Welcome to Episode 23 of the Martin Bailey Photography Podcast. Today I’m going to talk about what actually constitutes a telephoto lens, briefly touch on some general applications, and the difficulties we face when using medium to super-telephoto lenses. I’ll also introduce some techniques to help overcome these difficulties. Thanks to Marisa, one of the long time contributors in the MBP forum, for suggesting the topic for this week’s Podcast. Also congratulations Marisa on getting your Canon EOS 350D Digital Rebel and the 70-300mm IS lens.
I’d also like to say thanks to everyone for your patience during the upgrade of the online gallery and forum over the last week or so. If anyone comes to the site after a period away and you have any problems logging in, please try to clear your cookie cache to get rid of the cookie from the old version and try again. That should do it, but if you continue to have problems, please mail me from the Contact Form.
So firstly, let’s define what actually constitutes a telephoto lens. On a 35mm format SLR camera, a 50mm lens is considered “standard”. That is, it does not magnify or de-magnify the subject. Strictly speaking, any focal length shorter than 50mm is wide angle, and anything longer than 50mm is telephoto. I’m sure there are varying opinions on this, but generally, from 60mm to 100mm could be termed “short telephoto”, a 200mm lens would be considered “medium-telephoto” and a 300mm long telephoto. Anything from 400mm and above is considered super-telephoto.
There are of course prime lenses at many of these focal lengths, and there are zoom lenses, such as the 70-300mm lens that Marisa just bought, that cover wide ranges from the short to long telephoto ranges. There are even lenses nowadays, such as Canon’s 28-300mm L lens that covers from wide angle to long telephoto, but obviously the price is not to be sniffed at either. Prime lenses will provide better quality images, but they lack the flexibility of zoom lenses and for the majority of applications, the image quality with the zoom lenses is more than enough.
Whether zoom or prime, telephoto lenses have many applications, including shooting things far away allowing you to get in closer to them, such as cutting out the parts of a landscape that interest you, as I discussed in Episode #8 on Composition, called Getting in Close in Landscapes, but can also seen in many shots in my online gallery. Another, and perhaps more common application is for capturing things that might not necessarily be so far away, such as birds, but capturing them large enough in the frame to be able to make out fine detail in the subject, or maybe even sometimes filling the frame with the subject. Yet another application is to shoot things quite close to you, often in my case very close to the minimum focusing distance, filling the frame with the subject.
As I mentioned, there are difficulties when using telephoto lenses. The most serious issue that you really need to bear in mind is that the longer the focal length the more susceptible to camera shake your images will be. This is because you are magnifying the subject more and more as the focal length increases, and so magnifying any movement in the camera and lens when shooting it. Therefore, the degree to which you need to worry about this also becomes greater as the focal length increases.
From episode 1 of this Podcast, a number of times I’ve mentioned a rule of thumb to calculate the minimum shutter speed to help avoid camera shake when hand-holding. I haven’t mentioned this for some time now though, so let’s go over it again quickly. Basically you use the focal length you are shooting at as the slowest shutter speed. This is independent of ISO or aperture, but you do need to work in the crop factor if you are using a digital SLR that has one. Say for example you are using a 100mm lens. The slowest shutter speed you should aim for is 1/100 of a second. If you are using a DSLR with a 1.6 crop factor, the effective focal length is 160mm so your slowest advisable shutter speed would 1/160 of a second. If you have a camera with a 1.5 or 1.3 crop factor, this will make a 100mm lens 150 or 130mm respectively, and the slowest advisable shutter speed of course changes respectively.
If you are using your lens at 300mm on a 1.6 crop factor camera, that’s an effective focal length of 480, so you’ll need a minimum shutter speed of 1/500 of a second. Remember this is only a rule, and there are things that you can do to lower the risk of camera shake, such as those explained in Episode 2 on Stable Posture in Low Light. This will also vary from person to person. Some people can simply physically hold a camera more steadily than others.
Another factor that we must bear in mind here is that many lenses nowadays come with IS, that is Image Stabilizer for Canon and VR or Vibration Reduction for Nikon. This can reduce your necessary minimum shutter speed by up to 3 stops, and for the Nikon VRII system it seems up to four stops. So say you are shooting at 300mm, usually this would need a minimum shutter speed of 1/500 of a second on a 1.6 crop factor DSLR, but if you turn on Image Stabilizer, that becomes as low as 1/60 of a second if your IS gives you three stops. Remember to calculate the time you gain per stop, simply double the shutter speed for each stop. When we’re working in fractions of a second, that basically means halving the number. The first stop from 1/500 of a second takes you to 1/250 of a second. The second stop takes you from 1/250 of a second to 1/125 of a second, and the third stop takes you from 1/125 to 1/60 of a second. If you get four stops from your lenses image stabilizer, that would give you an amazing 1/30 of a second. Of course, this is all based on the example of 1/500 of a second, and this will change depending on your focal length and amount of available light.
If you are still a little shaky on calculating how much time a stop will increase or decrease your shutter speeds or aperture value, or both, take another listen to episode 10 of this Podcast on Exposure and Manual Mode. This Podcast is pretty heavy going, but should help you to understand how to calculate increases or reductions shutter speed and or aperture in stops to achieve the same Exposure Value.
Now, in theory, you could go down to shutter speeds as slow as this with a 300mm lens, but I my experience, relying on IS or VR will only prove successful some of the time. For still subjects the success rate will be higher, but in wildlife photography for example your subject will also more than likely be moving. It’s no use shooting animals at 1/60 of a second as they are likely to move during that time, even just very slightly, and that will cause motion blur in the subject.
Of course, another option to avoid camera shake when using telephoto lenses is to use a tripod. I know that many people shy away from using a tripod unless absolutely necessary, but using one will without a doubt improve your images. It will also help you to be more methodical in your composition and perhaps improve composition too, but that’s going off topic a little.
Using a tripod is not going to solve all ills though. There are times when you can’t use a tripod, say if there are rules against using a tripod in the location you’re shooting from. Also, for many situations, such as wildlife photography when the subject might be moving around a lot, using a tripod can restrict your movement. Both of yourself physically moving around and the movement of the camera, even from a static position, and this can limit your ability to successfully capture your subject on film. If there is enough available light, I personally like to use up to 400mm hand-held for this reason. And of course, as I mentioned earlier, in wildlife photography or any type of photography where the subject can move around, subject movement will cause problems if you go with too slow a shutter speed. If you are shooting birds in flight for instance, you really want to aim for a minimum shutter speed as calculated by the rule of thumb I mentioned earlier, or maybe one stop slower if you are using IS, especially when using super-telephoto lenses of 400mm and longer. Much slower than that and your success rate is going to drop dramatically.
If there is simply not enough available light to enable us to get a fast enough shutter speed we need to start thinking of other options. The first thing you’ll want to think of is raising the ISO. Most cameras will start to introduce grain from around 400 ISO though, especially in the shadows, so you don’t want to rely on this too much.
Also popping in a little fill-in flash or using a reflector may be an option if your subject is in range. The range of your flash will depend on the guide number. You can usually check the distance your flash will reach in the instruction manual. There are actually zooms available that you fit on to the front of your flash that project the light further than normal. One I’ve heard of but do not yet use myself is the BetterBeamer. Apparently the Better Beamer will add approximately 2-stops of light output to your flash by concentrating the light emitted and is recommended for use with telephoto lenses of a focal length of 300mm or longer. This and loads of other great photography gadgets can be bought from the naturephotographers.net gift shop. I will add a link to the show notes in case you’re interested.
Even having when putting all of this into practice you’d be well advised to shoot in bursts when using long lenses. That is, don’t just take one shot then wait for your subject to change position or you yourself move on to another location, take bursts for 3 shots or more. I don’t mean for exposure bracketing. I’m talking about with the same settings. What you usually find is that the bird moves at exactly the time one of your exposures is made, or you get camera shake that affects some, but not all shots. If you take a minimum of three frames, more if possible, you give yourself a better chance of getting a winner out of the batch. I often find, especially when shooting birds in flight, at least half of the resulting shots are too soft to be of any use. You’ll probably also find that shooting single shots will introduce a snappy movement, that you can avoid by simply keeping the shutter button pressed for a number of frames, allowing you to concentrate on tracking the subject.
Before we move on to another problem you may not be used to if you are new to longer telephoto lenses, there’s a lot talk happening here, without much to look at, so let’s take a look at a photo I made last Sunday, that is February 5th, 2006. It is shot number 834, which is of a Whooper Swan cygnet about to touch down on the Kotokunuma Pond in Ibaraki Prefecture, a couple of hours north of Tokyo. This shows the results of putting much of what I’ve just said in practice. The sun was now behind some trees, almost below the horizon, so the cygnet was in total shadow. I was using a super-telephoto lens. The Canon EF 600mm F4 IS USM L lens and had the ISO set to 400. The aperture was F8, just about enough to get the entire bird in the depth of field and the shutter speed was 1/500 of a second. I had IS turned on, and was using mode 2, which will only stabilize horizontal or vertical movement, allowing me to track with the swan and not have the lens try to stabilize the whole scene.
I should just mention that I was using a tripod. It really is just not possible to hand hold this behemoth of a lens. Earlier I mentioned that I like to hand hold up to 400mm when there’s enough light, because it gives you more freedom of movement. To help me when using this 600mm lens, I use a Wimberley Head on my Gitzo tripod. The Wimberley Head uses gimbal-type design that allows you to rotate your lens around its center of gravity, and is really the closest you can get to the freedom of hand holding with a lens this size.
If you are not shooting wildlife or sports shots where the subject is moving, you can of course use a tripod and go to much slower shutter speeds. I’m really focusing here on the difficulties when shooting things that may move.
So, moving on, the second thing you’ll need to bear in mind when using a telephoto lens is that the depth-of-field gets shallower and shallower as the focal length gets longer. I shot the image that I just introduced of the swan coming in to land at F8. I could have possibly gone to F5.6, but at the distance I shot this at, which was probably about 20 meters or 65 feet, I’d have ended up with a depth-of-field of just 40cms or 12 inches, and with a bird this size, that would have meant that the wings were quite out of focus. Even at the aperture I chose, F8, I only have 57cms or just over 18 inches of DOF, but this is just about enough to get most of the bird in acceptable focus.
Also note that the closer the subject is, the shallower the depth-of-field gets. And likewise, the further away the subject, the deeper the depth-of-field gets. I’ll add a link to an online depth-of-field calculator to the show notes, so you can have a play and see the relationship between the focal length, aperture, distance to subject and size of the film or sensor. This calculator actually gives slightly different results to that of the one I have installed on my computer, and I don’t know which is more accurate, but it is going to be accurate enough to give you an idea of what I’m talking about.
Basically, what I’m getting at here is that when using telephoto lenses, you have to be much more conscious of the widest aperture you can shoot at and still have enough depth of field to get your subject in focus. Of course, the benefits of this are that it is really easy to get the background out of focus enough to stop it from being a distraction. If the background is not distracting though, it is often nice to be able to make out the environment of your subject if it’s a wildlife shot. Take a quick look at shot number 830 on my Web site. This is a Black Kite also shot last Sunday, at probably three times the distance of the last image, at about 60 meters or almost 200 feet. I actually cropped a little, about 20% off the left and 15% off the bottom, of this shot, so the bird is a little larger in the frame than the original. This was shot at F5.6, which is plenty at this distance to get the smaller bird of prey totally in focus, but you’ll see that the background is quite out of focus. You can though make out the environment enough to know that there are trees and hills in the background. This again was at ISO 400, and the shutter speed was 1/800 of a second.
So, that is about it for today’s episode. To briefly recap; the longer the lens, the shallower the depth of field and the higher the risk of camera shake. Use the rule of thumb to determine your slowest advisable shutter speed based on your focal length, and bear in mind not to blindly rely on image stabilizer systems when your subject is moving around.
If you are interested to see any of the other images from the Kotokunuma Pond last Sunday shot with the 600mm F4 lens, I’ll drop a link into the show notes to list them all. There’re just six of them. Next week I’ll be following on from this episode, talking about Extenders as Canon terms them, or Teleconverters. These allow you to increase the focal length of your lenses relatively cheaply, but, at a cost. Tune in next week to find out more.
Enjoy your week, and keep on shooting. Bye Bye!
The Music in the first 28 Podcasts is copyright of William Cushman © 2005, used with kind permission.
You can also check out the other great gadgets at the naturephotographers.net gift shop here: http://www.naturephotographers.net/gs.html
Check out the Wimberley Head that I use primarily for long lenses when using a tripod here: http://www.tripodhead.com/
Here is a link to an online Depth-of-Field calculator to have a play with and see the relationship between the focal length, aperture, distance to subject and size of the film or sensor: http://www.dofmaster.com/dofjs.html
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