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Old Oct 19, 2003, 10:30 PM   #1
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Default Perspective on DSLR

I have one serious question about perspective on a DSLR and I hope you guys can help me out. Say I would like to take a head and shoulder portrait in 80mm(through a 50mm lens with the x 1.6 multiplier).

Normally on a 35mm film camera, using a 50mm lens to take head and shoulder will make the face of the person looks kinda weird. But with a lens around 80-135mm, it will looks just nice. So on a DSLR with the 1.6 crop factor, my 50mm lens will be just right to take the head and shoulder portrait, as it would act like a 80mm lens.

Now here’s the serious question:

A) Will my 50mm lens have the same perspective as if I was using a 80mm lens on my film camera?

B) Or does the it have the SAME perspective of a 50mm, just that the camera crops part of the image, take the middle part of the picture, enlarge it to fill the frame and make it APPEARS to look like a picture taken with a 80mm lens?

If B is correct, then the focal length multiplier acts like some sort of illusion isn’t it? The perspective is the same means that I’m still using a 50mm lens though it looks like a 80mm?

Perspective is important to me because I also take pictures of people including backgrounds especially during my travels. I’m a newbie in the digital world and very confused in this matter. I intend to get a dslr and with two prime lens to do normal shots and head & shoulder portraits first. So I’m thinking of getting a 35mm and 50mm or a 50mm and 85mm (as I would if it’s a film SLR). With the crop factor in issue, the matter become somewhat confusing. Please advice. Thanks.
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Old Oct 19, 2003, 11:20 PM   #2
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Perspective is determined entirely by the distance to the subject - it has nothing whatsoever to do with the focal length of the lens.
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Normally on a 35mm film camera, using a 50mm lens to take head and shoulder will make the face of the person looks kinda weird. But with a lens around 80-135mm, it will looks just nice.
That is due to moving closer to the subject to get the same framing as you did with the longer lens.

In this sense, your 50mm lens with a 1.6 multiplyer will work exactly the same as your 80mm lens. There will be a difference in depth of field though.
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Old Oct 20, 2003, 12:04 AM   #3
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Thanks Bill, that helps alot to clear my confusion!
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Old Oct 20, 2003, 2:26 AM   #4
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Default Re: Perspective on DSLR

Quote:
Originally Posted by Zan_MT
Normally on a 35mm film camera, using a 50mm lens to take head and shoulder will make the face of the person looks kinda weird. But with a lens around 80-135mm, it will looks just nice.
Many photographers say that ~100mm (35mm equivalent) is nicer for portrait shots. I was at a lecture where a newspaper photographer who only takes people shots says she prefers using the 100mm equivalent on the camera she uses (she uses Hasselblad medium format).
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Old Oct 20, 2003, 8:08 AM   #5
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I believe I read some where that MF cameras have different DOF properties because of the larger glass. If so, than I don't believe you can try to transfer the logic of which lens to use over to 35mm.

Eric

ps. It should be stated that I am very MF ignorant, so I could be wrong.
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Old Oct 20, 2003, 6:26 PM   #6
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With relative aperture being the same and same COC size then DOF will be determined by magnification ratio. That's why for a given area of view - head and shoulders - a digicam with a small CCD will have a deep DOF and a large format will have one that is razor thin.
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Old Oct 20, 2003, 7:56 PM   #7
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Standing at the same distance while doing a head-and-shoulder shot will give the same depth perspecive regardless of anything to do with the camera. However, all photographers will want to fill their film/sensor with the image. So if a 100mm lens puts you at the distance you want with a 35mm camera, a 400mm lens would be about right to do the same job with a 4x5" camera - the film is four times the size and the increase in focal length matches. So using a camera with a sensor 62.5% of 35mm film would want a lens of 62.5mm to match the depth perspective of a 100mm lens. Or 50mm to match an 80mm's depth perspective on a 35mm camera.

As padeye points out, the depth of field changes. That can be a real problem if you want to shoot the eyes in sharp focus while letting the ears go soft.
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