how about a DOF tutorial??

M

matthewd5

Veteran
hello.

i have been struggling a bit on how to really get a handle on Depth of Field

i was thinking, we all have the same camera, so how about one of you guys who not only has DOF mastered, but can explain it in step by step directions with some specific settings, like what camera and lens settings and how far you are from the subject/background etc?

it is one of the most asked questions and it seems extra easy to do a tutorial when everyone reading it has the same camera.

matthew
 
Re: how about a DOF tutorial??

DOF is influenced by three factors: closeness to subject, focal length of lens, and aperture setting.

Simply put, the factors work like this:

SHALLOWER DOF -------------- DEEPER DOF
Close to subject -------------- Far away from subject
Telephoto Lens --------------- Wide-Angle Lens
Open Aperture ---------------- Smaller aperture

So: to maximize the area that's in focus (to get the most deep DOF), use a wider-angle on your lens, and stop down the iris as much as you can, and back away from the subject.

To minimize the DOF (to get the shallowest focus possible): zoom in as far as you can, get as close to the subject as you can, and open the iris up as much as possible.

With a camera like the DVX, your optical possibilities for shallow DOF are quite limited: the maximum telephoto is only 45mm.  Longer lenses are the #1 factor in getting the shallow-DOF look.  35mm cameras usually use a lens in the range of 25-250mm, the DVX is only 4.5-45mm, and wider-angles (shorter focal lengths) exaggerate the effect of everything being in focus.  So the DVX has a major strike against it.

You can cheat in a number of ways.  First and foremost, get your subject as far away from the background as possible.  The further they are from the background, the more the background will be out of focus.

Second, you can get a close-up lens like the Century Achromatic Diopter.  That lets you focus closer, so you can get the camera closer, and closer to subject = shallower DOF.

Third, you can use a telephoto adapter like the Century 1.6x.  That'll extend your telephoto range to 72mm, giving a shallower DOF look.

Fourth, you can use a product like the mini35 (www.mini35.de) or the SoftScreen (http://indietoolbox.com) to give you results that are simply not possible in-camera alone.  You can achieve amazing shallow DOF looks with those products, but each involves its own set of compromises.

So, to reiterate: for the shallow DOF look, do these in the following order:
1.  Zoom in as far as you can.  If you can't zoom in all the way to 45mm, try backing up some so that you can continue zooming in.  Max telephoto is the most important factor.

2.  Open the iris as much as possible.  If that means using the ND filters, use 'em.  Get that iris as close to "open" as you can.

3.  Position your subject to be as far away from the background as possible.  You cannot underestimate how important that is.  If it means changing your shot or composition, change it.  Move your subject across the street if you can -- it'll make all the difference.

4.  Get as close as you can.  Proximity counts for a lot.  Use a close-focus diopter if you must.

------------------
DOF myths:

Myth 1: "imaging size affects DOF, larger imagers = shallower DOF".  False.  The imaging size has nothing to do with the depth of field.  The imager size (whether larger like 35mm film, 16mm film or 2/3" CCD's, or small like 1/6" CCD's) affects the FIELD OF VIEW, but not the DEPTH OF FIELD.  And larger imagers require longer lenses to deliver usable fields of view.  Smaller imagers require shorter lenses.  A 35mm camera uses 25-250mm for a zoom, a 1/6" CCD camera might use 2.5-25mm.  So the 35mm camera gets its shallower DOF from its longer lenses, not from its imager size.

Myth 2: "focal length is irrelevant in DOF.  To use telephoto, you have to back up (which increases DOF).  To get close, you have to use wide-angle (which increases DOF).  They cancel each other out."  No they don't.  I mean, yes, technically they do, but just try it, look at your shots and you'll see, the telephoto shot clearly, clearly looks like the background is more out of focus.  Whether it's technically as "in-focus" or not is irrelevant, the telephoto lens delivers the optical illusion that the background is more out of focus, and that's what we want: the APPEARANCE that the background is out of focus. For comparison, reference these shots:
www.icexpo.com/dvx100/DOF-Test2Wide.jpg
www.icexpo.com/dvx100/DOF-Test2Tele.jpg
Both were shot at identical aperture (f/2.8 ) and in the wide shot, I moved as close as possible and focused as close as possible to minimize DOF. On the Tele shot I zoomed in as far as possible, then got as close as I could (while maintaining the same image size). I think most viewers will agree that the tele shot, while maintaining the same aperture and the same image size, looks like it has much shallower DOF.
 
Re: how about a DOF tutorial??

Barry Green, you've out done yourself!

I'll be the first to say a big THANKS! Thats one of the most comprehensive lessons in DOF I have read in a long time. Thanks again.
 
Re: how about a DOF tutorial??

I think we should add an new thread, pinned up to the top the board, with the title

"Thank You Barry Green"

;D ;D

Thanx for ur time
 
Re: how about a DOF tutorial??

In fact we should give it a tiltle

" Thanx Jarred and Barry"
 
Re: how about a DOF tutorial??

While I cannot add much to Barry's comments, I would just like to paste a few points from some of my old notes on this subject. These basically relate to traditional filming (for film speed etc) but are nonetheless fingertip recount of the important factors to be kept in mind ifor controllong the depth of field.


DEPTH OF FIELD
Shallow depth of field:
1. LOWER F/STOP NUMBER (f 1.4)
2. LESS LIGHT
3. LOWER E.I. (ASA/DIN) OF FILM (50ASA)
4. FASTER FILMING SPEED (48 fps, film is moving faster so less light hits each frame)
5. FASTER SHUTTER SPEED (1/80th of a second, film is exposed to light for a shorter period of time)
6. NARROW SHUTTER ANGLE (90 , again film is exposed to light for a shorter period of time)
7. ND (NETURAL DENSITY) FILTER (cuts out amount of light striking film, allows you to open up to a lower f/stop number, i.e. you are outside and you get a reading of f8, you can add a ND filter of .6, a loss of two stops, and open up to f4)
8. THE CLOSER THE OBJECT/SUBJECT IS TO THE LENS
9. LONGER FOCAL LENGTH OF LENS (75mm)


Deeper depth of field:
1. HIGHER F/STOP NUMBER (f11)
2. MORE LIGHT
3. HIGHER E.I. OF FILM (400ASA)
4. SLOWER FILMING SPEED (12 fps, film is moving slower so more light is hitting each frame)
5. SLOWER SHUTER SPEED (1/60TH of a second, film is exposed to light for a longer period of time)
6. WIDER SHUTTER ANGLE (180 , film is exposed to light for a longer period of time)
7. THE FURTHER THE SUBJECT/OBJECT IS FROM THE LENS
8. WIDE ANGLE LENS (10mm)
9. SPLIT FIELD DIOPTER (goes on the front of the lens and allows half the frame to be focused on far distances and the other half to be focused at close distances)
10. HYPERFOCAL DISTANCE (the closest distance setting such that the far limit of depth of field extends to infinity, i.e. when lens is focused at 10’, the depth of field extends from 5’ to infinity)
 
Re: how about a DOF tutorial??

Does the shutter speed intervenes in any way? all things being equal , would the DOF changes wether I am at 1/60 versus 1/250? :-[
 
Re: how about a DOF tutorial??

No, not at all.

DOF is strictly a function of the lens. If you change your shutter speed like that, your EXPOSURE would change, but the DOF wouldn't... unless you adjusted the iris to compensate for the exposure, in which case the DOF would change as well.
 
Re: how about a DOF tutorial??

can we use the Century Achromatic Diopter "WITH" the anamorpher lense ?
 
Re: how about a DOF tutorial??

Barry, I do want to take one issue with your post. Depth of Field is based on something called "zone of confusion", which is not an improper name for a Love and Rockets song. Resolution of the recording system, density of the pickup device's recording elements, and the size of the recording element all play into the depth of field. Since these three things are not usually able to be modified by a user of a film camera or a video camera in a comparable manner, this is not often known, especially since the optical theory of zone of confusion is a bugger for most people to understand and is thus not often trotted out.

I posted elsewhere a discussion of zone of confusion, but basically, assume all other factors are equal:

Higher the resolution = lower area in zone of confusion = smaller depth of field.

Larger pickup size = higher area in zone of confusion = larger depth of field.

Higher density of pickup elements = lower area in zone of confusion = smaller depth of field.

To prove this you basically need to take different cameras with different resolution / element density but similar lenses and repeat your test of shooting an object at the same angle of view. Except for engineers in major studios with access to studio and field versions of the same camera with HD and SD pickups, this is unlikely to be a common experiment, and is thus not well known.

One way that it was tested by some was to use soft detail, essentially a deresing at the CCD, and noting that as an image dereses, the depth of field appears to increase.
 
Re: how about a DOF tutorial??

Slapdragon, you're my new favorite poster, and I look forward to learning much from you.

Question is: if the imager's density of pickup elements (i.e., CCD pixel array) exceeds the final sampling size (in DV's case, 720 x 480) then does it really matter? Other than a bit of a rounding error, the 720 x 480 is not going to be able to hold the detail being resolved by the higher-res imager, it's all going to get rounded off, so is there a real-world, observable effect?
 
Re: how about a DOF tutorial??

[quote author=Barry_Green link=board=news;num=1083366247;start=0#12 date=07/02/04 at 21:20:26]Slapdragon, you're my new favorite poster, and I look forward to learning much from you.

Question is: if the imager's density of pickup elements (i.e., CCD pixel array) exceeds the final sampling size (in DV's case, 720 x 480) then does it really matter?  Other than a bit of a rounding error, the 720 x 480 is not going to be able to hold the detail being resolved by the higher-res imager, it's all going to get rounded off, so is there a real-world, observable effect?[/quote]

Correct.  There is not an effect with regards to depth of field.  The issue is the number of used pixels versus area of space photographed and this effects the number of photons which impact each pixel to activate it.  There are some good reasons to have higher resolution imagers with regards to resolving lines, but they do not affect depth of field.  

Further, although technically 720x480, DV is a high compression codec.  
 
Re: how about a DOF tutorial??

Barry, you rock man!!!
You too slapdragon. (Tu eh fera, ein cara!)

You guys are really cool.

Thanks a lot for this tutorial.

All the best

Fidel.
 
Re: how about a DOF tutorial??

[quote author=araujofh link=board=news;num=1083366247;start=15#15 date=07/07/04 at 13:35:12]Barry, you rock man!!!
You too slapdragon. (Tu eh fera, ein cara!)

You guys are really cool.

Thanks a lot for this tutorial.

All the best

Fidel.

[/quote]

Obrigado muito muito, amigo.
 
Re: how about a DOF tutorial??

De nada cara! A gente ta aprendendo muito aqui. E eh gracas a voces.

For the guys that don't speak portuguese,

I was just congratulating and thanking slapdragon for his contributions to the forum.

The same goes to Barry Green who has been given me invaluable advices.

All the best

Fidel.
 
Re: how about a DOF tutorial??

Question: I was reading up on the Thomson Viper and noticed that it has 3 CCDs at 9.2 megapixels each. The output it provides however is only 1080 horizontal lines of resolution. I noticed in an article about it that this increased size in CCD resolution increases the latitude of the camera by about 2 stops. Wouldn't this as a result affect the exposure and then DOF? This would mean that CCD resolution does have a part to play in a camera's DOF...
 
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