What is a telephoto lens?

If asked the question above, what would you say the answer is? Is it:
a) A lens with a focal length greater than 200mm?
b) A lens which can change it's focal length?
c) A lens whose physical length is less than the focal length?

I expect most of you will go for answer "A" but you'd be wrong. In real terms, anything with a focal length over 200mm is termed a telephoto lens in common parlance...but, there is a clue in the fact that you often find lenses shorter than 200mm refered to as telelphotos. So what are they talking about?

Well, the answer lies in techie talk.

According to the Canon Lens Work book, a telephoto lens is defined as follows:
With general photographic lenses, the overall length of a lens (the distance from the apex of the front lens element to the focal plane) is longer than its focal length. This is not usually the case with lenses of particularly long focal length, however, since using a normal lens construction would result in a very large unwieldy lens. To keep the size of such a lens manageable while still providing a long focal length, a concave (negative) lens assembly is placed behind the main convex (positive) lens which is shorter than its focal length. Lenses of this type are called telephoto lenses. In a telephoto lens, the second principal point is located in front of the frontmost lens element.

Translated into simple terms, a telephoto lens is one that has a physical length (from the front lens element to the the focal plane) which is less than its stated focal length.

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Focus distance limit switches on lenses

Some of the Canon lenses feature a little slide switch to let you restrict the range of focus distances the lens will operate over, but why? 

With the longer focal length lenses there's often quite narrow depth of field and also quite a large range of movement for the optics to cover from the closest focus distance out to infinity. If your subjects easily fall in to the range covered by a lens restricted limit switches then you get a much faster focus shift from minimum to maximum subject distance as the focus assembly only moves a small set of it's possible range. There are quite a lot of lenses in the range with focus limit switches including the EF100mm f/2.8 MACRO USM, EF135mm f/2L USM, EF70-200mm f/4L IS USM. In fact most L series lenses with focal lengths longer than 100mm have focus limit switches. In the case of a mega lens like the Ef800mm f/5.6L IS USM there's three positions for the limiter including the full 6 metre close focus to infinity range!

Coming back to something more normal the popular EF70-200mm f/4L IS USM has focus limit ranges 1.2m to infinity and 3m to infinity. So if you are shooting say motorsport and are over 3m from the track boundary choose the restricted range of focus, the lens will move from the new 3m minimum focus to infinity much faster than it would from 1.2m to infinity. This makes the AF seem more snappy when you pick up a camera and the initial focus is way off. There's just less time spent hunting for the subject while the lens racks in and out from minimum to maximum focus distances.

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A star in the range - EF100mm f/2.8 Macro USM

The second part of our 'star in the range' series sees us looking at the EF 100mm f/2.8 Macro USM lens. Those of you with this lens will know how good it is, those without can only wonder what all the fuss is about. The truth is, this lens really is quite remarkable. It offers full 1:1 (lifesize) reproduction without having to change the length of the lens when focusing, and the results are stunningly sharp. So sharp in fact, that a common question asked is "Why is it not an L-Series lens?" The answer is that it doesn't use some of the technology required to make it an L-Series model, however the optical performance is more than enough to justify it.

If there are any complaints leveled at this lens, it's that it is in fact too sharp in some situations. Portraits usually. This lens seems to resolve detail that you just don't see, meaning that in a portrait shoot (for which the 100mm focal length is actually very useful) you end up with lots of images that need retouching to remove skin blemishes you didn't know where there!

So, should you buy it? Well, if you want to get into macro photography, it is the obvious choice in the range. The MP-E 65mm f/2.8 1-5x Macro photo is too specialised and lacks the ability to focus at infinity, the EF50mm f/2.5 Macro only does shalf life size unles you add the life size adaptor and the EF180mm f/3.5L Macro USM is more designed for subjects that need a longer working distance - butterflies and dragonflies for example. The 100mm is the all-rounder. You can shoot insects with it as long as you're careful about what you're doing, you can get in close to flowers and fungi and you can use it for portraits and general photography.

Is there anything missing from this lens? Well, I wish they'd box it with a lens hood included and I'd like to have this lens with an image stabiliser fitted like the N!kon VR Macro lens. Other than that though, it's a stunning lens that anyone interested in macro photography should seriously consider.

Have you got one? If so, what are your thoughts on it? Would you buy it again if you had to?




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The lens you take...

I was talking to a friend the other day about lenses and we had a difference of opinion - until I explained myself more clearly. We were talking specifically about the EF85mm f/1.2L II lens. An absolute beauty of a lens and one which I owned for a while until I sold it and replaced it with an EF85mm f/1.8 USM. He was, to be honest, incredulous. He has and loves his f/1.2 lens and while he conceded that he also loves the 85mm f/1.8, he just couldn't see the rationale behind the apparent 'downgrade'. 

So I explained.... I'd bought the 85mm f/1.2L II lens for a steal. It was a really great price, bought as part of a deal with another lens. I used it and loved it. But then came the day when I had to travel abroad. I started packing my bag. In went the camera body, in went the 35mm f/1.4L, in went the 135mm f/2L, I then picked up the 85mm f/1.2L, weighed it in my hand and put it back down again. While I loved the lens and it's results, I didn't love it enough to carry that weight around (for those that don't know the lens, it's a little over 1Kg). 

If I shot weddings or lots of studio stuff, then there'd be no question. I'd have kept the lens. The fact is I do shoot those subjects now and again, but not enough to justify it. What I do do though is walk a lot with lots of camera kit. For me, the 600g saving is quite a lot and the optical quality between the two is not sufficient to warrant it. That and the faster focusing of the 85mm f/1.8 lens were the deciding factors for me. 

Now my friend did make a couple of valid points - the f/1.2 lens gives you a look you just can't achieve with 1.8. It also has a different look even at f/1.8. It's not that it's better or worse, just different. And in low light, the extra stop can really save your bacon. 

Now, if money was no object, well, I'd have both and just pick and choose as I needed to! 

If you're wondering about the title of this post, it was our joint conclusion: The lens you take is better than the one you leave at home....

So, which would you choose and why? Tell us in the comments.....

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