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Author Topic: H4D-40: Sample files  (Read 19634 times)
Dustbak
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« Reply #140 on: April 08, 2010, 12:17:52 AM »
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Quote from: gwhitf
Yair,

Here's another educational exercise I'd like to do: I'd like to take a MF body, any brand, and set it to any particular fstop, say, f5.6. And then, shoot a frame with a digital back on it, and then shoot another frame with a film back on it, and then check the relative depth of field at that same fstop.

I know, in theory, you'd think that the depth of field would carry the same with both the digital back and the film back, but everything in me says there's somehow less depth of field with a digital back than with film.

And that, somehow, this factor plays into this giant mystery about focus issues with digital, in general.

This is all pure speculation on my part, (but based on lots and lots of jobs shot, both with MF film, and MF Digital). Just a gut feeling.

I remember those tests I did, years ago with digital, and I'd set up a shot in the studio, on tripod, with nothing moving or changing, and I'd set the fstop to say f8, and then I'd press the Depth Of Field Preview button down, on the camera body, to somewhat previsualize how much focus would carry at that f8. But then, I'd shoot the digital file, tethered, and I'd check it on the monitor, and there would always be radically less depth in focus in the actual digital file than what was shown in the Depth Of Field Preview button.

I'm not a Scientist; I never knew why. You'd think, in theory, they would match.


Sofar I have heard 2 explanations for this phenomena, which indeed I agree with you having experienced the same thing;

1) There is no DoF, it doesn't exist. There is just 1 point sharp within the focal plane, the rest is acceptable sharpness. With digital we now look at 100% on our monitors and we have redefined what we feel is acceptable sharpness.

2) Film has more depth than a sensor and thus is more forgiving and shows more DoF or more acceptable sharpness so you will.

Not sure which is it if any of the 2.
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Dick Roadnight
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« Reply #141 on: April 08, 2010, 01:17:37 AM »
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Quote from: gwhitf
Yair,

I know, in theory, you'd think that the depth of field would carry the same with both the digital back and the film back, but everything in me says there's somehow less depth of field with a digital back than with film.
There are several very good reasons why focus seems more critical with digital:

We are over concerned about diffraction, so we tend to use f8 for digital, when f11 or f16 might be optimal... and we would have used f16 or f22 on film.

We like to think that digital gives us higher res, and if you set higher standards for ¿what is sharp? you get less DOF.

We like to try to enlarge more from digital, making focus more critical.

With digital it is very easy to (instantly) check focus.

With digital more of us rely more on autofocus... and before the H4D that was a problem.
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yaya
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« Reply #142 on: April 08, 2010, 01:28:36 AM »
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Quote from: JdeV
Done it. Shot for 20 years on view cameras. More than 10 years with neg. printed 16" x20" by me. Shot in all conditions, all round the world. I have filing cabinets full of negs. Just about none have missed focus.
On the other hand, give me a P65 on a view camera or an H and I have to have an operator check on a screen or I have to zoom in myself on the crappy LCD. If I don't I lose images because of focus.
This is not principally a matter of judging digital to a different standard because we are looking on screens at 100% it is simply much harder to hit focus with digital.

I agree that on a view camera, focusing a 645 sensor area on the GG is more difficult than a 4X5 sheet film area, given an equivalent focal length. On a 645 camera there is no difference in focusing in my experience.

My suggestion was to run that test side-by-side; same framing/ light/ aperture etc. and if possible, scan and view at the same magnification.

Yair
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bcooter
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« Reply #143 on: April 08, 2010, 02:43:44 AM »
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Quote from: yaya
I agree that on a view camera, focusing a 645 sensor area on the GG is more difficult than a 4X5 sheet film area, given an equivalent focal length. On a 645 camera there is no difference in focusing in my experience.

My suggestion was to run that test side-by-side; same framing/ light/ aperture etc. and if possible, scan and view at the same magnification.

Yair


This all may be true.  I don't think so, but I haven't shot film in a long time.

What I do know is how different the optical viewfinder is from the final results and not just in focusing on the desired subject, but the way it throws focus.

Yair, do this with your aptus.  

Walk around London and shoot some out of focus back ground plates.  Focus using the groundglass (plastic) and try to throw the background street signs just slightly out of focus.

Then shoot and look at the lcd.  What was slightly readable as a sign that says MG motorworks, becomes a big blur of non recognizable background.

I've shot hundreds of background plates for windows, car reflections, and have done it with all sorts of cameras and they all look very different in the optical viewfinder than the lcd, or the computer.

Did film do this?  I don't remember, but I do know digital cameras do.

The only exception is the live view cameras.   You pretty much see what your going to get.

BC
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ErikKaffehr
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« Reply #144 on: April 08, 2010, 04:04:18 AM »
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Hi,

In my view both.

Film has a certain thickness and has some curvature. Both factors affect and reduce maximum achieveable sharpness.

Some articles I have on these issues:

http://echophoto.dnsalias.net/ekr/index.ph...vs-mfdb-vs-film

http://echophoto.dnsalias.net/ekr/index.ph...ng-the-dof-trap

http://echophoto.dnsalias.net/ekr/index.ph...-sony-alpha-900

Best regards
Erik


Quote from: Dustbak
Sofar I have heard 2 explanations for this phenomena, which indeed I agree with you having experienced the same thing;

1) There is no DoF, it doesn't exist. There is just 1 point sharp within the focal plane, the rest is acceptable sharpness. With digital we now look at 100% on our monitors and we have redefined what we feel is acceptable sharpness.

2) Film has more depth than a sensor and thus is more forgiving and shows more DoF or more acceptable sharpness so you will.

Not sure which is it if any of the 2.
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yaya
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« Reply #145 on: April 08, 2010, 04:27:17 AM »
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Quote from: bcooter
Walk around London and shoot some out of focus back ground plates.  Focus using the groundglass (plastic) and try to throw the background street signs just slightly out of focus.

Then shoot and look at the lcd.  What was slightly readable as a sign that says MG motorworks, becomes a big blur of non recognizable background.

I've shot hundreds of background plates for windows, car reflections, and have done it with all sorts of cameras and they all look very different in the optical viewfinder than the lcd, or the computer.
BC

That's 100% true but that's because on the LCD you're looking at a MUCH greater magnification of the scene/ subject compared to what you see through the finder.
On the LCD (the ones that actually show 100%, most don't) you're looking at small part of an image which can be 3 foot wide whereas in the finder it's less than 3 inches...

If you could have a loupe that magnifies at the same scale I think that you'll see the same blur (or sharpness).

Which is why I would recommend doing any focusing tests on short distances, so to increase the chance that what you see as sharp through the finder is actually sharp...

Yair
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gwhitf
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« Reply #146 on: April 08, 2010, 07:23:22 AM »
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Quote from: Dustbak
Sofar I have heard 2 explanations for this phenomena, which indeed I agree with you having experienced the same thing;

1) There is no DoF, it doesn't exist. There is just 1 point sharp within the focal plane, the rest is acceptable sharpness. With digital we now look at 100% on our monitors and we have redefined what we feel is acceptable sharpness.

I have always felt this way, and this whole term of "carrying focus by stopping down" is just a loose term, (and to me, a misnomer/fallacy). Yes, you might get a few more things recognizable in the background by stopping down, but just setting your lens to f16 is not going to pull things into focus, if they aren't on the focus plane. You know how, for years, you see those diagrams printed right on every lens you've ever bought, some kind of Depth of Field scale. It's just completely untrue, what they would lead you to believe. There is only ONE thing in focus, and that's the thing that just accidentally happens to be dead on where your lens is focused, and everything in front of that, and behind that, will sorta/kinda come into recognizability, they sure aren't going to "come into focus" by stopping down.

Ever experienced this when editing? You're editing away, looking at the frames, and you go "Yeah, that's sharp, and that's sharp", but then, you come to Frame 11 or whatever, and for some reason, it's just OMG in Super Focus? Like all along you were shooting 645, but this one particular frame is so super sharp it looks like you were shooting 8x10? You know that feeling? Why does that happen? I just think there's a lot more going on about this focus thing than we all know, (or admit).

The only other thing affecting Depth of Field, to me, is just the choice of lenses. Default optical focus, by mounting a 24 or 17 or something wide, and having built in depth already, by the optics alone. But even then, even with something wide wide, there's still just one plane of Super Focus, and everything else, in front and rear, is just Acceptable Focus. Even at f11 or so.

I cannot explain it, but i'm trying to describe it.
« Last Edit: April 08, 2010, 07:25:04 AM by gwhitf » Logged
John R Smith
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« Reply #147 on: April 08, 2010, 07:49:19 AM »
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Quote from: gwhitf
I have always felt this way, and this whole term of "carrying focus by stopping down" is just a loose term, (and to me, a misnomer/fallacy). Yes, you might get a few more things recognizable in the background by stopping down, but just setting your lens to f16 is not going to pull things into focus, if they aren't on the focus plane. You know how, for years, you see those diagrams printed right on every lens you've ever bought, some kind of Depth of Field scale. It's just completely untrue, what they would lead you to believe. There is only ONE thing in focus, and that's the thing that just accidentally happens to be dead on where your lens is focused, and everything in front of that, and behind that, will sorta/kinda come into recognizability, they sure aren't going to "come into focus" by stopping down.

All of this is completely true, and always was true with film as well. Depth of Field scales were worked out on the basis of an acceptable "circle of confusion" IIRC, which was fine in the 1930s when they were defined with the films of the day and relatively small-size standard prints. What I think happens with film (as opposed to digital) is two things -

* The thickness of the emulsion and the backing layer produces a degree of halation which means that film is never as sharp as a digital sensor (comparing like for like, same lens and sensor/film area).

* The grain structure of the film diffuses apparent focus over a broader plane in the image, giving the impression of greater focus depth. Hence very grainy shots on HP5, say, look very crisp even though critical focus may be nothing special.

And of course, if we did print MF to very large sizes back in the day, we expected it to look a bit soft. Now everyone expects pin-sharp detail even if the print is six feet wide.

However, saying as above that there is only one point in the frame which is actually going to be truly in focus, true as it may be, is of no help at all to those of us who do landscape or architectural work where everything must be in focus, or must at least appear to be so. The biggest problem occurs when one has foreground subjects and distant objects in the same shot, as with this one. If I focused for maximum depth of field, according to my old film paradigm, the only part of the shot which would actually be truly in focus in digital would be somewhere out in the middle of the river, where you would never notice it anyway, because the eye is naturally drawn to the foreground or the distant trees.

John
« Last Edit: April 08, 2010, 08:48:22 AM by John R Smith » Logged

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BJL
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« Reply #148 on: April 08, 2010, 08:23:23 AM »
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Quote from: John R Smith
All of this is completely true, and always was true with film as well. Depth of Field scales were worked out on the basis of an acceptable "circle of confusion" IIRC, which was fine in the 1930s when they were defined with the films of the day and relatively small-size standard prints.
Indeed, I believe that the standard criterion used for almost all DOF scales on lenses and traditional DOF chart is something like what will not be noticeably out of focus to reasonably sharp eyes when
- printed at 7"x5"
- viewed from 10", which is about the diagonal length of the print.

Since what counts most is the ratio between viewing distance and image size, or to get fancy the angular size of the image, I would summarize this as saying that:
traditional DOF guidelines try to ensure that everything within the stated range of distances will probably appear in focus to most viewers so long as they view from a distance at least as great as the diagonal length of the uncropped (or minimally cropped) image.

Problems arise when images are viewing more closely that that, whether it be close scrutiny of large prints, or by viewing only a crop from the full image size for which the DOF guidelines are computed. The latter happens big time when a small fraction of the image is enlarged to fill a computer's display, or the camera's rear screen. It also happens to a smaller degree with the "sensor crop" of DMF sensors smaller than the film format on which the DOF scale is based, and the related higher enlargement factor needed to get a given size of print.
« Last Edit: April 08, 2010, 08:25:37 AM by BJL » Logged
Dick Roadnight
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« Reply #149 on: April 08, 2010, 01:10:33 PM »
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Quote from: John R Smith
* The thickness of the emulsion and the backing layer produces a degree of halation which means that film is never as sharp as a digital sensor (comparing like for like, same lens and sensor/film area).

However, saying as above that there is only one point in the frame which is actually going to be truly in focus,

John
They used to like to imagine that the three colours got focused on the three colour layers in the emulsion.

There is one plane of sharpest focus, so, with a co-planar subject, you can have it all in focus, and, with a view camera, it is supposedly possible to get three points in perfect focus.
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