Hi,
Not that I disagree, some points...
To some extent, micro contrast you are talking about is MTF (Modulation Transfer Function) it simply measures how much of the contrast is kept for for detail of different size. MTF is decreasing as detail size diminishes. MTF is also limited by diffraction which is a law of physics, so lens designers cannot do anything about it.
Now:
Feature size (which is measured in lp/mm) is depending on film/sensor size. So larger sensors/film has larger feature size. The fall of on MTF with decreasing detail size is different between lenses. In general lenses designed for smaller formats are better designs, they need to be to get the best from the small format.
Very good lenses can be made for large formats, but costs can be astronomical (think about "Hubble Space Telescope").
We can say that increasing the film/sensor format we will increase feature size, thus edge contrast would increase with format would all being equal. Now, things are not equal. Lenses for small formats like Hasselblad and Schneider digital lenses are extremely sharp, having perhaps an advantage of two regarding MTF at say 40 lp/mm over larger format lenses. This explains, in part, while it seems that MFDBs are said to match 4x5".
MTF at medium frequencies can be enhanced by sharpening. Certain developers achieve something called the "adjacency effect boost" which also acts as sharpening. Adjacency effect boost essentially depends on depletion of the developer, causing diffusion of developer from the less exposed areas to the more exposed areas. This effect is dependent on developer and development techniques. This is very similar to sharpening, and affects low and medium frequencies. Edge contrast is enhanced but resolution is not affected.
A good explanation is here:
http://www.normankoren.com/Tutorials/MTF1A.htmlDigital image processing involves a lot of sharpening. Every stage of the image process does have an MTF.
1) Lens
2) Film/developer
3) Enlarging lens
4) Photographic paper
In the digital world they would be:
1) Lens
2) Sensor
3) Printer
With digital we always apply sharpening between each step, which mean that we can regain a great deal of MTF. This may also help MFDBs to match 4x5".
An issue with film is grain and noise. Even if we scan film we cannot enhance sharpness as much as with digital, because we would also enhance grain. Good sharpening technique can enhance sharpness without increasing grain to much, "Real World Image Sharpening by Bruce Frazer and Jeff Schewe" contains a wealth of information on this.
One issue that comes to mind is that 135 and MF lenses are normally very well corrected. Highly corrected lenses often have a less than optimal "bokeh", some authors talk about overcorrecting spherical aberration can cause bad bookeh. As large format lenses are normally not very highly corrected they may tend to a better bookeh. Also the sharpening applied to digital images may make the edges harder.
One issue of grain is that it can actually improve impression of sharpness:
1) Gives the eye something to focus on
2) Can mask minor unsharpness
A final factor that may come into effect is that MFDBs don't have a OLP (optical low pass filter). The lack of OLP will result in some false detail, which can be perceived as extra sharpness. It's a guess that "digital photographers" like the effect of sharpening and the effects caused by the lack of aliasing filter while analogue photographers appreciate a different sort of imaging, with possibly higher resolution but less edge contrast.
Best regards
Erik
I think that part of the difference (at least between small and large film, but probably applies to sensors) is an effect of micro-contrast. Part of this is lens resolution, but part is grain/noise and an ability of film to differentiate between small local contrast points, like specular reflections on a dark leaf. As the contrasted areas become smaller, the grain would tend to obscure the definition. On film, there is also an issue of infectious development that can reduce micro contrast and detail. Larger film reduces this problem. There is some debate, but developers like Pyro can create edge effects that increase perceived sharpness and micro-contrast. Being more linear than film, I would think that digital would show this mico-contrast differently, and have a different look than film with its curve. However, with curves applied, digital should look similar in theory. On the other hand, some digital systems have issues with very high micro contrast and can have weird edge effects that don't happen with film.
I have a 16M hassy back and find that it is great for smooth gradations, especially out of focus areas due to being pretty "grainless" (pixelless?), but is not as resolving as LF. I would love to try a very hi-res back.
On a different point, while I have no scientific basis for this, I always find that prints from 8x10 can look sort of hyper-real, since they seem to me to present more resolving power than the human eye (e.g. a life size portrait where you see every skin pore or vein in the eye), while 4x5 doesn't seem to do this for me. i have not yet seen prints from high megapixel backs to see if this effect still is there.
