Vic,
You are right about DOF tables being agreed and these being employed at shooting and no application thereafter. You're also right (of course) that these tables are based on agreed diameter of the circle of confusion, which does need to be understood (we've talked previously about this, anyway). The circle of confusion is the size of spot that will be perceived as a point under the defined viewing conditions. Perhaps most convincing if I quote directly from the American Cinematogrpher Manual:

" The circle of confusion.....can be briefly described as the image of a point situated outside the focused distance plane that will therefore not form the image of a point in the film plane, but a blurred circle of diameter Cc.
"Acceptable sharpness in past editions has been calculated as 0.002 inch image of a point (Circle of Confusion), for images on 35mm film. Because of larger magnification in present-day theaters, manufacturers have been using 0.001 inches in recent years, and these new tables follow that practice (0.0006 inches is used for 16mm film). Acceptable sharpness is affected not only by the geometry of the cone of light imaging a point object; it is also affected by:
1. the imaging quality of the lens both on-axis and off-axis at the plane of best focus.
2. The imaging quality at large and small, as compared to intermediate iris diaphram apertures.
3. Diffusion or flare, whether intentional or not.
4. The imaging quality of the films and printing methods used (negative, intermediate, and print).
5. Viewing conditions.
6. Object illumination and contrast.
"If for any of these reasons the sharpness of the best image is less than the arbitrarily established norm, the apparent depth of field will be affected also.
"Because DOF has no sharply defined limits, the distances in the tables have been "rounded off" to figures compatible with the distance."

So as Bob & I have said, the DOF depends on the size and distance of the viewed image. DOF is determined by how much a point can be out of focus before the viewer can see that it isn't focused. No absolutes. The point Bob was making about HDV is that because the image has greater resolution correct focus is more critical and a point out of focus is more easily detected. However view that from 20 screen widths and the point will have to be pretty fuzzy before you realise that.

Serena

Serena -

We are clearly talking about two extremely different uses (and sort of definitions) of DOF.
The one to which you and Bob are speaking relate to, "Is that sharp?". It's subtle and subjective, and totally related to a myriad of other infulences; size of screen, resolution, etc.

The DOF, or use of it to which I am so frenetic is the purposeful blurring of everything but the item which I as artist wish to draw my audiences' attention. There can be no doubt that the background in my close-ups are clearly out of focus. That observation will be clear at any size of projection.

And it is that very tool that I miss the most in DV production. It is also one of the most obvious "missing elements" in the forever sought after holy grail of the "film look". I even hated 16mm for the very same reason. My stuff never looked the same in 16mm (too small an image size - too wide of lens angle) and I gave it up very quickly.

I can't wait for the new, still unseen, but rumoured about, generation of video cameras that will sport "full sized" sensors. They already exist in still photography so it can't be too far away.

best,
v

Thanks to all for submitting their responses.

The future image pickups are rumered to be the answer to the "Look".
The cost is a major concern and makes me want to wait on HD purchases.

Will spending $600 or more now on an adapter give me something to put in the
Yellow Pages ad this coming phone book make money? ("Film look at video prices")

I don't think I'll ever get one of those little statues for my work or knowing all the
proper F stops but I do like the look.

Thanks.

Vic,
this is the sort of discussion that really needs a common pot of coffee and freedom to wave our hands about to clarify points. I think you can't redefine DOF to suit your argument -- it's what it is: a mathematically determined term (once you state your conditions). And that's what you launched off with before veering into the artisic use of restricted DOF (which I mentioned in similar terms some way up the thread). Absolutely agree -- need larger sensors. Even 2/3 inch are only S16 size. In the meantime, things like the Redrock Micro enable one to achieve that narrow DOF even if they do involve compromises. And I think you're saying that for artistic reasons the image compromises are well worth it. And when it comes to artistic questions, there are bound to be variations in approach.

all best,
Serena

DOF is a fuzzy subject, but the true of the matter is, the DOF area or cone radius is not linear in "sharpess" but closer to a bell curve. Of course, the the center of the bell curve has the "greatest acceptable sharpest", with the edges of the bell curve having the "least acceptable sharpest" for the DOF area. Buzz words are nice, but too many times the buzz words have multiple meanings for different professions, ie artist vs DP vs film school vs optical engineering. Sometimes, This leads to some wild explanations about CCDs, CMOS, lens, ie., that was become accepted "facts" .

Apit,
Accepted. "Perceived as a point" incorporates all the usual variabilities of observers.

Serena

Victor,
you are entirely correct. We are talking about the same thing but from a different direction.

In the case of say the typical product shot the product is totally sharply in focus and the background which is some distance removed is very clearly out of focus. And it's so far out of focus that you'd have to reduce the overall resolution to such a low value that no one could probably ever tolerate to look at it to make it all look "in focus" or equally sharp (they are much the same thing). I'd guess your real concern here about DOF is to ensure that the whole of the product is within the DOF, the client wants the audience to clearly see the product, and the out of focus background is there to force us to look at the product, the eye looks first for what it can clearly see.

You see for many years I took 35mm stills, I'd never claim any of them were very good as I'm no artist but I did look at the markings on the lens many times to check just how much would be in focus at the f stop I was using.

And then I read all the scientific stuff about DOF and optics and how the only way to get a shallow DOF was a bigger imager or else use a screen and take the image from that. Life was blissful.

But then Sony came out with the FX1, same dinky 1/3" sensors as say the trusty PD150, so from a DOF view nothing had changed. BUT one of the first shots posted from the FX1 was of a girl leaning against a tree, looked wonderful. But some nitpicker pointed out that if you looked at the image at a decent size the shot was focused wrong, it was focussed on the tree, not the girls eyes. Now this was never an issue with SD video so something must have been happening to challenge my blissful ignorance and the answer lies in resolution.

Now I'm not for a minute suggesting that with an FX1 you can get to the holy grail that you seek unless as you say you move the camera so far away from the subject that you really do need a megaphone for them to hear you and in the process totally blow your shots composition. No, not at all am I suggesting that.

What I am suggesting is that with a higher resolution camera projected onto a cinema size screen you get closer to your goal. Or in a more practical message. If you're shooting HD for a big screen what you learned about DOF with SD video has now changed. This isn't a small issue either, many have found this out the hard way, even a big SD monitor doesn't cut it for checking focus.

Now on a completely different matter here's my gripe about lenses and cameras. Testing a HDV camera a few days ago and just playing around I thought I'd try my hand at a rack focus, had a shallow enough DOF BUT, the optics in the Z1 render this pretty damn useless in my opinion, as you change focus so does focal length! Not a huge amount but it sure will never look like the real deal.

More research reveals that this is pretty common issue with cheaper lenses and their design. Now I don't know just how much this relates to using 35mm adaptors but I have read of others striking this problem. This isn't the fault of the adaptor but rather of the lens in front of the adaptor. Not relevant if your only intention is to gain a shallow DOF though.

Bob.

As Serena suggest, we all should share a pot of coffee (or a pint) one day, could make for some interesting discussions :)

"More research reveals that this is pretty common issue with cheaper lenses and their design" This has always been the case, cheaper lens usually have less lens elements, cheaper glass materials in making the len's elements, glue.....etc.. less fine machining and QC in assembly.

P.S.
This has been posted before, but its an interesting link that does discusses resolution/sharpness..... in HD and other things. link:"http://theschubinreport.com/archives.shtml"