Image plane difference between film and digital chip

A

awilder

Alan Wilder
Local time
3:41 AM
Joined
May 12, 2005
Messages
1,449
Location
Baltimore, MD
View My Gallery
Can anyone clarify if there is a significant 3D difference in the "thickness" of the plane of focus within the image sensor on an M8 or M9 compared to the emulsion layer of fine grain film such as Velvia 100? In other words, assuming the use a highly corrected lens like a 50/2 Summicron or 50/1.4 ASPH, does film provide a slightly thicker plane for critically sharp image reception than a digital chip which is truely flat compared to film? If different, does it impact on the appearance of softness with respect to a lens' CoC for dof?
 
In my experience, the digital is always sharper than film, where film grain artifacts will start to show up at 10x magnification or less, and it will take much further magnification to see any artifacts with digital.

There is no DOF difference, if same lens, angle, and distance is used to take photos. However you use your barrel focus markings on film is going to work the same on the M8/M9.
 
WRT thickness, there is at least an order of magnitude difference. Very thin high resolution films have an emulsion layer thickness of about 7um and up. I'm guessing that Velvia is much thicker, but I don't have data for that. Transistor junction depth in a CCD is about 0.5um or less, depending of course on process technology.

The sensitive CCD layer is so thin, that packaging ("CCD flatness") often is more important, i.e. how the CCD is mounted in the camera, and how this can change with temperature, etc.

Have a look also here (no numbers though): http://www.imx.nl/photo/optics/optics/page63.html.

Roland.

PS: forgive me for not commenting on depth of field 🙂
 
Last edited:
impossible to say. You may be assuming that any lens is focussed on a flat plane and projects a flat plane onto sensor.
I don't think lenses are quite that precise. So it would depend on the arc of the focus curves in the subject and the projected focus curve and not only the depth of the film and sensor receptive planes.
So I guess that implies that if film is thicker then it should have more dof but there are other factors at play such as how do you get that out of the film. With digital you can project direct to paper from a laser, pixel by pixel so there is no loss whereas there is with scanning or lens enlargement.
 
FWIW my experience with digital backs on view cameras is that focus with the digital back is much more critical than with film as the difference between in and out of focus areas is much more pronounced.
 
The M8 Kodak sensor has a pixel pitch of 6.8um (H and V). It works perfectly with lenses developed for films over the past 60 years, including those made by Leica, Canon, Konica, CV, and others.

Velvia 50 Pro (RVP) is a very thick emulsion, especially in 135 - 127um, 120/220 - 98um. The thickness of Velvia is also a factor when scanning, known to be one of the more difficult films to scan sharply.
 
So I guess the microplane surface allows for the use of regular M or LTM lenses without resorting to telecentic lens designs as in the micro 4/3 format where light rays much approach more or less perpendicular to the image plane.
 
You must log in or register to reply here.
Back
Top Bottom