Distortion and Distance between the Subject and the Background in MFT system

John King

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To put this very simply, perspective depends on the relative angle of view (AoV).

The AoV for a given focal length is a function of the crop factor, so a 25mm FL lens on a micro four thirds camera has (sort of, more or less, approximately) the same AoV as a 50mm lens on a 35mm camera. There will be a slight difference due to different aspect ratios - 4:3 vs. 3:2.

What is far more important to understand is that apparent DoF is a function of the ratio of camera to subject vs subject to background.

With this latter, different lenses with the same AoV will perform differently due to differences in optical design.
 

pranavanarp

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To put this very simply, perspective depends on the relative angle of view (AoV).

The AoV for a given focal length is a function of the crop factor, so a 25mm FL lens on a micro four thirds camera has (sort of, more or less, approximately) the same AoV as a 50mm lens on a 35mm camera. There will be a slight difference due to different aspect ratios - 4:3 vs. 3:2.

What is far more important to understand is that apparent DoF is a function of the ratio of camera to subject vs subject to background.

With this latter, different lenses with the same AoV will perform differently due to differences in optical design.
Thanks for this John King. This is something I can look up more on, these concepts are fairly new to me but I am getting a sense of it. Thanks!
 

RAH

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Thanks for this John King. This is something I can look up more on, these concepts are fairly new to me but I am getting a sense of it. Thanks!
One other tip about using this forum that took me years to realize - if you want to address someone by name, as you did with John King, if you want them to get a notice that you said something directly to them, you put an @ in front of their name. When you do this, as you type a window pops up and you can choose exactly who you mean. So, for example, if I wanted to say something to him, I'd do this: Hey, @John King , you are soooo smart! (this, of course, is not something he would ordinarily hear... :dance3: ).
 

PakkyT

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To put this very simply, perspective depends on the relative angle of view (AoV).
Sorry, have to correct this line. Perspective depends only on your position from what you are shooting. It is independent from focal length and therefore independent of different AoVs from changing the focal length. Stand in one spot without moving and you can shoot at 12mm, 50mm, 100mm, etc, and all of the shots will share the same perspective.
 

ac12

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One another concern I had regarding similar topic was the argument that Full Frame users have over mft lenses that a 1.4 advertised lens for a mft body is actually 2.8. Now, with my limited understanding, that makes me feel that a 2.8 aperture would also affect the exposure meaning that the 1.4 lens of the mft actually allows light equivalent to a 2.8 lens of a full frame. But I looked over the internet and that seems to be wrong, the difference in aperture does not affect the exposure but only the 'bokeh' effect. Is this a correct understanding?

The f/stop is a result of a formula; focal length of lens / diameter of the aperture = f/stop
100mm lens / 50mm aperture = f/2
There is nothing in the formula about sensor/film format.

So, f/4 is f/4 no matter the format of the sensor/film, be it m4/3 or 11x14 inches.
If I put a FF 200mm lens with an f/4 aperture on a m4/3 camera, the lens is still a 200mm lens with an f/4 aperture. The lens does not change when it is put onto a different sensor camera.
In general I can use the SAME exposure on my 4x5 camera and on my m4/3 camera and get a similar exposure.

So, anyone telling you that your 25/2 m4/3 lens is actually a f/4 lens does not know what they are talking about.
Or as is usually the case, they are not telling you all the parameters of their statement. IOW you only got a slice of the answer.


From my point of view, besides exposure, the aperture primarily affects depth of field (DoF). Or what is in acceptable focus.
The larger the aperture (like f/2) , the shallower the DoF, so the sooner the objects go out of focus, as it gets further from the plane of focus.
The smaller the aperture (like f/8), the deeper the DoF, so the further from the plane of focus, before the objects go out of focus.

And this is tied to both the focal length of the lens and to a lesser degree the sensor/film format.
f/4 on a short lens like a 25mm, will always have a greater DoF than f/4 on a longer lens like a 50mm. So on the longer lens, you will always need a smaller aperture to give you a similar DoF to a shorter lens.
If you are curious, there are online DoF calculators that you can play with to see this.
But it does not have m4/3 as one of it's format/camera options. You may find another online DoF calculator that does have m4/3 as an option.​

I think the bokeh you are referring to is conceptually the reverse of DoF. The degree that the image is OUT of focus.
The further the object is from the plane of focus, the more out of focus/blurry the objects are.
So if you want more blur, increase the distance between the subject and background.

Bokeh as I understand it's general use, is how the optics of the lens displays the out of focus image.
As I said, this is of no interest to me, so I have not gotten into it.
 
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John King

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Sorry, have to correct this line. Perspective depends only on your position from what you are shooting. It is independent from focal length and therefore independent of different AoVs from changing the focal length. Stand in one spot without moving and you can shoot at 12mm, 50mm, 100mm, etc, and all of the shots will share the same perspective.
I agree Patrick. I really meant AoV and distance to frame tge subject in a similar way. @ralf-11 Ralf's reference covers what I meant.
 

PakkyT

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Ralf's reference covers what I meant.
Right, the article covers both concepts. Perspective is determined by camera to subject distance (what i said) and what I think you were alluding that then using a wide angle on a close up shot or a telephoto on a distance shot helps to exaggerate the effect to the viewer. Frog protection!

{edited to add link for those (outside the USA) who may not get the Frog protection reference}
 
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John King

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Right, the article covers both concepts. Perspective is determined by camera to subject distance (what i said) and what I think you were alluding that then using a wide angle on a close up shot or a telephoto on a distance shot helps to exaggerate the effect to the viewer. Frog protection!
Patrick, I'm still not really thinking straight after Lizzie's death. We both knew that she had pretty serious health problems, and coped with them. However, when the day finally arrives, one is never really prepared for it.

I wouldn't say that Rosa is outwardly distressed, but her behaviour has changed, and she is well aware of her sister's absence, even though not looking for her.

We are still in that numb phase. We have had them both for over half our married life! Rosa is demanding lots of attention. All night ...
 

ralf-11

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Hello all,

This is my first post here at Mu4/3 and this feels quite exciting! I own a Gh5s and I am slowly starting to love this whole realm of M4/3. I upgraded from Canon 600d which is a aps-c camera so this whole eco system of M4/3 is quite new to me.

I am trying to learn as much as possible about this new system and there are always some questions whose answers are difficult to find on the internet maybe because I can't articulate some topics quite well. So, I will give it a try here:

I have two questions. First, regarding focal lengths. I have learned that a 25mm in mft is equivalent to a 50mm in full frame. I also came to know that if you're a 'bokeh freak' it's better to have full frame but that's not much of a concern for me. My question is related to the distortion you get on portrait faces when they are taken from different focal lengths. For instance, on a full frame body, the 85mm portrait has a more natural shape to the human face, when say compared to a 35mm. So, if I want to get that same look with the minimum distortion as that of 85mm on a full frame, will the 42.5mm focal length work for me for my Gh5s or do I actually need a 85mm lens to have that same exact look like a full frame body?

Second question is related to the difference in distance produced when different focal lengths are used (I don't know the exact term for it). For instance, say in a 50mm lens on a full frame body the background is much further than the same picture on a 85mm body. So bringing this equation to my mft system, to get the same distance as that of 50mm on a full frame body, will my 25mm do the same thing, or will the 25mm on my camera push the background much further than the actual 50mm on a full frame? I hope my question makes sense.

Also, it would be really helpful if you could post some links to pictures doing these comparisons.

Thank you!


back to the OP's question

There are several things involved. The simple answer is to get a short tele lens for portraits. 1. For m43 that means about a 45mm.

But other things count too:

2. a fast lens (like f/1.2 instead of f/2.8) - this allows you to blur the background
3. getting the subject away from a background (which should be suitably chosen too) - e.g. backing up a cute young barista against the brick wall on her building isn't best - put the subject a few feet away
4. lighting (!!) northern light is best and mood can be induced by putting the model near a north facing window
5. some lenses (and bodies) work particularly well to give a sort of 3D pop, a glow, etc. - that may mean buying or renting a Leica M system; maybe with an old lens or lens design

- Oly makes 3 Pro m43 lenses specifically designed to have not just smooth bokeh but smooth bokeh transitions

the last 2 items obviously involve $$$
 

pranavanarp

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back to the OP's question

There are several things involved. The simple answer is to get a short tele lens for portraits. 1. For m43 that means about a 45mm.

But other things count too:

2. a fast lens (like f/1.2 instead of f/2.8) - this allows you to blur the background
3. getting the subject away from a background (which should be suitably chosen too) - e.g. backing up a cute young barista against the brick wall on her building isn't best - put the subject a few feet away
4. lighting (!!) northern light is best and mood can be induced by putting the model near a north facing window
5. some lenses (and bodies) work particularly well to give a sort of 3D pop, a glow, etc. - that may mean buying or renting a Leica M system; maybe with an old lens or lens design

- Oly makes 3 Pro m43 lenses specifically designed to have not just smooth bokeh but smooth bokeh transitions

the last 2 items obviously involve $$$
Thanks for your thorough answer @ralf-11
also thanks for the tagging tip @RAH
 

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