Size Does Matter; The Power of the Square of the Focal Length

Size Does Matter; The Power of the Square of the Focal Length

In the original “The Art of Bird Photography” I wrote something to this effect: the size of the bird in the frame is not a factor of the focal length but rather a factor of the square of the focal length. In other words, if you go from a 400mm lens to an 800 mm lens, the bird will be four times bigger in the frame (not twice as big). 500mm f/4 lenses are surely the most popular focal length for folks photographing birds. And most folks do quite well with the 500 and a 1.4X teleconverter.

Yesterday afternoon at Westhampton Beach, Long Island, NY, Denise Ippolito and I were photographing a young Royal Tern while standing next to each other. She was using the Canon 500mm f/4L IS lens with the 1.4X II teleconverter and the EOS-1D Mark III. I was using the Canon 800mm f/5.L IS lens, the Canon 1.4X III teleconverter, and the Canon EOS-1D Mark IV.. The animated GIF above shows the huge difference in magnification. In addition, note the smoother background in the image created by the 800 lens.

Both ISO 400. Denise: Evaluative metering at zero: 1/2000 sec. at f/7.1 in Manual Mode. Artie: Evaluative Metering at zero: 1/1000 sec. at f/10 in Av Mode. Coincidentally, each of us opted to stop down 2/3 stop from the wide open aperture. Each image was leveled using the Ruler Tool and cropped just a bit using the Straighten button.

Shopper’s Guide

Below is a list of he gear used to make the three mages in this post. Thanks a stack to all who have used the Shopper’s Guide links to purchase their gear as a thank you for all the free information that we bring you on the Blog and in the Bulletins. Before you purchase anything be sure to check out the advice in our Shopper’s Guide.

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Canon 800mm f/5.L IS lens. Right now this is my all time favorite super-telephoto lens.
Canon 500mm f/4L IS lens. A fast, sharp, versatile super-telephoto lens. I owned and used two for close to a decade. I now own only one and will be selling that when the Series II lenses are available.
Canon 1.4X III Teleconverter. The new 1.4X TC is designed to work best with the newer Series II super-telephoto lenses but it works just fine with the current lenses.
1.4X II Teleconverter. Most folks including me believe that the 1.4X II TC is as sharp as the 1.4X III TC.
Canon EOS-1D Mark IV professional digital camera body. My two Mark IVs are my workhorse digital camera bodies.

And from the BAA On-line Store:

LensCoats. I have a LensCoat on each of my big lenses to protect them from nicks and thus increase their re-sale value. All my big lens LensCoat stuff is in Hardwood Snow pattern.
LegCoat Tripod Leg Covers. I have four tripods active and each has a Hardwood Snow LegCoat on it to help prevent further damage to my tender shoulders :)
Gitzo GT3530LS Tripod. This one will last you a lifetime.
Mongoose M3.6 Tripod Head. Right now this is the best tripod head around for use with lenses that weigh less than 9 pounds. For heavier lenses, check out the Wimberley V2 head. (Note: Denise prefers the Wimberley head to the Mongoose.
CR-80 Replacement Foot for Canon 800. When using the 800 on a Mongoose as I do, replacing the lens foot with this accessory lets the lens sit like a dog whether pointed up or down and prevents wind-blown spinning of your lens on breezy days by centering the lens directly over the tripod.
Double Bubble Level. You will find one in my camera’s hot shoe whenever I am not using flash.
Be sure to check out our camera body User’s Guides here.
The Lens Align Mark II. I use the Lens Align Mark II pretty much religiously to micro-adjust all of my gear an average of once a month and always before a major trip. Enjoy our free comprehensive tutorial here.
BIRDS AS ART Camera Body User’s Guides. Why spend $2-5 grand on a camera and not learn to use it properly and efficiently?

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13 comments to Size Does Matter; The Power of the Square of the Focal Length

  • avatar Mike Forbes

    I read a comment below saying that you can’t put a 2x TE on a 7D and a 600mm f4 lens? Or that it does’t work well or am I missing something?

    You can put it on a 600 f/4 and focus manually or use Live Mode AF to focus in Live View as per the 7D User’s Guide (slow and cumbersome) but you will not have normal AF with that combo as the 7D focuses only to f/5.6. artie

  • avatar Bill G

    Points taken, Artie. Thanks! –bill

    YAW. artie

  • avatar Bill G

    Thanks for the feedback!

    KR said: “At the image level, smaller pixels mean less noise, other things being equal.”

    The noisy pixels are smaller, but there are more of them (both because there are simply more pixels and because they are closer together). The 7D has aesthetically pleasing noise, and it is hard to see in a physical print at ISO 1600 or below. No doubt color and contrast suffers some from the noise, which is harder to measure by pixel peeping, but maybe is why Art prefers his 1D IV files.

    AM said: “…I do believe that many folks have a problem with 7D noise because they are under-exposing their RAW files.”

    I completely agree. I now consistently increase the evaluative metering exposure +1/2 stop, going to +1 stop in low light (as per ABP II – thanks!), and I get much better results. (I even do this with my 5D II.) Unfortunately, increasing exposure 1 stop in low light means that I’m effectively lowering my ISO when I need it most!

    I’ll probably stick with my sveldt 7D and get a bigger big lens. I’m really looking forward to trying the 500 f/4 II….

    Bill, Several comments with regards to this:

    “I now consistently increase the evaluative metering exposure +1/2 stop, going to +1 stop in low light (as per ABP II – thanks!), and I get much better results. (I even do this with my 5D II.) Unfortunately, increasing exposure 1 stop in low light means that I’m effectively lowering my ISO when I need it most!”

    Adding a given amount of light by rote is not a good plan….. Best to learn to evaluate the histogram in a given situation and add enough light to get data in the right-most histogram box, the closer to the highlight axis the better (as long as you have only a few blinkies at most). Do check out the blog post here where +2 1/3 stops (in the opening image) was not nearly enough compensation….

    It is easier to cheat on the exposure with the MIV than it is with the 7D. You need to add light as in the paragraph above and raise the ISO if you wish to avoid mega-noise. artie

  • “given that the higher pixel density of the 7D increases noise” That’s simply – and unequivocally – not true, Bill. At the image level, smaller pixels mean less noise, other things being equal.

    Keith, Though Bill’s statement is generally accepted as fact (and I may have passed it along once or twice myself…) I am not sure who is correct but I do believe that many folks have a problem with 7D noise because they are under-exposing their RAW files. That said I still prefer the quality, look, and feel of my Mark IV images to the quality, look, and feel of my best 7D images. artie

  • avatar Bill G

    I’ve often thought about upgrading from my 7D to a 1D IV so that I can put a 2x on my big lens (using the central sensor to focus at f/8). However, my crop sensor multiplier goes down from 1.6x to 1.3x, negating most of the gain. I understand that the crop multiplier is largely psychological, given that the higher pixel density of the 7D increases noise, and is pushing the resolution limits of the lens/multiplier combination. What do you think?

    A 7D with the 1.4X TC is a viable option with a big lens. My thoughts on the 7D have been very clear: I like the images made in the sun but do not like the images made on cloudy days. And even with the sunny day images I am not huge fan of those tiny pixels. Do see the dozens of great 7D images that I posted both in Bulletins and on the blog. artie

  • avatar Steve M

    Artie,
    I’m a little confused on this. I have always read that focal length vs subject size is a linear relationship (or darn close to it) but I’ve never really tested it or given it much thought. So I was surprised to read you saying that it is non-linear (squared). Maybe my logic is wrong but I decided to measure the two bird images on my monitor to compare – it did seem like an awfully dramatic difference so I wanted to check it out. I measured the bird at 700mm (500×1.4) to be 3.2″ long. I measured the bird at 1120mm at 4.95″ long. My math says that 1120mm / 700mm = 1.6. And 4.95″ / 3.2″ = 1.55. Which looks a lot like a linear relationship, not a squared relationship.

    I realize that the TC is adding only 200mm of length to the 500mm lens versus adding 320mm extra to the 800mm and I think that’s the dramatic effect. But I don’t see this example showing a squared relationship where 400mm vs 800mm yields a subject four times larger.

    Can you (or anyone else) clear this up for me? I’m confused.

    The size of the bird in the frame is the area that it covers. Area is a function of the length times the width, and thus, a function of the square of the focal length. artie

  • avatar David Policansky

    Artie: I comepltely understand what you wrote here: “Low and closer is always a great option but one that is not always available with birds. artie”

    And getting a bigger lens = getting closer. But that’s $7000 or so closer… :( Thanks again. David

    I completely understand that spending $7-12K is not an option for many folks; do the best with what you have. Here is a guy with a 100-400 and a 7D who consistently makes great avian images due to his great skill, knowledge, and patience. artie

  • avatar Charles Scheffold

    I did a very similar comparison when I first purchased the 800 – my 500 went up for sale the next day :)

    I’ll wait for the verdict on the new 600. I’m almost always using the 800 w/1.4x right now, so I’ll have to see how the new 600 + 2x compares against this setup.

    Hey Charlie, Enjoy the hurricane this weekend. JBWR is a total waste. So is Westhampton Beach. Nickerson is rocking. I will be getting both the 500 II and the 600 II. :) artie

  • avatar Jim Kranick

    Artie,

    Your reply points out more of those problems that come with purchasing a big white lens. When I ordered the 500 it was easy to decide I may as well get the 1.4x II. The 2.0x II did not have a wonderful rep and would not AF with the 50D I had then. Then I ran down to ILE and got the Gitzo, Wemberly V2 and LensCoat leg covers from you and Jim.

    Many thanks for stopping by; few folks have been there!

    If I get the 600 II I’ll need the new 1.4x III and want the 2.0x III. But a 1200 f/8 won’t AF with my pair of 7Ds. So, while the 500 needed the tripod, head and stuff the 600 will need a 1D IV (or 1D V by then).

    Now I just need to talk to my wife.

    :) With the new 600, the 1.4X III, and the 7D you will have lots of reach… artie

  • avatar David Policansky

    Thanks for that demonstration. How I agree, and how hard it is for me to justify spending significantly more than my 400 f/5.6L cost me. Here’s a related way of looking at the same issue; a friend of mine, also an avid amateur photographer, and I were talking about our “Rules # 1″ of photography last week. I said my Rule # 1 is “get closer.” He said that’s his Rule # 2; his Rule # 1 is “be there.” David

    Low and closer is always a great option but one that is not always available with birds. :) artie

  • avatar Jim Kranick

    I’m happy with my 500 f/4 + 1.4x II but wonder about the new, lighter 600 f/4 II (+ 2x III.) It’s just that I’m a little more than $10,000 short right now.

    Thanks for the comparison/lesson.

    Hey Jim, YAW, The new 600 II with the 2XIII will give us 1200mm with central sensor only AF as compared to 1120mm with central sensor only AF with lots of other benefits. See Will the 800mm f/5.6L IS Soon Become Obsolete? for more info. artie

  • avatar Myer Bornstein

    Well since all nikon has is a 500 and 600 and I have a 500 would putting on a 2x tc help?

    Myer, Good question.

    Assuming that you have the newest 2X TCE (the older versions were terribly unsharp), learning to make sharp images with either lens–it takes solid technique and some practice) would yield a subject four times larger (covering four times the area) than with the prime lens alone. Do see Advanced Sharpness Techniques in ABP II. Note: many folks try the 2X with a super telephoto lens, fail miserably at making sharp images, and then give up. It does take good technique and practice. With my 500mm and 600mm IS L lenses I was able to consistently make sharp images down to 1/60 sec. Again see ABP II for lots of examples. artie

  • Must you make me lust after an 800?! :)

    Just the facts…. artie