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piblondin

Depth of Field on Film vs. Digital

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I recently moved from doing most of my photography with an M7 and 50/2 to an M9 with a 50/1.4. The most difficult thing has been getting used to much smaller DOFs at every aperture. Whereas I felt very comfortable focusing and reframing on my M7 without compromising any sharpness, I have had trouble with my M9 even in what I think would be very simple scenes. See, for example, the attached photo in which I focused on the letters of the sign and reframed by tilting my camera down. I shot this at f/5.6, which I thought would be enough DOF to compensate for the reframing, but clearly it wasn't. At 100% crop--also attached--you can see that the lettering is not in focus. Now, there's still the possibility that my lens/body are not calibrated correctly in some way, More likely, it seems that I'm just not used to having to focus and reframe so precisely at f/4 to f/8.

 

I felt like this article did a good job of helping me understand the difference in DOF between digital and film. Depth of field and digital sensors | Artfx - Le blog It suggests that the DOF on digital is nearly 1/3 that of what it would be on film--quite a difference!

 

Have other people had similar experiences with moving from film to digital bodies?

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I think the cue lies with the term 100% crop. You are looking at that part of the image at a vastly larger scale of magnification than you used to for your film images. Under that circumstance the old rule of thumb for the DOF no longer holds true.

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Well, yes and no. I scan my film shots to a resolution higher than that produced by my M9. When I print at 16x20 inches, the grain certainly shows, but it never looks like I missed focus--i.e. that some area other than the intended one appears sharper.

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Technically what you're seeing isn't really a difference in DOF, assuming that the shot is perfectly focused. Firstly film is a three dimensional thing. It has depth. For all practical purposes sensors are 2D. And the spectrum of light doesn't focus all colours at the same plane. Newer lens designs reduce this with special glass and element shapes but don't eliminate it. Secondly DOF is directly related to the circle of confusion. On digital you need nine pixels to create a circle. There are some visual differences because of this.

 

Finally sensors all have a piece of glass covering the sensor. The M9 may not have an AA filter but that cover glass does become part of the optical formula of the system. You'll need to have some sharpening of the file to counteract the cover glass even if the Leia one is thin and not anti aliasing.

 

At 5.6 there should be more than enough DOF to focus on that sign. You might need to look at a capture sharpening routine to offset the digital capture process.

 

Mind you it doesn't look out of focus to me. Just not adequately sharpened. Are you sure your film scans aren't being sharpened. That would do it for sure.

 

Gordon

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When working like this - focus, recompose, shoot - you might add an extra step:

focus, shoot, recompose, shoot

The first image is a handy debugging tool for your recomposing movements

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Also looking at the number 5 it looks like you may have a very slight amount of camera movement in this shot. In high pixel count digitals the old rule of 1 over the focal length isn't a great rule of thumb. You really need to do this test on a tripod to be sure.

 

Gordon

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When working like this—focus, recompose, shoot—you might add an extra step: focus, shoot, recompose, shoot. The first image is a handy debugging tool for your recomposing movements.

That's a good idea. Thanks for the suggestion.

 

May I suggest another step, like this: focus, (optional: shoot), recompose, (optional: shoot), lean body backwards an inch or two, shoot. The problem with this sequence, however, is: You will lean backwards too much, hence over-compensate the recompose error. It takes quite some practice to get it right.

 

In general, the problem with digital vs film is not less depth-of-field but more sharpness. The extreme sharpness of digital at the very plane of focus immediately raises the user's standards and makes the fall-off towards the limits of the DOF range just more obvious, as well as the loss of sharpness due to less-than-perfect focus.

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The issue is depth of focus, not depth of field.

 

Better now?

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Good catch.

 

s-a

 

I'm not sure I understand what "depth of focus" means. I Googled the phrase, and what I've gathered is that it refers to changes in the distance between the sensor and the lens. I'm not sure how that would be applicable here. Can you explain further?

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Also looking at the number 5 it looks like you may have a very slight amount of camera movement in this shot. In high pixel count digitals the old rule of 1 over the focal length isn't a great rule of thumb. You really need to do this test on a tripod to be sure.

 

Gordon

 

That's quite possible. I was hoping that 1/90 second would be enough to eliminate the camera movement, but it seems like I may need to go for faster shutter speeds.

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I'm not sure I understand what "depth of focus" means. ?

 

 

It addresses the focus at the sensor or film plane. Briefly, the longer the lens, the greater is the zone of focus. We large format people are grateful of the principal.

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Hello Piblondin,

 

There seem to be a number of additional variables in these 2 parralel equations which might make it difficult to ascertain what is actually causing whatever is happening to happen here.

 

One way to determine what is actually happening as per depth of field might be to try the following:

 

Pick a subject like the sign in question & place yourself at a 45 degree angle to it.

 

Set up a strong solid tripod.

 

Put 1 camera on the tripod with 1 of the lenses.

 

Focus on something in the MIDDLE of the sign being viewed from a 45 degree angle. Take 5 pictures refocussing each time & record the distances the lens barrel says the photos were taken at.

 

Remove the camera you were using but do NOT reposition the tripod.

 

Put the other camera on the same tripod which is still at the same spot.

 

Put the SAME LENS that you used before on the second camera. Repeat as above.

 

Do you notice any difference in your ability to focus the lens between the .68X of the M9 & whichever magnification the range/viewfinder magnification is of the M7?

 

Compare the 10 photos & show us what the differences are as per depth of field, etc.

 

Then we might be able to proceed without a number of the additional variables that are in your current set of circumstances.

 

Best Regard,

 

Michael

Edited by Michael Geschlecht

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As an alternative point of view to those already given to me it looks like there is camera shake, and looks like it hasn't had any micro contrast applied or been sharpened. All of which on a digital camera make for a softer image because of the intrinsic smoothness between tones with higher megapixel sensors.

 

It is why a B&W film image can look sharper against a digital image that is straight out of the camera, but it isn't sharpness you see, it is the edge effects of the emulsion and grain giving the eye something to focus on, which the brain processes to read 'sharp'. It is also why a low megapixel digital camera can initially appear sharper in a print than a un-manipulated high megapixel image, because the transitions in tone are cruder with bigger jumps between tone and colour, so giving the impression of sharpness.

 

So instead of going back and forth asking 'was the camera on a tripod, has the image been sharpened or had some contrast applied?' I'll jump in and say it is all about perception, steadying the camera with a tripod, and post processing. I may be right or wrong, but somebody needs to ask the obvious question.

 

 

Steve

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Camera shake for sure. If you have a heart-best you have camera movement at 1/90th.

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Camera shake for sure.

Hghi MPixel digital systems are more likely to show up camera shake in much the same way that they 'reduce' perceived Dof and increase the requirement for precise focus. Looking at files at 100% will reveal any 'sloppiness' in their production. Film was (sorry, is;)) much more forgiving as grain impinges where digital noise (today) does not.

 

I've found that with digital now use smaller apertures when possible or at least use DoF scales for an aperture 2 stops wider than set and 1~2 shutter speeds higher than the reciprocal of the focal length (all relative to film days). I also concentrate of focusing and ensure that my point of focus is well considered and accurate. And when relevant I use a tripod (although I try to avoid this with the rangefinder).

 

All that said, it is possible to get very 'sharp', 'crisp' images with no signs of camera shake, at significantly lower than usual shutter speeds. Its just rather more hit and miss and never guaranteed.

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Old fashioned dof scales assume that the print is viewed at a 'normal viewing distance' which I can remember being defined as a multiple of the diagonal of a print made from the full frame, but for practical purposes you can think of as a distance so that you can comfortably see the whole picture.

If you are loooking at a 100% crop on your monitor at about a foot away you are considerably closer than that so that 'acceptable' sharpness is not so acceptable any more.

 

Gerry

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I shoot film (M6) and digital (M-E) in tandom when I'm out and about and I've noticed that in general my film prints tend to appear sharper than my digital images (particularly for images shot during early morning w/o a tripod). I didn't realize that the 1/FL rule doesn't hold as true for digital as it does for film, but it really does explain the results I've seen.

 

Much thanks to the OP and the people that posted responses. I just got learned.

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I didn't realize that the 1/FL rule doesn't hold as true for digital as it does for film,...

 

I suspect it would if the film used is as fine-grained as "is" the sensor. If anything the pixel has sharper edges, by far, than does a filigree edge of a grain of silver. Digital has long since surpassed Kodachrome and probably will the microfilms as well soon enough. New rules-of-thumb to learn, that's all. I'd probably gain a stop of steadiness if I cut out the alcohol and coffee...

 

s-a

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