 BetterPhoto Member |
Portrait lens I have a Canon 40D camera and I would like to purchase a lens that would be great for portraits, especially with good background blur. What would you recommend?
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Alan N. Marcus |
The classical concept of the portrait: Eyes in focus – nose and ears out slightly out of focus. This is achieved by using a large aperture setting. The larger apertures are f/4 or f/2.8. Large apertures yield reduced depth-of-field. Most would agree that the background should also be noticeably out-of-focus, also achieved by shallow depth-of-field. Additionally, working is a spaciousness studio allows positioning the subject several feet away from the background which keeps it out-of-focus. When space does not permit subject-background separation, focus just ahead of the subject. This technique calls for you to use the subject’s hand as a focusing target. Instruct the subject to hold their hand in front of their face a few inches forward. Focus on the hand by partial depressing of shutter button. Keep up this partial pressure as the subject repositions themselves. Complete the shot by fully depressing the shutter button. The classic portrait lens is one that has a focal length about 250% longer than normal. Such as lash-up approximately duplicates a prospective the subject is highly familiar with i.e. as they see themselves in the make-up or shaving mirror. This prospective is best as it circumvents statements like “I don’t photograph well”. Use of a lens 250% longer than normal is actually not necessity if you can bring yourself to step back further away from the subject as you compose. This further back position goes against nature as we all have an overwhelming desire to compose for minimal space around the subject via the camera’s viewfinder/view screen. Mounting a long lens or setting the zoom to an elongated focal length forces the needed increased camera-to-subject distance. What is the focal length of a lens about 250% longer than normal? For the 40D it is 2.5 times the diagonal of the sensor chip which measures 14.8mm by 22.2,, with a diagonal of 26.7mm Thus 26.7mm x 2.5 = 66.7 thus the ideal portrait focal length for this camera is 65mm ~ 70mm. No need to be exactly set to this computed value, Hollywood uses 3x in their close-up work. Also photography is both art and science thus you are free to use any focal length your heart desires. Alan Marcus (marginal technical gobbledygook)
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John P. Sandstedt |
Everything I've ever read, and in discussions with many photographers, the "ideal focal length" for portraits ranges from 90-125 mm [35 mm film equivalent.] Canon used to make a 90 mm portrait lens with a soft focus feature for film cameras; I'm not whether it's still around. You might think about a f/1.4 or f/1.8 50 mm lens. With the 1.6 lens factor of your camera, this works out to ~80 mm, just short of the 90 mm focal lens described above. But, in the case of the f/1.8, how can you go wrong for the $84 price tag [Amazon.] Today's typical digital zooms have variable apertures starting at f/3.5. Not great for selective focus. This includes most kit lenses and even my Canon 17-85 mm IS zoom [for my Canon 30D.] Tamron does make the 17-50 mm f/2.8 for Canon and Nikon. A great lens - OK for for selective focus. The Canon f/1.4 [~$330] and the f/1.8 will absolutely allow you to use Selective Focus.
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Alan N. Marcus |
The ideal portrait lens for a 35mm format is considered to be 105mm. That’s precisely in the center of the range John S. mentioned. The 35mm format is 24mm by 36mm the diagonal is 43.3mm. In keeping with my statement 43.3 x 2.5 = 108mm an odd value generally rounded to 105mm. The 40D format diagonal is 26.8mm thus 43.3/26.7 = 1.6 the crop factor or the inverse 26.7/43.3 = 0.62 meaning the 40D is 62% of the size of a full frame 35mm thus 105 x 62% = 65mm the ideal portrait lens for this format which is call APS-C for Advanced Photo System Classical meaning it is exactly the ratio of a 4x6 print. Alan Marcus (marginal technical gobbledygook)
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Alan N. Marcus |
Perspective: Correct perspective is always achieved when an image is viewed from the same distance as the focal length of the taking lens. Consider a full frame 35mm size image 24mm by 36mm with a 50mm lens mounted. If a thumbnail size (contract print) is made, the correct viewing distance is 50mm or 2 inches. Such tiny images and such a close viewing distance is inconvenient. If this image is viewed from 10 inches, a more comfortable viewing distance, the perspective seen is no longer correct. Under these conditions near objects will appear relativity larger and distant object smaller, in other words the perspective is distorted. Now if the image is enlarged 8X the viewing distance becomes 50mm X8 = 400mm which is approximately 16 inches. Under these conditions the resulting image measures 8x12 inches and perspective is restored and the viewing distance is well-situated. As to portraiture, the typical print made will be an 8x10 or 8x12 and framed and placed on a mantel or dresser. Now the typical viewing distance is about 32 inches. So the question comes up, what focal length to use that preserves prospective? 105mm to the rescue! The 105mm is 4 inches. We do the math. 4X8=32 inches. Suppose we use an APS-C format like the 40D sensor size 14.8mm by 22.2mm. To make the same 8x10 image the magnification required is 13.7X. We mount a 65mm lens to preserve perspective. 65mm = 2 1/2 inches. Thus 2.5X13.7=34 1/4 inches. That’s why 65mm is the focal length of choice for this format. Suppose you want to make a 16x20 and mount it on the wall to be viewed from 6 feet. Let’s do the math: 6 feet = 1,829mm. Now to make a 16x20 from an APS-C requires 28x magnification. Thus 1829/28=65mm. This is how portrait lens focal lengths are derived. Different size prints and different viewing distance prescribe different focal lengths. What happens if you mount a lens that is too short or too long? Things close to the camera are rendered large; things far from the camera are rendered small. If the focal length chosen is too short the nose of the portrait subject will be rendered too big and the ears too small. If the focal length used is too long the nose-to-ears distance appears compressed. In both cases distortion creeps in. The good news is: Likely distortion will be minimal unless the focal length of the lens chosen is bizarre. This math serves only to calculate a ‘ballpark’ focal length. Photography is both an art and a science. In cases of perspective the art must prevail. Alan Marcus (more marginal technical nonsense)
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- Carlton Ward Contact Carlton Ward Carlton Ward's Gallery |
Hi Susan, I use either the 50mm f/1.4 or the 135mm f/2 L with my prefernce being the 135mm because that lens rocks... I will occaisionally use the 24-70mm f/2.8 or the 70-200mm f/2.8 but you cant beat a prime lens for portraits IMO. The 70-200 is one of my very favorite lenses because it is so versatile and does a great job with portraits. my .02 - Carlton
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Oliver Anderson |
The 2 lenses I'd look to purchase are the 50mm 1.4 or 80mm 1.8. they're both fantastic deals for the $$ and very sharp. The 135mm is unbelievable but with 40D a little long.
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