Third Party Lens Correction, how is lens recognition done?

[VAujoulet]

Bonjour,

 

In Exif data, I find nothing that says exactly my lens was being use:

-- on Canon 760D / Rebel T6s

-- lens Sigma 18-35mm f/1.8 DC HSM [A]

 

So, how can a Lens Correction be done in Affinity Photo?

And how can I force a Lens Correction based on the Lenses database?

 

Thanks

[v_kyr]

APh uses the lensfun library, though in a static linked app context related way and not system wide shared. See the lensfun FAQ and the other topics there to get an idea of lensfun. The Sigma lens you named is usually supported by that library and as far as APh can determine from the RAW files EXIF data the used lens type, it should also apply the related lens correction data to developed images.

You can also apply a manual lens correction in cases where the used cam/lens combo isn't recognized automatically (look over the APh help topics here). - Though you can't force an own update of the lens database contents data, since the lensfun database/library isn't used by APh in a dynamic system wide shared context here. The latter means you have always to wait for Affinity program updates, which then hopefully add additional functional cam/lens combinations to that library.

[VAujoulet]

OK.

So, in APh, is there a way to find out/have displayed what Lens Correction is being applied to a RAW during the development process: at least Lens Brand (Sigma)+Name (18-35 Art) and Sensor Crop Factor (1.62) or "none"?

Thanks.

[walt.farrell]

How are you opening the image? Do you use File->Open, or drag-and-drop? I think I've seen reports that using the File menu includes more EXIF data than dragging does.

[v_kyr]

1 hour ago, VAujoulet said:

OK.

So, in APh, is there a way to find out/have displayed what Lens Correction is being applied to a RAW during the development process: at least Lens Brand (Sigma)+Name (18-35 Art) and Sensor Crop Factor (1.62) or "none"?

Well personally I don't use the APh develop RAW engine for RAW developments, thus AFAIK there is probably only the way to urge from a visual image comparison like shown here ...

• Automatic Lens Corrections - video

Also as shown there, if the cam and lens data from the RAW EXIF data is recognized, it should be indicated on the top toolbar next to the [Develop] [Cancel] buttons. Then also the EXIF tab on the right tab panel area should list among the image's EXIF contents the used lens specs.

[VAujoulet]

Hello,

 

I do "File/Open..." to open the CR2 raw.

 

To v_kyr: I missed the info. displayed on screen with the Lens Correction data. Thanks!

So, decided to do an image comparison with and without the Lens Correction set in the Assistant. And, yes, Lens Correction works.

Sigma Art 18-35mm is seen as 18-35, which is fine, yet the crop factor stored in LensFun data seems not correct to me (1.5 instead of 1.6).

 

Thanks for you hints. Have a nice evening.

[v_kyr]

25 minutes ago, VAujoulet said:

...Sigma Art 18-35mm is seen as 18-35, which is fine, yet the crop factor stored in LensFun data seems not correct to me (1.5 instead of 1.6).

The crop factor is cam sensor related and thus here the lensfun entry is probably from someone who calibrated that lens on/with a different APS-C cam, maybe a Nikon DX or Sony A cam, which have a crop factor of 1.5x instead of the Canon Rebel 1.6x here. - See also: Adding lenses to the database, especially there the statements made related to the crop factor description.

[VAujoulet]

G8.

So, if I get it right, the crop factor used to measure the distortions of Sigma Art 18-35mm being 1.5 means sensor used is bigger than Canon 760D/T6s 1.6 crop factor sensor --Canon APS-C sensor is included in the sensor used to do the measurements-- and so the distortions measurements are valid. Thanks v_kyr.

I think I would make a profile for Canon 760D/T6s + Sigma Art 18-35mm someday.

[v_kyr]

Yes no worries here, the Canon APS-C sensor size is (22.3 x 14.9 mm) and the Nikon APS-C sensor size is (23.5 x 15.7 mm). The crop factor results from the ratio of the two sensor diagonals FF (fullframe) vs APS-C, so 43.3 (FF) : 27 or 28 (APS-C).

So if the 35 mm lens is used on a camera with APS-C sensor, the FF diagonal length must be divided by that of the APS-C format, which varies between approximately 27 mm and 28 mm depending on the manufacturer here. In the case of your Canon, this would give 48.3 : 27.1 or about 1.6, where instead the APS-C DX Nikon sensors have a diagonal of 28.3 mm, resulting in a crop factor relative to the small format of about 1,5x.