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I burnt through my shutter cloth :(


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My friend purchased an old Leica IIIf from a garage sale.  It had a ton of tiny holes in the curtain and led to some crazy artifacts

 

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On 4/11/2018 at 10:23 AM, pinchers of peril said:

My friend purchased an old Leica IIIf from a garage sale.  It had a ton of tiny holes in the curtain and led to some crazy artifacts

 

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I have a question about this issue of burned shutters: How much more durable (if at all) are the metal shutters of modern Leica digital cameras? I am in the habit of using hoods and filters and not putting caps on my lenses. Once I accidentally left an M9 sitting on my car seat for a few hours on a hot day. The camera became very warm- luckily the sunlight was not shining directly on it. In Australia the summer sun can be quite brutal. How long in the sun might it take to destroy a shutter I wonder? I guess the moral of the story is to always use a lens cap and/or always store the camera in a bag when not in use.

Edited by jaques
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What an awful coincidence- and hour after I posted here I got some fiLm back from processing from my Minolta CLE. The last half of the photos had a huge flare in the same place! What do you know I’ve gone and burned a hole through the shutter curtain! 😩
 

just took it to my local repair man- he says a patch will resolve it no problem:

 

 

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19 hours ago, jaques said:

I have a question about this issue of burned shutters: How much more durable (if at all) are the metal shutters of modern Leica digital cameras?

Sorry about your Minolta! Good it can be patched - there likely are no original curtains available for the Minolta shutter after 35 years!

.....................

As to metal vs. cloth shutters and "burns".

1) Metal is a very good conductor of heat - the heating of a single point by the sun's image will be conducted to the whole shutter blade/curtain (and eventually to other parts of the camera) fairly rapidly, preventing enough heat building up to damage the focal point (except with a high-intensity laser ;) ).

Cloth - as we know from winter clothing - is a fairly good insulator that does not conduct heat easily, thus heat builds up rapidly at the hot focus point (but only at the focus point).

2) The actual damage at the focus point gets rather complicated when comparing silk and rubber (rubberized silk curtains) with, say, titanium-foil curtains (Nikon F/F2/F3) or solid metal blades. Depends on what exactly is defined as damage - scorching, charring, melting, igniting.

Metal is of course, metal. Silk is animal proteins (fibroin and sericin, from silkworms, etc.). Natural rubber (latex) is a polymer of organic plant molecules, primarily isoprene (C5H8).

Silk generally chars (decomposes to nearly-pure carbon) at ~170°C. It scorches (discolors and loses structural strength) at 148°C You can see some brown scorch marks at the extremes of your Minolta burn hole.

Rubber ignites at 260-315°C and melts at 180°C

Titanium ignites in air at about 1200°C - it has the property of igniting at a lower temperature than it melts (1650°C). ;)

For blade shutters:

Magnesium ignites at 473°C and melts at 1200°C (similar to Titanium in that regard).

Aluminum is very hard to ignite - 1000°C-plus in pure oxygen - but melts at 660°C

Alloys of those may have different properties.

In any event, metal requires far more heat to damage than silk and rubber.

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still- I am guessing it is better to be safe than sorry even with a metal shutter. 148C is hot! Also I wonder about cameras that don't have a shutter at all?

 

The repair guy was very confident he would be able to fix it fingers crossed. I am really loving my CLE. I had it stashed away for years and recently took it out and rediscovered just how good a camera it is...  Burning the shutter wasn't all bad- I got some interesting images out of the disaster:

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Edited by jaques
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On 8/18/2017 at 11:45 AM, Michael Geschlecht said:

Hello lb1800,

 

Welcome to the Forum.

 

I had a similar experience long ago, back in the 20th Century.

 

Leitz (The predecessor to Leica.) repaired the pinhole with some sort of goppish stuff which is cosmetically challenged. None the less, after years of use (But no more new pin holes.) the repair is still fine.

 

No need to replace the shutter blind(s).

 

Best Regards,

 

Michael

Hello Jaques,

This is my Post in this Thread in 2017. Please read.

Everything still works fine.

The repair still looks goppish.

Best Regards,

Michael

Edited by Michael Geschlecht
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Hmmm - I'd always heard references to Leica's silk shutters, and assumed Minolta copied Leica.

(This guy is selling silk + rubber material for making 35mm shutter curtains: http://aki-asahi.com/store/html/curtains/shutter-curtain.php )

But if that's a myth, then cotton allows a little more leeway - oxidation and decomposition at ~205°C.

BTW, I see a reference to the Nikon FM2/FE2 blade shutter, which went to 1/4000th sec., being honeycomb-reinforced titanium.

And that previous blade shutters (Copal Square) had stainless-steel blades, which might ignite at about 375°C

Edited by adan
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Hello Andy,

Is there any data in your seemingly endless cornucopia of knowledge as to what temperature would be created by the Sun when an "M" film camera (Not an M5 with the shutter cocked.), with a Dual Range Summicron, focused to Infinity, was pointed directly at it, on a clear day, when you could see forever, at 15:00 in the afternoon? A nice Summer day.
Best Regards,

Michael

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I don't know where Leica shutter material/cloth is made nowadays but my understanding was that pre-war it was made in Lancashire, UK. It was woven from a mixture of long staple cotton with the addition of some silk (even longer staple) for added strength and stability. The material was woven on special looms called Ventile looms, which weave the threads together so tightly that it is both waterproof and close to light proof, thus needing minimal additional light blocking coating. This material was used later in WW2 to make British pilots' immersion suits, which have a slightly silky feel and appearance. Obviously this material could no longer be bought after the outbreak of WW2, hence the change to the red Kodak/Graflex 3 layer shutter cloth, which as a lot of us know, has a finite life, after the bituminised rubber light proofing middle layer starts to liquify. This information came from my father who was in the textile business as well as being a Leica enthusiast. Shortly before the businesses were sold to an industrial group in the early 1960's, my father looked at buying some used Ventile looms from a mill that was closing down in Lancashire but in the end, went for new Swiss Pfaff air blast looms instead, as he was concerned about the wear on the Ventile looms. 

Wilson

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3 hours ago, Michael Geschlecht said:

Hello Andy,

Is there any data in your seemingly endless cornucopia of knowledge as to what temperature would be created by the Sun when an "M" film camera (Not an M5 with the shutter cocked.), with a Dual Range Summicron, focused to Infinity, was pointed directly at it, on a clear day, when you could see forever, at 15:00 in the afternoon? A nice Summer day.
Best Regards,

Michael

Hmmmmm.....

The maximum insolation (radiant energy) from the sun at the earth's surface in cloudless noon daylight is somewhere between 950 and 1120 Watts per m^2. Let's call it 1000 W/m^2.

The front element of a 50 DR would be the "collecting area" - and if we assume that has a radius of 1.25cm, then its circular area is 4.9cm^2. or 0.00049m^2

So it would collect 0.49 watts, or 0.49 joules/second.

Those collected joules/sec have to pass through the actual aperture opening. We'll assume it to be wide-open at f/2, but you would halve the amount for each f/stop smaller.

Now we have to estimate transmission losses through, and attenuatation by, the glass.

The first depends on the coatings and the refractive indices of the elements. Without coating, each air/glass surface would reflect about 4% of the light - let's assume with the single coatings of 1957, that is reduced to 0.5% per surface. The DR summicron has 10 air-glass surfaces, so we lose 5% there (a 10th of an f/stop). We're down to .4655 joules/sec.

Attentuation (light actually being absorbed by the glass atoms, not reflected) is about 0.002% per inch (2.5cm) for borosilicate glass. That's pretty close to the sum thicknesses of the DRs elements, so let's just use that. Negligible - still at .4655 joules/sec.

Now - the 50mm lens focuses all that light down to a small area (and volume and mass) on the shutter. Let us say the sun's image will heat up 0.1g of shutter cloth.

Now we have to know the specific heat capacity of shutter cloth/rubber. That is, how many joules will it take to heat a given mass by X-many degrees? There is not a lot of data on that value for cloth.

https://en.wikipedia.org/wiki/Table_of_specific_heat_capacities

But let us assume that dry cloth + rubber can be reasonably simulated by paraffin wax. For which the value is > 2.325 Kilojoules will heat a kg of paraffin wax 1°K (or C).

Let us assume the shutter in the camera on that Summer day is already at a temperature of 25°C. To get to the danger zone, we need to heat our 0.1 gram of shutter by another 145°C to get it to 170°C total temperature.

The required heat (in joules) will equal the mass in kilograms (0.0001) x the change in degrees (145°K/C) x the specific heat capacity (2.325) = 0.0337125 kilojoules (or 33.7125 joules)

Since our lens is projecting 0.4655 joules/sec, it would take about 72 seconds to add enough energy to heat 0.1 gram of the shutter to a "dangerous" temperature.

Change the assumptions - change the numbers - get a different result.

(Not responsible for misplaced decimals ;) )

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