a question about 1.6x multiplier for dSLR.. serious question.


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sequitur

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#1
okay guys here goes.

for portraiture headshots the best theoractical focal length to use is between 85mm-135mm or somewhere around that range. this is the range where your headshots won't come out too flat or too long, and more or less "just the right size". okay basically this is not the main question..

the main question is..

if i want to achieve let's say 128mm (80 x 1.6). there're actually 2 ways of looking at it. that is i use an 80mm lens, and the focal length is multiplied to 128mm and the headshot lies within the range. (yes i'm being stubborn but pls, this is not the issue)
OR
i use an 80mm lens, the picture actually comes out either too flat or too long, and the camera CROPS out part of the picture to make it SEEM like the picture was taken using a 128mm lens.

so my question is.. which is more correct ? that if i use an 80mm lens, the focal length is 128mm and i take a "proper" picture,

or that i use an 80mm lens, i take a "wrong" picture, and the camera CROPS the picture to make it look like it was taken with a 128mm lens ?


hope someone can help.. lol.. just occured to me. sorry. thanks.
 

sequitur

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#3
majere2sg said:
What you see thru the eyeviewer is almost what you get.

and that means ?


which way is the image captured ?

-_-

the point is the difference to the eye is minimal because the eye can self-adjust but the lens cannot. so whatever turns out on the picture would be affected by perspective and distortion and the lot.
 

darrelchia

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its would be (B) ... the photo would still have the perspective of a 80mm lens, but its cropped to what you get with 128mm. Magnification factor is an inaccurate term, accurately, it would be called cropping factor.

The (simplified) theory is that the sensor size is smaller than that of a 35mm film, so the edges get cropped, giving it the look of (using) a longer lens, but the perspective remains the same.
 

sequitur

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so that means if i use a 80mm lens, i'd face the "distortions" and all right ?(theoractically) as much as the picture appears to have been taken with a 128mm ?
 

sequitur

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#9
actually i got this off a few books.

basically if you shoot portraiture out of the 85-135mm range or something like that, the overall body length will be longer or shorter depending on which side of the range it lies to. i can't really remember which gives you a longer or shorter body length, but the authors had pictures to prove it.

especially with headshots. i guess it's quite impt in a sense coz you don't wanna be flattening the head of an already plump face or something like that.
 

wacko

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#10
shooting at 80mm (actual) on such a DSLR will give you DOF at 80mm, not 128mm, that's another difference you might want to take note.
 

darkness

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#11
Actually the "distortion" you are referring to is greatly affected by the subject distance. You can shoot a person using a 28mm lens and still look ok if the person is far enough (of coz, the person will end up really small in the frame). I think the 80mm is just a rough guide assuming a cretain subject distance, say 5m.
 

reflecx

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#12
darrelchia said:
its would be (B) ... the photo would still have the perspective of a 80mm lens, but its cropped to what you get with 128mm. Magnification factor is an inaccurate term, accurately, it would be called cropping factor.

The (simplified) theory is that the sensor size is smaller than that of a 35mm film, so the edges get cropped, giving it the look of (using) a longer lens, but the perspective remains the same.
Perspective is a function of subject distance, not the lens. By using a 80mm lens on a DSLR with a 1.6x FLM, you stand where you would if you were using a 128mm lens on a SLR. So the perspective would be identical. But the DOF of the pictures will be different, so the two pictures are not identical.
 

showtime

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#13
yes perspective does not change... so if in theory, you need the flattering nature of a 135mm lens, then please do not assume that 90 x 1.5factor will do the trick on a dslr...i would give the equivalent cropping but not the perspective of the 135...

solution, use the 135mm but one might need more studio space because the camera has to back up a bit to compensate for the 1.5 or 1.6 time cropping...
 

Zplus

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#14
Also, if you are talking about distortion due to the curvature of the lens then usually for film some lens tend to distort at the edges (pincusionning and vignetting - OK i use distortion loosely).... because DSLR with 1.6 crop factor only takes the center portion of the images, these get cropped out. However, the net resolution that a lens deliver is lesser since some of it gets cropped away.

In any case, shooting with a 80mm lens and a 1.6x crop factor DSLR is the equivalent of a shooting a 80mm lens on film, developing the film and then cutting away the edges leaving the centre portion of the photo. Notice you end up with a smaller photo versus having a full sized photo from a 128mm lens.

Does this matter in real life? Well, in any case lens performance varies between different brands and range of lenses and the only way you can be sure is to test it out. Especially because of the crop factor, a mediocre lens for film may be quite acceptable on a DSLR siince it only captures the centre portion (usually the most trouble free area of a lens).

Besides, if you like teles, the effect is like a 1.6x 'multiplier'.
;)
 

TME

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#15
But if the image from a DSLR's viewfinder is what u should get, does it then mean that if u were standing at the same distance with a film SLR with everything the same (focal length, aperture, etc), u should be able to see more through the viewfinder of the film SLR?
 

#16
TME said:
But if the image from a DSLR's viewfinder is what u should get, does it then mean that if u were standing at the same distance with a film SLR with everything the same (focal length, aperture, etc), u should be able to see more through the viewfinder of the film SLR?
Yeah, with a DSLR, I think its something like a digital zoom.
 

jasonpgc

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#17
If you are using a 85mm lens to frame the shot. For the same composition, you'll get a more compress view with a 1.6X DSLR than a 85mm on a 35mm Film SLR. Meaning, you really gets the equivalent perpective of the 135mm(on film) for your DSLR. Cropping an image will achieve the same Perspective of a longer lens. Look at part 9 of this page.http://www.luminous-landscape.com/columns/composition-3.shtml
 

wacko

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#18
jasonpgc said:
If you are using a 85mm lens to frame the shot. For the same composition, you'll get a more compress view with a 1.6X DSLR than a 85mm on a 35mm Film SLR. Meaning, you really gets the equivalent perpective of the 135mm(on film) for your DSLR. Cropping an image will achieve the same Perspective of a longer lens. Look at part 9 of this page.http://www.luminous-landscape.com/columns/composition-3.shtml
we are talking about portraiture shots and you link an article by a landscape photographer (albeit a good one), what gives?
 

YSLee

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#19
Oh my, so many posts, and so few on target.

Perspective is affected by subject to camera distance, a little thinking through of what causes perspective compression and distortion will show this to be true.

DOF is a lil' tricky, for all purposes, it's best to think of it in terms of a new format with its own set of calculations.
 

TME

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#20
YSLee said:
Oh my, so many posts, and so few on target.

Perspective is affected by subject to camera distance, a little thinking through of what causes perspective compression and distortion will show this to be true.

DOF is a lil' tricky, for all purposes, it's best to think of it in terms of a new format with its own set of calculations.
What about my question?
 

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