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Author Topic: effects of focal length  (Read 1650 times)

orc73

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effects of focal length
« on: February 24, 2012, 03:46:23 am »

Hi

for 35mm it is recommended to use at least 85mm or even 135mm for portrait due to compression effect prefered to a wide angle.
On the other hand 50mm is seen as "normal" while around 80mm would be "normal" in MF.

How is the 80mm effect resulting in an MF compared to a 50mm in 35mm?
Does it just show the same frame or does it also give the same effect?

Is it as fine to do a close up portrait with a 80mm on a hasselblad like doing it with 80mm on a 35mm?
Or would this result in longer nose and so on as the 50mm?


best regards
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Rob C

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Re: effects of focal length
« Reply #1 on: February 24, 2012, 04:26:33 am »

Hi

for 35mm it is recommended to use at least 85mm or even 135mm for portrait due to compression effect prefered to a wide angle.
On the other hand 50mm is seen as "normal" while around 80mm would be "normal" in MF.

How is the 80mm effect resulting in an MF compared to a 50mm in 35mm?
Does it just show the same frame or does it also give the same effect?

Is it as fine to do a close up portrait with a 80mm on a hasselblad like doing it with 80mm on a 35mm?
Or would this result in longer nose and so on as the 50mm?

best regards




You are treading on very dangerous sands; the risk of being sucked down into the Underworld is great, so beware what you ask!

Your question is basically about the effect of distance on the human face, and the main factor affecting that is simply the distance between you the photographer, and the subject.

Whichever camera format you use it remains the same problem. You have first to decide the distance away from your subject that you feel gives the best look to him/her. Your eye should tell you that. Then you select the lens that allows you to fill the frame at that distance (assuming you are only interested in a head-shot). In my own case, I seldom wanted to work closer than about six feet from the model, so I used a 135mm lens on 35mm cameras or a 150mm on 6x6 cameras. On the latter, I would have preferred a 180mm, but though I had that with my old Mamiya TLR, I could only find a 150mm for the ‘blad when I graduated to it; the 180mm didn’t exist in the range at the time I was buying into the system.

(Specifically regarding your question, I wouldn't dream of doing a close-up of a face on a 500 series 'bad with an 80m lens if I wanted to remain friends with the subject afterwards.)

That’s the simple answer. Unfortunately, that leads to different problems as you go to noticeably larger camera formats, mainly because of the change in the depth of field that you’ll run into as you change the magnification of the image on screen.

Rob C

ondebanks

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Re: effects of focal length
« Reply #2 on: February 24, 2012, 04:57:58 am »

Hi

for 35mm it is recommended to use at least 85mm or even 135mm for portrait due to compression effect prefered to a wide angle.
On the other hand 50mm is seen as "normal" while around 80mm would be "normal" in MF.

How is the 80mm effect resulting in an MF compared to a 50mm in 35mm?
Does it just show the same frame or does it also give the same effect?

Is it as fine to do a close up portrait with a 80mm on a hasselblad like doing it with 80mm on a 35mm?
Or would this result in longer nose and so on as the 50mm?


best regards

Rob's given a great answer. A little more from me:

"Is it as fine to do a close up portrait with a 80mm on a hasselblad like doing it with 80mm on a 35mm?"
No, because the camera will be much closer to the subject in the Hasselblad case.

It's best to stop thinking solely about focal lengths and start thinking in terms of angle covered by the lens. A 50mm lens on 35mm format covers the same angle as an 80mm lens on (a rectangular crop of) 6x6 cm format. Once these angles are the same, plonk your tripod down at any given distance from the subject and the photograph will be the same. To fill the frame with a headshot on 35mm you have to move in objectionally close with a 50mm lens. To fill the frame with a headshot on 6x6/645 you have to move in equally close with an 80mm lens. You wouldn't do the former so you shouldn't do the latter. So instead, you back off from the subject and use a longer lens in both cases - e.g. a 90mm on the 35mm camera and 150mm on the 6x6/645. These also cover the same angle as each other.

Ray
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orc73

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Re: effects of focal length
« Reply #3 on: February 24, 2012, 07:55:53 am »

thanks for both your clarifications!
makes sense for me. so its about the angles.

the explanations imply that if i take a shot from 10 feet distance with a 50mm and a 135mm and crop the face, both shots will have the same effects. Is that correct?

the result would be by buying a higher resolution camera might safe me from buying a longer lense, by just cropping.
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BJL

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effects of focal length: thanks; it's about the angles
« Reply #4 on: February 24, 2012, 11:11:30 am »

Ah, one of those rare threads where the first response gets it so right and understandable! Thanks Rob.

And I would like to thank Ray and orc73 for a new catchphrase: when it comes to composition, cropping and such ...
... it's about the angles.
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Martin Kristiansen

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Re: effects of focal length
« Reply #5 on: February 24, 2012, 02:06:09 pm »

Phew! Thanks Rob. Feel like we dodged a bullet there. I was nervous just opening the thread.
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theguywitha645d

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Re: effects of focal length
« Reply #6 on: February 24, 2012, 05:06:38 pm »

Learn you format diagonals and then just use angular coverage.

A 35mm diagonal is 43mm. Divide the focal length by the diagonal and you have your angular factor. 85/43= (almost) 2X

My 645D has a 55mm diagonal and a 110mm lens will be same FoV as the 85 on 35mm
6x4.5 diagonal is 70mm, so a 140mm lens would be equivalent
4x5, with a 150mm diagonal, would use a 300mm
8x10 would need a 600mm lens.

It gets a bit hairy as a rule of thumb when comparing formats with very different aspect ratios--6x6 and 6x17--but there are other was of applying the same idea.
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Wayne Fox

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Re: effects of focal length
« Reply #7 on: February 24, 2012, 10:25:53 pm »


the explanations imply that if i take a shot from 10 feet distance with a 50mm and a 135mm and crop the face, both shots will have the same effects. Is that correct?

Yes.  If your camera remains in the same position, and you crop the image taken with the 50mm to match the 135mm, the two images will be basically the same other than the resolution.

When doing portraits, the goal is make sure the lens doesn't distort the size of the nose and ears in relationship to the overall face.  What determines that is how far away you are. So the standard guideline in the portrait business has been "double" the "normal" focal length.  That was easy back with there were only 3 main formats, 35mm, 645/6x5, and 6x7.  So 100, 150, 180 were the ones recommended.  The result is really more about forcing you to shoot further away than you might do so instinctively ... getting even further doesn't really change the face much (and those changes don't look weird), but getting closer can.

Understand this applies to head/shoulder crops or tighter ... if you are shooting fuller,  then wider works (because you're farther away to get that field of view).
« Last Edit: February 26, 2012, 02:02:14 am by Wayne Fox »
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