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Wednesday, 21 January 2015

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Now you can also see why secure delete programs exist.

I believe the phenomenon is called a Brocken Spectre, commonly observed by climbers and mountaineers. It is named after a German mountain called the Brocken where the effect was first noticed.

I think that what you are seeing at work is the wear-leveling built into the controller on the SD card. Flash memory can only be written to a certain number of times (in the thousands to hundreds of thousands, depending on the technology used), so the controller on the cards is designed to even out where on the card your data is stored. With such a large card, if you don't fill it up each time before you format, the old data hidden by the new format, but can still be there (note that this is why when you sell computers, flash drives, and even hard drives you should run a utility that writes random data and erases it). If the card didn't do this, you would always write to the same area of the card and wear it out quickly (every time you write or delete a file, the table that stores the file information is updated).

Good that you got the images back. Very interesting phenomenon too.

The reason you got your older pictures back is because the format doesn't really do a TRUE format. It just cleans out the index to all the photos. Pretty much what a delete all does.

A true format rewrites each sector of the card. I don't know what these modern memory cards actually do during a TRUE format (Which you cannot do.) but if it really did a true format you wouldn't be able to get anything back.

It's the same for your hard drives. The drive is given a true format at the factory where it finds defective sectors and uses spare sectors as replacements. A quick format just resets the index. So whenever you do format a hard drive just do a quick format and you can then recover your data if you formated the wrong drive.

Security experts tell you to physically destroy your disk drives for this exact reason. Or use a powerful electric magnet on the thing.

So if you do a format or delete all then use the recovery utility and get them all back.

That being said I haven't worked on this stuff for many, many years so things could have changed but I don't think so.

I'm glad you succeeded.

Those circular rainbows can be seen in the sky occasionally while walking around the Bay Area. Not common, but not rare either. It must be the fog, which is often lurking somewhere nearby, providing water vapor that gets blown into the sunny sky.

If there were no one present to see the glory, would it be there?

Not the tree falling in the wilderness question. Is the obstruction to the light causing the phenomenon?

Btw, a good introduction into such phenomena is "Color and light in nature" by David Lynch and William Livingston. Right now, Amazon has only used versions, but reprints are apparently available from the author: http://www.colorandlightinnature.com/

I think you benefited from a difference in how space is managed on these cards versus hard drives. Hard drives always start writing in the first available space. Delete a file, and it's likely to be overwritten by the next file. Cards don't.

The way I understand it, the card controller spreads the activity to all areas of the card to maximize the life expectancy. If you had completely filled the card after reformatting, I think your story would have had a different ending.

I hope someone who understands this better will fill us all in.

Mike, I'm guessing you know this, but the essential workflow for out of airplane window shots is to crank the contrast slider up pretty high - which overcomes the loss of contrast from atmospheric haze, double windows and dirt. We unconsciously adjust for for the low contrast when we are looking out the window.

I follow the site silently, absorbing as much information as my hobbyist background can manage. I understand the frustration of data loss much better than exposure, tonality, etc, in photography, and I was so glad to learn you were able to retrieve the images.

Here is an excellent site for atmospheric optics (and Glories).

A recent entry on my web site includes a photo of a Glory and Brocken Spectre inside the Grand Canyon.


Dear Michael,

A fair question.

There are diffractive effects that occur around the shdow, but they are subtle and wouldn't be visible in a photo like this. The glory is entirely the result of the light bouncing around in the fog droplets-- it'll be there even if the observer is very small (or absent).

pax / Ctein

Usually when you see that halo around your shadow it's a strong indicator of icing conditions. My pilot instincts have me reaching up to turn on the engine and wing anti-ice.

Mike, your account of "Buddha's light" is accurate, according to the in-house discussion of the phenomenon in Buddhist circles in China. Mt. Emei is the Buddhist mountain in Sichuan Province and Mt. Huang is usually identified as a Daoist mountain. On the top of Mt. Emei the corona/spectrum/halo surrounding your own shadow projected onto misty clouds has been a startling and ethereal sight since the Han Dynasty, as you report. Do the Daoists on Mt. Huang witnessing the phenomenon call it "Buddha's Light?" I think not, sectarian rivalry having been a part of the Chinese religious scene since the Han Dynasty as well.

I recommend PhotoRec, which is both free and open source. I have only needed it a couple times, but it has worked perfectly.

http://www.nature.com/scientificamerican/journal/v306/n1/full/scientificamerican0112-68.html

Mike, my first reaction when I saw your post was: oh! he's used one of the pictures I've sent him to illustrate his post! That lasted only for a split second, of course, but I did consider sending you my shot of this amazing phenomenon for the Keck Observatory contest. As you must know, I ended up chosing other images to send you but that was an eerie feeling for sure.

Oh and glad to hear your valued shots are safe!

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