Buying any camera lens is a process – at least, if you take the time to do it right, instead of just slapping cash down on those impulse purchases. I’d posit that buying a telephoto lens is an even more involved process due to the nature of the equipment in question; a telephoto lens is a specialized tool, with variables between lenses more finely tuned to specific individuals and applications.

The first step is always to identify the need. In my case, I had a Canon 70-300mm IS). It’s primary use was for wildlife photos – specifically birds. The problem was, even at 300mm, most songbirds are still small in the frame – extra reach was necessary for the shots where moving physically closer wasn’t an option. So there’s the need: a bird/wildlife lens with more than 300mm of reach. And for me, an Image Stabilization system is a necessity, especially on long lenses, so add that to the list.

Step two is research. There are several manufacturers and a lot of lenses out there. The trick is to figure out which one fits your needs best. Unfortunately, that’s where most photographers stop their research, never moving past the lens specifications page on B&H. The reality is a good deal more involved than that. Specifications are an essential starting point, but they are just cold facts on a page. What you really need is information that’s alive and breathing, and for that you need to go find other photographers who own/have used the lenses.

My research started on Tamron’s lens page, where they have a very nifty focal range simulator.  It is an excellent visual for seeing the difference between, say, 135mm and 300mm. Or in my case, 300mm and 400mm/500mm. It’s one thing to talk about having more reach, but being able to study a scene and see just how much additional reach you’re getting is invaluable.

Increases in lens length fall off dramatically from one model to another. For instance, going from a 100mm lens to a 200mm lens, you double your reach. From 300mm to 400mm, however, by 1/3. For me, the increase from 300mm to 400mm was the breakdown point; the boost from 400mm to 500mm simply wasn’t enough to engage my interest at the prices I’d knew I’d find there.

So what I knew at this point was that I wanted a lens with a 400mm maximum zoom length & IS system. Since I am a zoom guy, I wanted a zoom lens instead of a prime. And a quick check at the old bank ledger gave me a price range I had to work within. Since I shoot Canon, I have 4 options for lenses: Canon, Sigma, Tamron, & Tokina. I’ve used all four brands over the years, so I have a feeling for the strengths and weaknesses of each. I pulled up each of their websites to see what they offered; Tamron and Tokina both immediately fell out of the running, as neither offers a lens with a stabilizer in the range I wanted.

Dealing now with just Canon and Sigma, my options boiled down to four lenses: the Canon 100-400mm L, the Sigma 120-400mm OS, the Sigma 150-500mm OS, and the Sigma 80-400 OS (discontinued).

I like having options, which is why I included two lenses that at first glance seem odd. The Sigma 150-500mm exceeds the range I was interested in, but if the reviews were good and the price was right, it’s not like the extra range would hurt. The discontinued Sigma 80-400mm fit the bill, and just because the manufacturer isn’t making it anymore doesn’t mean I can find one used.

If you haven’t noticed by now, this research step is rather long. In fact, you can plan on spending a couple of hours of computer time investigating, and it’s my opinion that you should. It’s better to be over prepared than to spend a lot of money on a lens you’re going to be disappointed with. So as I mentioned before, the next bit of research was to find some live opinions.

I like Fredmiranda.com’s review sections best of any index I’ve found, when it comes to lenses. I looked up all four of my potential purchases and read several pages of reviews on each – enough so that I felt like I had a good idea of what each was like, a collective average opinion.

I also read the user reviews on B&H, although I take them with a much larger grain of salt. I searched the forums at Fredmiranda.com and DPChallenge.com for discussions on the lenses. And during this survey my interest narrowed down to the Sigma 120-400mm lens.

The other resource you should use in your research is Flickr. Sound strange? Think about it – Flickr is designed for photo sharing, and there really is no substitute for seeing actual images from the lens you’re considering. If you run a Flickr search, you’ll find that most lenses actually have specific groups dedicated just to photos taken with that lens. Study photos taken in the conditions you expect to encounter, photos taken of subjects you plan to work with. You still need to take that grain of salt – after all, poorly focused, blurry shots are just as likely to be the result of bad photography as they are a bad lens. Once again, you’re looking to establish an average here.

Here’s what the reasoning came down to: the Canon 100-400mm L uses a push/pull zoom with a reputation for sucking in dust. I’m not entirely convinced on the dust part being a huge issue, but I don’t like push/pull lenses in general. Add to that the price tag (it is an L lens, after all), and I simply wasn’t enthused.

Both the Sigma 150-500 and the Sigma 80-400 were reported to suffer from quality issues, the later especially having difficulties with its AF system. The 150-500 was somewhat attractive, but the reviews just weren’t compelling, and the price was at the very high end of my range.

Leaving the Sigma 120-400mm OS. It had all the features I wanted and all the reviews I read said that it was a solid performer. It’s actually the replacement for the 80-400mm I had considered, and the reviews noted that it succeeded, or at least improved markedly, in the areas where it’s predecessor had failed.

Step three is where I always think of the dad in the movie A Christmas Story, in the scene where he haggles down the price of the family Christmas tree.

Unfortunately, unless you’re dealing on Craigslist, you’re not likely to be able to haggle anyone down in price. What you can do is shop around. The internet is full of retailers and there is no shortage of choices – even after you weed out the NYC scam shops. I generally begin by checking B&H, Beachcamera, Calumet, Amazon, J&R, and a couple of others. I check Retailmenot.com to see if there are any promotional coupon codes. I look to see who offers free shipping, and who will get it to me the fastest.

The final step is the tricky one, especially for the instant-gratification crowd: sleep on it. Even after all the research, all the reading, sleep on it for a night before you place an order. It’s easy to get drawn into the lens frenzy, to think that you really need something new or something different. But sometimes if, after you’ve decided what you want, you just set it all aside and then come back to it the next day, you’ll realize that you may have operated under some false assumption.

So yes, that was a little long-winded. But I’m not sure how to get the information out there in a more succinct package. There are a lot of variables to juggle, and lot of options to consider before you finally place an order. The trick is, if you did it right, you’ll take that lens out of the box when it arrives and you’ll be happy with it.