Sigma 28-105mm f2.8-4 Aspherical IF

[ameermukmin]

I bought this Sigma lens to replace my kit lens. The reason i got this lens was because it had an aperture size of 2.8!!! and the lens size of 72mm.

That meant that this lens could capture light and is very fast. Since it has aperture from 2.8, it must have a better Bokeh and suitable for low light, night/indoor photography and for portraiture as well. The lens focal length of 28mm-105mm meant that it was a well covered focal length to be a suitable walkabout lens.So i thought that i would give this lens a try and seriously see if this performed well with the Sony Alpha and if it was better than the kit lens.

The older version of this lens with an f3.5-5.6 had an average rating as it didn't perform well in the Nikons or the Canons as many of them couldn't get a good focus it seems. But having the f2.8 and a reasonable price that didn't burn my pockets, it was a steal.

It took some test shots attached below.
The test conditions were as follows:
Spot focus on object in M mode with a F5.6, 0.5" shutter at 35mm, 50mm and 70mm. he reason for choosing the F-stop 5.6 is only because the kit lens cold only go as low as that at the given distance to object at 35mm. So i had to set the same f-stop for the Sigma lens as well. This was the result:

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F5.6 0.5" 35mm kit lens


F5.6 0.5" 35mm Sigma lens


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F5.6 0.5" 50mm kit lens


F5.6 0.5" 50mm Sigma lens


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to be cont.

[ameermukmin]

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F5.6 0.5" 70mm kit lens


F5.6 0.5" 70mm Sigma lens


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From the comparisons above, it is obvious that the Sigma lens color is softer due to the Wider lens diameter of 72mm compared to 55mm lens diameter on the kit.
The Bokeh on the Kit lens is harsher and the Bokeh on the Sigma lens is more softer and refined.

Overall i like the Bokeh and the result of the Sigma lens. Probably will test in daylight outdoor shoot next and Night shot comparisons as well.

The clarity is similar (to be more reserved on the comments), but truly, i think the quality is better on the Sigma lens.

Any comments?

[calebk]

Filter size has no major impact on image quality. I think that is something you've been mistaken on.

[ameermukmin]

Correct me here, if the lens diameter is bigger, more light right? It won't affect the quality of pic, but it will affect the exposure of the pic.

[ameermukmin]

Night shot taken with the lens

[ameermukmin]

another night shot with the lens

[calebk]

Originally Posted by ameermukmin Correct me here, if the lens diameter is bigger, more light right? It won't affect the quality of pic, but it will affect the exposure of the pic.

No it won't, not by enough for you to notice. Where did you ever hear that?

And if lens diameter affects your exposure, then how come when you only vary shutter speed, aperture and ISO to achieve your exposure, and don't have to calculate lens diameter?

[ameermukmin]

Bro that's because lens diameter is fixed on any given lens. That's why you don't need to calculate lens diameter. very straightforward.
When you compare two different lens, of course diameter size will affect same shot taken with both different lenses too.
That's why there is a diameter difference for say a Sony Sal75-300 and Sal70-300G. Both focal length about similar, but outcome different. The G lens is way bigger than the normal one. In length and in DIAMETER size too. Ever considered why?
Of course f-stop gives more difference than a diameter radius difference.
I will agree that the difference may not be enough, but if you say it does not affect at all, then you are wrong.

Originally Posted by calebk No it won't, not by enough for you to notice. Where did you ever hear that? And if lens diameter affects your exposure, then how come when you only vary shutter speed, aperture and ISO to achieve your exposure, and don't have to calculate lens diameter?

[calebk]

Originally Posted by ameermukmin Bro that's because lens diameter is fixed on any given lens. That's why you don't need to calculate lens diameter. very straightforward. When you compare two different lens, of course diameter size will affect same shot taken with both different lenses too. That's why there is a diameter difference for say a Sony Sal75-300 and Sal70-300G. Both focal length about similar, but outcome different. The G lens is way bigger than the normal one. In length and in DIAMETER size too. Ever considered why? Of course f-stop gives more difference than a diameter radius difference. I will agree that the difference may not be enough, but if you say it does not affect at all, then you are wrong.

Ever considered that the G lens may give a different outcome not because of the diameter but because of the design and arrangement of lens elements, and usage of optical elements? Never have I heard of physical diameter affecting image quality or exposure. Consider also how the filter diameter may not be the same diameter as that of the rest of the lens, or the front element, or the other elements inside the lens. How then are you to judge how much light is gathered by the lens based on lens diameter?

That's why there is such a thing as aperture, and it is what sets the standard for exposure. F/stops (or to be correct, T/stops) are universal. I can have two 50mm f/1.4 lenses from different manufacturers, and one may have a 58mm diameter while the other, a 52mm diameter, but at any f/stop with same shutter speeds and same ISO readings, you will still get identical exposure.

[Isaiahfortythirtyone]

i agree with calebk. this is the first time i've heard that lens diameter can affect image quality.

The tamron 17-50mm has a filter size of 67mm. The canon 17-55mm uses 77mm. there are a few possible reasons for the canon having a larger diameter: (i) use of special glass like UD, (ii) the tamron uses XR glass which tamron claims to be able to make the overall size of the lens smaller, (iii) IS mechanism? and (iv) just a simple standardisation objective for canon to have most of their lenses at 77mm.

[ameermukmin]

I see your point and caleb point. No arguments there. Just saying larger diameter lens, more surface area to collect light. That does not necessarily mean best quality photos or sharpness unless the mechanism is able to handle that more light effectively (maybe, the points stated and listed out by Isaiahfortythirtyone)

Maybe this article is of interest to us to shed some light.

http://www.howeverythingworks.org/page1.php?QNum=1525

By the way, guide us newbies and point us in the right direction. I'm not here in this forum to argue and state my points. I cannot have more knowledge than the pros like yourselves. I'm here to learn and pick-up. Humbly request help.

Anyway, whole idea is to see if there is any difference to the lenses. whether Sigma is "ok" or "good" or "better" compared to the Sony kit lens. Any comments on this guys? (my comments above were just my opinion, that's all. Guide me what i should look for in lenses). Any comments to the comparison picture and which seems "better" or "no difference" would be greatly revered and appreciated. Would help me and other newbies alike. Thanks guys.

[calebk]

From a physics point of view, obviously when he says there is a difference in collecting light, he is talking about if from a precision PoV - that of a scientist. As a photographer, the diameter of the lens itself does not affect the image significantly enough compared to the f/stop itself.

The 85mm f/1.2L has a smaller filter thread than the 70-200 f/2.8, for instance, but the 85 f/1.2 can gather more light because of its maximum f/stop opening.

[ameermukmin]

Originally Posted by calebk From a physics point of view, obviously when he says there is a difference in collecting light, he is talking about if from a precision PoV - that of a scientist. As a photographer, the diameter of the lens itself does not affect the image significantly enough compared to the f/stop itself. The 85mm f/1.2L has a smaller filter thread than the 70-200 f/2.8, for instance, but the 85 f/1.2 can gather more light because of its maximum f/stop opening.

Been pushed to do some reading about it, you and isaiah are correct in every way. My humble apologies and Thank you so much for good insight. See, us newbies can learn too. Just that we perceive things differently due to lack of knowledge. We trip and fall, we learn when you guys pick us up. Thanks again. Lesson learnt.....