The Falacy of FF Cameras having Flatter DOF

[ajohnw]

Clearly in that shot the woman has less dof - just look at the Canon on the cameras.

One would expect them to get that sort of shot right. Why does the crop shot look better.

Personally I find the link I posted far more useful and interesting than the various other blurbs on the subject. I fell out with Ted's when I got to microscopes. In that area fallacies get repeated over and over. It's pretty obvious in this case that the correct answer is 1/4 wave otherwise the so called resolution limit wont be reached.

John
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[Stagecoach]

Some more examples

http://neilvn.com/tangents/full-fram...epth-of-field/

[george013]

Some more examples

http://neilvn.com/tangents/full-fram...epth-of-field/

I agree completely with him (who am I ).Except.......what is perspective. It so much used in discussions but never defined.

George

[ajohnw]

There are ways of getting blur other than just increasing the format size so in a sense even M 4/3 could produces something very similar to FF. There are other variables that also set the degree.

Some examples that go through a number of factors.

http://digital-photography-school.co...-in-portraits/

John
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[dem]

I agree completely with him (who am I ).Except.......what is perspective. It so much used in discussions but never defined.

Reading through the comments, it appears that he means "perspective distortion".

I did not like his approach as he deliberately used identical apertures on both formats (both cameras shot at f/2.8) and did not show the obvious: how dof is affected by aperture.

On the plus side, someone mentioned this rather interesting link in the comments:

http://howmuchblur.com/

that can tell you, for example, at what subject-background distance you get more blur in a head-and-shoulders portrait with 50/1.4 or 85/1.8 lens. It turns out that they are quite close but if the background is more than 1.5 meters away, the 85/1.8 wins.

[george013]

Reading through the comments, it appears that he means "perspective distortion".

I did not like his approach as he deliberately used identical apertures on both formats (both cameras shot at f/2.8) and did not show the obvious: how dof is affected by aperture.

On the plus side, someone mentioned this rather interesting link in the comments:

http://howmuchblur.com/

that can tell you, for example, at what subject-background distance you get more blur in a head-and-shoulders portrait with 50/1.4 or 85/1.8 lens. It turns out that they are quite close but if the background is more than 1.5 meters away, the 85/1.8 wins.

He showed 2 identical pictures with the same aperture but different dof.

No, he doesn't mean perspective distortion. I think the point of view is meant.

George

[ajohnw]

I've looked at that page in the past and assume that the blur relates to sensor size. Change the numbers to these

http://howmuchblur.com/#compare-1x-5...m-wide-subject

Then assume for a print or screen view that the enlargement is twice as much for the crop factor I have used and there isn't really any difference.

John
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[Tronhard]

For what it is worth I think this video may be of some interest as it actually demonstrates some of the issues under discussion.
https://www.youtube.com/watch?v=f5zN6NVx-hY

Be patient, it gets to the most interesting stuff if you wait.

[ajohnw]

Interesting one Trev. I don't agree with all of the points. When there was some good info on relative noise levels about full frame was worth about 3 stops but the pixel count keeps going up and that was against the normal crops who's pixel count is also going up.

Any way if I needed to take a head shot on m 4/3 that matched a 50mm F1.4 wide open this is what I would use

http://howmuchblur.com/#compare-1x-5...m-wide-subject

It would be a better photo too due to the better depth of field close to the focus point but who would seriously use the 50mm at F1.4 for that sort of shot. It would be ok probably at very small sizes. So in this case in my view 75mm on M 4/3 is better but say some other full frame lens was used. There will still be some longer focal length that should get close to the same result. Same on aps etc too.

Having tried some full frame lenses on m 4/3 I should also mention that it's very often not a good idea as the resolution of the lens itself isn't good enough. I do pixel peep though.

John
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[xpatUSA]

Personally I find the link I posted far more useful and interesting than the various other blurbs on the subject. I fell out with Ted's when I got to microscopes.

Downgraded to an utterer of a "blurb" as opposed to what I thought were Great Truths . . oh, the humiliation, (sob)

[William W]

George et at, re-iterating that we should not take the sample in Post #13 as depicting any serious study or example,

Please read Post #17 - that outlines the test that the students actually did.

The image in Post #13 was a Student and me mucking around.


***

In answer to Dan's question about cropping - I concur with Dem and for the reasons given.

WW

[george013]

George et at, re-iterating that we should not take the sample in Post #13 as depicting any serious study or example,

Please read Post #17 - that outlines the test that the students actually did.

The image in Post #13 was a Student and me mucking around.


***

In answer to Dan's question about cropping - I concur with Dem and for the reasons given.

WW

I didn't take the sample as a serious study. I just mentioned

It also shows how subjective dof can be

I made some drawings showing the difference between FF and DX. I post them later.

Still the question about perspective isn't answered.

George

[ajohnw]

Perspective to me as far as photography is concerned relates to focal length, easily noticeable with longer telephoto lenses. In the past things like 100mm on FF gives the same perspective as the human eye were often stated. Personally I feel that this is the right sort of number for scenes with objects spaced out into the distance. That length will give that sort of effect. On things like faces I am more inclined to feel that other than very extreme variations it doesn't make much difference. Having said that though I have come across people who can see a model and the photo at the same time and tell that it was taken with the once popular 135mm lens. I suspect via dof really or more likely just suspected the photographer didn't have 100mm available.

More for fun than anything else I'll add another comparison of blur.

http://howmuchblur.com/#compare-1x-8...m-wide-subject

I adjust the distance scale to 1cm to 200m. In some ways that one is more interesting as given the FF 85mm available the M 4/3 lens will also more than match it for resolution. Resolution is usually the bug bear that has to be put up with on crop cameras.

Why do I post them? Simple really there are always more than one way of cracking an egg.

John
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[george013]

Perspective to me as far as photography is concerned relates to focal length, easily noticeable with longer telephoto lenses. In the past things like 100mm on FF gives the same perspective as the human eye were often stated. Personally I feel that this is the right sort of number for scenes with objects spaced out into the distance. That length will give that sort of effect. On things like faces I am more inclined to feel that other than very extreme variations it doesn't make much difference. Having said that though I have come across people who can see a model and the photo at the same time and tell that it was taken with the once popular 135mm lens. I suspect via dof really or more likely just suspected the photographer didn't have 100mm available.

More for fun than anything else I'll add another comparison of blur.

http://howmuchblur.com/#compare-1x-8...m-wide-subject

I adjust the distance scale to 1cm to 200m. In some ways that one is more interesting as given the FF 85mm available the M 4/3 lens will also more than match it for resolution. Resolution is usually the bug bear that has to be put up with on crop cameras.

Why do I post them? Simple really there are always more than one way of cracking an egg.

John
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You don't define perspective. You subscribe a feeling for what is perspective for you. Van Niekerk is mentioning perspective in the link comparing ff and dx. From the link.

With a zoom, the perspective does not change – you are merely enlarging the image.

In my opinion this is not true.

George

[MrB]

......what is perspective. It so much used in discussions but never defined.

Perspective to me as far as photography is concerned relates to focal length, easily noticeable with longer telephoto lenses.

Perspective is the apparent three-dimensional (3-D) spatial relationships (relative distances and angles) between different parts and objects in a 2-D representation of a 3-D scene.

In photography, perspective depends on the position of the photographer relative to the different parts and objects in the scene. It is independent of focal length. The latter changes the angle of view and, therefore, the field of view recorded on the rectangle of the sensor, but the perspective remains the same when the shot is taken from the same position using different focal lengths.

Here is an example anyone with suitable gear can try for themselves. It was done using an 18-50 kit lens on an APS-C camera - handheld, so allow for a few slight errors. From the same viewpoint, an image was recorded at both 18mm and 50mm. The 18mm image was then cropped to give roughly the same field of view as in the 50mm image - the perspective recorded by both focal lengths is the same.



Using the 18mm focal length to see the building at a similar size as it appears in the 50mm image, one would have to move closer. That change of position would alter the perspective in the image. Also, to get all the building in the wide-angle lens shot from ground level, it would be necessary to tilt the camera upwards, which would introduce perspective distortion - more exaggerated converging of vertical lines.

Cheers.
Philip

[ajohnw]

You don't define perspective. You subscribe a feeling for what is perspective for you. Van Niekerk is mentioning perspective in the link comparing ff and dx. From the link.

In my opinion this is not true.

George

I agree 100% with you on that George. It is incorrect. On recent example that is strikingly obvious which many people will have watched is various races in the Olympic games. The camera men are fond of using long focal lengths with competitors approaching them. They look closer than they do when when they switch to a side view with a wider lens. In fact that view can be misleading.

One thing for sure I will continue thinking about that as perspective. When I took this I didn't run up behind them and get the framing the same with a wide angle or have some one further away with a telephoto. They would all look different in terms of apparent depth.

LandAwalking by John, on Flickr

John
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[george013]

Perspective is the apparent three-dimensional (3-D) spatial relationships (relative distances and angles) between different parts and objects in a 2-D representation of a 3-D scene.

In photography, perspective depends on the position of the photographer relative to the different parts and objects in the scene. It is independent of focal length. The latter changes the angle of view and, therefore, the field of view recorded on the rectangle of the sensor, but the perspective remains the same when the shot is taken from the same position using different focal lengths.

How do you combine those two statements?

Here is an example anyone with suitable gear can try for themselves. It was done using an 18-50 kit lens on an APS-C camera - handheld, so allow for a few slight errors. From the same viewpoint, an image was recorded at both 18mm and 50mm. The 18mm image was then cropped to give roughly the same field of view as in the 50mm image - the perspective recorded by both focal lengths is the same.





Using the 18mm focal length to see the building at a similar size as it appears in the 50mm image, one would have to move closer. That change of position would alter the perspective in the image. Also, to get all the building in the wide-angle lens shot from ground level, it would be necessary to tilt the camera upwards, which would introduce perspective distortion - more exaggerated converging of vertical lines.

Cheers.
Philip

But does the left picture have the same perspective as the right one?????

George

[MrB]

.....When I took this I didn't run up behind them and get the framing the same with a wide angle or have some one further away with a telephoto. They would all look different in terms of apparent depth.

They would look different, not because of different focal lengths (wide-angle or telephoto), but because moving closer or further away would change the perspective.

Cheers.
Philip

[MrB]

How do you combine those two statements?
George

A simple sketch can show that, if the photographer changes position, e.g. moves closer to the subject, it changes the relative angles and distances between himself and objects in the scene and, therefore, changes the perspective.

But does the left picture have the same perspective as the right one?????
George

Yes. It must have the same perspective because it is the same picture - just showing a smaller part of the scene.

Cheers.
Philip

[dem]

Perspective is something I find I start losing when I spend too much time on photo forums.