the perspective that a lens renders and not necessarily its total angle of view.

The short and easy rule proven over time is that a camera format’s normal lens is equal in length to the diagonal measure of the camera’s film frame or sensor. This lens length will capture the world showing subjects in perspective to one another as the scene would be viewed through our own eyes.
An average APS-C sensor measures 22.7X15.1mm which gives us a diagonal of 27.26mm. Nikon uses a sensor that is slightly larger and yields a diagonal measure of 28.4mm. There have been other variations of size in APS digital sensors but they all hover around a 28mm diagonal measurement. This is why I have chosen to state that a 28mm lens length is generally considered “normal” on all APS-sized digital cameras.
The math looks like this: 22.7mm2 + 15.1mm2 =743.3mm. Then we find the square root of 743.3mm, √ 743.3mm = 27.26mm

Summary: When purchasing digital cameras the options available for lenses to purchase can be confusing. A little understanding – and cutting through irrelevant jargon – can help increase confidence in our decision and get the right lens in our camera bag.

As I mentioned in yesterday’s post I’ve been using a lens group for a while that I think will add up to a great set of optics for almost any photographer. This group consists of Tamron’s 10-24mm, 28-75mm and 70-200mm lenses.

While yesterday’s post talked about the very unique Tamron 18-270VC today’s discussed lenses aren’t all that unique. In fact it would be possible to purchase similar lenses under the Nikon or Canon brand names. However from my experience the branded lens group would cost over $2,000 more and not yield enough image quality or performance difference to benefit the average photographer.

Another important difference – none of the Tamron lenses mentioned in today’s post have image stabilization. I have to admit that I do like a stabilized lens; however I don’t consider the lack of the feature to be a deal breaker. In fact it would be possible to substitute Tamron’s 17-50 f2.8 VC stabilized lens for the 28-75 I have in my kit and not miss a beat.

To start the conversation let’s take a look at the lenses we find in most manufacturer kits. Largely we find that basic kits on entry to hobby level cameras come with an 18-55mm or 18-105mm lens paired to the body. More advanced kits might have a 17-85mm or even an 18-200mm lens tucked in the box. All of these options are actually great lenses, they do exactly what they are supposed to do and they deliver very good images. Unfortunately these kit lens options are a little limiting in their capabilities beyond basic family or vacation photography.

How can I describe a lens as being both “great” while also calling it “limiting”? Well, I have a five iron in my golf bag that is my favorite club because I’m comfortable using it in many situations. However I wouldn’t want to be limited to using only that one club on a golf course. My favorite five iron is a middle range club just like an 18-105 zoom lens is a middle range lens. It takes more than one lens to adequately cover the subjects that I like to shoot.

I have found that I like a fairly specific range of lens lengths when I set out to shoot. My needs tend to cover wide angle to moderate telephoto, or lens lengths from about 10mm to 300mm. I could just carry a 10-24mm and an 18-270mm and at times that is indeed what I carry. However my style of photography relies heavily on controlling depth of field and for that I need good aperture range to match my focal length range. I solve this by using the three different lenses mentioned at the beginning of this post: 10-24mm, 28-75mm f2.8 and 70-200mm f2.8.

When I’ve purchase a new camera I have never purchased the manufacturer’s kit with lens. Instead I spend a little more money and buy the body I want and a mid-range zoom with a f2.8 maximum aperture. The Tamron 28-75 f2.8 or their 17-50 f2.8 make great lenses as a foundation. The fast f2.8 aperture extends my control over depth of focus and the compact size is never awkward to carry. The sharpness of these lenses is exceptional. (It is possible to get the 17-50 f2.8 in an image stabilized VC version.) And when the Tamron price is compared to the Nikon or Canon brand lenses that cost three times as much it’s easy to see why the Tamron alternative is so popular.

The next lens in the kit is the Tamron 10-24mm wide angle zoom. Wide angle is where most photographers are missing the boat. In the world of APS-C digital cameras a lens that starts at 17mm or 18mm just isn’t very wide angle at all. To experience wide angle photography you need to get below 14mm lens length. Canon and Nikon offer their own lenses that widen our horizons but the Tamron version rivals the quality at a lower price. There is a little more distortion in the corners at the very widest setting compared to the branded lenses, but I haven’t found it objectionable. When you are using a wide angle lens the need for image stabilization all but disappears.

The last lens in the trifecta is the Tamron 70-200 f2.8. Comparable in size to most other lenses of this length, the Tamron 70-200 f2.8 is again a value priced alternative. And what a value! Compare the Tamron lens at $770.00 to the Canon at $1,369 or the Nikon 80-200 version at $1,149. The Tamron lens is again sharp with great contrast and color. There is one noticeable difference with the Tamron lens – it focuses just a hair slower than the branded lenses. (Tamron has improved the focus speed of this lens in the last year).

To increase the range of the 70-200 f2.8 lens I added a 1.4X teleconvertor to the kit. With the 1.4X mounted behind the 70-200 f2.8 I have the equivalent of a very useful 280mm f4.0 lens.

To wrap up this review: I like a three lens kit because it offers great flexibility in lens length while maintaining control over depth of field. It is possible to build a similar kit from Tamron, Nikon or Canon but the price differences are staggering – Tamron $1,769.97, Canon $3,639.97, Nikon $3,859.97 (all without 1.4X converter). Are there differences in build and performance? Yes there are and if you are the type who will use your equipment daily and you are willing to pay for a tough lens that will take a good banging around go with the Nikon or Canon offerings. However if you are an average photographer who doesn’t mind treating your gear with normal care save a few thousand dollars and go with Tamron – especially when you consider that your pictures will look just as good.

Yesterday I discussed using the Tamron 18-270 VC lens and I described the VC image stabilization as being both effective and useful. After publishing the article I found two more images that support the review.

Most often we think of image stabilization as a way to prevent hand tremor from causing blurry pictures. I have found that another effective use of image stabilization comes from capturing images under ambient light with the camera hand-held.

In the example images below we see how this is an advantage. Neither image has been altered or cleaned up other than to be resized for this blog post.

While touring the battleship Texas we found the ship’s radar room. Historically the Texas was the first US naval ship equipped with radar so the opportunity to capture an image of the room was appealing.

The room was quite dimly lit so for my first attempt I used my flash. As you can see the flash cast shadows from the cage across the door and the exposure, though adequate, didn’t allow any details to stand out. The exposure was 1/60, f4.0 at ISO 400.

For the second image I turned the flash off and in Program mode simply snapped a picture. The resulting image shows more detail and has a much better rendition of the available light. While it can be argued that there is a very slight amount of possible motion blur to the image, overall I find it a much better capture. The exposure information with the VC image stabilization turned on: 1/8, f3.5 at ISO 800. I’m blown away by the ability to hand hold a camera at 1/8 second shutter speed and still being able to capture a very usable image.

Click to see the image larger (remember to allow pop-ups for this blog if you are asked!). In fact you may switch the large view back and forth between the two images using the arrow control button in the lower right corner of the viewing window.

In DSLR photography nothing causes more consternation, comment or confusion than the topic of lenses. We invest so much time in reading review after review about our cameras that it’s easy to overlook a most significant detail: Without a lens a camera is nothing but a lightproof box.

Lenses gather the light that our cameras need and then focus it into an image on our film or digital sensor. Lenses are a 50/50 partner in the technology of imaging. As such we owe it to ourselves to pay as much attention to our glass as we do to our megapixels.

Before I begin to offer my opinions on the lenses I have lined up I’d like to offer three points that you may consider as coloring my objectivity. First, I believe that there is no such thing as one lens that does everything. Second, I am of the opinion that brand names matter far less than performance. Third, that there is a practical limit to measurable comparisons – in other words I look at finished pictures not pixels before I make a judgment.

Over the last year I have had the opportunity to use my camera with two very different lens configuration groups. I set out to do this in order to provide guidance for my friends and customers based on firsthand knowledge. And I gotta tell you that this wasn’t easy for me as I have an advanced case of lens envy – if my buddy has lens X and I don’t then what he has must be better than the lens I currently shoot.

Now to the two different lens kits: First was a Tamron 18-270 VC coupled with a Canon 50mm f1.8. This is the kit I’ll discuss today. Next up will be a kit that adds some increased creativity, this kit had three lenses: Tamron’s 10-24, their very excellent 28-75 f2.8 and the Tamron 70-200 f2.8 with 1.4X tele-convertor. I used all of these lenses on the same Canon 40D. (I also borrowed a Nikon D300s with appropriate Tamron lenses with identical results)

To answer the first question which is “Why Tamron and not Canon, Tokina or Sigma lenses?” I chose the Tamron lenses for several reasons not the least of which is because our customers choose them 4:1 over the other brands. Tamron offers lens lengths that the other brands don’t. Tamron lenses work well with my camera where the Sigma lenses… not so much. Canon offers excellent lenses at almost any length but in most cases at price points that far exceed what the average customer can afford to pay.

And in the spirit of full disclosure, of the lenses discussed I currently own only the 28-75 2.8 Tamron lens and the Canon 50mm f1.8. The others lenses I borrowed for extended periods just for this commentary.

OK, the niceties have been observed so let’s get to it. The Tamron AF18-270mm f3.5-6.3 Di II VC Zoom lens – or the 18-270 for short. I had the opportunity to use this powerhouse super-zoom over an extended vacation in Texas. I wanted to pack light so I took my camera with this lens and the Canon 50mm f1.8.

Do you recall when I said that there is no such thing as one lens that does everything? Well, even though the Tamron 18-270 encompasses a huge zoom range I wanted a good low light lens in my kit and a lens with aperture f1.8 fills the bill.

Guys and gals, if you don’t have a 50mm f1.8 in your kit yet I have only one question – why not? They are the cheapest lens you will ever purchase and they are all incredibly sharp. At an aperture of 1.8 there is little need of strong flash in most living rooms. The focal length is very flattering to faces and once mounted on your camera body the whole rig is light and fast. Get one and you will never be sorry that you spent the bucks.

By contrast the Tamron 18-270 is a big piece of glass. Once mounted to your camera you will be very aware that it is present. However the extensive zoom range and unusual sharpness of this lens will make the slight increase of weight more than tolerable.

Let’s take a moment to look at that lens length. 18-270mm in one lens hasn’t been done before. And then to top it off Tamron added image stabilization with their VC technology. In terms that relate to a 35mm film camera this is a 27mm to 405mm lens – or about 15X magnification from wide angle to telephoto.

On my trip I had the Tamron 18-270 mounted at all times. I switched to the Canon 50mm as needed during two dinner parties but otherwise the 18-270 saw uninterrupted use. The tremendous zoom range gave me control over composition I haven’t had before. In handling the lens made the camera definitely hang nose down on the neck strap. The zoom range was accessed through the twist barrel and it was smooth throughout the travel. Focus speed was what I expected from such a large lens – slower than what I experience on an 18-55 or 70-300 USM but just as fast as on Canon’s own 18-200 IS.

The lens comes with a petal shaped lens hood which was a plus under the Texas sun. On shore or on the water lens flare was never an issue. As with almost any hood polarizing filter use was a little awkward. With the hood mounted you have to reach inside the hood to rotate the filter, leaving a few fingerprints behind in the process.

As for picture quality I had no complaints out of more than 600 final images. I did shoot twice that number of images over the week but most of the overage was in attempts to fool the lens or as insurance shots that it turns out I didn’t need. Contrast was great and color rendition was awesome.

I had an opportunity to take a helicopter ride over Galveston Island. I was in the rear seat and had an open window to shoot through. With my trusty 40D set for 400 ISO and the 18-270 mounted we took off on a hazy evening flight. I snapped over 75 pictures during our 20 minute tour and not one of them showed the slightest blur – even when I rested the lens barrel on the window frame on purpose (see the shot below). That’s how good the Tamron VC image stabilization is.

Just for fun, the zoom effect with the Tamron 18-270 -

1/6 second f/22.0 ISO 200

In conclusion, I took a slight risk on a unique trip by taking along a lens that I hadn’t used before. However I had confidence in the lens based on high praise from our customers and from fiddling with it in the stores. The results were a camera kit that was highly portable and pictures that were outstanding in every respect.

I would recommend this lens to anyone who is looking for high picture quality from an extreme zoom range, one lens option. I would strongly suggest adding a 50mm f1.8 as a supplement for lower light situations. The lens isn’t cheap but it is less costly than the pairing of a 17-85 and 70-300 image stabilized lens from either Canon or Nikon.

Would I own this lens? In a heartbeat, and it wouldn’t be at the expense of the next lens outfit that I’m commenting on.

Tomorrow we look at what I think is an option for an “ultimate lens group”. The Tamron 10-24, 28-75 and 70-200. Though I still would add a 50mm f1.8 to this grouping these three lenses together add up to a Dream Team for almost any photographer.