4/3 system confusion

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danielisaiah

Active member
So I want to get some primes for my GH1....specifically some wide angle fish eye stuff. I have ordered a NIkon lens adapter because my wife has a host of Nikon lenses I can take advantage of.

I guess my question is the "doubling" factor of of the 4/3 system. Is it a true 2x conversion across the board? I ask because my wife has a Nikon 8mm fisheye that theoreticly should net me 16mm on the GH1...correct?
 
Here's what an 8mm fisheye (Peleng) looks like when used on the GH1:


That same lens results in a circular fisheye picture on 35mm film, but on the GH1 you'll see there's not even any vignetting, just some extreme barrel distortion wide-angle goodness.
 
Something I hadn't appreciated before is how great that wide angle looks for general use eg for the panoramic stuff rather than just the bizarro foreground distortions.
 
danielisaiah said:
So I want to get some primes for my GH1....specifically some wide angle fish eye stuff. I have ordered a NIkon lens adapter because my wife has a host of Nikon lenses I can take advantage of.

I guess my question is the "doubling" factor of of the 4/3 system. Is it a true 2x conversion across the board? I ask because my wife has a Nikon 8mm fisheye that theoreticly should net me 16mm on the GH1...correct?
Click to expand...

Yeah just to make it clear (I'm not sure it was from the thread), the "doubling" is due to the fact that the inner portion of the lens, on a standard 35mm equiv lens is cropped. With a fish eye lens, this means that you'll get a 16mm equiv, but you'll also be cropping some of the "fish eye" effect out of the image, because only the light hitting the center of the lens is also hitting the sensor, and the light from the edges, where the extreme distortion would occur, is not.

-kap
 
PhilD said:
My question to the techies is, why is this lens wider than the 14-140?

http://www.vimeo.com/5473689

Shouldn't it be equiv. to 20-44?
Click to expand...

It is equiv. to 20-44, but the GH1 kit lens is equiv. to 28-240.

So my Canon lens is actually 8mm wider than the kit lens, which makes for quite a bit difference!

All Canon / Panasonic / Lumix / Olympus / Nikon, etc. lenses (apart from those on fixed lenses on bridge cameras & compacts) have the 35mm focal lengths stated unless they have in brackets afterwards something like (35mm equiv.) like on the Fuji S100fd bridge camera.
 
The focal length of lenses is a constant, what differs is the field of view (FOV) depending on the size of the sensor chip / negative gate. From that follows that 10 mm is wider than 14, always.

All this blabber about "crop factor" or "XX mm equivalent" is just sales people too lazy to take a extra minute to explain some basic optical facts. And the misconception that 135 mm still photography field of view vs focal length is the golden standard that everything else is measured by.
 
I like to think of it as the lens creating a circular image, which hovers over the sensor. The round glass at the back of the lens projects the image over the sensor.

The projected image has to be big enough to cover the sensor otherwise you get the black borders and light fall off, like on the 16mm C Mount lenses.

In the case of the GH1 the image has to have a diameter of at least 22mm.

The wider the lens, the smaller the diameter of the projected image. The challenge for the lens manufacturers is to get a large projection from a very wide lens. That's why the 10-22mm Canon is for 1.6x crop EFS mounts and not the full frame 5D. However you get a wider image from a 16mm lens on a full frame camera as you do from a 1.6x smaller sensor, as the sensor covers a larger part of the projected image from the lens. So you wouldn't NEED a 10mm lens on a full frame camera to get a nice wide angle picture.

In real practical terms, it means the field of view is what the lens projects and how much the sensor sees of it.

That's where the equivalence (based on old 35mm film standards) comes in - to describe what kind of picture you'll get from the lens on your sensor size.

So for the GH1 it's x2 whatever the focal length stated on the lens is, because the sensor is 2x smaller than 35mm film, thus covers half of the projected image from the lens.
 
Martti Ekstrand said:
The focal length of lenses is a constant, what differs is the field of view (FOV) depending on the size of the sensor chip / negative gate. From that follows that 10 mm is wider than 14, always.
Click to expand...

I think I've finally got my head around the crop factor.

So, if you were to look through a GH1 with a 28mm lens and a 35mm camera with a 28mm lens, things would look exactly the same distance away (focal length constant). However, the image wouldn't be as wide on the GH1, you wouldn't be able to see as much of the periphery (FOV).

True?

Edit: One last thing that's confusing me. Are the micro 4/3 lenses the same? Are the focal length and FOV of the GH1 kit lens the same as attaching a 14-140mm 4/3 lens to the GH1?
 
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The difference between 4/3 and m4/3 are that there are no mirrors in the m4/3 cameras. Lenses is the same and sensor share roughly the same size.
 
Lenses are lenses are lenses. The main differences are if they can mount onto the system, and if they project an imaging circle big enough to cover the imager/film.
 
Fluke said:
I think I've finally got my head around the crop factor.

So, if you were to look through a GH1 with a 28mm lens and a 35mm camera with a 28mm lens, things would look exactly the same distance away (focal length constant). However, the image wouldn't be as wide on the GH1, you wouldn't be able to see as much of the periphery (FOV).

True?
Click to expand...
No. Only slightly true, and that's going to make things more confusing.

The PERSPECTIVE is going to be the same, so the difference between the subject and the background would look the same. But the image magnification would be different.

Imagine that you put a 28mm lens on a 35mm camera, and took a picture. Now, if you want to know what the GH1 would look like from that same position with that same lens, get out a pair of scissors and cut off the top, bottom, left and right sides, leaving the central 1/2 of the image.

That's what you'll get.


Edit: One last thing that's confusing me. Are the micro 4/3 lenses the same? Are the focal length and FOV of the GH1 kit lens the same as attaching a 14-140mm 4/3 lens to the GH1?
Click to expand...
Yes, identical. The difference between 4/3 and m4/3 is only in that the m4/3 doesn't use a mirror, so the backfocus is engineered differently, but the lenses are identical. You can get a simple 4/3 to m4/3 adapter and use all 4/3 lenses exactly as if they were m4/3 lenses.
 
So on the GH1 the kit is actually giving you a 28-280 35mm equivelant FOV? That would seem right to me...my Nikon 50mm and the kit lens @ 50mm both look about the same (in terms of FOV.)

Hey so how does this relate to the crop factor of say, an HVX using a 35mm adapter (assuming your zoomed out of it as far as you can and still have the image fill the screen?)
 
A millimeter is a millimeter. A 50mm Nikon mounted on the GH1 will look exactly the same as the stock lens zoomed to 50mm.

It's just that the 35mm still camera "sees more" around it.

And an HVX with an adapter -- that depends on the adapter. The Brevis and Letus can deliver a 1.0 crop if you want. But normally you want to emulate the movie frame size, which is a lot closer to the GH1 frame size than to the still camera size, so normally you'd want to be zoomed in some on the ground glass of the adapter.
 
Look at this chart. The picture represents a full 35mm frame. The black box represents APS-C and the red box represents the Gh1. Inside of each box is what you'll capture if you use the same lens on 3 different camera's. You focal distance stays the same, but your field of view is cropped.

Chart.jpg
 
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