How wide is Tamron 17-70mm at 17mm?

Shiny Object said:

The Sony 18-105 is more like 19 or 20mm when distortion correction is applied. I'm wondering what the situation is with the Tamron 17mm. Is it really 17mm or more like 18 or even 19mm when distortion correction is applied?

Some lenses, like the kit 16-50mm or the Sony A-mount 16-50mm 2.8 have abundant distortion, but make up for it by providing a wider image circle, so you get more than 6000x4000 pixels (on a 24mp sensor) before distortion correction is applied. This leaves you with the full 6000x4000 pixels after distortion correction is applied. The Sony 18-105 gives you 6000x4000 pixels before applying distortion correction, then crops off when you apply correction, so you never quite get to full 18mm unless you don't correct for distortion. With the 18-105, this happens at other focal lengths as well...

So... do any early adopters of the Tamron 17-70 have any insights on this? Do you get more than 6000x4000 pixels at 17mm in your raw files before distortion correction is applied? After distortion correction is applied, how many pixels are left?

I'm loosely considering buying the lens, but it would be a less attractive purchase if I'd lose much of the frame after applying distortion correction at wide angle.

Thanks in advance.

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And-roid said:

Shiny Object said:

The Sony 18-105 is more like 19 or 20mm when distortion correction is applied. I'm wondering what the situation is with the Tamron 17mm. Is it really 17mm or more like 18 or even 19mm when distortion correction is applied?

Some lenses, like the kit 16-50mm or the Sony A-mount 16-50mm 2.8 have abundant distortion, but make up for it by providing a wider image circle, so you get more than 6000x4000 pixels (on a 24mp sensor) before distortion correction is applied. This leaves you with the full 6000x4000 pixels after distortion correction is applied. The Sony 18-105 gives you 6000x4000 pixels before applying distortion correction, then crops off when you apply correction, so you never quite get to full 18mm unless you don't correct for distortion. With the 18-105, this happens at other focal lengths as well...

So... do any early adopters of the Tamron 17-70 have any insights on this? Do you get more than 6000x4000 pixels at 17mm in your raw files before distortion correction is applied? After distortion correction is applied, how many pixels are left?

I'm loosely considering buying the lens, but it would be a less attractive purchase if I'd lose much of the frame after applying distortion correction at wide angle.

Thanks in advance.

Click to expand...

The lens seems to be consistent with 17mm setting of my Fuji 16-80, unfortunately there is no profile in Lr and I appear to have switched off the jpg correction in-camera, but I can show you some comparisons later, just crude comparison with my Fuji set-up to show it's definitely delivering around 17(25mm).

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And-roid said:

First f2.8, wide open,

Tamron 16-300 profile, actual profile when arrives will be similar, there's minimal distortion imo.

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cxsparc said:

I posted here an overlay showing the extra area of the picture available when doing raw in Capture 1 with the Tamron 1770.

https://www.dpreview.com/forums/post/64754549

The light bars left and right are minimal, so in effect you get what you get.

For comparison, the 1650 and as shown also the 1655 have a much larger picture area available not only due to 16mm but also due to the overly conservative default cropping in both JPG and default raw area.

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PhotoFactor said:

cxsparc said:

I posted here an overlay showing the extra area of the picture available when doing raw in Capture 1 with the Tamron 1770.

https://www.dpreview.com/forums/post/64754549

The light bars left and right are minimal, so in effect you get what you get.

For comparison, the 1650 and as shown also the 1655 have a much larger picture area available not only due to 16mm but also due to the overly conservative default cropping in both JPG and default raw area.

Click to expand...

So are we saying that on the Sony 1650 and 1655 they give you 16 after correction (they're really a bit wider) but somehow the 18135 doesn't do the same thing and only gives you 19 when corrected?

Doesn't make sense that Sony would appoach the 18135 differently, yet could be true. Perhaps I'll check it against my Sigma 19.

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Sympa said:

Using corrections will never make the image wider than the captured one.

Also, any megapixel increases are a side effect of the software used. If the image center is compressed, it may be better to keep that part 1:1 (it is likely sharp) and magnify the rest of the image 'around' it. However most software just keeps the original captured number of pixels.

As for distortion correction, when one is not photographing architecture, some distortion can add usable field of view and make the image more pleasing. People at the edge of a wide angle image often seem stretched a bit and the average distortion compensates a little.

As far as test shorts of FL, take them at long distances. A big lens means the optical center is further in front of the camera, making the distance to subject smaller.

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PhotoFactor said:

Sympa said:

Using corrections will never make the image wider than the captured one.

Also, any megapixel increases are a side effect of the software used. If the image center is compressed, it may be better to keep that part 1:1 (it is likely sharp) and magnify the rest of the image 'around' it. However most software just keeps the original captured number of pixels.

As for distortion correction, when one is not photographing architecture, some distortion can add usable field of view and make the image more pleasing. People at the edge of a wide angle image often seem stretched a bit and the average distortion compensates a little.

As far as test shorts of FL, take them at long distances. A big lens means the optical center is further in front of the camera, making the distance to subject smaller.

Click to expand...

Perhaps I wasn't clear.

I know that for example, the kit 1650 actually is a bit wider than 16, so that once it is corrected and cropped for distortion, it reaches 16 and lives up to the label. So I am assuming that if the 18135 is labelled "18", it might also be similarly more like 17 due to its significant distortion and will be adjusted and cropped so that it would produce the labelled 18 after correction.

I'm assuming that if Sony has a general approach to make their lenses a bit wider than labelled to enable a crop for distortion/adjustment, they would do that for all of their lenses that exhibit this problem. But some posters have suggested that they do that for some but not other of their lenses which are all distorted on the wide end.

Click to expand...

cxsparc said:

I posted here an overlay showing the extra area of the picture available when doing raw in Capture 1 with the Tamron 1770.

Click to expand...