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17 mm shows 19mm in EXIF on 17-40mm f4

Started Mar 17, 2019 | Discussions
(unknown member) Senior Member • Posts: 2,349
17 mm shows 19mm in EXIF on 17-40mm f4

Hello,

My Canon 17-40mm f4 lens shows a focal length of 19mm in Lightroom and Zoombrowser, on pictures that were taken at 17mm.

I re-tested it, on both 6D and 6D MkII and it is the same.

Lens is set to 17 mm but EXIF shows 19mm.

Does anyone know what would be an explanation?

I am asking out of simple curiosity, it does not present a problem in any other way.

By the way, when picture is taken at 40mm, it shows 40mm in EXIF.

Canon EOS 6D
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D3v1L Junior Member • Posts: 46
Re: 17 mm shows 19mm in EXIF on 17-40mm f4

It would be good to compare with another 17-40 lens, just to see if you get same field of view as other lens, or do you actually get "only" 19mm. Is your lens still under warranty?

OP (unknown member) Senior Member • Posts: 2,349
Re: 17 mm shows 19mm in EXIF on 17-40mm f4

D3v1L wrote:

It would be good to compare with another 17-40 lens, just to see if you get same field of view as other lens, or do you actually get "only" 19mm. Is your lens still under warranty?

Exactly my thoughts, I may do that.

It is not a pressing issue though. But a good question, am I getting 17mm at the wide end, or, is the data from my lens read incorrectly?

It is an old lens 10 times over its warranty, I normally do not use it but tested it to see if it is good enough for my next trip. We'll be in the city a lot, a wide angle may come in handy.

Steve Balcombe Forum Pro • Posts: 15,582
Re: 17 mm shows 19mm in EXIF on 17-40mm f4

I don't have one to compare, but I've seen countless images with the correct 17mm value in the EXIF, and I've never seen this issue reported so I don't think it can be a common problem.

So something is out of alignment. If it's an old lens bought used, maybe it has been repaired and reassembled incorrectly. I once bought a used lens (not a 17-40) from a reputable source, which had clearly been wrongly assembled.

Trevor Sowers
Trevor Sowers Senior Member • Posts: 1,605
Re: 17 mm shows 19mm in EXIF on 17-40mm f4

Marek M wrote:

Hello,

My Canon 17-40mm f4 lens shows a focal length of 19mm in Lightroom and Zoombrowser, on pictures that were taken at 17mm.

I re-tested it, on both 6D and 6D MkII and it is the same.

Lens is set to 17 mm but EXIF shows 19mm.

Does anyone know what would be an explanation?

I am asking out of simple curiosity, it does not present a problem in any other way.

By the way, when picture is taken at 40mm, it shows 40mm in EXIF.

When I bought my 17-40 I fell on ice an banged the lens hard.  I had the same exif issue so I sent the lens in under warranty and explained the problem.  They returned the lens and said they couldn't find any issues and the exif has been normal ever since.

I'm not sure this helps you but it is a relevant story.

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BG454 Veteran Member • Posts: 7,345
Re: 17 mm shows 19mm in EXIF on 17-40mm f4

I'm interested in how the EXIF information is created.

Does anyone know of a website that explains how a lens generates the EXIF data?

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SEdward New Member • Posts: 5
Re: 17 mm shows 19mm in EXIF on 17-40mm f4

Mine does exactly the same thing. Have you ever received an answer?

Canon AL New Member • Posts: 5
Re: 17 mm shows 19mm in EXIF on 17-40mm f4

I have the same lens and it does the same thing. I found it odd to start with, now i just know that 19mm=17mm

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BG454 Veteran Member • Posts: 7,345
Re: 17 mm shows 19mm in EXIF on 17-40mm f4

Interesting that this should come up again after such a long time.

At one time, in the days of APS-C, the 17-40 f4L was my only lens.
I just examined some of the images it created in On1 PhotoRAW2022.5. Using my Canon 30D there are definitely some images that show 17mm in the EXIF, so maybe it depends on either the camera or the EXIF reader to show the correct result.
I later used the same 17-40mm lens on my 6D Mk1 and examining the results shows images with 17mm as the focal length recorded in the EXIF.
The OP says he was reading the EXIF using Canon's DPP software, which I do not use. I can only say that displaying the EXIF using On1 shows focal lengths written as 17mm in the EXIF which appear to be correct.
Unfortunately, I have now sold the lens, so I am unable to carry out any further tests.
I never did find out how the actual EXIF information is generated, but since it is written to the memory card, I would assume it is genrated "in camera" but how the focal length is passed from the lens to the camera is outside of my knowledge.

I can only say that reading the focal length in On1 shows the correct focal length, and is not subject to this "19mm" limitation.

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Ray UK Contributing Member • Posts: 977
Re: 17 mm shows 19mm in EXIF on 17-40mm f4
1

Inside a modern lens there is a flexible PCB glued around the inside body, this rotates as the lens is zoomed. On the outer moulding there is a contact strip with tiny fingers that ride against the PCB, as the lens is zoomed different contacts will be made and the inbuilt processor of the lens will read this information and transfer it to the lens contacts so that the camera can use it for the EXIF data.

Usually if it is reading incorrectly it means that the contact strip is misaligned and the contact fingers are not touching the right place on the PCB.

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