A Question

[Black Pearl]

On another site a member has posted an image of his Nikon D7100 shutter with a hole burned through it - literally melted right through the centre of blades which he said happened when he was shooting a sunset with a 300mm f4 lens.

I can't get my head around this and it is driving my insane.

Even assuming he was using mirror lock-up (because if he wasn't it would be in the way) and had the camera sitting for quite some time without actually taking a picture it would seem implausible that a disc as large as the sun would be could have the intensity to burn through the metal blades.

Any theories?

From the site:

[DanK]

I don't know what the material is, but focusing the sun through a simple magnifying glass is enough to ignite some materials.

[Tringa]

The light and heat from sun certainly has enough power to burn through a number of materials if it is concentrated.

I agree Robin this is very puzzling. At sunset the intensity of the sun is substantially lower and therefore the chances of burning through the blades is less.

Seems odd that someone using mirror lock up for a shot (which with a 300mm lens and, I assume the camera on a tripod would be a good idea) would lock the mirror up then leave the camera pointing at the sun without firing the shutter.

However, I can't think of any other explanation. Perhaps the lens concentrated the suns light and heat very quickly (anyone got an old 300mm to experiment with?) or could the could the mirror lock up continue until it is turned off? I mean, mirror lock up is turned on, a shot is taken and because the lock up is not turned off, the mirror goes into lock up again. Sounds unlikely I know.


Dave

[PhotomanJohn]

I also agree that this is strange. The Nikons I am familiar with will only leave the mirror up for around 30 seconds each time.

John

[pnodrog]

If it is true I think it would also have cooked the sensor. In the photo the sensor shows no obvious signs of heat damage.

[Black Pearl]

I can't make head nor tail of it - I get the feeling its a spoof post but it is getting lots of comments (quite a few stupid ones) and so far the lad isn't backing down.

[Stagecoach]

Not through my first cup of coffee of the day yet but is there a chance Liveview was in use for a while?

[Black Pearl]

If Live View was used the shutter would be open...or it wouldn't be a Live View.

Have another coffee :-)

[Stagecoach]

If Live View was used the shutter would be open...or it wouldn't be a Live View.

Have another coffee :-)

That was a perfect example of why it's so important to wake up fully before engaging brain

[Saorsa]

The nikon AF is in the bottom of the camera. There is a sub mirror behind the primary mirror which is half-silvered at the center.

If the sub mirror were not in place, half the light would be focused on the shutter at just aboiut exactly that position.

[Black Pearl]

True but why wouldn't the sub mirror be there.

Not being awkward I'm just playing devils advocate.

[Saorsa]

It moves when the mirror does and possibly if you go to manual focus. I'm not sure of the details of the operation but if there were a flaw with the submirror mechanism or an operation that moved it out of the way it could account for the burn.

We really don't have enough information to solve the problem. I was just looking at a potential mechanical reason.

[Manfred M]

The only mechanism how this could have happened is letting the camera sit in mirror up mode. In all other modes, the shutter would have had to have been open or the mirror would have been up. The talk of secondary mirror failure seems unlikely as the mirror (primary and secondary) would have been up while the image of the damaged shutter mechanism we see here was taken.

Now, let's look at the situation that could have caused this. At sunset, the intensity of sunlight is quite low, as it has to travel a long distance through the atmosphere, where it is scattered by particulates and molecules that make up the air. Given that the sunlight is rather read at sunset, we can also assume that only the (relatively) low, long wavelengths of red light are coming through, so any heating action would be less intense than earlier in the day.

Assuming the shutter blades are made of steel (a commonly used material with good wear properties), which melts at around 1400C / 2500F. I find it difficult to believe that a lens could concentrate enough sunlight to reach temperatures like the ones claimed. The flow patterns are intersting as well. The image shown is upside down, and we see flows that are consistent of having the camera having in both landscape and portrait orientations. The other thing that is strange is that I don't see any signs of discolouration ("blueing") that occurs when steel is subjected to high temperatures (well below the melting temperatiure). I also see no damage to the sensor surface; again, I would expect that heat intensity that is high enough to melt steel to show some crazing or other damage. That being said, we would need a better view of the sensor to make a definitive call on that.

I'd have a better thought on this if I could examine the camera, rather than just looking at an image, but frankly something does not look quite right here.

[Stagecoach]

A search found that shutter blade materials of Titanium were used on earlier high SLR cameras and reference also to most such shutters now being manufactured from cheaper aluminium (though some high-end cameras use materials such as carbon-fibre and Kevlar).

This may be something worth considering, exactly what material is used for the D7100 shutter. I agree with Manfred's observation regarding the appearance should it be steel.

Grahame

[Manfred M]

Grahame - with either carbon fibre or kevlar as a material, I would have expected to some form of roughness. Both materials are a matrix of a the material itself with a resin binder. I would have expected some form of oxidation damage at the edges and some evidence of rough edges where the binder and the material met. I see only a single edge, leading me to believe that we are looking at a single homogeneous material.

Aluminum oxidises very quickly and should show a layer of silvery coloured aluminum oxide around the edges of the melt zone. The black colour we see suggests a material other than aluminum.

Titanium has a high melting point 1560C / 3000F, making it even more unlikely to melt under the proposed conditions. It's the one material I have limited knowledge of so can't comment on what it looks like when it melts.

[Stagecoach]

Manfred, out of interest I did find a couple of pics of burn holes through older metal shutters and they clearly showed the discolouration as would be expected.

Interestingly I also found an article with pic that showed a melted burnt area on the plastic below the shutter that occurred when the user was using a 400mm towards the sun so goes to show that a reasonable heat can be generated hence warnings in the manuals not to point at the sun, but of course depends on duration

I wonder how the user spotted this? If you were not aware immediately and took further pics it would be likely that damage would be seen on the other blades at least some marking.

[ajohnw]

Robin. It's a pity that the link to the site seems to have gone. I would love to see it.

John
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[Black Pearl]

John the post got deleted, not sure by who.

Has to be a wind up because none of it makes sense.

[Manfred M]

Manfred, out of interest I did find a couple of pics of burn holes through older metal shutters and they clearly showed the discolouration as would be expected.

Interestingly I also found an article with pic that showed a melted burnt area on the plastic below the shutter that occurred when the user was using a 400mm towards the sun so goes to show that a reasonable heat can be generated hence warnings in the manuals not to point at the sun, but of course depends on duration

I wonder how the user spotted this? If you were not aware immediately and took further pics it would be likely that damage would be seen on the other blades at least some marking.

The melted plastic on other parts of the shutter assembly makes sense; metals are good conductors of heat so as they heat up the resins used in the shutter assembly would get hot enough to melt. The type of damage shown in the image would have to be very intense to get up to the melting point of metals without being able to conduct heat away to cause some secondary damage.

As for taking pictures, I don't thing that would be possible with this level of damage to the shutter mechanism. We obviously saw signs of melting / flow which increases the thickness of the shutter blades. The three blades would overlap in shutter down position. I see no damage (creasing) in the upper blade, so I would conclude that the shutter was never fired after the damage was done.

As I said before, something does not seem to add up...

[ajohnw]

I tried to find the post with google. Lots turn up so not sure what to make of it including a case where Nikon replaced a shutter FOC after some argument. One person had a hot spot at higher ISO in shots after taking one with the sun just out of the view. Hot spots didn't line up shot to shot so that thread died and became a hole in shutter. Some comments about old fabric shutters being burnt - more likely deterioration of the stuff they used to be coated with.

They seem to be using a carbon fibre kevlar blend according to the info around here but only mentioned on the top models. The consumer stuff has to make do with tested to 100,000 and no details. They did use titanium extensively. Easily capable of taking well over 1000C before melting but can loose strength over 400C. Bit like aluminium alloys, they vary. Epoxy varies. Some are heat cured at up to 200C especially in relationship to precision carbon fibre items. Believe that the glues can have problems above 150C.

http://www.nikon.com/news/2011/index.htm

Having used an 11in F2.8 parabolic mirror to concentrate the sun when it was about 45 degrees above the horizon and failing to produce a real flame on wood I have difficulty believing the sun has much to do with it on any form of metal shutter - given that holes do actually appear. The real problem though is that the shutter is never exposed for long unless mirror lock up is used. and even then the image of the sun isn't in focus on the shutter. Live view might put the sensor at risk.

One silly thought. If I wanted to take direct pictures of the sun - heaven knows why as the rest would be jet black, I'd guess where to point and guess the focus and maybe use mirror lock up. But why bother it wouldn't be a good idea to look through the camera anyway.

Manufacturing defect after prolonged or otherwise use - pass. Canon produce google hits just like Nikon.

John
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