Curiosity

[bohdan]

Okay, the physicist in me is kicking in...

"In some cases, particularly when using the camera models Leica M9, M9-P, M Monochrom or M-E with smaller apertures (5.6-22), effects caused by corrosion of the sensor glass may be encountered. Leica offers a free replacement service for the CCD sensors of cameras affected by this problem as a goodwill arrangement."

I'd be curious to see what other Scientists, Engineers or anyone else that gives a care see on this issue.

Here we go. First, when I got my M-2 from my dad he told me never to leave the cap off of a Leica. He mentioned that if you have an uncovered lens with a smaller aperture (f/16 or f/22) can result in burns in the curtain.

From a physics standpoint, it makes sense. The rays would be concentrated and the result would be similar to the magnifying glass used to burn holes in paper. It would burn holes in the curtain.

So, simply stated. Could leaving the lens cover off be cooking the interior of the camera on sunny days with setting above f/5.6? While I appreciate that there is a metal barrier between the sensor and the lens and the sensor...could it be cooking the sensor. Is delamination the issue? I don't know....

 

[JoeV]

Good advice.

And now I have a question for the physicist in you. How is infinity focus possible?

~Joe

 

[mfunnell]

"In some cases, particularly when using the camera models Leica M9, M9-P, M Monochrom or M-E with smaller apertures (5.6-22), effects caused by corrosion of the sensor glass may be encountered. Leica offers a free replacement service for the CCD sensors of cameras affected by this problem as a goodwill arrangement."

I had assumed that statement indicated that at narrower apertures defects on the surface of the sensor would be more visible in photographs. I'd not even thought use of narrow apertures might contribute to the cause(s) of the problem. I'm still not sure I think that...

...Mike

 

[Freakscene]

This is not the issue with the sensor covers. Small apertures make burns less likely, not more (get out on a sunny day with a lens and a piece of paper) and the glass (Schott BG38, BG39, or S8612) corrodes when exposed to moisture-this is well documented by Schott in the technical data for these glass types. It is a well known property on this type of glass. The coating can be breached by physical contact but not by focused light. Leica's advice to use wide open apertures is to limit depth of field to decrease the visibility of the sensor spots.

Marty

 

[Nr90]

I'm limited to high school physics but here are my thoughts.
A smaller aperture does not change the direction of the light, only the amount that passes through the entire lens. Thus a smaller aperture does not increase the amount of lens to hit a certain area, it only stops other parts of the curtain from being hit by light.
Think about it, when you want more light to hit your sensor/film you open the lens to increase light, not spread the same amount of light over a larger area.
The rays that hit the aperture blades are reflected back out of the lens, not pushed towards the smaller lens opening.
Taking your example of the magnifying class. By covering part of the lens you are not increasing the magnification of the glass. At the exact focal length every ray that hit the glass should intersect (setting aside aberrations). Thus with a smaller aperture the density of lighrays is reduced when you get closer to the focal point.
If you want to increase the amount of light that hit a spot, you can move that spot closer to the focal length or increase the size of the lens.
So I agree with Freakscene, a smaller lens opening should reduce the chance of burns, not increase it.

On the subject of infinity focus, infinity focus does not actually exist.
Only one point in the distance is truly in focus.
That said, at a larger distance the depth of field is larger then when something is closer. You can easily see this when taking an image of the same thing with the same aperture from two distances. The image taken from further away will have a larger depth of field (ceteris paribus).
Thus when distances become very large the depth of field becomes so large that it appears to be in focus to a distance of infinity.

An illustration to this can be found by looking at the distance scales on lenses. A longer lens has a smaller depth of field then a shorter lens. If my explanation about focussing to infinity were to be true, a lens with a shallower depth of field would have to focus further into the distance to approach a focus in infinity.
If I look at the 28 and 135 mm lenses that I have in front of me, this is clearly true. Setting both to an aperture of 16:
-The distance scales on the 28 mm indicate that infinity is in focus when focussing at about 1.5m
-The distance scales on the 135 mm indicate that infinity is in focus when focussing somewhere between 20m and infinity.

Thus, true focussing to infinity does not exist, however larger depth of field effectively covers infinity when focussing further.

 

[willie_901]

From a physics standpoint: photosensitive sensors and fabric are made from different materials and have different abilities to resist damage from heat caused by intense light energy.

For example, senors in digital video cameras used to broadcast sporting events operate continuously for hours in bright sun at reasonably small apertures day after day, week after week, without any damage to the sensor assemblies.

Another example are video surveillance cameras which commonly operate in very bright sunlight for long durations.

As others mentioned, debris on digital camera sensor covers such as dust, dried oil droplets, etc is essentially out of focus at wider apertures. Although I have seen blurry blobs from rather large dust balls on a dirty sensor when the aperture was wide (f 2 or so).

Your speculation about the effects of heat is relevant as it heat could accelerate the deamination process. The rate of chemical reactions increases with temperature. So the rate of sensor-cover deamination from humidity would be increased for sensors chronically used or subjected to excessive heat. At the same time, the sensor electronics generate some heat whenever the power is on. So the sensor cover glass is subjected to a moderate amount of heat for long periods time during normal operation.

 

[Jamie Pillers]

With the Buzz Lightyear camera, you get infinity and beyond.

 

[bohdan]

Moving the conversation forward

Moving the conversation forward

Let me address some of the good points here.

"photosensitive sensors and fabric are made from different materials and have different abilities to resist damage from heat caused by intense light energy."

Response - Granted. Yes, black curtain will absorb a crapload ( a physics term) of heat...the lighter spot (on my M6 spot meter target) will reflect more. So, question. Would those micro-lenses that reside above the pixel receptors have an issue with this. I mean, most engineers would count on the fact that not many photographers would purposefully shoot f/48 directly at THE light source (the sun).


"Another example are video surveillance cameras which commonly operate in very bright sunlight for long durations"

Response - Agreed Willie, but point that sensor directly at a point source and you will have burn in. I don't know about NOW, but old days (betamax), that was the quickest way to burn out a sensor.

"Your speculation about the effects of heat is relevant as it heat could accelerate the deamination process. The rate of chemical reactions increases with temperature. So the rate of sensor-cover deamination from humidity would be increased for sensors chronically used or subjected to excessive heat. At the same time, the sensor electronics generate some heat whenever the power is on. So the sensor cover glass is subjected to a moderate amount of heat for long periods time during normal operation."

Response - Agreed again Willie. Lets add it all up...

Heat from Sun + Oils/dust + dampness = Crap


Question: And now I have a question for the physicist in you. How is infinity focus possible?

Okay, a bunch of math happens...Nr90 was illustrating that. The very simple answer is that at certain distances, when you are focused correctly, the lightwaves are travelling parallel to each other from the perspect of the viewer (film plane). At that point, it looks like a flat field. The distance of that plane where that happens depends on the focal length and the aperture.

If you really want to have some fun, start asking about the distance when you can resolve two point sources (headlights from a car). At a far distance, they will appear to be one.

To do the math 1/D + 1/d = 1/f . D = distance from plane to object, d = distance from plane to film plane, f is focal lenght. You know the focal length; you know the film plane distance...Now, infinity would actually be an estimate...it would be something that is very very very very very large ( 5 varies). So, if the distance to the film is measured in inches and the focal plane is inches...then you can make an assumption, that measuring in miles ( sufficiently large) is infinity. It's not...I know, but it's like the relationship of dropping a feather on the earth. Both have their own gravity but the earth can be though of as sufficiently large compared to the feather to be estimated as infinite. I am sure I clouded this up.

Looking forward to more mental masterb....you know. Thanks for indulging me. I have no idea about the materials on the internals...and I am a RF guy, not an Optiker.

 

[bohdan]

Won the Internet

Won the Internet

With the Buzz Lightyear camera, you get infinity and beyond.

Okay, discussion is done. Close this thread. This is the best answer yet.

 

[bohdan]

This is not the issue with the sensor covers. Small apertures make burns less likely, not more (get out on a sunny day with a lens and a piece of paper) and the glass (Schott BG38, BG39, or S8612) corrodes when exposed to moisture-this is well documented by Schott in the technical data for these glass types. It is a well known property on this type of glass. The coating can be breached by physical contact but not by focused light. Leica's advice to use wide open apertures is to limit depth of field to decrease the visibility of the sensor spots.

Marty

Okay Marty, this is good stuff. I'll check this out. And thanks for the correction. I was backwards with the relationship...I could probably figure this out easier if I broke out the optics book and bothered to do some math.

 

[tbhv55]

Okay, discussion is done. Close this thread. This is the best answer yet.

+1 to this... 🙂

 

[JoeV]

Bohdan,

I was being rather flippant with your post, sorry. Your question about focused sunlight being a factor in sensor delamination is valid, one which I can't say for sure without knowing more about the details of the sensor and filter.

My question about infinity focus was really about the inverse square law. We shouldn't be able to see light from infinity. Which is much further distant than a mere 15 billion light years. 😉

~Joe

 

[willie_901]

Let me address some of the good points here.

...

"Another example are video surveillance cameras which commonly operate in very bright sunlight for long durations"

Response - Agreed Willie, but point that sensor directly at a point source and you will have burn in. I don't know about NOW, but old days (betamax), that was the quickest way to burn out a sensor.

...

Maybe, but if so this applies to all contemporary PIN diode based imaging sensors. Why don't M8 cameras (and all the other mirrorless brands) also fail from the scenario the OP suggested? Why aren't those cameras damaged from the situation you described? Only the CCD assembly in the M9 family of sensors has this specific delamination problem and these are the only cameras that require an ultra-thin, high-efficiency IR filter/cover glass assembly. To be complete, in rare cases other brands (according to Thom Hogan) have experienced cover glass coating problems.

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Infinity does not exist. It is a just a symbol to represent an abstract concept beyond our understanding. This solves your riddle as well.

----------
My favorite physics question involving photography involves photon noise.

o How come the amplitude of all light (even coherent light from a laser!) has a predictable distribution of amplitudes? While photographers call these amplitude fluctuations noise, are they in fact part of the signal itself and not noise at all?

o What does photon noise tell us about the nature of light and more importantly the mechanism for light generation. Does photon noise contradict Einsteins famous declaration "As I have said so many times, God doesn't play dice with the world."?

 

[bohdan]

Bohdan,

I was being rather flippant with your post, sorry. Your question about focused sunlight being a factor in sensor delamination is valid, one which I can't say for sure without knowing more about the details of the sensor and filter.

My question about infinity focus was really about the inverse square law. We shouldn't be able to see light from infinity. Which is much further distant than a mere 15 billion light years. 😉

~Joe

Sorry, it's my geek gene...I gotcha. Don't apologize, I do have a sense of humor. I am just a little slow on the uptake.

 

[bohdan]

Maybe, but if so this applies to all contemporary PIN diode based imaging sensors. Why don't M8 cameras (and all the other mirrorless brands) also fail from the scenario the OP suggested? Why aren't those cameras damaged from the situation you described? Only the CCD assembly in the M9 family of sensors has this specific delamination problem and these are the only cameras that require an ultra-thin, high-efficiency IR filter/cover glass assembly. To be complete, in rare cases other brands (according to Thom Hogan) have experienced cover glass coating problems.

----------

Infinity does not exist. It is a just a symbol to represent an abstract concept beyond our understanding. This solves your riddle as well.

Boom!

We had a mathematician that loved physics and loved to hang out in the physics department. God knows what that's all about. Anyway, he was like the Hunter S Thompson of physics. Sunglasses and all. We used to discuss how the theoretical infinity really wasn't an absolute. He was making the came up with some interesting cases where things would diverge quadratically, and when you jumble the number around you have something that was very very large in comparison. I think if I look around I can find my notes.

----------
My favorite physics question involving photography involves photon noise.

o How come the amplitude of all light (even coherent light from a laser!) has a predictable distribution of amplitudes? While photographers call these amplitude fluctuations noise, are they in fact part of the signal itself and not noise at all?

o What does photon noise tell us about the nature of light and more importantly the mechanism for light generation. Does photon noise contradict Einsteins famous declaration "As I have said so many times, God doesn't play dice with the world."?

See, now we are talking.

One man's noise is another man's...ahhh, you get it.

you should see the look my step kids give me when I try to explain the interference patterns when they are playing with their flashlights.

 

[Rob-F]

Infinity does not exist. It is a just a symbol to represent an abstract concept beyond our understanding. This solves your riddle as well.

"Infinity is not a number, it is the process of allowing a quantity to increase without bound."

--One of my calculus professors, sometime in the 1980's.

 

[Beemermark]

Good advice.

And now I have a question for the physicist in you. How is infinity focus possible?

~Joe

Infinity focus is not possible if you are a Physicist. it is possible for an Engineer because we tend to focus on the practical based on observation.

 

[bohdan]

Infinity focus is not possible if you are a Physicist. it is possible for an Engineer because we tend to focus on the practical based on observation.

Being an algorithm analyst, I have to have multiple personalities to keep my job.