GH2 Variable Aspect Ratio

Started Apr 23, 2012 | Discussions
Vlad S
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75 degrees
In reply to Jimbo70, Apr 23, 2012

Jimbo70 wrote:

I guess my question should have been; is the angle of view 75 degrees when the camera is in the native 4-3 ratio or 75 degrees in 16-9 ratio?

75 degrees is the diagonal angle of view. In the GH cameras it does not change with the aspect ratio because all of the aspect ratios fill in the same circle 21.58mm in diameter: you loose a little vertically, but you gain a little horizontally at the same time.

You see more on the sides because the horizontal angle of view of a 14mm lens on the micro 4/3 sensor is 63 degrees in 4:3, and 68 degrees in 16:9.

For comparison, the diagonal angle of view of a 28mm lens and FF sensor is also 75 degrees, but the horizontal AoV is 65.5 degrees, which is wider than 4:3 and narrower than 16:9 on the ยต4/3 sensor, as expected.

Vlad

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Jimbo70
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Re: 75 degrees
In reply to Vlad S, Apr 23, 2012

Vlad S wrote:

Jimbo70 wrote:

I guess my question should have been; is the angle of view 75 degrees when the camera is in the native 4-3 ratio or 75 degrees in 16-9 ratio?

75 degrees is the diagonal angle of view. In the GH cameras it does not change with the aspect ratio because all of the aspect ratios fill in the same circle 21.58mm in diameter: you loose a little vertically, but you gain a little horizontally at the same time.

You see more on the sides because the horizontal angle of view of a 14mm lens on the micro 4/3 sensor is 63 degrees in 4:3, and 68 degrees in 16:9.

For comparison, the diagonal angle of view of a 28mm lens and FF sensor is also 75 degrees, but the horizontal AoV is 65.5 degrees, which is wider than 4:3 and narrower than 16:9 on the ยต4/3 sensor, as expected.

Vlad

Thank you, I didn't realize such an innocent question could cause such a discussion.

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Detail Man
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The Angle of the Dangle is inversely proportional to the Heat of the ...
In reply to Jimbo70, Apr 23, 2012

Jimbo70 wrote:

Vlad S wrote:

Jimbo70 wrote:

I guess my question should have been; is the angle of view 75 degrees when the camera is in the native 4-3 ratio or 75 degrees in 16-9 ratio?

75 degrees is the diagonal angle of view. In the GH cameras it does not change with the aspect ratio because all of the aspect ratios fill in the same circle 21.58mm in diameter: you loose a little vertically, but you gain a little horizontally at the same time.

You see more on the sides because the horizontal angle of view of a 14mm lens on the micro 4/3 sensor is 63 degrees in 4:3, and 68 degrees in 16:9.

For comparison, the diagonal angle of view of a 28mm lens and FF sensor is also 75 degrees, but the horizontal AoV is 65.5 degrees, which is wider than 4:3 and narrower than 16:9 on the ยต4/3 sensor, as expected.

Vlad

Thank you, I didn't realize such an innocent question could cause such a discussion.

Why not submit any questions you may have surrounding "Depth of Field" for a real imbroglio ...

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Mike Ronesia
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Re: Here are your angles
In reply to Adventsam, Apr 24, 2012

Adventsam wrote:

14mm in 16:9 is 25mm
7mm in 16:9 is 12.5mm

Horizontal FOV!

So what does 12.5 correlate to in horizontal degrees? A square room would be 90 degrees between walls when in the corner. The fish eye states 180 degrees but I don't know if they are talking corner to corner or if if it means 180 degrees as in half a circle.
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Detail Man
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Re: Corrected: GH2 Image Sensor Diagonal and Horizontal Crop Factors
In reply to Steen Bay, Apr 24, 2012

Steen Bay wrote:

Detail Man wrote:

Shouldn't it also be taken into account that the effective diagonal of the FF sensor is reduced when the native 3:2 FF image is cropped to 4:3 and 16:9? I'd say that both the diagonal and horizontal crop factor is 2.0x when shooting 3:2 images with the GH2, and less than 2.0x when shooting 4:3 and 16:9 images, because the multi-aspect ratio GH2 sensor uses the full image circle with all three aspect ratios, whereas the FF sensor only uses the full image circle when shooting 3:2 images.

All Diagonal Crop Factors :
4:3 - Crop Factor = 2.069320
3:2 - Crop Factor = 2.087004
16:9 - Crop Factor = 2.087553

So, none of them are exactly 28mm, all of them are a little bit "narrower" than 28mm (in terms of the Field of View), and the 4:3 aspect-ratio mode is the "widest" of them all (by a miniscule amount, anyway), having the smallest Crop Factor.

All Horizontal Crop Factors (corrected):
4:3 - Crop Factor = 2.586650
3:2 - Crop Factor = 2.508267
16:9 - Crop Factor = 2.395354

The 16:9 aspect-ratio mode is clearly the "widest" of them all, having the smallest Crop Factor.

So 14mm is not 14mm. It is 14mm multiplied by the Crop Factors listed above.

Do the math ... I used a 3.63 Micron pixel-pitch and the JPG sizes from the GH2 Op. Instructions.

OK. If cropping a 3:2 FF image to 16:9, then the effective sensor diagonal is reduced from 43.267mm to 41.3mm, and the effective crop factor between FF and GH2 (with a 21.63mm image circle) is therefore 1.91 when shooting 16:9 images. For 4:3 images the effective crop factor is 1.85 (40.0mm / 21.63mm), and when shooting 3:2 images the crop factor is 2.0 (assuming that the GH2 uses the full 21.63mm image circle with all three aspect ratios).

35mm equivalent focal length has nothing whatsoever to do will cropping a 3:2 aspect-ratio full-frame of physical dimensions 36mm width, 24mm height, and 43.267mm diagonal. Nothing ...

It is derived by comparing any given image-sensor's (aspect-ratio mode relevant) active-area physical width, height, or diagonal dimensions with that of 35mm full-frame size (listed above).
.

Since:

FOV = (2) x ( Arctangent ( ( S ) / ( ( 2 ) x ( L ) ) ) )

where:

FOV is Field of View;
S is the frame-size (either width, height, or diagonal);
L is the Focal Length.

Re-arranging the identity stated above yields:

EFL = ( S ) / ( ( 2 ) x ( Tangent ( ( FOV ) / ( 2) ) ) )

where EFL is the 35mm Equivalent Focal Length; and
S is the width, height, or dagonal dimension of 35mm full-frame.
.

Calculate the physical dimensions of the (aspect-ratio relevant) active area for any image-sensor in order calculate these things, and then compare those particular dimensions with the physical dimensions of 35mm full-frame. That is all that there is to it. Nothing more; nothing less ...

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Bart Hickman
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They don't call you the detail man for nothing!
In reply to Detail Man, Apr 24, 2012

We're talking about 1% variation here--I bet the lens itself is more than 1% off of 14mm anyway.

Detail Man wrote:

4:3 - Crop Factor = 2.069320
3:2 - Crop Factor = 2.087004
16:9 - Crop Factor = 2.087553

Horizontal Crop Factors:

4:3 - Crop Factor = 1.721763
3:2 - Crop Factor = 1.736477
16:9 - Crop Factor = 1.736934

So 14mm is not 14mm. It is 14mm multiplied by the Crop Factors listed above.

14mm is 14mm. I assume you mean the f/l in FF that has the same FOV is 14mm times those factors. Isn't the important thing the FOV stays constant (give or take 1%) as you change the aspect ratio on the GH2?

Bart
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Detail Man
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Re: They don't call you the detail man for nothing! - Gee, Thanks !
In reply to Bart Hickman, Apr 24, 2012

Bart Hickman wrote:

We're talking about 1% variation here--I bet the lens itself is more than 1% off of 14mm anyway.

Indeed. When I run calculations I figure that it really does not hurt to show the answers to a few digits. No offense intended towards any persons who may chop off digits for justifiable reasons ...

Detail Man wrote:

4:3 - Crop Factor = 2.069320
3:2 - Crop Factor = 2.087004
16:9 - Crop Factor = 2.087553

Horizontal Crop Factors:

4:3 - Crop Factor = 1.721763
3:2 - Crop Factor = 1.736477
16:9 - Crop Factor = 1.736934

So 14mm is not 14mm. It is 14mm multiplied by the Crop Factors listed above.

14mm is 14mm.

The OP asked how close his 14mm (actual) Focal Length lens would be to a (35mm equivalent stated form) 28mm lens. I was simply answering the question by calculating and providing the Crop Factors involved - based on DxOMark's statement that the GH2 pixel-pitch is 3.63 Microns, and using the pixel-dimensions for the GH2 (JPGs) in various aspect-ratio modes that are found in the GH2 Operating Instructions.

I assume you mean the f/l in FF that has the same FOV is 14mm times those factors.

The product of (any) Focal Length multiplied by those Crop Factors equals the (35mm equivalent) Focal Lengths for any aspect-ratio on the GH2 - based upon DxOMark's 3.63 Micron pixel-pitch specification, that is, but Adventsam has referenced a Panasonic "spec sheet" for the image sensor which states that the GH2 image-sensor's pixel-pitch equals 3.8 Microns (4.7% larger). See:

MN34070 Data: http://www.semicon.panasonic.co.jp/en/catalog/cat/pdf/T12013CE.pdf?bcsi_scan_0003A2F8FAC96BED=0&bcsi_scan_filename=T12013CE.pdf

Isn't the important thing the FOV stays constant (give or take 1%) as you change the aspect ratio on the GH2?

Well, it is true that the (diagonal only) FOV is relatively constant on a multi-aspect-ratio image-sensor. I assumed that the OP knew that already - and that the OP (similar to many DPR forums readers in the past) may have been asking about the (horizontally referenced) "width" (as in FOV, or as expressed as 35mm equivalent Focal Length).

The matter of how the GH1 and GH2 differer from all other M43 cameras is an interesting one. The percentage differences in the relevant specifications of common concern were covered here:

http://forums.dpreview.com/forums/read.asp?forum=1041&message=40326952

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dp88
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a lot of "photographers" don't know about compression/expansion
In reply to Detail Man, Apr 24, 2012

They think fov is just about making things closer or farther away, or wide angle lenses are just to fit more things in a frame.

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Vlad S
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Harder to tell for fisheye
In reply to Mike Ronesia, Apr 24, 2012

Mike Ronesia wrote:

The fish eye states 180 degrees but I don't know if they are talking corner to corner or if if it means 180 degrees as in half a circle.

In the case of Panasonic 8mm lens 180 degrees is the diagonal AoV: the arc shown between opposite corners will span the full 180 degrees. What it is going to be along the sides is hard to tell: the relation between the points in the image and the points in space is described by a mapping function, and there are many different ones that fisheye lenses can use. If someone learns the mapping function of the Panasonic or Samyang lenses then it will be possible to tell the AoV side-to-side.

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Detail Man
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Re: a lot of "photographers" don't know about compression/expansion
In reply to dp88, Apr 24, 2012

dp88 wrote:

They think fov is just about making things closer or farther away, or wide angle lenses are just to fit more things in a frame.

At the same time, the phrase "perspective distortion" is in itself a misnomer - in that it is not the lens-system that (necessarily) "causes" the distortion (right?). It is the proximity to the subject-matter, and the physical perspective that exists as a result - combined with the fact that human vision using two eyes (at some subject distances, anyway) serves to partially reduce our perceptual awareness of the differences in perspective arising out of a close proximity to subjects viewed ...

Please feel free to educate and/or to correct me if you have relevant/interesting knowledge here !

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Steen Bay
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Re: Corrected: GH2 Image Sensor Diagonal and Horizontal Crop Factors
In reply to Detail Man, Apr 24, 2012

Detail Man wrote:

Steen Bay wrote:

Detail Man wrote:

Shouldn't it also be taken into account that the effective diagonal of the FF sensor is reduced when the native 3:2 FF image is cropped to 4:3 and 16:9? I'd say that both the diagonal and horizontal crop factor is 2.0x when shooting 3:2 images with the GH2, and less than 2.0x when shooting 4:3 and 16:9 images, because the multi-aspect ratio GH2 sensor uses the full image circle with all three aspect ratios, whereas the FF sensor only uses the full image circle when shooting 3:2 images.

All Diagonal Crop Factors :
4:3 - Crop Factor = 2.069320
3:2 - Crop Factor = 2.087004
16:9 - Crop Factor = 2.087553

So, none of them are exactly 28mm, all of them are a little bit "narrower" than 28mm (in terms of the Field of View), and the 4:3 aspect-ratio mode is the "widest" of them all (by a miniscule amount, anyway), having the smallest Crop Factor.

All Horizontal Crop Factors (corrected):
4:3 - Crop Factor = 2.586650
3:2 - Crop Factor = 2.508267
16:9 - Crop Factor = 2.395354

The 16:9 aspect-ratio mode is clearly the "widest" of them all, having the smallest Crop Factor.

So 14mm is not 14mm. It is 14mm multiplied by the Crop Factors listed above.

Do the math ... I used a 3.63 Micron pixel-pitch and the JPG sizes from the GH2 Op. Instructions.

OK. If cropping a 3:2 FF image to 16:9, then the effective sensor diagonal is reduced from 43.267mm to 41.3mm, and the effective crop factor between FF and GH2 (with a 21.63mm image circle) is therefore 1.91 when shooting 16:9 images. For 4:3 images the effective crop factor is 1.85 (40.0mm / 21.63mm), and when shooting 3:2 images the crop factor is 2.0 (assuming that the GH2 uses the full 21.63mm image circle with all three aspect ratios).

35mm equivalent focal length has nothing whatsoever to do will cropping a 3:2 aspect-ratio full-frame of physical dimensions 36mm width, 24mm height, and 43.267mm diagonal. Nothing ...

It is derived by comparing any given image-sensor's (aspect-ratio mode relevant) active-area physical width, height, or diagonal dimensions with that of 35mm full-frame size (listed above).
.

Since:

FOV = (2) x ( Arctangent ( ( S ) / ( ( 2 ) x ( L ) ) ) )

where:

FOV is Field of View;
S is the frame-size (either width, height, or diagonal);
L is the Focal Length.

Re-arranging the identity stated above yields:

EFL = ( S ) / ( ( 2 ) x ( Tangent ( ( FOV ) / ( 2) ) ) )

where EFL is the 35mm Equivalent Focal Length; and
S is the width, height, or dagonal dimension of 35mm full-frame.
.

Calculate the physical dimensions of the (aspect-ratio relevant) active area for any image-sensor in order calculate these things, and then compare those particular dimensions with the physical dimensions of 35mm full-frame. That is all that there is to it. Nothing more; nothing less ...

The active area of a FF sensor when shooting images with the three different aspect ratios is :

4:3 - 32x24mm - diagonal = 40.0mm and crop factor = 1.85 (40mm/21.63mm = 1.85)
3:2 - 36x24mm - diagonal = 43.3mm and crop factor = 2.00
16:9 - 36x 20.25mm - diagonal = 41.3mm and crop factor = 1.91

Anyway, that's the comparison I find most relevant, if talking different aspect ratios and FF vs. GH2.

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