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Author Topic: This puzzling business of "35mm lens equivalent"  (Read 17721 times)
allegretto
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« on: January 16, 2012, 11:25:32 AM »
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Perhaps, maybe certainly, this has been addressed previously. But I see it everywhere I turn in Cameradom. m4/3; "this 24mm lens is a 48mm in 35mm equivalent" and so on..

When I see the pictures, NO, IT'S NOT!!! It is indeed a 24mm lens. It may occupy the space that a 48mm lens would in a FF sensor photo, but it suffers from (or benefits from, whatever the situation) the same distortions of any 24mm lens. Or a least that's the way it looks to me. Portraits shot with small-sensor cameras and short focal length lenses make faces look pear-shaped and noses big. It seems many of the gear peddlers try to avoid this being noticed by playing with the image or lighting, making it "artsy" but distorted just the same.

Is my impression correct, or am I missing something?
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madmanchan
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« Reply #1 on: January 16, 2012, 11:31:08 AM »
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The "equivalent" is referring to field of view (angle of view) only.
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Big Mike
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« Reply #2 on: January 16, 2012, 11:37:27 AM »
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Amen Brother.

I'm a moderator on another photography forum and it seems to me that there is a lot of misinformation floating around about the dreaded 'crop factor'.  

Actually, I think that a lot of people do have a decent understanding of it...but they way they express it, is often incorrect...and on a medium like an internet forum, that can lead to a lot of other people getting the wrong ideas.

It does bother me when I read people saying that a 50mm lens is an 80mm lens on ________ camera.  Roll Eyes
No it's not (I shout in my head)...it's a 50mm lens and the camera is only seeing a certain portion of the frame (field of view) that is similar to what an 80mm lens would see on a 35mm film (of full frame) camera.  

As we get farther and farther away from 'the old standard' of 35mm film...I think we should put the 'crop factor' to rest.  Most of the people on photography internet forums (the one I mod for especially) have never used a 35mm film SLR, so the crop factor has no meaning to them...except to confuse them.  
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Walter Schulz
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« Reply #3 on: January 16, 2012, 11:54:39 AM »
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The "big nose effect" is caused by short distance.
You may use a compact camera at 40 cm distance or a full format at 40 cm. It's just the same and it's called perspective.

Ciao, Walter
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Atlasman
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« Reply #4 on: January 16, 2012, 12:25:08 PM »
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"it's a 50mm lens and the camera is only seeing a certain portion of the frame (field of view) that is similar to what an 80mm lens would see on a 35mm film (of full frame) camera."

Except that an 80mm lens on a full frame has slightly more compression than the 50mm.
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Slobodan Blagojevic
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« Reply #5 on: January 16, 2012, 12:32:55 PM »
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... Except that an 80mm lens on a full frame has slightly more compression than the 50mm.

Care to define "compression'?
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Slobodan

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« Reply #6 on: January 16, 2012, 12:35:11 PM »
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... Portraits shot with small-sensor cameras and short focal length lenses make faces look pear-shaped and noses big...

Not correct. As Walter pointed out, it has nothing to do with sensor size or focal length, but everything to do with the distance from the object.
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langier
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« Reply #7 on: January 16, 2012, 01:48:19 PM »
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Let's pose this another way...

If I was shooting a 50mm lens on 35mm, to swap my camera to 6x6 cm, I'd be shooting with about a 75-80mm lens. For 6x9 cm, I'd need maybe a 90-105mm, for 4x5, a 150mm is the lens. That's the was we figured before digital.

Today, with the 4/3, DX, etc., we're implying the same idea, but using a little different terminology. A 50mm on 35mm would work on a DX frame as though we were shooting with a 75mm to 80mm lens and on 4/3 as though we were shooting with a 100mm lens on the 35mm/FX/Full-frame. The meaning is about the same, though those of us from the glorious days of film (1990s) sometimes get picky...

As for me, I'm shooting both full-frame and DX and it's second nature what lenses I need and use to have a similar angle of view between the two formats.

Neither good nor bad, just a mind set. No reason to take offense or get bent out of shape. As for me, I'd rather be shooting than arguing. So now stop worrying about the terminology and simply go out and create a nice image!
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Larry Angier
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mediumcool
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« Reply #8 on: January 16, 2012, 01:56:17 PM »
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As folks have pointed out, perspective is created by distance; it is the relationship between different objects in the scene being photographed front to back (foreground, midground, background). Focal length determines magnification and field of view. Neville Maude at Amateur Photography magazine used to speak of steep vs shallow perspective.

A thought experiment:

Pinocchio asks you to take a corporate portrait (he’s in PR these days, but keeps in the background due to his *problem*). He poses 1m from your camera; his nose when tumescent is 500mm long which means it is half the distance to the lens than where his head is. Thus the *distortion ratio* (just made that up) is 50%. You have used use a standard 50mm lens, but think the effect is a little *in-your-face*, so you switch to a 135mm and back off to 2.7m. Pinocchio’s head will fill the same amount of the frame, but the ratio between the end of his wooden hooter and his face will have changed, relative to the greater distance. Do the sums for the 135: distance to face is 2.7m; distance to end of nasal stick is 2.7m – 500mm = 2.2m. Result 0.814 (three figures).

Or you could read this.
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allegretto
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« Reply #9 on: January 16, 2012, 02:39:59 PM »
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Not correct. As Walter pointed out, it has nothing to do with sensor size or focal length, but everything to do with the distance from the object.

Hmmm

Isn't a 25 mm lens a 25mm lens regardless of sensor size?
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Walter Schulz
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« Reply #10 on: January 16, 2012, 02:44:51 PM »
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Yes, it is.

Ciao, Walter
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simonstucki
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« Reply #11 on: January 16, 2012, 02:55:47 PM »
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if the focal length had this effect cell phone cameras or 8x10" would be absolutely unusable for portraits.

it really only is the perspective.

the exact same discussion was very popular a few years ago (at least in the german speakin community) when the first (crop)dslrs became affordable. unfortunately I can't find one of those comparison that show absolutely no difference for different focal lengths with the same perspective (except resolution or things like that of course).

if you don't believe it just try it out. do a blind test, otherwise might see what you want to see.

simon
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mediumcool
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« Reply #12 on: January 16, 2012, 02:57:37 PM »
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Hmmm

Isn't a 25 mm lens a 25mm lens regardless of sensor size?

Yes.
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simonstucki
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« Reply #13 on: January 16, 2012, 03:08:44 PM »
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Hmmm

Isn't a 25 mm lens a 25mm lens regardless of sensor size?

of course, but a 25mm can be an extreme wide angle with a large image circle (medium format) or a rather long tele lens with a very small image circle (ps with small sensor).

maybe another thought experiment helps. take a camera with a lens and take a picture, now think of the exact same camera just 1:10 of the size. would you expect the shrunk camera to produce a different image that the big one? (I know, diffraction, noise and stuff will be different, but that can be "easily" explained, and that's not what I mean)
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feppe
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« Reply #14 on: January 16, 2012, 03:17:48 PM »
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As we get farther and farther away from 'the old standard' of 35mm film...I think we should put the 'crop factor' to rest.  Most of the people on photography internet forums (the one I mod for especially) have never used a 35mm film SLR, so the crop factor has no meaning to them...except to confuse them.  

The "35mm equivalent" is extremely useful shorthand for figuring out that a 24mm is a wide angle lens on a full-frame camera but a normal lens (ish) on a Micro Four Thirds camera. Without that short-hand we'd have to know what the crop factor of each camera is (and we're back to square one), or be experts at every single camera system (crop factor) out there, which is not feasible.

I'm not aware of a better and more intuitive way to compare lenses and focal lengths of cameras across formats, especially the ones we don't use regularly.

More on the subject here.
« Last Edit: January 16, 2012, 03:24:29 PM by feppe » Logged

allegretto
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« Reply #15 on: January 16, 2012, 03:21:14 PM »
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Well if one uses the 25mm lens at 3M then yes, it doesn't get what I'll just call 'perspective distortion" (I just made that up and perhaps there is a better expression).

but I don't think that is what happens to the average amateur photographer. They want to fill the frame and thus get closer. No? And I just think that camera manufacturers don't want to do much to overcome that tendency. In fact, the "35mm equivalent" talk promotes it to folks who don't know better.
« Last Edit: January 16, 2012, 03:24:53 PM by allegretto » Logged
Rob C
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« Reply #16 on: January 16, 2012, 03:31:52 PM »
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The "35mm equivalent" is extremely useful shorthand for figuring out that a 24mm is a wide angle lens on a full-frame camera but a normal lens (ish) on a Micro Four Thirds camera. Without that short-hand we'd have to know what the crop factor of each camera is (and we're back to square one), or be experts at every single camera system (crop factor) out there, which is not feasible.

I'm not aware of a better and more intuitive way to compare lenses and focal lengths of cameras across formats, especially the ones we don't use regularly.


I agree with that 100% and wonder why 'old' experience should be discarded just because some neophyte doesn't understand. I'm quite sure that, should mankind last that long, by the time nobody around ever worked with full 135 format, then the 'new' way of mental adjustments will happen at is own speed; now is not yet the time.

As for bringing cellphone optics into it - be real; they have different applications and are not likely ever to offer real interchangeable lenses; easier to buy several cellphones equipped with different focal lengths, if you just use a cellphone to do your shots. Now that would be a new market for the 'phone makers!

Rob C

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Walter Schulz
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« Reply #17 on: January 16, 2012, 03:34:55 PM »
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@allegretto: You lost me. Maybe it's because I'm not a native speaker but I'm not able to understand what your point is.

Have we reached common ground about your statement in the first post? Your conception about small sensor problems was wrong.

Ciao, Walter
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feppe
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« Reply #18 on: January 16, 2012, 03:36:21 PM »
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As for bringing cellphone optics into it - be real; they have different applications and are not likely ever to offer real interchangeable lenses; easier to buy several cellphones equipped with different focal lengths, if you just use a cellphone to do your shots. Now that would be a new market for the 'phone makers!

Rob, prepare to have your mind blown. It takes pro-grade pictures *wink wink nudge nudge*.
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allegretto
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« Reply #19 on: January 16, 2012, 04:45:23 PM »
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@allegretto: You lost me. Maybe it's because I'm not a native speaker but I'm not able to understand what your point is.

Have we reached common ground about your statement in the first post? Your conception about small sensor problems was wrong.

Ciao, Walter

Thank you Walter. I don't think I'm getting the proper point across and I'm trying to figure out the right way to phrase the question. I'm thinking about the optics and divergence of differing focal lengths.

How's this question;

Is a 4/3 with a 24mm lens merely a crop of the center of the same scene shot with a 24mm lens on a FF? Is it the "same" as a 48mm shot on a FF? Or is there a further consideration? A photo is a two-dimensional rendition of a three dimensional event (OK, let's leave M-theory and General Relativity out of it Wink).  as a Mercator projection introduces linear distortions of the relative sizes of the continents, is there another factor attributable to product? It seems a possible paradox to me that the perspective is unchanged when the field of view is changed. But that's why I'm here.

Is that question more clear?
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