THe Myth of the 'Portrait Lens'

Started Apr 26, 2010 | Discussions thread
Great Bustard Forum Pro • Posts: 39,296
Have to disagree right down the line.

Ilkka Nissilä wrote:

You can photograph people with any lens. But the reason some 85mm to 135mm primes are called portrait lenses is because their optical design is optimized to produce a smooth, beautiful rendition of skin so as to minimize the visibility of blemishes while delivering good sharpness of the general features of the person and they're also designed for accurate (rather than saturated) rendition of colour.

You'll have to tell me exactly how photos in the 85mm - 135mm (EFL) range "minimize the visibility of blemishes while delivering good sharpness of the general features of the person". You'll also have to tell me how the lenses in that range have more "accurate (rather than saturated) rendition of colour" than lenses outside that range.

In my opinion, you are way wrong on both counts.

This kind of design is/was important in this focal range because you would typically use such focal lengths to photograph the head of the person so blemishes in a large print become very obvious. As an alternative, you could use a macro lens for such shots, in which case the blemishes would be accentuated.

Any lens is going to clearly reveal blemishes on a shot framed as tightly as a headshot.

For shorter focal lengths you include more of the environment so the head takes up only a small part of the frame, making it unnecessary to smooth out blemishes. Thus there is no compelling need to specifically develop lenses in shorter focal lengths that are optimized for portrait applications - any sharp lens will do for people subjects and others.

You can most certainly frame tighter with shorter lenses (although this increases persective distortion which may, or may not, be desirable).

However, wide lenses are often used for landscape photography, and sharpness is key for that type of photography. So, your argument that sharpness matters more for longer focal lengths than shorter does not hold water.

In summary, the 85-135mm lenses are not called portrait lenses because they are what you would use for a portrait - that's much too restrictive and not in any way realized in practice. 50mm and 35mm are great lenses for portraits (on FX) just as much as an 85mm. They just don't need to be designed specifically for the task to work well.

What, specifically, makes a lens "designed spefically for the task" of portraits? In particular, what attirbutes would be desirable for a portrait lens that would not be desirable for another type of lens (aside from focal length), and vice-versa?

The only thing I can think of is that a lens specifically designed for portraits would not have edge performance as a strong consideration, and would place more emphasis on good bokeh than sharpness (which are often at odds with each other).

However, Canon's premiere "portrait lenses", the 85 / 1.2L and 135 / 2L, are renowned for sharpness, bokeh, and corner performance, so, it would seem, that if there is anything special about the 85mm - 135mm range, it's that it's easier to design a lens that has it all in that focal range than at other focal ranges. Well, more specifically, since all long lenses seem to be stellar, let's say that lenses 85mm or longer seem to be able to "have it all", whereas shorter lenses, at least for Canon, seem to require more compromises.

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