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08-12-2012, 09:30 AM   #1
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EXIF Data from Zooms

So... I was taking a look at my pictures the other day taken with my DA 18-135, and I noticed that there are a few focal lengths that never show up. I was analyzing my focal lengths so that I can justify a limited lens.

I have tons of photos at 18 and 20... But no 19?
I have tons of photos at 68 and 70... But no 69?
76 and 78... But no 77?
38 and 40... But no 39?

Edit: (these numbers aren't accurate, had some other lenses mixed in the folder)

Anyone else notice this pattern on other zooms? I have not used my other zooms near as much so I don't have enough stats to compile. This lens has probably 5000+ photos versus hundreds through my other zooms.

So is my data just being rounded off to the nearest even number? If it is, I'm pretty ticked about not getting all the lengths. I paid $500 for a 18-135 and I am only getting half of those lengths!

Just kidding. I just found it odd that the only odd number I could find was 135. And yes, my lens is fantastic, I love it very much, and no I will not part with it.


Last edited by calculator01; 08-12-2012 at 06:41 PM. Reason: Had other lenses in mix, incorrect lengths
08-12-2012, 09:40 AM   #2
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Yeah, they seem to have certain points at which they report the length and others that you will just never see, so it is not a continuous real-valued number but chosen from a pre-determined set of points, not exactly calculated from its true position.
08-12-2012, 09:50 AM - 1 Like   #3
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It is coded in some discrete steps, coded in 3, 4, or 5 bits, sliding contacts and using a Gray code I presume.
Some info here
08-12-2012, 10:09 AM   #4
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QuoteOriginally posted by glasbak Quote
It is coded in some discrete steps, coded in 3, 4, or 5 bits, sliding contacts and using a Gray code I presume.
Some info here
That is some fantasticly interesting information there. Thanks for that. I wonder why they chose some of the numbers they did, kind of random where there is a gap of 3, then 3, then 5, then 4, then 3, then 5...

08-12-2012, 10:33 AM   #5
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QuoteOriginally posted by calculator01 Quote
I wonder why they chose some of the numbers they did, kind of random where there is a gap of 3, then 3, then 5, then 4, then 3, then 5...
I did not redo the calculations, but I expect that when you take the field of view range of a lens, and divide that in a handful equidistant steps, and then convert and round it to the focal length, you get what they encoded.
08-12-2012, 04:04 PM   #6
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I took 257 photos with the 28-135 Friday and got some at 21, 31, 53, 115, and 135 (According to exposure Plot)
08-12-2012, 06:25 PM   #7
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I didn't use Exposure Plot, I was just looking at the info in Windows Explorer. Now I wonder if there might be a difference...

Okay, now I have separated all my 18-135 photos from the 55-300, and I get:

18,21,24,28,31,36,40,48,53,60,68,78,88,100,115,135

One thing I found interesting is when at the zoo, I tend to only use even numbers + 135... Which originally led me to believe the lens was even only...
When I shot a gig for an oilfield company, I tend to use the odd numbers, 31,53,115,135 + 18,78

Still interesting to learn that zooms don't report all lengths, which makes since to save space on the little electronics that must be in the lens
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