Question on minimum focus distance for m4/3 system

[Alan Ang]

hi, i have a question on the minumum focus distance for lenses adapted to be used on m4/3 bodies.

as i understand, the focal length of lenses adapted to be used on m4/3 bodies are doubled... however, what i would like to know is if the minimum focus distance to object is also doubled?

can anyone help shed light on this?
thanks in advance.

 

[monza]

Minimum focus distance remains the same.

 

[photoSmart42]

as i understand, the focal length of lenses adapted to be used on m4/3 bodies are doubled... however, what i would like to know is if the minimum focus distance to object is also doubled?

The lenses stay the same, including the focal length and focusing distance. What you're seeing is a cropping of the image that comes from the lens by half of the field of view because it's a smaller sensor, so you're only seeing the middle portion of the image.

 

[Alan Ang]

thank you both for the answers. this ends the argument that i am currently having with a colleague of mine...

 

[pellicle]

just to clear something up, while the focal length remains the same, because you are taking only the center portion and magnifying it the lens does not behave as you may expect. If you think of a 24mm as being wide, a 50mm as being normal and a 90 as being mild tele; you will be surprised.

So "effectively" the focal lengths are doubled.

as mentioned the focal distance remains the same ... and of course extension tubes will allow you to focus closer

 

[laptoprob]

you will be surprised.

Perspective behaviour depends on subject distance only, not on focal length.
So the 20mm Panny is a true standard lens on the m4/3 format, not a wide angle like a 20mm on 'full frame' 35mm film.

 

[pellicle]

Perspective behaviour depends on subject distance only, not on focal length.

it would be nice if you quoted me in a meaningful way. Please identify where I mentioned perspective?

I think I understand this issue well enough, I even wrote this post to help out people who were confused:

http://cjeastwd.blogspot.com/2010/02/focal-length-angle-of-view-aperture-and.html

People are often ill experienced with hopping between formats, often using 35mm as their only frame of reference. Thus somehow a 24mm is equated as a wide, while it is not a wide on 4/3 format. The same with a 90mm, which is a wide on my 4x5 but is not a wide on 35mm

none of this has anything at all to do with perspective (which is why I did not mention it as you seem to imply I did with your quote of my "you will be surprised")

To clarify what I wrote, if you're used to using the numbers of focal length to assist you in translating:
* very wide
* wide
* normal
* telephoto

then when you put that on a 4/3 camera expecting to see the same thing, then you will be surprised

as you say:

So the 20mm Panny is a true standard lens on the m4/3 format, not a wide angle like a 20mm on 'full frame' 35mm film.

so I have no idea why you mention perspective in your start and then do nothing to discuss it.

 

[Alan Ang]

just to clear something up, while the focal length remains the same, because you are taking only the center portion and magnifying it the lens does not behave as you may expect. If you think of a 24mm as being wide, a 50mm as being normal and a 90 as being mild tele; you will be surprised.

So "effectively" the focal lengths are doubled.

as mentioned the focal distance remains the same ... and of course extension tubes will allow you to focus closer

i think i sort of understand what you are trying to say already... noted with thanks.

 

[laptoprob]

then when you put that on a 4/3 camera expecting to see the same thing,

Many people expect just that. I was puzzled myself at first until I realized the distance thing. So I just added that to the other meaningful remarks.
I wasn't suggesting I was surprised by your post or something like that, I just wanted to quote the surprise part.

Sorry if I hurt your feelings.

 

[pellicle]

Many people expect just that.

which is of course why there is all the discussion about effective focal length.

it is quite close to the approximation of twice the effective focal length when used on a 4/3 camera and the DoF is approximately that of 2 stops smaller aperture, though clearly the light is not 2 stops darker.

http://cjeastwd.blogspot.com/2010/03/43rds-dof.html

I was puzzled myself at first until I realized the distance thing.

the distance remains the same ... could you explain what you mean here?

 

[laptoprob]

Well, that distance governs perspective behaviour. And that a telephoto lens behaves like one only compared to subject distance, because a wideangle will give the same perspective when used from the same distance, as you showed on your blog.

 

[Godfrey]

Perhaps this will help de-mystify things:

- Focal length is an optical property of a lens. It is the distance from the primary nodal point to the imaging plane with the lens focused to infinity. Has nothing to do with a format, with a field of view, or with perspective.

- Field of View is the result of combining a particular focal length with a particular format, presuming the lens' image circle is larger than the format. 35mm Film has a format size of 24x36mm, FourThirds cameras have a format size of 13x17.3mm. Since the diagonal of 35mm Film format is roughly twice the length of the diagonal of FourThirds format, the same focal length lens fitted to FourThirds presents a Field of View which is cut in half by comparison. This is what makes a 50mm lens fitted to a FourThirds camera seem to look like a 100mm lens fitted to a 35mm Film camera.

- Perspective is the relationship of the apparent relative size of objects in a scene. It is governed entirely by the distances from the camera to the objects in the scene. Neither focal length nor field of view directly influence perspective ... the field of view defined by a focal length and format simply allow more or less of the scene to be apparent in an image capture.

So, an example:

If you put a 50mm lens on a 35mm Film camera and frame a scene, you establish a "reference scene" with a particular field of view and perspective.

Fitting the same 50mm lens on a FourThirds camera you will see a scene which has one quarter the area (1/2 the angle of view in both horizontal and vertical dimensions) that has the same perspective as the reference scene. If you move the FourThirds camera back far enough to include the reference scene, you will change the perspective due to the change in distance.

If you change the lens on the FourThirds camera to have a focal length of 25mm instead of 50mm and position the camera in the same place as before with the 35mm Film camera, you will reproduce the reference scene, with the same perspective.

In any case, the other optical characteristics of a particular lens, like the focusing distance range made possible by its lens mount and the amount of light gathering power it is capable of made possible by its aperture, do not change. They are invariant across the formats a lens' image circle can cover.