I have a +Sony SLT-A55V camera. The “V” means that it has a built-in GPS, which I am finding surprisingly helpful. I like lots of things about it, from the versatile 18-250mm lens from the alternate kit I got, though the great dynamic range, the small camera body, the 10FPS mode, the in-camera JPEG development, the usable in-camera panorama stitching, the sensor-shift anti-shake; the list goes on and on. Given the option to go back in time and “do it over”, I’d make the same choice. A few minor gripes, though…

It has no setting for “put a GPS stamp on the picture only if the camera has achieved GPS lock in the last some time period” so the times when the camera has the most trouble getting GPS lock (after travelling long distances) is when you have the most images that include GPS readings with a ridiculously wrong location.

It has the ability to set the time zone (great!) but records local time without the timezone in the EXIF data; at least, I can’t find any way to get the time zone out to automatically compare to the GPS timestamps to know how old the GPS fixes are relative to the picture. This makes stripping old, unreliable GPS fixes out of the EXIF data harder to come up with a general algorithm for. I’m trying to develop heuristics based on lots of other EXIF data, but so far it’s a struggle.

Finally, I keep hoping for firmware updates for various software annoyances but Sony seem to have moved on.

Arjan van de Ven July 12, 2013 23:38

I got the A57 last year.. love it (but no GPS option)

I did get a used Minolta 75-300 lens; one of my two favorites…. really worth looking on ebay for.

Michael K Johnson July 12, 2013 23:50

What aperture range on that lens?

Arjan van de Ven July 12, 2013 23:56

4.5/5.6 on the fast end, 22+ on the slow end.

if you want to see some examples, my flicker stream has various pictures taken with it


Michael K Johnson July 13, 2013 13:46

I should clarify about the out-of-date GPS data problem. The camera does tell you whether it has GPS lock at the time that the shutter was pressed; the GPSStatus field says “A” (Measurement Active) instead of “V” (Measurement Void). The problem is that it gets intermediate GPS fixes while the camera is on, so it’s common that I’ll get two pictures in close success, each of which says Measurement Void, but for which the camera had very recently had GPS lock, so I really want to honor those measurements.

That’s where the difficulty reconciling the time bases comes in; I can’t directly compare the GPSDateTime to the DateTimeOriginal even if I assume that the camera is keeping its internal clock in sync by GPS. The best I can do is to calculate an offset each time I see Measurement Active and see that the GPSDateTime and DateTimeOriginal are within epsilon of being an integer number of hours apart (now you can tell I haven’t traveled yet to any 30-minute offset time zones…) and use that to determine freshness.

Arjan van de Ven July 13, 2013 14:31

Would it be useful to calculate the distance between pictures and then do a MPH calculation…. And if its an impossible speed, strike the first pictures location as invalid

Michael K Johnson July 13, 2013 14:41

Yes, unreasonable rate is one of the heuristics I had in mind. Though right now I’m only calculating cartesian distance because it’s easier and most of the time good enough for a heuristic… Of course the possible exception is my recent Scandinavian trip which is the whole reason I’m looking into this right now, but it is such a rough metric it hardly matters… :-)

Michael K Johnson July 13, 2013 14:43

I actually thought of using altitude to determine what speed is virtually impossible. A speed of 200 kph makes more sense if I’m more than 1000 meters above sea level (I do take pictures while flying)

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