question abt the 4/3 system


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uginz

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in the 4/3 system, the focal lengths are all halved. so does this mean that images' sizes are also halved compared to normal 35mm cameras? if this is so, then 8MP would effectively become 4mp?

or is this the other way ard? :dunno: :think:
 

chancy

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Hello Uginz,

You will find official information on the 4/3 system here.

At the risk of reproducing what's already stated and only to summarise, a quick answer to your question would be

1) No change in focal length (FL) at all. "The focal length of a lens is defined as the distance in mm from the optical center of the lens to the focal point, which is located on the sensor or film if the image is "in focus" as defined Vincent Bockaert in an article on Dpreview. It is the same regardless of sensor size or camera system.

2) The only variable is the sensor size. Since dimensions of the most common imaging format is based on the 35mm format introduced by Leica. The 4/3 standard defines a lens mount specificiation that covers a sensor that's approx half the length & height dimensions of a 35mm format sensor (ie. a quarter for the surface/imaging area).

For a lens of given focal length relative to the 35mm standard, 4/3 standard image captures half the field of view of the former. Since most people are familiar with the angle of view of 35mm lens system, the equivalent field of view for a 4/3 lens translates loosely to a lens with twice the focal length of a 35mm system. eg. a 4/3 system 11mm lens gives the same field of view as a 22mm lens on a 35mm camera. It's either a half or a double depending on which system you're basing the sensor format on.

3) Sensor resolution is independent of sensor size although it becomes technically difficult to increase sensor resolution for smaller sensor sizes. Sensor resolution is variable for a given sensor size. Sensor resolution is not the sole criteria for image quality though. So a 8MB 4/3 sensor contains 8 million sensor elements, a 8MB 35mm full frame sensor contains the same number of elements.

Hope this clarifies more than confuses :) You seem to be looking for underwater photography gear, you will find Oly wide angle lenses for the E system to perform admirably underwater if only someone figures out how to rotate the zoom ring and waterproof their better flashes ;-)

Cheers,
 

uginz

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ok thanks..
so am i correct to say that using a 4/3 camera would focus at the same distance and produce an image of the same size compared with a normal 35mm one.

and this is due the smaller size of the sensor hence being place abt half the distance from the lens to obtain the same image field of view compared to the 35mm one?

hope i'm right....



yeah, i'm looking to upgrade my cam for UW photok. dunno abt the zoom ring but i guess is doable coz 3rd party manufacturers figured out a way to this on their housings. lighting issues are solved with UW strobes which are much stronger.
 

serene

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Hi,

From a greenbie understanding. Have you ever try to enlarge a projected image on the wall (for eg at a presentation) by moving the projector further away? By moving the projector further from the screen, we are increasing the focal length (ie, longer lens) and if we want a smaller image, we move the projector nearer to the screen. This is my intuitive understanding. Chancy, nightpiper and other experts, please correct me if I am wrong. Thanks :)
 

uginz

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serene said:
Hi,

From a greenbie understanding. Have you ever try to enlarge a projected image on the wall (for eg at a presentation) by moving the projector further away? By moving the projector further from the screen, we are increasing the focal length (ie, longer lens) and if we want a smaller image, we move the projector nearer to the screen. This is my intuitive understanding. Chancy, nightpiper and other experts, please correct me if I am wrong. Thanks :)
so in this case, the screen is the sensor, and the transparency is the object right?
 

nightpiper

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uginz said:
ok thanks..
so am i correct to say that using a 4/3 camera would focus at the same distance and produce an image of the same size compared with a normal 35mm one.

and this is due the smaller size of the sensor hence being place abt half the distance from the lens to obtain the same image field of view compared to the 35mm one?

4:3 format is 2x smaller than 35mm in terms of surface area. i dun think the 8MP will become a 4MP. its simply using 8MP to represent an image. this is where people were arguing about MP density. if the lens is hi rez enuf to capture every detail, the 8MP FF will show the same amount of detail as the smaller 8MP sensor (assuming the object size has been adjusted to have the same FOV). whether the details is intelligible is dependent on the noise management of the camera. so far DSLRs r very good in this area compared to digi compacts.

i dun see any significant diff between 20D 1.6x crop 8MP with the E300 2x 8MP crop. the only diff is the noise & aspect ratio. both will deliver the same amount of details. just look at the comparison between E1(5MP) & D100/10D & u will know what i mean.

as to why 4:3 aspect ratio? well, thats the same thing u see on your TV. :bsmilie: but seriously, its simply becos of more printing sizes r in 4:3, so u dun waste the image of the 2 sides.

lastly, im no expert. so dun take me seriously. ;p
 

chancy

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Allow me to disagree with:

1) The diagram by uginz
2) The slide projector analogy by serene

For uginz's diagram, I'm inclined to believe that the 4/3's sensor lies in the same plane at the 35mm sensor rather than ahead. This is consistent with the focal length definition. More importantly, it shows the commonly referred 'crop factor' as the smaller 4/3's sensor grabs only a portion of the image received by the 35mm sensor. This partial image can be perceived as a magnified effect or similar to using a lens of a 35mm system that has a longer focal length.

By throwing away the convergent rays at the periphery & capturing the more linear incident rays in the image circle of the 4/3 sensor, a higher quality digital image with good peripheral sharpness is obtained.

If we consider uginz's diagram, the FULL image will be capture by the 4/3 sensor as well well the 35mm sensor. Both will have the same angle of view for each focal length which is not the way the 4/3 system is positioned.

Same for the erhm slide projector analogy, the projection screen which represents the sensor is a fixed distance from the projector, it's a matter of using screens of different sizes but same distance from the projector ... however after that stage with the screen moving, the analogy breaks down, robbing me some sleep figuring what each stage represents :)

To draw a slide projector parallel (maybe), Contax had a film SLR model AX which moves the entire film assembly backwards & forwards to bring autofocus capability to its fine line of manual focus Zeiss lenses, in no way does the focal length of their lenses change except put extra macro (close focus) capability to them.

Hope this clarifies ... somewhat.
 

chancy

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... just to post a correction ... for the projector analogy, I meant moving the projector rather than the screen. The Contax AX example is analogous to moving the screen though. My apologies Serene.
 

uginz

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hmm... the diagram's wrong..?

tot was correct based on the definiton of FL.
distance from lens to film or sensor. hence explaining the 4/3 system's equivalent ratio of 0.5 that of film.

for film, the lens has to be twice as far away as compared to 4/3 sensor to capture the same image size as the 4/3 system. :think:

if both the film's and sensor were at the same distance, the 4/3 sensor will actually only capture half of what the film sees.

so, in order to make it such that both sensor and film will "see" the same image, the sensor as to move closer to the lens.
 

serene

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chancy said:
... just to post a correction ... for the projector analogy, I meant moving the projector rather than the screen. The Contax AX example is analogous to moving the screen though. My apologies Serene.
Hi Chancy

My intuitive thinking here indicates that the screen is a point when the image and the sensor meets. When we move the projector away, we get a bigger image (ie. the 2/3 sensor) and if we move the projector nearer, we get a smaller image (ie. 4/3). There is no measurement here, just an idea of the relationship between the focal length and the size of the sensor (ie, the 2/3 vs 4/3)

Thanks again
 

nightpiper

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uginz said:
if both the film's and sensor were at the same distance, the 4/3 sensor will actually only capture half of what the film sees.

so, in order to make it such that both sensor and film will "see" the same image, the sensor as to move closer to the lens.

yep, the 4/3 will capture only half the image. well, not exactly half in reality, its abit more than half.

as to how both media 'see' the same image size (FOV), the 4/3 uses a 14mm to have the same FOV as a 28mm on film. u can see that u change the focal length & not the distant of the sensors. with a diff FOV from diff sensor size (1.5x nikon, 1.6x canon, 1.3x canon, 1.7x sigma, 2x Oly, etc), there introduce a diff kind of debate, the DOF of diff sensor sizes with the same FL lens.

well, that will leave it to another thread for discussion. :)
 

chancy

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Hello Uginz,

Let me repeat the FL definition of a lens that has a subject in focus as "The focal length of a lens is defined as the distance in mm from the optical center of the lens to the focal point, which is located on the sensor or film if the image is "in focus".

Putting my earlier explanation aside and considering your diagram and the FL definition. Let's use a normal 50mm lens (35mm system) as example. When mounted on a 35mm system camera, the focal length is measured as 50mm from optical centre to the point when the image is focused on the film plane.

Well, let's mount this 50mm lens on a 4/3 system camera. From your diagram, am I correct to say that the 4/3 sensor needs to be closer to the optical centre of the lens to get the same image and if so, should the FL naturally be reduced ? Now that means that the 50mm lens (35mm system) now has an FL of less than 50mm (4/3 system). But the FL of the lens is suppose to be equivalent to one twice as much not half as many. ie. suppose to get a telephoto effect (FL increase) nor a wide angle effect (FL reduction).

An example in reality, I have an Olympus MA1 adapter, which is functionally similar to the Kindai adapter Nightpiper is getting except that it allows me to reuse my manual OM lenses instead of Nikon lenses. When I mount my OM standard 50mm lens on my E1 (4/3 system), I don't see the same coverage as that on my OM4Ti. It's a telephoto effect I see, not a wide angle effect. The E1 takes only the centre quarter of my OM lens and by magnifying it, it gives my 50mm lens a field of view equivalent to a 100mm lens.

If I repeat what I originally said by quoting your words "if both the film's and sensor were at the same distance, the 4/3 sensor will actually only capture half of what the film sees". This is actually what's happening. But just consider that in this case besides capturing less, it magnifies/enlarges the 'cropped' portion in the viewfinder. This is the same as telephoto effect.

When you read Olympus's product literature, they position their 50-200mm & their 300mm Digital Zuiko's as lightweight competitors to 35mm system of 100-400mm & 600mm equivalents (field of view). These suggests that focal length is doubled not halved and the imaging effect is a telephoto one.

If the goal of Olympus for their 4/3 system is to maintain the same image area as 35mm system as you suggest, the 50-200mm & the 300mm would not be offered as their double FL equivalents.

I'm not good at coming out with good examples, hope this serves its purpose.

Cheers,
 

uginz

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ok. i think i got it.

to summerize,
given that both the film and sensor are at the same position,
and the same object at the same distance is in focus,
the image seen by the sensor is actually equilavent to that seen by the film if the film system had a 2x telephoto enhancement.

so if a the focal lenght of the sensor is 54mm, the equivalent image on the film would result if the the film system used a 104mm lens.
 

chancy

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Hello Uginz,

Yes, you are absolutely correct :)

This concept is not new & the best way is to see it in relative terms. In the age of films, many format exists. Small (35mm), medium (645, 6x6, 6x7, 6x9) & large formats (4x5", 8x10") cameras follow the same concept. Mount an 80mm lens on a Mamiya, Hasselblad and you get a field of view of a normal lens, mount a lens that's FL 80mm on a 35mm system & you'll get a mild telephoto lens that's good for portraiture.

With the progress of technology, the variety of film format that has resulted for economic and aesthetic reasons has progressed to digital sensor format.

And the most important concepts are the terms 'relative', 'equivalent', and 'field/angle of view'. Actually, the notion of FL should be dropped because of the variety in sensor/film size, but these terms are retained because it's very commonly used. It's rare to hear people speak of the 50mm lens giving an angle of view of 47° on a 35mm film camera and an 81° on a 6×6 film camera. But doing so helps to clarify concepts better.

As a factiod which I'm sure you've heard about it, the 4/3 system is like a phoenix of the old Pen F series of half frame film cameras unsuccessfully marketed by Olympus in the 70s. It's half the size of regular 35mm film but of different aspect ratio. Once more the same concept applies.

Cheers,
 

chancy

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Hello Serene,

If you take the projector analogy to a camera system, just bear the following in mind.

1) The projector's position is fixed.
2) The projected image to the projector must be fixed.
3) If you use a screen that captures the full slide image as denominator (eg 35mm system), then the 4/3 system would be equivalent switching to a screen that's half the size of the former. Yes the entire image will be still be projected, but the 4/3 screen will only take in the central half of that image.

Hope this finally addresses Uginz & your views on this thread.

Cheers,
 

uginz

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oly pro site on 4/3 FL

the site says dat the sensor is moved closer to the lens to achive the 4/3 system FL contrary to what was previously agreed on.

actually i think both are correct, coz if i remember my physics classes correctly, the light paths are reverisble.
 

kahheng

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#18
chancy said:
Hello Serene,

If you take the projector analogy to a camera system, just bear the following in mind.

1) The projector's position is fixed.
2) The projected image to the projector must be fixed.
3) If you use a screen that captures the full slide image as denominator (eg 35mm system), then the 4/3 system would be equivalent switching to a screen that's half the size of the former. Yes the entire image will be still be projected, but the 4/3 screen will only take in the central half of that image.

Hope this finally addresses Uginz & your views on this thread.

Cheers,
Actually, the 4/3 'screen' will be a little over 1/4 the size in area terms of the 35mm 'screen'. If you use the fixed 'projector' distance way of describing it.



The previous link mentioned has a good explanation of how focal length is determined, and thence, using a standard lens as a reference, how the angle of view 'equivalents' is determined, vis a viz the other imager/film formats.



http://www.olympus-pro.com/index.eu.en.html?content=/eu/en/product/lenses/focallength.html

The key thing is that the 'imager' to flange distance is a LOT shorter in the 4/3 system compared to many 35mm SLR type film cameras.
 

chancy

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Hello Kah Heng & Uginz,

After checking out your references & subsequent comments, I must admit error of reasoning on my part by putting the imager & film in the same plane. Apologies for causing earlier confusion.

To clarify my thoughts further, can I say than the 4/3 standard uses the 25mm lens to base the imager to flange distance. And any FL greater or less than this normal FL uses lens designs to maintain this imager to flange distance ?

My second question concerns the image circle. Do 4/3 native lenses (ie. Digital Zuikos) project the entire subject image into the image circle and onto the sensor, or is does portion the picture spill to outside the image circle but is discarded.

Glad to have your views on this.

Thanks Uginz for locating the Olympus link, appreciated :)
 

kahheng

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#20
chancy said:
Hello Kah Heng & Uginz,

After checking out your references & subsequent comments, I must admit error of reasoning on my part by putting the imager & film in the same plane. Apologies for causing earlier confusion.

To clarify my thoughts further, can I say than the 4/3 standard uses the 25mm lens to base the imager to flange distance. And any FL greater or less than this normal FL uses lens designs to maintain this imager to flange distance ?

My second question concerns the image circle. Do 4/3 native lenses (ie. Digital Zuikos) project the entire subject image into the image circle and onto the sensor, or is does portion the picture spill to outside the image circle but is discarded.

Glad to have your views on this.

Thanks Uginz for locating the Olympus link, appreciated :)
1. "can I say than the 4/3 standard uses the 25mm lens to base the imager to flange distance. And any FL greater or less than this normal FL uses lens designs to maintain this imager to flange distance?"

No


2. "My second question concerns the image circle. Do 4/3 native lenses (ie. Digital Zuikos) project the entire subject image into the image circle and onto the sensor, or is does portion the picture spill to outside the image circle but is discarded."

Whilst the 4/3 design aim is for the rays exiting the rear pupil to be as telecentric as possible, in actual practice, it still is a matter of degree as to how much the rays hitting the edge of the imager is perpendicular to the sensor. Some rays hitting the edge of the sensor would not be perfectly 90 degrees but they'd be already much more telecentric than conventional film SLR lenses.

Is there 'spillage' (your term)? Inevitably there'll be some, as is true of all types of lenses, but you'd have to go ask Olympus exactly how much with each lens.

You can always write them and ask them. They may not want to tell you the actual answer of course :D

Always remember that an excessively large image circle relative to the size of the imager/film would give rise to unwanted internal reflections. I think you can be sure that the 4/3 lenses from Oly would be designed with this problem in mind.
 

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