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11-28-2012, 07:44 PM   #1
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unflattering portrait distortion vs FL logic

A few questions on the logic of "portrait lens" focal lengths:

1) does it depend on actual focal length or FF equivalent?

I'm asking this because I've tried a bit to use a point and shoot vs a dslr for portrait testing...and there's observable distortion even at a longer equivalent focal length on the point and shoot, so by observation, it must depend on actual focal length and not the equivalent on FF. Or, it could be the inherent distortion of the point and shoot lens that I tried.

So, by logic, if it depends on real focal length...one would state that the common APS-C replacement for the 70-200 as a portrait zoom (the 50-135) is not theoretically correct, since it does not depend on the equivalent (except on the overlap range).

2) by consensus, which are the optimal focal length range for portraits (FF and/or APS-C)?

3) I've read some stuff online, and it states that it depends more on distance than focal length...is this true? Is there a psychology to this, or it's optical science?

Sorry if this is newbie topic, I'm just sort of confused with all the online opinions about this topic. So far, I've been making my portrait lens choice based on working distance and the desired crop...with no regard to real focal length whatsoever, is this sort of logic the optimal?

(For instance, most of my indoor shots, if I have only a clearance within 1 and 1.5 meters, I would use a DA40)

11-28-2012, 07:58 PM   #2
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I would think your logic is optimal. It's certainly my logic as well. Let's set an arbitrary 100mm lens as the "best portrait FL". If you dont have the space to use that length, why use it? In that case, the "best FL" would end as more of a hindrance. A 70mm (once again, arbitrary FL) may fit your working space better and allow a better variety of angles. For that situation, a 70mm would be the best focal length.
11-28-2012, 08:03 PM   #3
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It always depends on actual focal length, regardless of format.

I like 50mm and longer for a portrait, my final choice depends what I want to do with the background and how far away I can stand.
11-28-2012, 08:30 PM   #4
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To OP,

It's only about the actual focal length, never about the equivalent.

11-28-2012, 08:39 PM   #5
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I generally use the DA* 50-135 for portraits (or the 77LTD). I am in the 100-135mm range for most portraits. F4 (if not 2.8)

example image:

http://www.modelmayhem.com/portfolio/pic/25906755
11-28-2012, 08:42 PM   #6
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Optimal focal length, to my knowledge:

APS-C: 50-135mm (oh hay, look at the DA*50-135mm~)
FF: 75-200mm

Although nothing's really stopping you from going 150-200mm on APS-C.
11-28-2012, 08:43 PM   #7
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It's all about the relative distance of the nose and the ears from the camera, which is why the actual focal length is what counts.
11-28-2012, 08:50 PM   #8
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What am I misunderstanding about the question? It most certainly has to be the equivalent focal length. A 35mm focal length on a micro 4/3 body would be a good portrait lens, but a 35mm focal length on a full-frame camera would look very distorted. Someone correct me please.

11-28-2012, 09:13 PM   #9
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This is true, but only if you step back to the same distance you would take the image with the 24x36 for the framing. It's all about whether the nose is 50% of the distance to the ears or 10%. The distortion (so called wide angle distortion) is because of the relative distance of the bits in the image. I personally like the longer lens, even on 16x24, because of the "flatter" head. Your opinion is entirely correct, if you look at it one way. In scenics I love the huge pebble tiny mountain effect I get with 12mm, but I'm sure any portrait subject would certainly not appreciate the effect!
11-28-2012, 09:14 PM   #10
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QuoteOriginally posted by Tanzer Quote
What am I misunderstanding about the question? It most certainly has to be the equivalent focal length. A 35mm focal length on a micro 4/3 body would be a good portrait lens, but a 35mm focal length on a full-frame camera would look very distorted. Someone correct me please.
It is a composite effect of focal length and distance to subject since you need to be closer to fill the frame with a short focal length.

Good reference from Stephen Eastwood - Stephen Eastwood|Beauty and Fashion Photographer | Tutorials
11-28-2012, 10:27 PM   #11
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OK, I can agree that it is the relative distance that really matters. We could reduce the distortion from a 35 mm focal length lens on a full-frame camera, simply by standing as far away as we would with the same lens on a micro-4/3 body -- but then we would need to crop the resulting image to get rid of the stuff you didn't want, and then enlarge it. And to extend the argument, I guess one could say that the focal length -- whether actual or effective -- doesn't even matter, provided that you can arbitrarily crop and enlarge the result!

But it seems obvious to me that the field of view is part and parcel of composition. For a given FOV, the crop factor enables (or encourages) the photographer to stand farther away from the subject, which is what reduces distortion. In other words, given the relationship of the crop factor on the FOV, it is the effective focal length that matters.

Getting back to the OP, if you were a good distance from the subject and you were using an equivalent focal length in a mild telephoto range of say 85mm or longer (in full-frame equivalent terms), then I think that the distortion may have been due to the poor quality of the camera's lens. It is also possible that your point-and-shoot camera doesn't even go that far into the telephoto range.
11-29-2012, 12:05 AM   #12
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It's all about perspective, and therefore camera-to-subject distance. For a reasonable looking portrait (i.e. one whose subject's features aren't particularly exaggerated or flattened) this distance will be around 3 feet.

Having set the subject distance, the correct lens is the one which results in the framing that you're after. For a tight head-and-shoulders shot, this might result in a focal length of 60-70mm on an APS-C camera (or about 100mm for full-frame, or for a point-and-shoot, whatever FL corresponds to "100mm equivalent"). To include more of the subject's body, you reduce the FL. In practice, you'll avoid very wide-angle FLs, because the lens itself may start inflicting its own distortion on the image, so for whole-body shots you may end up accommodating the subject by moving away a little.
11-29-2012, 03:04 AM   #13
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Reading posts from various portrait photographers it would seem that the optimum distance is more than the 3 feet one poster mentioned. More like 10 feet. For me the most natural focal length is 105mm, or something around that, whatever the format.

Portrait Lenses Ken says you should shoot from 15 feet. Not sure of that, but he's a pro

The Ideal Focal Length for Portraiture: A Photographer's Experiment 100mm looks best here too

"Just be aware, that perspective has nothing at all to do with the focal length of the lens. Perspective is only dependent on the distance between your camera and the subject."

"Because the longer the FL, the further away you will tend to stand in order to take a portrait (assuming you want the head the same size in the frame). Because people take portraits from greater distances with longer focal lengths lenses, they often attribute the change in perspctive to the Fl, but it is indeed the distance. Even people who know that's the case will still often refer to the "perspective" of a given FL, even though they know that's not really correct. Just as I know that technically, a kilogram is a measure of mass, not of weight, and that the usual formula for converting between kilograms and pounds only works on earth."

"For me, itís the 70-200mm. To keep the backdrop out of sharp focus I prefer to position the subject roughly 8 to 10 feet in front of the backdrop"
11-29-2012, 09:04 AM   #14
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QuoteOriginally posted by les24preludes Quote
Reading posts from various portrait photographers it would seem that the optimum distance is more than the 3 feet one poster mentioned. More like 10 feet. For me the most natural focal length is 105mm, or something around that, whatever the format.
If you agree that perspective distortion is all about the distance to the subject, this does not make sense. For a given framing, the distance to the subject with that 105mm will vary with the camera format, so if you prefer 105mm on FF, it would be logical to prefer something around 70mm on APS-C.
11-29-2012, 09:19 AM   #15
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A key point that is often ignored in forums centered around gear rather than aesthetics is that what's 'unflattering' very much depends on the subject. Not all faces are created equal. For a more roundish face with a short nose I might choose to get a little closer and I'll use a lens with a wider FOV, while towards the 'hawkish' features end, I might try to step away as far as I can.

Last edited by Ikarus; 11-29-2012 at 09:30 AM.
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