Wow my post started a pretty heavy technical discussion on DOF, haha. Anyhow, thanks to everyone for their input, definately learned a lot. I guess I'll make a thread specifically in a more genral section of the forum abiout people who have used the Redrock micro adapter.

Hi Pasha, instead of starting a new thread about those adapters, please join one that's already in progress... they are a popular topic of discussion around here and we already have more than enough ongoing discussions about them.

There is nothing "illusive" about different techniques of achieving shallow depth of field... either the background is in focus, or it isn't... moving the camera back and zooming in certainly is one way to do it. Maybe not the best, as Jeff Donald explains in the DVi article linked above, but definitely the easiest and least expensive method.

I dislike pointilism. Therefore, all very fine paintbrushes should be thrown into the trash.

Who's to be the definitive judge of what's artistic and what isn't? Beauty is in the eye of...blahh...blah...blah. It seems very short sighted and closed minded to issue such blanket assassinations of technique.


And this is a pointless discussion.

Sorry... I'll stick to hard facts in the future.

It seems very short sighted and closed minded to issue such blanket assassinations of technique.

Ahh but it is in fact a reverse. Striving for short depth of field when the camera is not capable of it instead of exploiting what the camera can do out of the box. So the saying goes that art is born of restriction and dies of freedom. And that is the problem, that the overuse of a technique is killing it. Anyone seen a Bullet Time effect in a movie recently?

C'mon guys, DoF is DoF and I'm sorry Simon, but the images I posted clearly show differing DoF which is no "illusion".

You have missed the point. The DOF wasn't different, it was just more apparent. Its the same as if you showed, say some ever so slightly out of focus HD video on a small display. Because it was a small display (such as a viewfinder) it looks in focus. Now you blow that same footage up onto a big screen and it looks really soft because now you can see the error in the focussing. And that is the same effect you are getting when you zoom in.

What looks in focus in a wide angle actually isn't. But you cannot see just how out of focus it is until you zoom in. This is precisely the reason why the zoom in, focus, then zoom out method is used, because it ensures focus even though you may not be able to see it in a small viewfinder.

and it should be clearly understood that moving the camera back and zooming in will indeed decrease the apparent depth of field

Yes, the key thing there is the word 'apparent'. And I agree with you Chris, it doesn't matter whether it is an illusion or not, whatever gets the job done. However it should be corrected that shallow depth of field is not achieved by the act of zooming in. You could for example, on a small chip camera, zoom in at f8 and everything would still be in focus.

So to be correct when we talk about these things the advice should be:
1. Open your iris wide open to create a shallow depth of field.
2. Zoom in to increase the visual differential between the subject and background that has been caused by that shallow depth of field.

Otherwise many people get caught in the trap of suggesting zooming in as a way to create shallow DOF when it is mainly the iris setting that allows it to happen.

The background just looked better when you couldn't see the detail - wasn't an ideal background, but when out of focus it worked with the composition.

Oh I agree fully. You need to use these techniques in a motivated way. But a lot of people use them in an overly distracting way, for example close ups of peoples faces with 35mm adaptors where one eye is totally out of focus from the other. Now this may work in an artistic sense depending on the video, I don't dispute that. I've seen some amazing videos, particularly the wedding videos by a company called Stillmotion that use this. But many people are using the 35mm adaptors and seemingly leaving the lenses jammed on f1.7!

That brings some hope back to this adapter, haha. So we have one thumbs up and one thumbs down. Anyone else have comments about the Redrock micro?

The RedRock Micro M2 doesn't work well on an EX1, at least for me. I had major problems with side (border on left and right) softness, and apparently, the limitation is the achromat itself. I even bought the hardware to hardmount to adapter to the EX1 threads so that it wouldn't drift as I moved the rig around. I suppose you could find another achromat with a larger diameter, but there is more to that selection that one would imagine.

Also, the super shallow DOF that you seek is a problem with 35mm lenses. All of the Nikon lenses that open up to f/2 or wider are very soft across the frame at wide apertures and display horrific purple fringing. f/2.8 is where even the best Nikon f/1.4 lenses start to behave.

There is the potential extra DOF available with the Nikon 105/135mm f/2 DC (Defocus control), but it's an extra burden.

...it should be clearly understood that moving the camera back and zooming in will indeed decrease the apparent depth of field (it doesn't matter whether this is an "illusion" or not [...] -- all that matters is whether or not the background is out of focus, and the zoom-in technique, while only a work-around, definitely creates this effect... as we've all learned in Photography 101).


I disagree. As I see it, the issue here and elsewhere is the confusion between background blur and DOF. They are not the same. There are several methods for increasing background blur. The two which have been the subject of this thread are: magnification and DOF.

The magnification method, or "back-up-zoom-in" technique, has these effects:


Same amount of the subject is in focus.
Perspective is altered drastically (and often detrimentally).
Composition of background is altered drastically.
Background blur is larger due to magnification.


The DOF method, e.g. a wider f-number, has these effects:


Less of the subject is in focus.
Same perspective.
Same composition of the background.
Background blur is larger due to being more out of focus.


Everything about them is different. Even the one thing they have similar, background blur, is different: blur caused by DOF looks different from (and better than) blur caused by magnification. The flattening/compression of perspective takes away from the perception of distance ("3D" look). Loss of background removes the subject from their environment, whereas DOF allows the background to contribute to the image, even if it's blurred.

Despite the fact that these two methods are different in every way, 99% of people talk as if they do the same thing. Even film school books get this wrong, e.g. Cinematography: 3rd ed., page 24. (That was one area which David Mullen didn't edit; he's aware of the difference.) It would be better if this myth were squashed out, at least here on dvinfo.net.

Using magnification (back-up-zoom-in) is a perfectly viable way to achieve greater background blur, and in many circumstances, it's the only method to increase background blur, especially with small-sensor cameras.

Using DOF is also a perfectly viable way to achieve greater background blur, if the camera/lens is capable of it. Sometimes it's an undesirable method, for example if it causes important parts of the subject (e.g. one eye) to go out of focus. That's one reason why magnification (back-up-zoom-in) is used on 35mm films: it magnifies background blur without making parts of the subject more blurry. In other words: DOF stays the same. So even if you could use DOF, another method, like magnification, might be better.

In addition to understanding that DOF and magnification are two very different methods of increasing background blur, we should also know their differences and trade-offs. Right now, the DOF is too expensive for many people because large sensors are too expensive with today's technology. Cameras like RED ONE and Scarlet are changing that, but we should still know the pros and cons of each method.

Also, it should be said that there are a variety of ways to make DOF thinner for a given subject:


Wider f-stop.
Same f-stop, but larger sensor and matching lens (same AOV).
Zoom in without moving.
Move in without zooming.


Note that "back-up-zoom-in" is not one of those methods. Also note that the last two methods cause a change in composition (perspective, background, field of view). The first two methods cause the DOF to get thinner without affecting the composition.

Again, there a many reasons why it's important to distinguish the difference between blur-from-DOF and blur-from-magnification.

The biggest, I think, is perspective. Many people do not appreciate the vital importance of perspective in their composition. To downplay the difference between DOF and back-up-zoom-in is to say that perspective is not important. But it is vital. One may compromise perspective to gain background blur, but the image suffers as a result. Perspective is also the reason that "zoom with your feet" is bad advice: the perspective must be chosen that best conveys the purpose of the image, not whatever is forced on you by the focal length.

For example, say the subject is a headshot, and at f/5.6, the entire face is in focus, including both eyes, ear, and nose. But you decide the background blur is not diffuse enough. You open up to f/2.0, and the change in DOF causes the background to become much more blurry and diffuse, just as desired. Unfortunately, it also causes the subject to have thinner DOF: now only one eye is in focus, the other eye is slightly blurry, and the ears and nose are really out of focus.

At that point, you switch back to f/5.6, but increase magnification by backing up and zooming in (for the same field of view). Now much of the background is gone from the image, which could be either good or bad. The background is also much blurrier, because the slight blur was magnified more. And, most importantly, perspective is now much flatter. The subject takes on a slightly more "2D cutout" look instead of 3D, and the background seems much closer than it really is. BUT: the good things are that the face is completely in focus, and the background is blurred nicely. Given how often this technique is used in Hollywood and on TV, you would be in good company to use it. (I like it too, but I enjoy truly thin DOF more.)

Here's a reverse example. Let's say you're shooting a head-and-shoulders shot with a Canon 5D2 and a 200mm super telephoto lens at f/2.0. You want the ears and nose in focus, but they're just not inside the DOF. So you do the opposite of "back-up-zoom-in": you zoom out to a shorter 135mm telephoto lens, still at f/2.0, and move closer to compensate. But the DOF is still the same; the eyes and ears are still out of focus. So you try 85mm f/2.0, 50mm f/2.0, 35mm f/2.0, 28mm f/2.0, and even a 24mm f/2.0. Even with the super wide angle 24mm f/2.0, the ears and nose are still just not in focus. The DOF is the same, all that changed was perspective, background, and background blur. To get them in focus, you have to change something that actually changes DOF, not background blur.

...it doesn't matter whether this is an "illusion" or not...

It's not an illusion. Increasing background blur through the use of mangification (back-up-zoom-in) is reality. It may be a different blur than the background blur caused by DOF, but it's still blur. As Simon said, longer focal lengths increase magnification of the background, so even the tiniest bit of blur becomes larger in relation to the subject. If there is no blur (e.g. at the hyperfocal distance), then the magnification method doesn't work. Also, there are many subjects where it's hard to use that method (e.g. cramped rooms, wildlife, the moon, etc.) because it's impossible to backup or you're already using the longest lens you can afford.

A few quick quotes if you don't mind:

You can reduce depth of field on practically any camera, by moving the camera away and zooming back in.

That usually increases background blur, but it does not affect depth of field.

...it's more than just an apparent illusion. This looks exactly like a changing DoF to me.

DoF only refers to the in focus parts of an image. The background blur and other out of focus parts of the image are not a part of DOF. That said, making the DOF thinner does have the effect of increasing background blur in relation to the subject. In the case of back-up-zoom-in, the increased background blur is caused by magnification, not DOF.

I think the point Simon was wanting to make is that zoom/tele lenses don't, TECHNICALLY speaking, create a more shallow DOF. It only looks like it.

It does not look like it.

Shallow DOF is more blur on everything, including background and subject.
Back-up-zoom-in is is more blur on just the background.

Those are two very different things. DOF blur is different than the blur caused by magnifying the background, but it's close enough. In any case, the additional blur on the subject means that they do not look the same unless there was nothing in the image between the background and subject and the subject was thin enough already to be unaffected by the thinner DOF.

It comes down to knowing this: background blur and DOF are different and have different contributors.

Please, then, explain the differences in the fence area of the images I posted a few pages back.

In the first image, it's out of focus. (long focal length)

In the third image, it's in focus. (same f-top, shorter focal length)

According to what y'all are saying, they should be identical if focal length has nothing to do with "real" focus.

And yes, I agree that longer focal lengths have other effects like spatial compression. But my eyes aren't hallucinating.

Please, then, explain the differences in the fence area of the images I posted a few pages back.


I thought everyone in this thread was talking about back-up-and-zoom. In your post, you're talking about *just* zoom, with no backing up. I misunderstood what you wrote. You are quite correct that changing focal length without compensating by moving the camera causes a change in DOF.

Your demonstration proves that tighter compositions have thinner DOF. That is, an extreme closeup has thinner DOF than a headshot. A headshot is thinner than head-and-shoulders. Then waist-up, full body, environmental portrait, etc. But what if someone wants to do a full-body portrait with blurred background? Telling them to zoom in to a headshot wont help, because then it's no longer a full body. One option is to backup really far and zoom in to compensate. Then it's still a full body shot, but the background has magnified blur. That's what I understood this thread was mostly about.

Let us also not forget the affect that aperture blades have on the out of focus areas of an image.... Why some lenses are sought after for the "bokeh" the render, like that of the canon ef 85mm f1.2 L lens or my favorite, the carl zeiss V mount 110mm f2 with it's 10 blade iris.

I also enjoy seeing the hot spots in the bokeh from anamorphic lenses.... ovals.

Yeah, there's been several conversations taking place here ... and I'm not helping ;-)

But my issue is that very strong statements have been made here that focal length does not and cannot have any impact of DoF - that it's all some magical magnification effect of pre-existing softness. I'm just calling bs on that and providing actual images that say otherwise.

The results of my testing, btw, comparing the DoF of the EX3 with stock lens against the FX1 with various distances from the subject, etc., the differences were significant enough (for the kind of work I do) to justify the acquisition cost of the EX3. For me, having more control is key. On the FX1, it seemed that achieving anything but 1' to infinity was a rare edge case - okay, a bit of an exaggeration, but you know what I mean. The EX3 gives me more creative choices in a camera of its form factor (and price). I'm happy.

Sorry again for the hijack, but this side-thread actually was relevant in some ways to the original question.

you are absolutely right.... about the size of the sensor ( or let's call it the format size ) has everything to do with it. The focal length of the lens does not..... a 50mm lens has a wider angle of view as the format size gets bigger... but, if you were to crop in on a larger sensors image to the size of a smaller format, the depth of field would be the the same as if you "zoomed in" to the same crop from a larger format with the smaller format.

Daniel Browning - thank you for an interesting lesson.

But:

DOF depends of the distance and the iris, like Simon says.

But f8 of a telephoto lens is larger than f8 of a wide angle lens.

So I wonder if it is the opening in mm that should be counted on. If so, longer focal lengths give shallower DOF. That is what I have learned ...

If so, longer focal lengths give shallower DOF.

If you backup enough to compensate for the longer focal length, the DOF remains the same.

Back in the early-mid 90's, I had a Sony Video 8 camera that had a feature on it called 'Portrait'. I remember first pushing that button. What did it do? It blurred out the background. Sort of a built in DOF adaptor. This was a 500 dollar or so camera. Definitely a cool feature, but as someone who shot mostly film (Super 8 and 16mm), it didn't ever make me think it looked like film.

If you watch the Zacuto comparison video, it's quite ironic that the 35mm portion has deeper depth of field than the DOF adaptors shown (which almost seem overkill). I do like how the adaptors give a more 'organic' look to video though.

If you backup enough to compensate for the longer focal length, the DOF remains the same.Long time ago I learned, contrary to what I said in my last post, that DOF depend on only two factors:

- iris
- scale, i. e. the subject/image ratio

According to this, focal length has nothing to do with DOF. An example was given in the Hasselblad Close-Up brochure:

- when at scale 1:1 and f 11, DOF is 2 mm, regardless of focal length and film size (those days I used 24x36 mm or 6x6 cm).

As Daniel has shown, also the background (and foreground, I suppose) blur has to be accounted for when composing an shoot.

Interesting thread.

DOF depend on only two factors:

- iris
- scale, i. e. the subject/image ratio


Correct. If you boil everything down into the simplest terms possible, DOF can be fully described by just f/number and magnification [setting aside bellows factor for this post]. If you change focal length and distance at the same time (back-up-zoom-in), magnification remains the same, so DOF remains the same. If you change *just* focal length, and nothing else, then DOF will change because magnification is changed. If you move closer to the subject, that too increases magnification, which changes DOF.

So f/number and magnification is one way. Another way to simplify it is physical aperture and focus distance. Physical aperture is the focal length divided by f/number; 50mm divided by f/2 is a physical aperture of 25mm. In this way, one number encodes the DOF effect of both the focal length and the f/number: both have an equal effect on DOF. So for a given composition (subject distance, angle of view), the lens with greater physical aperture will have thinner DOF. That is, 85mm f/1.4 on full-frame has thinner DOF than 50mm f/1.2 on APS-C, even though they both have the same field of view. This is because 85/1.4 = 60.7, and 50/1.2=41.6.


According to this, focal length has nothing to do with DOF.


Correct, if magnification is kept constant.

Another way to say it is that focal length has nothing to do with DOF, as long as physical aperture is kept constant. 50mm f/2.0 has the same DOF as 200mm f/8, since both have the same physical aperture of 25mm. More about that in this thead:

http://www.dvinfo.net/conf/still-crazy/140533-more-about-dof-depth-field.html

> "... focal length has nothing to do with DOF."

Sony don't seem to know this - on the EX1, without touching the aperture setting, the DOF indicator, when zoomed back to wide covers from zero to infinity, and as you zoom in in, this gradually gets smaller, finishing at a fraction of a metre.

> "... focal length has nothing to do with DOF."


The "..." that's missing from your quote is important. Sverker correctly pointed out that DOF depends only on iris (f/number) and scale (subject/image ratio, or magnification).

A better way to quote Sverker would have been:

For a given f/number and scale, focal length has nothing to do with DOF.

Having a constant scale means any change in focal length must be compensated by another factor, such as moving the camera. If it is not compensated, then it becomes a change in scale, and therefore a change in DOF, just as Sverker said.


Sony don't seem to know this - on the EX1, without touching the aperture setting, the DOF indicator, when zoomed back to wide covers from zero to infinity, and as you zoom in in, this gradually gets smaller, finishing at a fraction of a metre.

Right. That does not conflict with what Sverker wrote. Changing the scale by using a longer focal length causes a change in DOF.

If you had kept magnification constant (by using the back-up-zoom-in technique), you would find that the EX1 DOF indicator would remain the same, despite the much longer focal length. That is what is meant by "focal length has nothing to do with DOF".

Sorry - I'm not trying to be obstinate, I'm trying to understand ...

If I shoot a given frame with my zoom back at full wide, my EX1 tells me depth of field is from zero to infinity.

If I go back a few metres and zoom in to the same given frame, the EX1 tells me the DOF is now less than half a metre.

Should I not believe the camera?

If I go back a few metres and zoom in to the same given frame, the EX1 tells me the DOF is now less than half a metre.


Did you remember to change the focus distance? (If you backed up 10 feet, the focus should also be changed by 10 feet.)

I didn't necessarily have to - if I make my subject sharp after moving back and zooming in, it is still in focus after moving closer and zooming back to wide.

But whether or not I did change what was in focus does not affect the fact that the camera reports a much shallower DOF after moving back and zooming in, and this is backed up by what I see in the viewfinder.

I didn't necessarily have to - if I make my subject sharp after moving back and zooming in, it is still in focus after moving closer and zooming back to wide.


That is only possible if the depth of field is deeper than the distance you move the camera. For example, say you start out wide and focus on a subject at 1 meter. Then you back up 6 meters and zoom in so the subject takes up the same portion of the composition again. When you focus on the subject the focus distance is now 7 meters. If you return to the original position without correcting the focus, your focus will now be off by 6 meters. If the subject is still in focus, then the DOF must be deeper than 6 meters.

In most circumstances, even with the tiny 1/2" sensor of the EX series, the depth of field will not be deep enough to make the subject sharp when focus is off by such a great amount. Such chance arrangement of DOF and subject depth does not allow us to draw conclusions about the DOF indicator in the camera: the focus must be centered on the subject for that purpose.


But whether or not I did change what was in focus does not affect the fact that the camera reports a much shallower DOF after moving back and zooming in, and this is backed up by what I see in the viewfinder.

You're right: moving back and zooming in, without changing focus distance, causes the DOF indicator to show thinner DOF. But once you also change the focus distance, I think you will find that the DOF indicator shows the same DOF.

Let me illustrate with a few DOF numbers from my Canon 5D2 using a CoC appropriate for 1080p (12 microns).


50mm lens, focus distance 1 meter, f/2.0 DOF = 17.3mm
100mm lens @ 2 meters, f/2.0 DOF = 17.3mm
200mm lens @ 4 meters, f/2.0 DOF = 17.3mm
400mm lens @ 8 meters, f/2.0 DOF = 17.3mm
500mm lens @ 10 meters, f/2.0 DOF = 17.3mm
800mm lens @ 16 meters, f/2.0 DOF = 17.3mm


The increase in focal length would normally make the subject take up a larger part of the frame. Moving backwards compensates for that so the subject takes up the same portion of the frame.

The longer focal lengths also normally cause the DOF to be thinner. The increased focus distance compensates for that so the DOF remains the same.

One thing I didn't read mentioned here is CoC or more to the point that it isn't constant for a given sensor size. I've shot with both a 1/2" SD camera and the EX1 and DOF is dramatically different because of the higher resolution of the EX1 when viewed in HD close the the monitor.
The other thing I notice with HD compared to film is there's a different aesthetic to the DOF. With projected film you see the subject pretty much all in focus and the background very blurred.With HD including the EX1 you can have the subject's nose clearly in focus, the ears slightly out of focus and the background not as blurred as film.
I believe this difference is at least in part due to the way film looses resolution through the printing process, there's certainly a very different look to film scanned and digitally projected compared to a traditional print. Perhaps the 35mm 'DOF' adaptors achieve much the same by reducing resolution and at the same time reducing DOF.

Bob:

Having used nearly all of the high-end 35mm sensor cameras (Genesis, F35, Red, D21), I can report that contrary to your theory (if I understand it properly), these deliver a very sharp image with LESS depth of field than the 35mm film equivalent, if anything. My focus pullers certainly have a tougher time of it than they would with film, they constantly report that they find it shallower and more critical. I've had a number of theoretical discussions with various people as to whether this is due to the lack of depth to a sensor vs film emulsion etc.

Seems simple enough what Simon is saying. DOF is defined as the "Area in focus". Zooming doesn't change the area in focus, it just further softens what's already out of focus. DOF measure AREA, not DEGREE of softness. It's a state of range, not intensity.

Except that Charles is right. Circles of Confusion are, in reality, 3-D volumes, wherein the point of focus is differing by the wavelength of the light. So, the point of perfect focus shifts from front to back in the space of angstroms, well withing the emulsion depth of halide on acetate.

Bob:

Having used nearly all of the high-end 35mm sensor cameras (Genesis, F35, Red, D21), I can report that contrary to your theory (if I understand it properly), these deliver a very sharp image with LESS depth of field than the 35mm film equivalent,.

But isn't that what Bob's saying? That focus is more critical on video? He said with video the nose is in focus and the eyelashes are softer and the film is more forgiving.

But isn't that what Bob's saying? That focus is more critical on video? He said with video the nose is in focus and the eyelashes are softer and the film is more forgiving.

Yes,
that's what I'm saying. In all fairness though the best film stocks I'm told can deliver 4K resolution. You do not see anything like that in a release print though, more around 700 lines according to SMPTE's tests.
I wouldn't say though this is a film Vs video argument. I think you'll notice a difference in DOF between a PD170 and a Z1.