Wednesday, May 18, 2011

M9Tether development - secret discovered?

Got some feedback from a M9Tether user in the UK, who likes to photograph in Canada on snowy mountains (I'm a stickler for privacy, so I won't mention his name without his permission).

He seemed quite happy with it, but had some remarks. One of them was the idea to overwrite the aperture field in the EXIF data, since it's a guessed value. The camera doesn't know the F-stop of the lens because there's no electronic connection between lens and camera body. The camera just guesses a bit through a secondary light reader (a small dot near the red label).

I liked the idea.

Set a value in M9Tether and the field is filled in properly, since you know what the F-stop is. Obviously there's a lot of room for error if you change the aperture but not the setting in M9Tether, but hey, then it's your own fault. And I won't touch the DNGs on the SD card. This would only be done on the transferred files, so the original is always there as a backup 'guess'.

So I dove into the EXIF of the DNG and JPGs produced by the M9.

Turns out the setting is in the Makernote field and overwriting it isn't too difficult, but it requires some more research on my part, plus some safety features, like anticipating firmware changes.

If the targeted field starts to shift after new firmware it could seriously corrupt files.

Then I discovered something else: the temperature of the camera is also stored in the Makernote.

And since reading is somewhat easier than writing, I decided to start with that one.


Then I got interested again in some mysterious fields I haven't been able to figure out. And low and behold, I think I discovered a Leica secret!

I've successfully enabled the RAM disk in the Leica (yes there is a RAM disk in there, I just don't know what I'm looking at: the buffer or something additional - if you read this and you know what it is, let me know) and I am now able to actually record a DNG on it. It has exactly enough space for one DNG.

So far that RAM always stayed empty, I've looked at it before.

I presume Leica put that RAM disk in there for either testing the M9 internally in their factories, or for tethered shooting. The option to turn on the RAM disk isn't documented (not that I know of anyway), but it's a very pleasant discovery if it does what I think it does.

Haven't tried to get the image out yet - which seems to be mandatory, because a second shot freezes the camera: the ram disk is full.

So at this point I'm not sure if this is going to lead to something. Also have to figure out if the necessary events for picking the DNG from the RAM disk are available, and if that succeeds, if the pick up can be done before the write to the SD card (if that's still going on, also something I have to test). I might then be able to start skipping the SD card reading (that would be a big bonus). If this succeeds it will speed up the transfer quite a bit.

Will keep you updated and I think I will release 1.9 soon with at least the temperature reading...

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