jtra
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Hi,
I have visited a Sony day event in Prague today.
I played with borrowed Sony 24GM for about 25 minutes and compared it to my Sigma 24/1.4 F-mount on manual Novoflex adapter. For a few shots I have also compared with my Sony 28/2 FE.
Technical details: shot on A7III, all outdoor shots were ISO 100, AF-C on center (except for scene 3 where I focused a bit lower) for AF lenses. For Sigma, I focused manually with Focus magnifier at highest magnification. With Sigma on Novoflex adapter, I could stop down, but only guess aperture change based on how auto exposure changed because there are no marks on aperture ring so all aperture information for Sigma shots that are stopped down is only approximate (more likely to be stopped down more than indicated because vignetting impacts exposure).
I have placed DNG lossless compressed raws converted from 14 bit uncompressed ARW here:
http://jtra.cz/foto/20181027-sony24gm-vs-sigma24art-vs-sony28fe/dngs/
I will keep DNGs there for a few weeks.
Lens shading compensation that affects raws was off.
There are also converted JPGs http://jtra.cz/foto/20181027-sony24gm-vs-sigma24art-vs-sony28fe/jpgs/
I used LR 5.7. I set shadows +100, highlight -40, unified WB, adjusted exposure (images were a bit underexposed on purpose) to be about same in center.
For Sigma I have enabled "Remove chromatic aberration" setting (which reduced LaCA, but not LoCA). Sigma has LaCA of about two pixels on sides so it was helpful.
Sony 24GM has very weak LaCA. I have noticed that on Scene 5 the Remove chromatic aberration function was working badly, it was reducing LoCA in middle and increasing it on sides so I turned it off for that scene. I kept it for other scenes because it was improving image by a tiny bit (e.g. in Scene 1).
Sony 28/2 did not seem to benefit from CA reduction, but kept it enabled.
I did not use defringe tool to reduce other CA or PF. I did not use distortion correction (this older LR 5.7 does not force it).
Sony 24GM has more purple fringing than Sigma, pictures show it a bit, but in this heavy overcast day contrast was never big enough for PF to be strong. No pictures has shown as strong PF as in this f/2.8 image (near corners) from Chinese review https://www.mobile01.com/newsdetail/27303/sony-sel24f14gm-review Strongest PF can be seen on a lamp in top left corner of the last scene.
Last scene also includes bokeh comparison where I focused at 1m, but I have failed to set same aperture, Sigma is wide open while Sony 24 is at f/2. This makes it hard to draw a conclusion.
My long term experience with Sigma tells that it has busy background bokeh at far (more than 1m) focus distance (but then it is small anyway) and smooth background bokeh near close focus.
Generally, Sony 24 GM has smoother background bokeh than Sigma 24/1.4, but difference is not big. I felt that overcorrected spherical aberration that gives Sigma more busy bokeh also makes bokeh in background a bit bigger, but I could not control focus distance precisely to be sure.
I was surprised by Sony 24 GM in the last scene on focused picture that near right bottom corner the highlights in background have a star shape. Sigma has weird shape there too, but bit more convex.
Sony 24 GM is sharp in corners even wide open while Sigma needs f/4 to get sharp in corners. Sharpness in center is good on both.
While doing a lot of lens switching, I was bit annoyed by aperture ring on 24 GM which I was turning accidentally while mounting or unmounting. I don't have other lenses with the ring but I'm might get used to it holding it in different way.
You may notice some angle of view differences: 24 GM is a bit wider than Sigma.
Sigma has some barrel distortion, Sony 24 GM has weak pincushion distortion, Sony 28/2 has strong barrel distortion (when you correct it the worst corners are cut off).
Sigma is a bit more yellowish then two Sony lenses.
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, shot from my 85 GM: 
