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I just got the above lens and have done some artificial star testing and I dont know if the lens has issues. It is clear my artificial star test is greatly exagerating aberations, but I am concerned the sigma is showing a higher level of aberation than it should? The below images are of my EF24-105 F4. The first is an actual image followed by an artificial star test. Camera is either a 6D or R8.   Now the Sigma at F1.4, F2 and F2.8    |
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Hi, i do not own a Sigma 28mm 1.4 Art. But I own a Canon 24mm 1.4 L and used it last autumn (fall?) for some shots of the milky way while I was in vacation. I can tell, that the stars in the corners looked nearly the same as yours. As you can see in your sample shots, the abberation gets better when stopping down the lens. This is exactly what I experienced back then. So I guess, your lens is behaving quite as usual. Those wide angle lenses usually have their problems at those high aperture settings and are quite soft in the corners as well. I know, the Sigma lens may be newer and maybe even better than the Canon one, but I assume, my lens is not that bad at all. You have to remember, that you are using your lens with the focus at the infinity setting. But a wide angle lens might be used with some subjects in the foreground with the focus set to some nearer distance. I assume, this is the distance the lens designers optimzed the optics for. The infinity setting might be a compromise here. With telescopes, you have other use cases and optimization might be much easier assuming you only use the lenses at infinity. I might be wrong on this, but in general there should be some truth in my words. CS Christian |
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It looks fairly typical for FF with a fast lens, discouraging as that may be. On the bright side, it doesn’t look like you have decentering.
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It should be performing decently at f/5.6 and with an APS-C at around f/4. And yes, there are better lens out there.
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Not certain about your issue, but there is an optical difference between the HSM and DN models and DN is known to perform better. I wouldn't be too surprised if HSM gave me this result in FF.
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this is my Canon RF 24-70 L lens aberrations at F/2.8 (70mm full zoom):  and my lens costed $2,400  |
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It is clear my artificial star test is greatly exagerating aberations, but I am concerned the sigma is showing a higher level of aberation than it should? Can you share the full image instead of just the corners. For instance this is my Sigma 28 DG HSM on APSC sensor wide open at F1.4. I am more than satisfied with my copy and all the "issues" can be corrected in software like BlurX.  |
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Luka Poropat:It is clear my artificial star test is greatly exagerating aberations, but I am concerned the sigma is showing a higher level of aberation than it should? On APS-C sensors, the corners should look much better which they do on Lukas image. But if you look closely, the aberations are still there. On full frame sensors, the quality decreases rapidly in the field that is missing in the APS-C image. So I am still thinking that the Art lens is ok. The images 2-5 in the first post have a really high contrast and therefore the stars look even worse. They almost look like sharpened this way. If you look at the first image where you can see the noise, it looks smoother (if you can say that). Going from the corners of the APS-C sensor to the corners of the full frame sensor, the look in James first image is to be expected. At least I personally feel this way. And this is what I saw in my own images as well. |
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Oh, I just even found my image. I put it on AstroBin a while ago. It was shot at f/2 with a 5D Mark IV. The image is cropped. Because I used a simple tripod without the az movement, I can't tell the influence the crop has on the aberations after stacking. But in the upper left corner they are really bad. https://www.astrobin.com/full/1irl0t/0/ |
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Kay Ogetay: Thanks, I have read this in a few places. Unfortunately the DN models are not available for canon, and I didnt want a DN model because they cannot be used with astro cameras. |
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I took some test exposures last night although it wasnt properly dark. It looks much better on real stars. The below range from F1.4 to F2.8        |
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Christian Großmann:Luka Poropat:It is clear my artificial star test is greatly exagerating aberations, but I am concerned the sigma is showing a higher level of aberation than it should? Thanks, I just posted some real images above. Do you have a similar image taken on FF? |
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I am not sure if I kept the data. Chances are bad. But I will look for the subs when I'm home today…
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Luka Poropat:It is clear my artificial star test is greatly exagerating aberations, but I am concerned the sigma is showing a higher level of aberation than it should? Do you have any taken with FF and sigma28? |
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I am not sure if I kept the data. Chances are bad. I will look for the subs when I'm home in the evening.
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