New generation of "digital" lenses: only a commercial strategy?

Started Jun 28, 2001 | Discussions thread
Thom Hogan
Thom Hogan Forum Pro • Posts: 13,661
Re: New generation of "digital" lenses: only a commercial strategy?

Bottom line you are not fully correct either -- the newer lenses
are sharper and visibly so with the D1X camera.

"The newer lenses" is vague. Be specific. Which lenses? Compared to which lenses? Having used Nikon for almost 40 years now, I've got a wide variety of older and newer lenses, and I just don't see what you claim. The lenses that were sharp on my film cameras are sharp on my digital cameras; the ones that were soft with film are soft with digital.

This has been reported many, many times - If I understand you reply
to me this should not be the case.

Again. Please give me specifics to respond to. "Reported many, many times" by whom? Which lenses? Under what conditions?

Oh and just why does the spillover fall of the adjacent pixels in
the first place?

Well, let me quote from The Manual of Photography, 9th Edition: "One element forms a 'well' for charge but its capacity is limited and excess electrons must be removed by a 'drain' circuit otherwise they will migrate to adjacent wells and cause degradation to the image seen as 'blooming' and noise." In practice, we're still a fair ways away from the perfect chip in this respect. Add to this the fact that CCDs are "read" by row shifting the data across the adjacent photosites to the edge, where the data is actually looked at one pixel at a time and converted from A to D, and there's plenty of opportunity for stray electrons to influence adjacent data points (and if your crystal isn't accurate, you'll get a regular pattern of noise--something we all saw in the early D1s).

The photosites get excited and vibrate and all the
wavelength can excite the photosite from any angle but a part of
this is outside the visible spectrum needed to cause a reaction (or
fast reaction) in film.

I don't understand that sentence at all. First, the photosites are physically stable (they don't vibrate). The electrons passed through the sites are active, and can move from well to well, but I'm not sure I'd call this vibration (the proper term, I believe, is excitation). Second, a filter array sits on top of the actual CCD, so every photosite is exposed to a different set of wavelengths. Finally, that same array filters out most of the light outside the visible spectrum. Again from the Manual of Photography: "The spectral sensitivity of a CCD array is that of silicon and similar to that of a silicon photodiode as used in a light meter, with response extending to some 1000nm, with a peak at about 750nm in the infrared...Some cameras use an interference filter behind or in front of the lens to reject IR..." In practice, virtually every manufacturer puts an infrared filter in place over the sensor (Kodak, I believe, is the only one that allows this to be removed).

Everything gets interpolated as noise is filtered and replaced with
“image” information, as you know only a small amount the vast
quantity of information captured by the CCD is actually used.

Huh? You've got it backwards. All current digital cameras ADD information (the "interpolation" process) to that which was captured by the camera. Again from the Manual of Photography: "The use of a Bayer filter array assigns a group of four pixels to one piece of colour information so an image 'point' is effectively 2 x 2 pixels [photosites], theoretically reducing resolution by a factor of four, but interpolation gives the best estimate of the missing values."

In the CCD capture the element of the “none image forming” light in
film is captured, this is not focused as you say but it is
interpreted by the digital processing systems as valid image data
to be retrained and not discarded and leading to an image softness.

I would like to see some attribution of source for this contention. In none of my references, nor in any of my experience in working with digital camera designers, have I ever heard such a claim.

This softness can be seen with different lenses from the same
manufacturer – by whatever means it exists. Now I am, obviously
open to correction, as, as you have stated other agencies have
printed incorrect information – I rely on these for my own
education and as best as I can understand it this is why the older
lenses are softer, simply because the film cannot see the
wavelengths that produce a “soft” edge to digital images (because
the CCD can see these wavelength and records them).

The light source would make a difference in your contention, as well. The spectral curves of incandescent, fluorescent, and sunlight are all quite different, and have energies that vary considerable. Mid-day sunlight, for example, has twice the spectral power at 400nm that incadescent light does, while incandescent has over twice spectral power at 700mm than sunlight.

You know, there's actually a pretty easy method to test your contention: simply put two filters in front of the "older unsharp" lens that cut off all wavelengths below 390nm and above 700nm (the last digital camera I worked on used a filter that started at 800nm, if I remember correctly, and most digital cameras are still slightly responsive to infrared, so they must be filtering in the same area). I doubt you'd see any difference in image sharpness. In fact, because infrared has less photon energy than ultraviolet, you probably only need to cut off the response below 390nm to verify your contention.

Finally, as Manual of Photography says "The sensitivity of photographic [film] materials to scattered UV radiation...causes a loss of contrast...increasing with increasing subject distance." That's right, film responds to energy outside the visible spectrum (though if you compare Ektachrome 100VS to the Ektachromes of 10 years ago, you'll see a vastly lower response to UV).

In short, until someone can explain the mechanics of how it is possible for light outside the visible range (and outside the range that the ubiquitous IR filter would let get to the array!), I'd say that if you see a difference in sharpness between a newer and an older lens, it is most likely because the newer one is sharper.

Thom Hogan
author, Nikon Field Guide

p.s. While I was re-reading relevent sections of some of my source material, it struck me that if you're seeing differences, they may be due to flare, not nonvisible spectrum energy.

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