Brain Fart - Nikon EXIF Question

I'm doing some focus testing of the Sigma 150-600mm and in my poking around I'm trying to determine my approx. focus distance. This is in the EXIF data but it's displayed as 126/10. I can't remember if this is in meters or not (i.e. 12.6m, which is probably right based on the photo). Help an aging mind remember.

It should always be meters, Asia uses meters. But what Exif viewer are you using? (rhetorical). The /10 numbers are always a property of the viewer not getting concept quite right.

I would strongly suggest any serious user as yourself should get the free ExifTool viewer. One way it is unique is because it is updated a couple times a month. Most others are years old, and obsolete, because Nikon changes the Manufacturers format now and then. This is how Adobe gets by about forcing updates for each new camera model. Raw only needs it to try to get white balance, but updates seem a good idea to them.

Note at first glance, ExifTool is a command line viewer, but there is also a nifty free Windows tool that converts it to a full GUI Windows app (see Camera Exif data - ExifTool for details).

Even so, the subject distance in a zoom lens is far from trustworthy, the extreme opposite. They simply indicate lens barrel focus rotation, which can be mapped in prime lenses fairly well, but zoom lenses are a real crap shoot, but most likely terrible. A better high priced lens can be less terrible, but accuracy still varies at each zoom, due to both zoom and focus distance (internal focusing, etc). Distance can be extremely inaccurate. See Nikon TTL BL flash - D-lens distance data accuracy for examples of Nikon lenses. Easy to test yourself. This D-lens distance inaccuracy can really mess up TTL BL direct flash (in Nikon flashes, it is ignored by the way third party flashes don't report head tilt).

I'm just using the Get Info feature in Photoshop. Yes, I could have used something else but that's just where I was.

BackdoorHippie said:

I'm just using the Get Info feature in Photoshop. Yes, I could have used something else but that's just where I was.

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Adobe is updated frequently too, so it might be a best case (of actually seeing the number).

But if distance is important, you ought to verify the actual distance on that lens (that reports the distance and zoom reported by Exif).


Or at least focus on something at one distance, like 20 feet etc (/3.28 = 6.1 meters), and take a few pictures at a few zooms, from minimum to maximum zoom. See what numbers you get. It should make a believer of you.

Then results at a different distance are probably different too, zoom internals change a lot with distance too.

I'm not looking for exact, just after the fact checking out what I'd expect DoF to be given focal length and aperture at that distance. I know about how far it is from my deck to the back of the yard, but something closer to exact would give me a better idea for what aperture I need to get half vs a whole squirrel in focus.

BackdoorHippie said:

I'm not looking for exact, just after the fact checking out what I'd expect DoF to be given focal length and aperture at that distance. I know about how far it is from my deck to the back of the yard, but something closer to exact would give me a better idea for what aperture I need to get half vs a whole squirrel in focus.

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OK, but my experience is that reported distance is typically not accurate enough for any use. A Nikon 16-85 mm lens may report from 37% to 157% of the measured distance (depending on zoom and distance). A Nikon 12-24 mm lens might say infinity at 5 feet 24mm, or 37% at 20 feet 12 mm. The DX lenses seem worse, my FX zooms are often within about 20% (less expense spared probably). But short lenses like to report infinity.

I don't find that useful at all.

I don't really care about distance proper, I don't need a number. My big complaint is that it sure messes up TTL BL direct flash (if using Nikon flashes). If the D-lens says distance is 37% of what it is, and so thinks TTL must be overexposing for that incorrect short distance, then it will cut the light down to be correct for 37% of the distance (imagining that it is preventing overexposure). We of course blame that on the flash, but the flash is merely a victim, the camera does all of the metering and control. And it could even be a plus, if the distance is ever correct (it would be a poor bet though).

I wish there were a menu to disable D-lens distance from affecting flash (it only affects TTL BL direct flash). We can choose TTL mode or FV Lock or use Commander to ignore D-lens distance (or tilt the Nikon head). But third party flashes like Yongnuo do not have the the head tilt switch, so metering does not know if they are bouncing or not, so camera dares not mess with them, so this makes them immune from this faulty D-lens tampering. IMO, third party flash seems the way to go.