chrismuc

Just as an example the visible effect of distortion correction in a Q3 image: https://www.dpreview.com/sample-galleries/9356330178/leica-q3-sample-gallery/3635322490 bottom left corner at 200% (I brightened both images a bit that the text on the sticker is better readable) top is dng, opened in Iridient Developer, distortion correction OFF, saved as tiff bottom is dng opened in PS, incl. distortion correction from the widths of the sticker, one can see that the bottom image is stretched in that corner area by about 25%, the reduction of sharpness is obvious, the lens with distortion correction cannot utilise the full resolution of the 60 MP sensor the MTF is reduced accordingly, and I am curious to know if the MTF curves published by Leica (for Q and SL lenses) are with or without distortion correction ON, they don't mention it (I asked Leica by email, but no reply yet)

I downloaded some SL lens raw files and opened them in Iridient but contrary to any other raw file I opened there, I did not succeed to deactivate the baked in distortion correction, so I was not able to verify anything regarding that matter.

Hi, my claim about the SL 35 Apo Asph was from Lloyd Chamber’s text and sample image he shows, if you scroll down his main website. Now as I read again, the text information is a bit confusing. He mentions first the 21 Apo Asph, then the 28 Apo Asph, then the ‘35f2’ without specifying which of the two he is referring to. Below the image is just written 35f2 Asph, not clear if the Apo version or the non-Apo Panasonic derivate. So, yes, sorry, I can be wrong, maybe he talks about the non-Apo 35f2.

Let’s assume you have a sensor 10.000 pixels wide and the lens has 10% barrel distortion. That means that the corners of the image are at every corner 5% of the image width too far inside. In order to achieve an image without distortion, the algorithm has to scale/ enlarge/ stretch (call it what you like) these 9.000 recorded pixels to 10.000 (very simplified) in a non linear way. As mentioned before that obviously leads to a reduction of resolution/ sharpness of the amount of distortion plus the interpolation softness.

Yes, basically all lens manufacturers today allow stronger distortion in their lens design and compensate this with digital distortion correction, mainly to achieve more compact lens designs. The digital distortion correction in the best case removes the distortion completely. But: It always reduces the resolution / sharpness, so it is definitely a compromise to apply it. If a lens has let's say 6% distortion, the whole image is squeezed to remove the distortion and all image pixels are 'stretched' and interpolated which leads to a reduction of resolution of that amount distortion in certain areas plus interpolation losses, in total, in our example maybe 10%. So that is quite relevant! And the big question is: Is the MTF data provided for example by Leica and Sigma for their L-mount lenses with or without distortion correction? Enclosed image edges from six Sigma L-mount lenses with distortion reduction turned off. The 20f2 and 24f2 are worst. I had both and kept the 24f2 which is generally sharper towards the image corners, so also after distortion correction. The 28mm lens in the Q cameras and the L 24-90 at 24mm have even stronger distortion than the Sigma L 20f2 and 24f2, so the digital distortion correction will have quite an impact on the corner resolution because the pixels are stretched to such a high extend. Btw. 1: In a lens with barrel distortion, the digital distortion correction will reduce the sharpness more in the image corners than in the center. In a lens with pincushion distortion, the digital distortion correction will reduce the sharpness more towards the image center while not much modifying the image corners. Btw. 2: the-digital-picture.com shows well the distortion of lenses. Unfortunately no L mount lenses, but some Sigma which are available in E mount and L mount. Sigma / Leica 14-24f2.8 https://www.the-digital-picture.com/Reviews/Lens-Distortion.aspx?Lens=1535 Sigma / Leica 24-70f2.8 https://www.the-digital-picture.com/Reviews/Lens-Distortion.aspx?FLI=0&FLIComp=0&LensComp=0&CameraComp=0&Lens=1518

Sigma 85f1.4 and 65f2 are marvelous on high resolution L-mount cameras … and the new 50f1.2 looks to be so too. Yes and so reasonably priced … and lightweight and small in relation to the speed of the lenses … and wonderful aperture rings 😋.

IMO Leica faces two issues: 1. They are much too late to the (medium format mirrorless) game. 2. How to achieve to create not just a ‚me too‘ product? The Fujiflm and Hasselblad systems are so mature already, which a large selection of excellent lenses. Before, the Leica S system differentiated also by being a DSLR, the 1:1.5 format sensor and by using three unique sensor generations. But a mirrorless Leica S would be mirrorless like the competition and - as the Q3, M11 and SL3 in 3624 sensor size use the common 3.76 um Sony sensor - highly probable use the 3.76 um 4433 Sony sensor which all others are using too.

I own L-mount versions of the Sigma 24f2, 35f2, 65f2 and 85f1.4 lenses. They all have very quick AF motors. I see no reason why the SL f2 Apo Asph lenses should have slower AF than these or the Panasonic f1.8 lenses or the Leica f2 derivates …, other than Leica’s lack of competence in the area of AF electro-mechanics.

[I mean … that’s the kind of Leica signature distortion: The 28mm lens in the Q1/2/3 is the same, the SL 24-90 @ 24mm too 😝.]

Can someone do an architecture photography, open the image in Iridient, deactivate the in-camera distortion correction and upload the image, then we see the real optical performance of the lens.

I don’t believe DXO, I think they were not really able to deactivate the automatic distortion correction. 0.1 % sounds completely unreasonable. Lloyd Chambers showed an image without distortion correction, it looks nearly like a fish eye lens.

The SL 35f2 Asph. Apo has very strong (maybe 6-8%) distortion which is hidden by the automatic distortion correction. But the distortion correction of course reduces the resolution towards the image corners. That may reflect in the not-stellar test reviews.

Cat eye shaped bokeh balls towards the image corners are directly related to the vignetting of the lens. If a lens is f1.4 at open aperture for example, typically only the center or the lens is that ‘bright’ and ‘fast’, outside the center it isn’t, it vignettes, it’s darker, mainly because the front element is too small and also because of cosine forth’ law of illumination fall off. That means, I think there isn’t any very fast lens (f1.4, f1.2, f1) without cat eye shaped bokeh balls in the image corners.

Exactly. The lower resolution mode has no influence on the DR, that is a common misunderstanding. The only benefit is lower storage requirement. I never would use it, a higher resolution always reduces potential aliasing artifacts and interpolates to a smoother printed image with better color and brightness gradients.

super: an der Isar? > you are also in Munich, mschuette? 🙂