A lens is a lens is a lens...

Great video. Sure could be helped to clear the air around the af-100 forums, if Barry hasn't already cleaned house!

What do you guys think he meant when he said 'apparent depth of field' at the end, before the EX-1 demonstration?

Apparent can either mean 'obvious' or it can mean 'seemingly so, but not'.... I think of the latter when I read or use the term... however that would then make what he was saying not quite right, which is why it caught me off guard. What do you think?

Either way, that should help many people out.
 
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I don't seem to have the bandwidth on my phone to watch it, but I have seen that video a while ago. Apparent dof as I understand usually refers to the perceived change in dof when one changes focal length and object distance but keeping the same shot size on the subject so that dof seems more or less. Actual dof is the same but backing up the camera and zooming in adjusts perspective so that the blurred bg is magnified giving the perception of shallower dof.

It could also refer to the fact that dof only really relative to human perception... nothing is ever really in focus, just more in focus than everything else. The field of focus only apparently has depth because of the limitations of all of the imperfections/limitations in imaging and viewing systems. Optically all that determines dof is fstop and object distance, but that's not all that practical of a way to think about it.
 
nyvz said:
I don't seem to have the bandwidth on my phone to watch it, but I have seen that video a while ago. Apparent dof as I understand usually refers to the perceived change in dof when one changes focal length and object distance but keeping the same shot size on the subject so that dof seems more or less. Actual dof is the same but backing up the camera and zooming in adjusts perspective so that the blurred bg is magnified giving the perception of shallower dof.

It could also refer to the fact that dof only really relative to human perception... nothing is ever really in focus, just more in focus than everything else. The field of focus only apparently has depth because of the limitations of all of the imperfections/limitations in imaging and viewing systems. Optically all that determines dof is fstop and object distance, but that's not all that practical of a way to think about it.
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DOF is simple ...and nothing to do with "perception" or "not really ever in focus"

Its in focus or its not. The eye can tell what is really in focus.

DOF is a term that quantifies the range between what is and what is not in focus ...and it also can quantify the range of what isnt and is in focus.

Hyperfocal describes a maximum range of DOF achievable by any lens.

I do hope you are not pursuing a career as a focus puller / 1st AC.
 
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nyvz said:
I don't seem to have the bandwidth on my phone to watch it, but I have seen that video a while ago. Apparent dof as I understand usually refers to the perceived change in dof when one changes focal length and object distance but keeping the same shot size on the subject so that dof seems more or less. Actual dof is the same but backing up the camera and zooming in adjusts perspective so that the blurred bg is magnified giving the perception of shallower dof.
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That's right. Depth of field is only truly determined by lens aperture, but at different focal lengths it appears to be different. The longer the focal length the shallower you depth appears, wider lenses appear to have more depth of field. Also check out our FOV Comparator.
 
Shipsides said:
That's right. Depth of field is only truly determined by lens aperture, but at different focal lengths it appears to be different. The longer the focal length the shallower you depth appears, wider lenses appear to have more depth of field. Also check out our FOV Comparator.
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"appears" to be different? Sounds like an illusion trick.

It IS different because... it IS more in or out of focus.
 
Shooter said:
"appears" to be different? Sounds like an illusion trick.

It IS different because... it IS more in or out of focus.
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That's true.. it is what it is, who cares about the semantics. True focus can only be set to one distance. Depth of field gives a range of 'acceptable' focus or a range of 'acceptable circles of confusion'. Yes, that acceptable range is determined by our eyes. It is in focus or it is not, and I suppose as an AC that is all that matters. :)
 
They should better explain focal length, Projection circle, Aperture, distance to object, DOF and angle of view.


>Depth of field is only truly determined by lens aperture

Don't think so. I changes with the distance.

>Its in focus or its not. The eye can tell that it is really in focus.

Not sure either. It is about how much our eyes (or our film) can hide the gradually increasing blur (away from the focus plane).
 
ustein said:
They should better explain focal length, Projection circle, Aperture, distance to object, DOF and angle of view.


>Depth of field is only truly determined by lens aperture

Don't think so. I changes with the distance.

>Its in focus or its not. The eye can tell that it is really in focus.

Not sure either. It is about how much our eyes (or our film) can hide the gradually increasing blur (away from the focus plane).
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We have no measure in units to describe degrees of focus but ..

You will never get a better or clearer explanation than this:

http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
 
Not to be the technical Nazi I always am, but....

The reason I asked that initial question was because if he was using the word apparent as to the definition; "appearing as such but not necessarily so; seeming"... than that is slightly inaccurate because since he left the other camera in 2k, there was a real DoF difference, as the wider lens did not need to be moved forward to attain the same composition. Both cameras had equal sub->cam distance but different focal lengths. Not the 'illusion' we talk about when referring to magnified background CoC of two different focal lengths with adjusted sub->cam distance.

:)

Otherwise great video. He could have simply meant 'apparent' as in obvious. But when I hear things like apparent DoF, or apparent soft focus, I think of the definition given above.
 
I was confused by the video but whatever...

Heres how I see it on the day...

I know "my" lenses relatively well so I will choose a lens from the kit ..with a degree of intention.

(Hopefully I have pre vized and planned accordingly...but hell.. theres only so many lenses on the planet to own rent or steal)

I will then frame and compose with the lens and THEN use lighting and filters and f/stop and fps and shutter angle to achieve DOF to suit the intention.

If it aint working... I wil change something till it does.

Note: DOF is controlled only by focal length AND aperture but the other elements are what controls the aperture.

We all know that we use DOF and composition to tell the story*. we dont just use it because we can and it looks pretty

( * Story action within this... is someone elses responsibilty - the Directors)
 
I guess here is my point.

DoF is based on three things.
Aperture, Camera to subject distance and focal length.
Changing focal length but moving the camera to get the same composition as before will usually cancel both factor changes and the DoF will remain the same.... however the background with either be magnified in comparison or become smaller in comparison. When this happens all those pretty little out of focus circles become larger or smaller. This does not mean the DoF has changed, but simply the perspective. What I described was how the illusion of shallower or deeper DoF can be attained at the sacrifice of how magnified the background is. Now when you start to change formats, such as S35mm and 8mm, you'll need different lenses to get the same composition (granted the cameras are the same distance away from subject). This is why you inherently get shallower DoF on S35mm and 8mm is almost always deep DoF.

My point was, in the video, the guy was shooting on two different formats, presumably the same F/stop, at the same subject to camera distance but with two different focal lengths. Thus there wasn't an apparent difference in DoF, as in seemingly, such as the illusion I've described previously... but there was in-fact a true DoF difference.

I don't know what the original presenter meant, but his use of 'apparent' did cloud a definitive meaning.




As for another poster, who said

It could also refer to the fact that dof only really relative to human perception... nothing is ever really in focus, just more in focus than everything else. The field of focus only apparently has depth because of the limitations of all of the imperfections/limitations in imaging and viewing systems. Optically all that determines dof is fstop and object distance, but that's not all that practical of a way to think about it.
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He is technically right kinda. (except he forgot focal length as what determines DoF. :( ) I'm just supporting his claim that we're never really focusing on the real focus plane, except if we're just super lucky. Otherwise we're always just in the 'zone'. The zone being DoF and what we consider acceptable focus.

Depth of field is a mathematical equation which represents a zone in which the incoming light rays are bent correctly to the film plane to what we find as 'acceptably' sharp. The true plain of focus is a tiny sliver, theoretically never exact as it's always going to be smaller than small... like dividing a number by two; you'll go on forever. So the poster above is technically correct. The theoretical plain of focus is actually an almost immeasurable sliver of space perpendicular to the lens. You'd have to get down to the physics and super small measurements to find it... if ever. Lucky for us, DoF is usually a matter of inches or more, so we don't have to get down to never-ending-dividing-microns. We can get pretty darn close, with our basic units of measurement and be just fine!

This can be supported by thinking about DoF and how shallow it can get.


I went to the panavision website and using S35mm (1.85) as the standard, the smallest DoF I could come up with was a 300mm lens, at an F/1, 10'1" away from subject.


Picture 13.jpg

The resulting DoF was 0.1894"... yes... that was the entire DoF range, from front to back. Less than 1/5th of only one inch. Now the exact plane of focus lies somewhere within there, at the atomic level. :)
 
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Hello everyone. I'm the fellow who made this video.

Ryan is correct. I used the word "apparent" in what was perhaps not the best way within my phrasing.

Shooter, you are giving a functional definition of depth of field as to how one might use it in practice, but it is not perhaps the complete technical definition of what it is.

Depth of Field is a function of aperture and combined resolving power of the capture medium and exhibition format. A lens does not know what occurs after light passes through it, but if the image is captured on an 18MP sensor and then blowup up to the size of a billboard and viewed closely, then it will yield a shallower depth of field than that same lens in front of a standard definition camera and viewed on an iPhone screen from two feet away. This end of the equation is defined by circle of confusion, which determines how fused the beams of light that define a point have to come together until they are considered to be in focus. In an absolute world this would be a single photon. In a slighly more practical world this would be a single photosite on a camera or pixel in an exhibition format. In the real world it is considerably larger still because we just don't notice that much.
 
My post was largely addressed to Post #3 and not an attempt to offer a technical definition.

I do know that something in focus ...is actually in focus.

I just consider anything I can not explain (due my dumbness) ... is simply "magic"

DOF is "magic" so I just get on with it .
 
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