how about a DOF tutorial??

Re: how about a DOF tutorial??

Hmmm. At this point we officially enter the realm of "I have no idea what I'm talking about" but... 9.2 megapixels would be over 4x as much as they need. I thought I read somewhere where they were using smaller pixels together as a "superpixel", so if they grouped 'em in 2x2 blocks, that'd bring it down to about 2 megapixels of "superpixels"... perhaps that's what they're doing?
 
Re: how about a DOF tutorial??

How does the anamorphic adapter for the DVX100 affect the DOF?

When shooting 35mm anamorphic, you deal with reduced DOF compared to spherical lenses. That's why some DPs prefer shooting Super35 to gain the extra DOF.

From what I've been reading about the adapter for the DVX100, apparently it increases DOF? I'm I getting this right?
 
Re: how about a DOF tutorial??

In film cameras you're dealing with a 2:1 squeeze factor, so it's much more pronounced than in video where it's just a 1.33:1 squeeze.

The anamorphic adapter affects DOF in two indirect (and contradictory) ways. First, because the adapter expands your field of view, in order to get the same framing with the anamorphic as you'd get with letterbox (or squeeze), you have to be zoomed in some on the anamorphic. That additional telephoto makes for *slightly* shallower DOF. (Not a big deal, but it's really been annoying me because I'm trying to get comparison shots to show how much sharper the anamorphic is, and the background's getting softer, which is the opposite of what I expected until I figured it out!)

Second, the anamorphic affects the DOF in that it limits how shallow you can get. With the DVX the key to shallow DOF is to zoom in all the way (or, as IAL has demonstrated, zoom out and get really, really, really close to the subject). But with the anamorphic you have to stop down the lens in order to get proper focus when you're at close focus distances or when you're zoomed in all the way. That means that you basically can't get the shallow DOF look with the anamorphic adapter, under many conditions.
 
Re: how about a DOF tutorial??

I'm definitely lost here.

From what I've been reading around on the net, is that anamorphic lenses produce a more shallow DOF.

"Third, these adapters [anamorphic] provide only a limited zoom range and a greater-than-usual minimum focusing distance. They also provide a shallower depth of field. Lastly, 4:3 cameras do not have switchable viewfinders, so composition is difficult with an adapter. These problems have limited the acceptance of this method."
http://www.findarticles.com/p/articles/mi_m0HFE/is_2001_Jan/ai_69703415


Even ASC Manual (8th edition) has a whole chapter discussing anamorphic vs spherical. And recommends that one should consider anamorphic DOF half that of spherical. But then again, like you said, the squeeze is much less with the panny adapter.

This link is also very interesting:
"Since anamorphic lenses "feel" more wide-angle because of their greater horizontal view, the tendency is to use longer lenses (hence the lower depth of field many people notice.)" - David Mullen, ASC
http://www.cameraguild.com/php/phorum/read.php?f=1&i=293&t=293

After going through this last link, I think I'm sort of getting it.

I think it comes down to FOV. How does this sound:
If we have both a 50mm spherical lens and a 50mm anamorphic (2:1) lens, the anamorphic would cover twice as much of a scene, horizontally. So in an effort to reach a similar FOV, you would need a longer anamorphic lens, thus reducing DOF (vertically, anyways)?
 
Re: how about a DOF tutorial??

That's exactly right. You've got it.

Like I said, the DVX's anamorphic exhibits a *little* bit of this effect, because you do have to zoom in to get an equivalent field of view. But with the mild squeeze, it's really not much to write home about. And with the smaller apertures you typically need to use to overcome the astigmatism, it usually nets out to where the DVX's anamorphic exhibits *deeper* depth of field.
 
Re: how about a DOF tutorial??

I went ahead and calculated the DOF for a few setups (ranging from MCU to ECU shots), considering Adam Wilt's chart for critical sharpness, and the conclusion is that because of the lens's imperfections and the need to stop down the lens, you end up with a more extended DOF than you would without the anamorphic adapter with a "similiar" FOV. So besides sharpness you also end up with "a lot" more DOF :(

If the lens were perfect or, may I say, less imperfect, we would actually benefit from a reduced DOF (in relation to a similar FOV setup with a spherical lens).
 
Re: how about a DOF tutorial??

Barry, please hurry with your tutorial DVD and i'll be the first one in line to buy it ;D
 
Re: how about a DOF tutorial??

Hi folks,

Still this COC, ZOC thing is very hard to get.

Anyway, found this site that might be also helpfull, don't know if it was already mentioned.

It is a depth of field calculator. You can input the lens multiplier factor (Lmf for dvx100 is 7.2) and the dvx lens focal lenght /apperture being used.

http://www.outsight.com/hyperfocal.html#digital

Please tech guys (Barry, Slapdragon, ..) check if it works and let us know!!! :)
 
Re: how about a DOF tutorial??

I've been a long time viewer of this forum and what can I say?
Barry is THE... pronounced as THEE... man.

thanks mucho barry!
 
Re: how about a DOF tutorial??

Thought you guys might like this multi format DOF comparison.

To give you a true sense of what each format will give you in terms of DOF I've kept the FOV the same and the distance between the camera and actor the same - thus different focal lengths between formats. I also used real world lenses commonly available for each format which explains the different minimum f/stops used. For the following comparison an actor is placed 10 ft from the cameras postion. The camera is never moved nor is the FOV changed. I choose a common composition - in this case a medium/CU shot (mid chest to top of head) of the actor. Here are the focal lengths and DOF of available lens in each format:

Medium Format (645) - 200mm(FL)/f2.8 = 2 inches(DOF)
35mm (Still Camera) - 135mm(FL)/f2.0 = 2 inches(DOF)
35mm (Motion Cam) - 85mm(FL)/f1.3 = 3.5 inches(DOF)
16mm (Super 16) - 50mm(FL)/f1.3 = 6.5 inches(DOF)
2/3" (CCD Video Cam) - 35mm(FL)/f2.0 = 2ft, 2inches(DOF)
1/3" (CCD Video Cam) - 18mm(FL)/f1.7 = 3ft, 4inches(DOF)

Again the reason why their are different FL for each format is because they all give the same FOV from the same subject distance so in other words they are the same equivalent lens for its format.

Medium format image size/gg is at least 2.7X larger than 35mm (Still)

Hope that gave a broad picture of the real world formats out there. See ya.

Brett Erskine
www.CinematographerReels.com
 
Re: how about a DOF tutorial??

"The imaging size has nothing to do with the depth of field."

Alone it does not, with a lens it certainly does. The 35mm format has a shallower depth of field than does the 16 mm format at a particular focal lengths just as a 1/3 inch CCD camera has a deep depth of field than does as 1/2 inch chip.

Or lets look at it this way. Say I had an Arri 35mm camera with an aperture set up for 4:3 TV. On that camera I had a 40mm lens set at f2.8. My total DOF would be 2.7066 feet with my near focus being 8.8266 and my far focus being 11.5332 feet. My circles of confusion on that set up is .025mm.

Take a DV camera and create the same set up. I get a DOF of 168.7203 feet. My circles of confusion are .011mm. My angle of view between the two would be considerably different. The 35mm has a angle of view of 21.5 degrees and the DV 5.2 degrees. Ok so you say, but they are not equivalent? Side by side I would see a body in the 35mm lens and a nose hair on the the DV camera at that equivalent? Correct.

In order to get a field of view similar to the 35mm camera I would need to put a 9.5mm lens on the DV camera. If I did, I would get a 21.5 degree field of view and much more like the same shot on the 35mm camera. In that case even though the DV camera is shooting nearly the same framing as the 35mm (DV frame= 5.0526' width x 3.8' height vs 35mm=5.05'x3.8') my DOF between the two cameras shooting identical fields of view is very much different. Everything from 9 feet to 11 feet would be in focus in the 35mm shot making a DOF that is only 2.7 feet while everything from five feet to infinity in the Dv camera would be in focus.

Here is a little article that might help:

http://www.dvinfo.net/articles/optics/dofskinny.php
 
Re: how about a DOF tutorial??

Walter, thanks for participating with us -- your posts and articles are excellent! We look forward to much more participation!

I am in complete agreement, in fact I had said that earlier: the imaging size doesn't affect DOF directly, but it does affect field of view, which dictates the focal length necessary, and it's the focal length that affects the DOF.

So you cannot have the same field of view AND the same depth of field, when using a different imaging size. You can match either one of those factors, but not both at the same time.
 
Re: how about a DOF tutorial??

I couldnt agree with both of you more so if you were trying to correct what I posted - no need. In fact my guide is based on what you guys are saying - then with that understanding it looks past all of the specs and deals with real world results that you can actually expect to be able to achieve from each format (taking in account for fl lens and min.f/stop available).

Basically its designed to give a TRUE understanding of the DOF characteristics of each format by laying each side by side.

Hope Im not overexplaining it. Anyone find it useful?
 
Re: how about a DOF tutorial??

ok i found this groovy calculator for DOF, can someone please tell me what to plug into the various fields?

and i assume this changes when you put on the anamorphic adaptor?

i am pretty sure barry's book will cover this, i'm on mailman stakeout for the next couple of days, hopefully it comes before the weekend, my wife is out of town and i have tons of spare time!

matthew
 
Re: how about a DOF tutorial??

The first batch is going out today! I should be caught up on all orders by Monday.

For a DOF calculator, go to the Panavision NZ site, and use the presets for 1/3" video.
 
Re: how about a DOF tutorial??

Yes using the anamorphic adapter will have a slight effect on the DOF but only because of the change of FOV (widescreen) and its association to DOF. Perhaps the exact numbers are listed in Barry's book.
 
Re: how about a DOF tutorial??

Hi guys, I know this thread was opened long ago, but I couldn´t help it to get in... hope someone is still following this thread

Regarding the DOF mith #1 (imaging size does not matter), I have some lack of knowlegde with this:

I have some Nikon's optics for a 35 mm reflex still camera, non digital. I recently bought the digital "sister" of it, so I can use the same optics, and I have to say that being focal length the same, being the aperture the same, and being the distance to subject the same, the DOF is different (and the Field of View!). To my knowledge this is because the created image is different: in camera #1, the film is 35mm size, and in camera #2 (the digital one), the image is 1/3 of an inch, which is roughly 8mm.


So, in my humble opinion, the imager size matters when talking about DOF, but that is nothing we should worry about since we cannot change the imager at will in our DV cameras.

If I'm wrong, please someone to chime in a explain why!. Thanx a lot
 
Re: how about a DOF tutorial??

The field of view is different, and that's what the imager size affects. The smaller the imager, the more wide-angle a lens you need to get the same field of view, and it is that wider-angle optic that dictates the deeper DOF.

The imager dictates the necessity of using wider-angle or more-telephoto optics, but it doesn't in-and-of-itself have any effect on depth of field -- the DOF is fixed by the lens as it gets projected on the imager, and the imager just records what the lens is giving it.

(now, we could get into discussions about the circle of confusion and magnification sizes, but that would just show why smaller imagers should technically have *shallower* DOF when blown up to the same viewing size, which just confuses things even more...)
 
Re: how about a DOF tutorial??

Hi Barry, thanks for the follow up... I have to say that I didn´t notice there were 2 more pages of this thread (I read just the first one), and after reading all of them, I better understand DOF and FOV.

Thanks again.
 
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