I've use a Sony Alpha A6000 and the PZ 16–50mm F/3.5–5.6 OSS kit lens with my computer as a webcam for a long time now. It's a lower cost option that has been very consistent outputting 1080p at 30 FPS to a USB based HDMI capture device. The kit lens is generally fine, but it has a few quirks. The biggest issue is that throughout the zoom range the maximum aperture value is not fixed. This introduces technical challenges when I want to show detailed views of product or similar use cases. There are also other considerations I'll talk about later in this article. So I decided to buy the Sigma 18-50mm F2.8 DC DN | C lens in E-mount as a replacement.
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I made a video unboxing the lens and trying it out with Open Broadcaster Software.
Unboxing and First Look
I purchased this lens used from KEH rated LN- ("like new minus"). You can also get it new from sites like Amazon and B&H Photo Video. When the lens arrived, I was glad to see KEH was consistent if not even better than in the past in regard to packaging.
Checking to see if KEH has any coupons or cash back before purchasing!
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| This box was in a shipping box. You can see the lens was double wrapped too. |
The lens came double-boxed with a good amount of padding, which is always reassuring when you're dealing with camera lenses.
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| A bit of scuffing on the composite material where the lens hood attaches. |
Condition looks pretty great. I see only tiny scuffs on the front material near the lens hood as well as the cap had a tiny bit of scuffing, but that's to be expected with a used item. The zoom ring is smooth and the back weather gasket looks good.
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| A weather gasket on the mount side of the lens. |
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| The lens hood. |
One thing to note is that this is an E-mount lens designed for APS-C format cameras While it can be used on full-frame Sony mirrorless cameras, it won't cover the entire sensor, so you'd need to use it in crop mode.
Build Quality and Design of the lens
Details from Sigma's official product page:
- Smallest and lightest F2.8 standard zoom for APS-C mirrorless
- Full-frame equivalent zoom range of 27-75mm
- High-speed autofocus with stepping motor
- Compatible with lens aberration correction (to some degree?)
- Minimum focusing distance of 12.1cm / 4.8 in.
- Mount with dust and splash-resistant structure
- High-precision, durable brass bayonet mount
- Designed to minimize flare and ghosting
- Thermally Stable Composite (TSC) construction
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| Lens design from Sigma's website. |
Specifications:
- Lens Construction
- 10 groups, 13 elements
- (1 SLD and 3 aspherical lenses)
- Angle of View:
- 76.5°（W）- 31.7°（T)
- Number of Diaphragm Blades
- 7 (rounded)
- Maximum Aperture
- F2.8
- Minimum Aperture
- F22
- Minimum Focusing Distance
- 12.1 (W) - 30cm (T) / 4.8 (W) - 11.9 in. (T)
- Filter Size
- 55mm
- Maximum Magnification
- 1:2.8（W）- 1:5（T)
- Lens weight
- 290g / 10.2 oz.
- Lens dimensions
- 61.6 x 76.5mm / 2.4 x 3.0 in.
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| The Sigma lens attached to the A6000 PC camera setup. |
Lens Performance
While I haven't had the chance to thoroughly test the lens yet, my initial impressions are positive. The constant F/2.8 aperture throughout the zoom range is a huge benefit and the reason I bought the lens. Though, I do wish the Sigma lens covered 16mm instead of 18mm on the wide end.
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| The Sony lens should have looked like the Sigma here, but it takes time to adjust the exposure with ISO as I move my hands in and out of the frame. You can see it better in the related video. |
The Sigma allows for a consistent exposure if I zoom, so I can keep the A6000's shutter speed, ISO, and aperture on that lens fixed. It make a large difference in video quality because the camera isn't trying to correct exposure with ISO.
When compared to the Sony kit lens, the difference in background separation is somewhat noticeable in my small space. This lens will especially be better with product shots and close-ups, which is perfect for my drink reviews and similar content.
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| How the lenses look at their maximum aperture around the same focal length. |
At the wide end, the Sony has an extra 2mm to get wider, but it still sacrifices aperture with f/3.5 compared to f/2.8. Zooming the Sony to around 18mm will likely loose a bit of additional maximum aperture.
The autofocus performance in video mode is good so far. I have a shelf with various objects in the background and often a microphone in the foreground. I don't see any issues with the lens being used on this older A6000 to focus on my face here. I would assume newer camera bodies are even better. Autofocus sound of the Sigma is a bit louder than the kit lens, but not within it being an issue.
The Sigma's zoom ring is a bit more challenging to rotate yet is more accurate than the PZ styled mechanical zoom of the Sony kit lens. It takes more hand force, but the zoom is smooth. It's probably best there is resistance because it should not shift zoom position on its own due to gravity or whatever.
One downside is distortion on the wide end of the Sigma lens. I currently turned all lens corrections in the A6000 off because I want HDMI output to be as fast as possible, but it could be something worth testing in the future to see which corrections exist and if they add latency to the A6000's output. I'm not sure if there are corrections available in video so don't take anything regarding this as fact.
On the other hand, the Sigma appears to have low focus breathing which is a big plus for video.
Final thoughts
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| Lower noise through the zoom range thanks to the f/2.8 maximum aperture, but it is tough to tell at 1080p or less resolution a lot of the time. |
This lens isn't cheap compared to the kit lens, but it offers significant improvements.
So far so good! As I write this article it's been around a month. I tend to zoom in slightly based on my recording area to remove some of that lens curvature at 18mm, but besides that it is very nice!
If at some point I can get a Sony FX30 for my hands-on recording area I'd be tempted to get another Sigma 18-50mm for that.