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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 10 Feb 2009 (Tuesday) 13:04
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50mm, 80mm, 1.6 crop, and portraits...?

 
bokchoi
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Feb 10, 2009 13:04 |  #1

Here's a question that has been bugging me lately:

I understand that a 50mm lens mounted on a 1.6 crop body has an equivalent FOV as an 80mm lens mounted on a full frame body.

I also understand that in portraiture, standing farther away from the subject yields a more flattering photo, as doing so de-emphasizes the size of the nose and other facial features.

My question is, if I use a 50mm lens on a 1.6x crop body for a head-shoulders portrait of someone, will the emphasis on facial features be different than if I use an 80mm lens on an FF body, assuming both shots are framed identically (that is, the head takes up the same area of the print in both cases)?

Another question is, will I be standing the same distance away from my subject with a 50mm on a 1.6x crop body as I would with an 80mm on an FF body in order to frame both shots identically?

I guess the real question is, is 50mm too short to be using for head-shoulder or head-only portraits on a 1.6 crop body, or is it just right since the equivalent FOV is that of an 80mm lens on an FF body?




  
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tkbslc
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Feb 10, 2009 13:25 |  #2

You should get the telephoto effects because you are standing farther away. I am not sure if it is exactly like an 80mm on a FF, but it would be better than a 50 on a FF for this effect.

50 is not bad, but the longer the better for portraits. As long as you have the room to work and your subject can still hear you tell them how to pose. :)


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actprivate
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Feb 10, 2009 14:00 |  #3

You asked two distinct questions. Answers are:

1. Yeah, a 50 on 1.6 gives exactly the same perspective as an 80 on FF. I was actually of a different view about this up to last week when the knowledeable guys on this forum kicked my backside and made me correct my understanding :) Apparently, the perspective is purely the product of the distance between you and your subject and FL/FOV detremine the distance.

2. There are people who believe 50 on 1.6 is a good FL for tight portraits. Some believe the other way. The classic recommended FL range for such shots is 85-135. Therefore, 80 (50 on APS-C) is sitting just at the shorter end of this range. A longer FL may be more desirable if the working distance is practical.

Remember that in addition to a more pronounced flatening effect by longer FLs, a narrower DOF is also achieved which translates into a better separation of background and typically a more pleasant shot.


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songexe
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Feb 10, 2009 15:02 |  #4

actprivate wrote in post #7296984 (external link)
1. Yeah, a 50 on 1.6 gives exactly the same perspective as an 80 on FF.

Is this correct? Since perspective is only a function of the distance between the camera and the subject, the perspective of a 50mm on a crop camera would be different than 80mm on FF. However, the field of view would be the same, no? The crop sensor just takes a smaller part of the image circle, which doesn't affect how far I stand from my subject.

Ack! Help!


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Wilt
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Feb 10, 2009 15:19 |  #5

songexe wrote in post #7297375 (external link)
Is this correct? Since perspective is only a function of the distance between the camera and the subject, the perspective of a 50mm on a crop camera would be different than 80mm on FF. However, the field of view would be the same, no? The crop sensor just takes a smaller part of the image circle, which doesn't affect how far I stand from my subject.

Ack! Help!

If you put a FF camera with 80mm lens at Point A, and then put an APS-C camera with 50mm at Point A, the photos will be identical in perpective. Any difference between the two would be DOF limits, if you shot a f/2.5 with the APS-C, and you shot at about f/4 with the FF camera, the DOF would be very similar.

'Perspective' is entirely due to camera position.
Here is a photo with 20mm lens and with 200mm lens taken with the same camera on the same tripod at the same position...

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/IMG_4601.jpg
IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/IMG_4600.jpg
...with cropping of the first photo to provide similar FOV. Same perspective! (of course, poor IQ from the 20mm photo due to the degree of magnification required, to achieve same final subject size in the photo)

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songexe
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Feb 10, 2009 15:37 |  #6

Oh, I was getting confused by switching focal lengths *and* crop factors, but *not* distance. I've managed to work the math in my head.

Thanks for your help, Wilt. :)


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toxic
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Feb 10, 2009 15:43 |  #7

perspective isn't "only" a function of distance...the focal length will change how much straight lines are turned into diagonals, and how near or far the background appears (something not apparent from Wilt's boring white wall). The former isn't so obvious when you cut off the sides, since most or all of it occurs away from the center, which is also why it isn't a big deal on a crop camera.




  
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Wilt
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Feb 10, 2009 15:49 |  #8

toxic wrote in post #7297662 (external link)
perspective isn't "only" a function of distance...the focal length will change how much straight lines are turned into diagonals, and how near or far the background appears (something not apparent from Wilt's boring white wall). The former isn't so obvious when you cut off the sides, since most or all of it occurs away from the center, which is also why it isn't a big deal on a crop camera.

NOT TRUE when camera position is unmoved! The relationship of the diagonals only changes when camera position is moved, not when the FL is altered!

The background, relative to the subject (the bottle perched on the yardstick) is altered only because of change of camera position used to hold the subject at fixed size in the frame....

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/IMG_0282.jpg
IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/IMG_0281.jpg

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xarqi
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Feb 10, 2009 15:50 |  #9

toxic wrote in post #7297662 (external link)
perspective isn't "only" a function of distance...the focal length will change how much straight lines are turned into diagonals, and how near or far the background appears (something not apparent from Wilt's boring white wall). The former isn't so obvious when you cut off the sides, since most or all of it occurs away from the center, which is also why it isn't a big deal on a crop camera.

I don't know how to say this politely, sorry.
You are completely wrong.




  
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mrkgoo
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Feb 10, 2009 15:55 |  #10

songexe - distance is the only factor for perspective (for rectilineiar lenses) - the 80mm on FF vs 50mm on crop have different perspectives WHEN you have a different distance to subject - which is normally NOT the case when you frame a subject similarly in the setup you describe. The lens FL, type of sensor doesn't matter to the perspective.

Toxic is wrong about FL. Those straight lines are just as 'diagonal' on any FL lens, it's just that you don't see them (or they don't exist rather) on a long FL with narrow FOV.

Think of it this way, or experiment with a zoom lens that goes from wide to tele, say the 18-55. Look through the viewfinder and zoom it back and forward. Are distorted diagonals changing as you zoom? No.




  
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Perry ­ Ge
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Feb 10, 2009 16:00 |  #11

Wilt/xarqi = correct.
toxic = wrong.

Perspective has nothing to do with focal length or format, it's entirely a function of distance/camera position.


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SkipD
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Feb 10, 2009 17:49 |  #12

perryge wrote in post #7297771 (external link)
Wilt/xarqi = correct.
toxic = wrong.

Perspective has nothing to do with focal length or format, it's entirely a function of distance/camera position.

Ditto - the honest truth.


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actprivate
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Feb 11, 2009 03:18 |  #13

SkipD wrote in post #7298603 (external link)
Ditto - the honest truth.

Yes, the evcidence is my sore backside!

But seriously, this lesson has relieved a lot of my pain as I do not need to constantly worry about perspecive when deciding on which camera/lens combination to use.

Life Is Good...


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actprivate
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Feb 11, 2009 03:26 |  #14

Wilt wrote in post #7297694 (external link)
NOT TRUE when camera position is unmoved! The relationship of the diagonals only changes when camera position is moved, not when the FL is altered!

The background, relative to the subject (the bottle perched on the yardstick) is altered only because of change of camera position used to hold the subject at fixed size in the frame....

QUOTED IMAGE
QUOTED IMAGE

As a side note, your example shots demonsrate another creative aspect of perspective and how different FLs can be used to create different feelings/effects in the composition: subject's size relative to the background's size (while subject's maginification is constant).


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mrkgoo
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Feb 11, 2009 03:32 |  #15

actprivate wrote in post #7301634 (external link)
As a side note, your example shots demonsrate another creative aspect of perspective and how different FLs can be used to create different feelings/effects in the composition: subject's size relative to the background's size (while subject's maginification is constant).

Indeed. One thing I always suggest to people taking snapshots on holidays with a landscape in the background is to stand very far away and use the tele end. This makes the back drop appear larger, and much more flattering, avoiding the "Oh it was bigger in person!" comments.




  
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