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Photography Question 

Focal length requirements

I was wondering if there is any information pertaining to the focal length of a lens that you need to fill the frame at any given distance for birds, deer, etc. I'm looking at purchasing a longer zoom lens in the future and I am not sure what length to look for. Due to budget, I think I'll have to stay in the 200 to 300mm range and was just wondering it that would be enough or if I need to save for some time.

I'm pretty sure that my interests for photography are going to lie in the wildlife, landscape, general nature shots. Currently, I'm just trying to learn as many aspects of photography as I can using the kit lens that came with the XTi my wife bought me for Christmas.

The lenses I've priced and researched reviews are the Canon 70-200 f4l, Canon 70-300 4-5.6 IS USM and the Sigma 70-200 F2.8. Any input would be greatly appreciated.

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2/9/2007 9:40:01 AM

Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
  You can figure out a focal length needed to fill a frame based on the size of an object. But with animals, you're dependent on how close you can get, whether they're used to being around people, the size of the animal.
A deer that's used to people at wildlife reserves or in an area that has such a large number that you occasionally see some cross the road or outside you window, you could possibly fill the frame with a 200mm if you shot from your car. One that hasn't gotten used to people, I doubt you'd fill the frame with a 300mm if you didn't have a blind and set out some food to attract them, or do some very good sneaking up on them.
Same with birds. Birds in your back yard, have a little tolerance to people. They may stay in a tree while you're at the bottom. But filling the frame may need at least a 300mm. Common species like grackles, you can even get within ten feet. That close a 200mm may fill the frame, but they may also fly away as soon as you look at them. Which is what birds tend to do, even when they're used to being around people.

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2/9/2007 10:37:32 AM

Alan N. Marcus   Hi Chuck,

Now when you photograph a distant bird, you want to magnify the birdís image. Thus you choose a longer than normal focal length lens. Best might be a zoom lens. Now your question is, how much zoom to I need or stated another way what focal length will do the job?

Now consider a bird 12 inches tall feet to crown, thatís 305mm tall.

Now we need to known the OD or object distance so letís say the bird is 50 feet away. We need to work this problem using just one unit of measure and so the object distance in millimeters 15,240.

You choose to use your lens at 300mm focal length. That means the lens is 300mm from the film we will call this ID (image distance) when camera is focused on a distance object.

Now we calculate magnification M.

Magnification is image distance divided by object distance IDųOD
What will be the birdís height on the frame?
Bird height actual x magnification = 305 x 0.197 = 6mm
Thus the birdís image heath on chip or film with 300mm lens will be 6mm.
A 35mm frame is 24 mm tall thus 6mm is 25% of this height.
On a non-full frame digital the chip is 15mm tall thus the 6mm image takes up 40%

Alan Marcus

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2/9/2007 3:05:52 PM

W.    Hi Chuck,

200mm or 300mm is not going to hack it if you're interested in "birds, deer, etc.". You need double that focal length or better.

How about an Dual Image Stabilized 500mm for the price of a top-of-the range compact camera?

You'll still need a tripod, though!

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2/9/2007 3:15:37 PM

W.    OR a Gorillapod?

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2/9/2007 4:06:05 PM

Bob Cammarata
BetterPhoto Member Since: 7/17/2003
  Greg is on the right track.
Try to develope your ability to stalk skittish subjects or implement auxilliary tactics to get your camera closer.
Shooting from inside your car is the most effective way I know to get full-frames of deer, raptors, and other wild things without mortgaging your house to buy that super-telephoto.
(A window-pod or similar device will add stability and increase sharpness when shooting from inside your car.)

State and national parks are great places to get up close and personal with larger animals...(especially the ones that usually have rifles pointed at them.)
In these parks and refuges the animals feel safer around humans and they can be observed and photographed from much closer than in the wild.

I've always found winter to be the best time to visit these santuaries.
There are less crowds, no ticks or misquitos, and the resident wildlife are more active during the daylight hours.


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2/10/2007 4:11:48 AM

Chuck    I'm sure the 500 and 600mm lense's are out of my budget except for maybe the Sigma 50-500mm so I'll have to figure a way to get the shots with the 200 or 300mm lens. I bow hunt deer, and although the angle for a picture would not be great from a tree stand 18' in the air, I've had deer right underneath me. You can get close on the ground also but your chances will be much more limited. I suppose that also could be considered part of the challenge.

Does anyone have experience with the Sigma 70-200mm 2.8 w/teleconverter?

Thanks for all the input...always learning.

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2/10/2007 5:25:12 AM

W.    Teleconverters multiply your focal length. On the downside: they cost you up to 2 aperture stops, they soften focus, and introduce flare and chromatic aberration (purple fringeing).

It's a trade off.

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2/10/2007 6:50:33 AM

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