M8's Kodak Sensor

[MP3]

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I remember a forum member have shown the spatial frequency response curve of M8's Kodak CCD sensor, leading to a interpretation that,

 

If the Kodak sensor really performs up to its specification, it shall be effective enough to block the majority IR and we will not have our current IR issue. ?????

 

1) So is Leica just received and employing a dump sensor which does not work up to the standard (a manufacturing negligence)?

 

Or is it by design to compromise between various image quality factors (as Leica claims)?

 

Really interested in the truth...

 

2) How thick is the cover glass in front of the CCD sensor?

 

Best

Matthew

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[Riley]

isnt IR a natural part of the spectrum

 

the coverglass is 0.5mm thick

[hankg]

So is Leica just received and employing a dump sensor

Sure, that makes perfect sense. They based the future of the company on below grade out of spec sensors.

 

The performance results and 'issues' of the M8 are perfectly consistant with commonly known constraints of digital sensors and lens to sensor distances. Leica did not have to deal with the digital unfriendly M mount when producing the DMR so the DMR had none of the IR sensitivity issues exhibited by the M. This has already been re-hashed adnauseum online.

 

Of course there are plenty of internet armchair engineers who think that it should be a piece of cake to stuff the electronics from a full frame DSLR into the M. Unfortunately Leica's engineers have to produce real products in the real world constrained by the laws of physics and currently available technology within a limited budget and at a price the market will bear.

[MP3]

Sure IR is part of a natural light spectrum.

 

However, is the sensor with a 0.5mm cover glass have a spec to block majority IR? as some have posted up in another thread.

 

Best

Matthew

[Riley]

The cover glass serves another purpose, that of microlenses, without it the whole thing simply wont work

 

The problem is that the lenses are quite wide in aspect to the register so light becomes more divergent, less telecentric. Digital film doesn't handle divergent light anything like 35mm film does. This will cause a vignetting (dark corners) or fall off.

 

To increase the sensibility (speed) of the sensor, the pixels have to have microlenses to collect more light. Again, if the light rays will fall on the film in a non-rectangular way, less or no light will fall on the pixels at the corners of the image.

 

Microlenses over each photosite to compensate for the fact that all image producing rays do not come in parallel to each other, but there are angular limits on this form of compensation.

 

Another feature of the short register is that reflections off the surface of the sensor are more prominent. So light may well travel through the IRcut filter bounce off the sensor and reflect back off the IRcut coated surface. This creates considerable shifts in edge contrast of an image, greatly affecting sharpness. This it seems is also true to the AA filter.

 

The filter combination will also break entry light rays up like a prismatic effect which also disipates sharpness. This limitation meant the coverglass could not be thicker than 0.5mm, which isnt enough to hold off IR effects. Hence an IRcut is carried externally in front of the lens. The AA filter to my knowledge is simply not included.

[sdai]

However, is the sensor with a 0.5mm cover glass have a spec to block majority IR? as some have posted up in another thread.

 

The Kodak sensor doesn't really fit into the "dump" category, if you look at the PDF file on Kodak's web site, you'll also find the measurement was done with the coverglass while for other Kodak sensors they probably only charted the values from a naked imager. So I believe they already knew the combo was bound to have problems ... just didn't figure out how to deal with it ... of course, the money has been burnt already and the investor demanded a product as return ... there you go - the M8.

[MP3]

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sdai, can you show a link to the corresponding Kodak CCD sensor? Thx.

 

Best

Matthew

[sandymc]

By way of some numbers, the angle from the center of the lens exit to the corner for a few camera formats is:

 

Nikon full frame: 24.96 degrees

Nikon DX: 16.98 degrees

Canon full frame: 26.19 degrees

Canon APS-C: 17.05 degrees

Leica M full frame exit pupil at the lens flange: 37.76 degrees

Leica M8 exit pupil at the lens flange: 30.09 degrees

Leica M full frame exit pupil 1cm in: 50.33 degrees

Leica M8 exit pupil 1cm in: 42.06 degrees

 

The limit for a conventional CCD with AA filter, IR filter and conventional microlenses is considered to be about 18 to 20 degrees, which is why the Nikon's, Canons's etc went to smaller CCDs. With offset microlenses and AA/IR filter probably somewhere in the low 30s, which is how Canon build their FF's. But some M lenses protrude backwards into the camera body, so Leica had to deal with the 42 degree angle, so no AA filter, minimal IR filter, offset microlenses, and software correction for remaining vignetting....

 

Actually, given the restrictions, the M8 is an optical marvel. Certainly not, in my view, below standard

 

Sandy

[sdai]

sdai, can you show a link to the corresponding Kodak CCD sensor? Thx.

 

http://www.kodak.com/ezpres/business/ccd/global/plugins/acrobat/en/datasheet/fullframe/KAF-10500LongSpec.pdf

[Riley]

Actually, given the restrictions, the M8 is an optical marvel. Certainly not, in my view, below standard

 

Sandy

 

 

thats how i see it too, no-one else could have made this camera but Leica

given the technical difficulties

and the image quality at hand

its a beautiful thing

[sandymc]

Well, optical marvel, but to be even handed, the lack of an AA filter is an issue in some situations, and as for the firmware:mad:

 

Sandy

[scott kirkpatrick]

When they moved from the DMR's Kodak sensor to the M8's Kodak sensor, Leica made a judgement call in reducing the IR filtration. Both systems leave out the AA filter. The specs for both are on Kodak's website, and the IR vulnerability is small but enough to be worrisome on specifications alone. Leica stumbled in thinking that it wouldn't matter. Had they paid more attention to the early experience of Kodak and Nikon DSLR's with weak IR filtration, they would have known what they were getting into.

 

This wasn't "internet engineers" making up instant analysis, this was the experience of photographers who had struggled with those DSLR's and real engineers who had designed technical cameras (including the people who build Leica's S-1). Leica didn't take advantage of that knowledge until too late. Then they responded quite quickly -- the marketeers with new marketspeak (e.g. the hardware "upgrade"), but the engineers with a reasonable set of workarounds.

 

scott

[mjh]

I remember a forum member have shown the spatial frequency response curve of M8's Kodak CCD sensor

The spatial frequency is a measurement of image detail; fine image detail = high spatial frequency, coarse image detail = low spatial frequency. What you are referring to is the frequency of the light waves.

 

leading to a interpretation that, If the Kodak sensor really performs up to its specification, it shall be effective enough to block the majority IR and we will not have our current IR issue. ?????

In the sensor’s spec sheet, Kodak states that its IR-absorbing filter reduces IR to less that 5 or 10 percent, depending on the actual wavelength. That sounds about right, as this amount of IR is sufficient for causing trouble. In other words, Leica should have known.

 

Or is it by design to compromise between various image quality factors (as Leica claims)?

Leica’s reasoning is absolutely sound; neither a thicker absorption filter nor an interference filter was a viable option here.

[scjohn]

I am sad to say that this whole thread smacks of the iconoclastic bias a few Leica users seem to have. "Kodak" appears to be almost a dirty word for some, right up there with "Microsoft" and any American car line I could think up. But Kodak appears fully competitive techonlogically with any other sensor manufacturer.

 

Leica's decision to use the Kodak sensor leads me to believe, not that Leica wanted a "dump sensor" to doom its flag-ship digital camera, but that Kodak was able to develop the sensor best-suited to the application at hand.

[mjh]

But Kodak appears fully competitive techonlogically with any other sensor manufacturer.

Kodak sensors appear to be good enough for Hasselblad, PhaseOne etc..

[scjohn]

Kodak sensors appear to be good enough for Hasselblad, PhaseOne etc..

 

thank you for that mjh. my point exactly! You are obviously NOT one of the iconoclasts!

[SteveP]

IR is not light. Light is electromagnetic radiation which stimulates the human retina. Oddly, a science based on perception. IR is part of the EM spectrum (like microwaves and X-rays) but is outside the area we see. Sometimes I see the term "visible light" which I think is redundant - visible radiation we can see?

 

It may be that the magenta blacks the M8 sensor "sees" are actually "real" but our eye can't see them that way since we can't see IR. The "fault" is that the sensor sees too well. We had this problem in film photography (remember film?) using studio flash with excessive UV output - many synthetic fabrics photographed oddly since they reflected (and in some cases fluoresced) UV light we also couldn't see but which was recorded by colour films. I'm surprised this hasn't been mentioned before. (Maybe I missed it.)

 

The solution was filters. In the case of existing flash units, we used 2B UV filters over the lights (and often over the lens as well) to kill the excessive UV. Newer flash units had UV filtering built in, so the problem went away. Also, synthetic fabric manufacturers tuned their production so that when people bought a blue shirt out of the catalogue, they weren't surprised with a purple one when they opened the package.

 

The spectral response of CCDs is not flat by any means (nor is the human eye) and matching these are always compromises. I expect what we really need is a better IR filter glass since we know that physically there is only room for a 0.5mm glass and that this is not working. So the challenge seems to be the development of a satisfactory IR blocking glass that is 0.5mm thick or less. I suspect dichroics would not work due to the reflections.

[Riley]

when we go through this again next week, well...

 

sdrawkcab etirw dluohs uoy gnileef eht teg uoy semitemos

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[Vivek Iyer]

IR is not light. Light is electromagnetic radiation which stimulates the human retina. Oddly, a science based on perception. IR is part of the EM spectrum (like microwaves and X-rays) but is outside the area we see. Sometimes I see the term "visible light" which I think is redundant - visible radiation we can see?

 

 

There are people who can "see" outside the "visible" spectrum (Google).

 

It may be that the magenta blacks the M8 sensor "sees" are actually "real" but our eye can't see them that way since we can't see IR. The "fault" is that the sensor sees too well. We had this problem in film photography (remember film?) using studio flash with excessive UV output - many synthetic fabrics photographed oddly since they reflected (and in some cases fluoresced) UV light we also couldn't see but which was recorded by colour films. I'm surprised this hasn't been mentioned before. (Maybe I missed it.)

 

Very few color films actually recorded any significant UV if the lens used ever allowed the UV to pass through it. It is a different matter (still) with B&W films. Fluorescence is a different case. Here, the light is in the visible region. The situation you refer to about changing colors of the fabrics was taken care of by the the use of "fast-dyes". These came in the market, eons ago!

 

The solution was filters. In the case of existing flash units, we used 2B UV filters over the lights (and often over the lens as well) to kill the excessive UV.

 

Color casts/balancing remained (did not matter for B&W films).

 

I expect what we really need is a better IR filter glass since we know that physically there is only room for a 0.5mm glass and that this is not working.

 

That is the rumor. How did Epson manage a better filter?!

 

So the challenge seems to be the development of a satisfactory IR blocking glass that is 0.5mm thick or less. I suspect dichroics would not work due to the reflections.

 

Again, Epson folks found it years ago!

[jaapv]

That is the rumor. How did Epson manage a better filter?!

Again, Epson folks found it years ago!

 

Yes - and a very simple solution it was: use a smaller sensor to cut out the edge and corner rays, where the problem lies, so one can use a more effective filter. Not that the RD1 filter is that effective, the Epson RD1 is -after the Leica M8, one of the most IR sensitive camera's around. The main difference is that they got spared the Internet hype.