topic Re: EOS 5D Mark III - Incorrect exif data re: focal length in EOS DSLR & Mirrorless Cameras

EOS 5D Mark III - Incorrect exif data re: focal length

MNshutterbug — Thu, 16 Apr 2026 21:23:06 GMT

I have a Canon 5D Mark 111 and just acquired a Canon 17-40 lens. Everything looks good and performs well but anytime I have the focal length at wider than 28mm, the exif still shows 28mm. It's correct from 28 - 40 but it's as if the camera isn't capable of registering the correct exif at anything below 28mm. I tried both jpeg and raw. Anybody else have this issue?

Re: EOS 5D Mark III - Incorrect exif data re: focal length

kvbarkley — Thu, 16 Apr 2026 23:32:45 GMT

Is this an RF or EF lens?

Probably a bad encoder in the lens. I suggest you see about getting it repaired

Re: EOS 5D Mark III - Incorrect exif data re: focal length

MNshutterbug — Thu, 16 Apr 2026 23:38:35 GMT

It's an ef lens. I doubt for what they sell for now, that it would be worth getting it repaired. Besides, it's not affecting my photos so it's just a tad annoying, but I can live with it.

Re: EOS 5D Mark III - Incorrect exif data re: focal length

FloridaDrafter — Fri, 17 Apr 2026 00:08:30 GMT

I wouldn't think so, but it's possible the lens may need a firmware update if Canon can/will do it. That lens is 9 years older than your 5D III and from what I understand, the EF 17-40mm f/4 USM's f/w isn't user updatable.

It could also be the reason it was on the market.

Newton

Re: EOS 5D Mark III - Incorrect exif data re: focal length

MNshutterbug — Fri, 17 Apr 2026 00:31:14 GMT

I'll admit, it was the best deal I could find on Ebay so that might be the reason. I rarely check exif data for focal length and the rest of the info makes sense so I'm good to go.

Re: EOS 5D Mark III - Incorrect exif data re: focal length

deebatman316 — Fri, 17 Apr 2026 01:39:14 GMT

Hi @MNshutterbug welcome to the forums. The lens reports the focal length to the camera. The camera records the information the lens provides it. If you’re using lens correction it slightly crops in. So the entire lens image circle isn’t used. But that shouldn’t affect the focal length. Now flash photography can be affected by this. If the lens reports the wrong focal length it will affect the speedlite’s motorized zoom head. Causing over or underexposed shots. E-TTL II uses both focal length and focus distance information (if the lens has a focus distance encoder). To help calculate flash power. Note all Canon brand EF lenses have a focal length encoder. Older EF lenses lack a focus distance encoder for E-TTL II. Most lenses released after about 1990 have a focus distance encoder. Ring Type USM lenses first got these focus distance encoders. Then started to be added to Micro USM & Micro Motor lenses. Note very old Arc Form Drive (AFD) lenses released between 1987-August 1990. Never had focus distance encoders instead Canon discontinued these lenses. With newer Ring Type USM or Micro Motor versions instead. Note some AFD lenses remained in production for years. The EF 50mm F/2.5 Compact Macro was in production from December 1987 until about 2020. This was one of the longest EF lenses in production.

Re: EOS 5D Mark III - Incorrect exif data re: focal length

MNshutterbug — Fri, 17 Apr 2026 01:49:38 GMT

It's a good thing I bought this lens for only landscape photography so no flash necessary.

Re: EOS 5D Mark III - Incorrect exif data re: focal length

Peter — Fri, 17 Apr 2026 05:22:34 GMT

When you apply lens correction for 17 mm your software will use the profile for 25 mm.

Re: EOS 5D Mark III - Incorrect exif data re: focal length

Peter — Fri, 17 Apr 2026 06:06:39 GMT

28 mm I mean.

Re: EOS 5D Mark III - Incorrect exif data re: focal length

MNshutterbug — Fri, 17 Apr 2026 11:53:11 GMT

Peter, are you saying it could be a software issue? I have no idea what you are talking about re: lens correction but I didn't apply anything.

Re: EOS 5D Mark III - Incorrect exif data re: focal length

MNshutterbug — Fri, 17 Apr 2026 16:24:26 GMT

I opened a file in DPP4 and performed a lens correction for this lens and instead of 28mm, it now shows 24mm in my exif viewer. I was going to run it again to see if it changes but once it's been done once, it doesn't give me the option of a 2nd time. It was an interesting experiment anyway.

Re: EOS 5D Mark III - Incorrect exif data re: focal length

Peter — Fri, 17 Apr 2026 16:37:55 GMT

I mean that your lens correction will be wrong when you want to apply one. DPP will not be able to read the right focal length and will over/undercorrect vignetting.

Re: EOS 5D Mark III - Incorrect exif data re: focal length

MNshutterbug — Fri, 17 Apr 2026 16:40:17 GMT

Why won't DPP be able to read the right focal length?

Re: EOS 5D Mark III - Incorrect exif data re: focal length

johnrmoyer — Fri, 17 Apr 2026 18:51:28 GMT

I have EOS R5, so this might be different. But, I hope some of this might be helpful anyway.

To find a photo made with this lens at 17mm on my web server, I ran the command:

egrep -i -l "17-40" ~/public_html/*/*.html | xargs egrep -i "focal.*len"

I had previously used exiftool free software and a Korn shell script to make the html files and did some manual edits of the html files after.

This is one I made with that lens at 17mm:

https://www.rsok.com/~jrm/2023Feb14_birds_and_cats/2023feb013_thunderbird_IMG_3165c.html

Lake Thunderbird in Norman, Oklahoma, United States on February 13, 2023