M and DOF

[viramati]

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I seem to be finding a reduced DOF on my lenses whether this due to the higher resolution I really don't know and hence my question to the more technical among you. I find that the DOF scale now seems less accurate with a reduced latitude. eg on my Cv 12 f5,6 V.1 which has a indent mark on it for everything to be in in focus from about 2' to infinity, this is no longer the case at 5.6 and I have to move the focussing slightly further towards the infinity mark. I have noticed the same with other lenses which makes using the DOF scale for zone focussing more difficult.

So observations welcome

[John McMaster]

Compared to what camera?

 

john

[lct]

Never tried with such a wide lens. Does it work when using the DoF markings corresponding to f/4?

[pgk]

So observations welcome

Nothing has changed in terms of the image from the lens - the lens is creating the same image with identical characteristics to those it has always produced but the sampling is slightly higher.You are quite simply examining the images in greater detail than previously and higher magnification = increased criticality of what may or may not be considered as being acceptably 'sharp'. I have used a simple rule of thumb of using the DoF scales for an aperture 2 stops wider than the one I'm actually using since the M8. You will need to determine your own levels of acceptability.

[01af]

The film's or sensor's resolution doesn't affect depth-of-field. Magnification does. So if you print bigger (and look at the big print from a short viewing distance) then your perceived depth-of-field naturally will become narrower accordingly.

 

It always was this way.

[lct]

I should redo my old tests with the M240 to be sure but DoF markings work fine for me with FF generally. Crop cams like the M8 are another story. More resolution could be more demanding when using 100% on screen magnification though.

[jaapv]

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01AF is right. However, the higher the resolution the more visible small differences become. So at 100 % (01AF's magnification!) you will notice things that are marginally out of focus that you did not see before.

In other words the zone of maximum focus becomes thinner. When you print smallish or medium size it makes no difference. When you print large you may notice a small difference, when you zoom in to 100% the difference is clear.

The same goes for small amounts of motion blur. On a lower res. sensor they may not be visible, on a high-res sensor they will. Visit D800 forums to find long threads on the subject.

 

Note that we are pixel-peeping here.

[viramati]

I am comparing to the M9 and am noticing a difference in scale at 1.1 magnification across all lenses. this is not a complaint or anything was just wondering on the technical reasons

[01af]

However ...

No. Not "however".

 

 

... the higher the resolution the more visible small differences become.

... the more visible small details will become.

 

 

So at 100 % (01af's magnification!) ...

No. Not "my magnification"

 

 

... you will notice things that are marginally out of focus that you did not see before.

Uh oh. I am afraid you still haven't fully grasped the difference between magnification and resolution.

 

So, for a real-world example: When used with the same lenses and printing to the same size then the Nikon D700 (35-mm full-frame format sensor with 12 MP) has exactly the same depth-of-field as the Nikon D800 (35-mm full-frame format sensor with 36 MP). Image size, focal length, focus distance, and aperture affect depth-of-field; megapixels don't.

 

 

... when you zoom in to 100 % the difference is clear.

Zooming in to 100 % on a high-resolution picture means a greater magnification than zooming in to 100 % on a low-resolution picture. And greater magnification means less depth-of-field.

 

 

The same goes for small amounts of motion blur.

The same indeed—just like depth-of-field, motion blur does not depend on resolution. Instead, it depends on subject speed, angle of motion relative to the optical axis, shutter speed, and magnification.

[IWC Doppel]

I'd do think that the graduation between in and out of focus is steeper on later produced lenses, the defined point where focus 'starts and stops' may well be the same however

[pico]

The larger your view, or print, the more critical (or smaller) an acceptable circle-of-confusion must become (depending upon anticipated viewing distance.) Since most of us view the screen from about the same distance, then viewing a greater number of pixels at 100% is like viewing a larger print.

[jaapv]

I'd do think that the graduation between in and out of focus is steeper on later produced lenses, the defined point where focus 'starts and stops' may well be the same however

I would not say steeper, more like "more sharply defined".

[pico]

I'd do think that the graduation between in and out of focus is steeper on later produced lenses, the defined point where focus 'starts and stops' may well be the same however

 

I could use some help with that. The greater contrast and abrupt transitions in OOF are so dramatic with some later lenses, that the term "over-corrected spherical aberration" comes to mind. My taste for such developed before super-lenses.

 

Sharpness is over-rated.

[thighslapper]

I seem to be finding a reduced DOF on my lenses whether this due to the higher resolution I really don't know and hence my question to the more technical among you. I find that the DOF scale now seems less accurate with a reduced latitude. eg on my Cv 12 f5,6 V.1 which has a indent mark on it for everything to be in in focus from about 2' to infinity, this is no longer the case at 5.6 and I have to move the focussing slightly further towards the infinity mark. I have noticed the same with other lenses which makes using the DOF scale for zone focussing more difficult.

So observations welcome

 

Didn't you recently tinker with the infinity roller adjustment ?????

[viramati]

Didn't you recently tinker with the infinity roller adjustment ?????

nothing to do with that my focus is now spot on at all lengths, what I'm talking about is the DOF scale, limit of perceived sharpness and all that malarky, and anyway the CV12 f5.6 v.1 isn't even linked to the rengefinder mechanism.

I should imagine anyway that DOF scales were calibrated for film and not digital sensors where I presume one had greater perceived DOF or am I wrong

[andybarton]

The depth of field on my DMR equipped R8 was definitely "thinner" when using the back, rather than when using film. If I was using, say, f5.6, I would use f4 as the indicator of depth of field. No reason to believe that this would not be the case for an M too.

[AlanG]

This has all been covered many times before. DOF scales are simply calculations using circle of confusion information. It is not as if each lens design and camera system is tested before the lens scales are marked. They assume the image is sharply focused and are generally based on test studies using 8x10 prints viewed from about a foot away by viewers with average eyesight. But there are no hard and fast rules and each lens manufacturer can calculate this as they wish. On a 5x7 print the DOF scales understate the DOF.

 

The idea is that DOF is the limit where the circle of confusion is still resolved as a point. So of course greater resolution and higher magnification is going to start showing this as a blurry circle. Thus if some areas are extremely detailed, at high magnification it is easier to see where other areas are not so detailed. You may even be able to tell that the center is sharper than the edges and this has nothing to do with DOF.

 

Any additional magnification or closer examination would cause the depth of field scale to be incorrect. It has to be recalculated for different magnifications and viewing situations. It assumes a "perfect" lens and reproduction system and of course would not make sense for a soft focus lens or a low res camera. Shoot some landscapes on a foggy day or handheld at long shutter speeds and see if the DOF information still applies to your images.