Sigma 18-50 vs Tamron 17-70 | Best Budget FX30 Zoom?


This is the Sigma 18-50mm f/2.8. This is the Tamron 17-70 f/2.8. Both are APS-C zoom lenses that are very similar, but which one is better for you? Let’s go over the differences, and I’ll tell you which one I choose at the end.

In my previous Best Sony FX30 budget lenses video, I said the Tamron 17-70 f/2.8 was my overall favorite zoom lens, but that was before I used the Sigma 18-50mm f/2.8. And did you guys let me know it in the comments.

So thank you guys for introducing me to this Sigma leans, and let’s get into comparing the specs.


Here is a table comparing each of the lenses.


First things first, the price. The Sigma 18-50mm f/2.8 retails for $550, while the Tamron 17-70 f/2.8 retails for $700. 

Let’s find out if the Tamron is $150 better than the Sigma.

Size, Physical Features & Build Quality

You'll notice the size difference right away when looking at the lenses side by side. The Tamron 17-70 f/2.8 is almost 2 inches longer than the Sigma 18-50mm f/2.8, and the Sigma’s filter size is is 55mm, while the Tamron’s filter size is 67mm.

The larger Tamron 17-70 f/2.8 is about double the weight, coming in at 1.2 lbs, while the Sigma 18-50mm f/2.8weighs .6 lbs.

Holding these up, you can notice a difference, but I’m used to full frame lenses, so both of these lenses are manageable to me.

If you prioritize a lightweight kit and have a smaller camera, the Sigma does win, as you barely notice it on your camera, but the Tamron doesn't feel heavy to the point where I wouldn’t want to take it around with me.

This one is subjective; let me know what you think in the comments.

They both have focus and zoom rings, however, I prefer using the rings on the Tamron 17-70 f/2.8. The Sigma 18-50mm f/2.8's size and rings being flush with the lens body make it difficult to adjust focus. I like using manual focus when filming stationary shots, so this was frustrating for me.

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Sharpness & Image Quality

When it comes to sharpness and Image quality, lets take a quick look at some charts to compare these lenses.

For full frame equivalents, the Sigma 18-50mm f/2.8is a 27-75 and the Tamron 17-70 f/2.8 is a 25 and a half to 105 - so you would think the restricted focal length of the Sigma is sharper than the Tamron.

Sigma 18-50 f/2.8 Image Quality

However, the Sigma at 18mm is very soft. The corners suffer from some heavy distortion if your subjects are close, and the edges of the frame are very soft. From f/2.8 to 5 the corners are soft. It is a little sharper at 7.1-10, then gets softer again at the higher apertures.

Some good news is that around 25-50mm, the sigma sharpens up and there is less distortion. Not surprising that the longer focal lengths have less distortion, but I'm glad to see the corners sharpening up around f/4 on the tighter end of this lens. Even at f/2.8 the corners are a little soft but sharper than the edges of the frame at f/7.1 at 18mm on this lens.

If you want the sharpest results, stick to the 25 to 50mm range on this lens. If you shoot a lot of wide-angle shots and want close results, you may be disappointed in the results with this lens. Especially if you’re near the minimum focusing distance.

Tamron 17-70 f/2.8 Image Quality

The Tamron 17-70 f/2.8 on the other hand is sharper wide open at 17mm. It’s a little soft around the edges at f/2.8, but at f/4 it’s almost as sharp as the center. Great performance wide open at 17mm.

The Tamron 17-70 f/2.8 at 70mm is still sharp in the center, but it takes until f/5.6 for the edges to sharpen up. This is a wider focal range than the Sigma, but I think the Tamron still is very usable at 70mm.

Image Quality Conclusion

The Tamron 17-70 f/2.8 is the clear winner here, especially at the wider end. The Tamron at 17mm at f/2.8 is as sharper than the Sigma 18mm at f/7.1.

At the longer end, the Sigma 18-50mm f/2.8 actually looks slightly sharper throughout the range. F/5.6 and f/7.1 are close, but still I think the Sigma is slightly sharper. That being said though, were comparing 50mm of the Sigma, to the 70mm of the Tamron. The Tamron is more in line with the Sigma at 50mm.

17mm vs 18mm

When it comes to the differences on the wide end, 17 vs 18mm isn’t that big of a jump. There is definitely an advantage to having as wide of a lens as you can have, especially if you’re using active stabilization that crops into your footage, but I wouldn’t make a purchasing decision alone on 17mm vs 18mm.

50mm vs 70mm

A much more interesting comparison is 50 vs 70mm. I find myself zooming in as far as I can on zoom lenses to show details, and here is where I did prefer the 70mm over the 50mm lens. 20 extra millimeters to show details is a pretty big difference here. What do you think? Let me know in the comments.


For autofocus, I took both of these lenses to Cleveland for some quick tests.

For these tests, my autofocus transition speed was set to 4. And my subject shift sensitivity was set to 5.

Both of these lenses did great in ideal lighting conditions at golden hour. The Sigma 18-50mm f/2.8 seemed like it was slightly slower to focus over the Tamron 17-70 f/2.8, but I had to arrow key through the footage to try to tell the difference.


When it comes to flaring, the Sigma 18-50mm f/2.8 seems to control the flares better than the Tamron 17-70 f/2.8. I was very surprised to see this, considering the image quality test results. This may be because of the physical size differences of these lenses? The glass on the front of the Tamron is much larger than the Sigma, so this may be helping the Sigma control the flaring better. Thats my speculation, I’m not exactly sure why the Sigma is handing these better, but these are the results.


For bokeh, both the Sigma and the Tamron have some texture happening on the bokeh. However, when it comes to shape of the bokeh, the Tamron has a more consistent size throughout the frame than the Sigma does.

Minimum Focusing Distance

When it comes to the minimum focusing distance, the Sigma 18-50mm f/2.8 is the clear winner here, coming in at 4.8 inches. Keeping in mind that that distance is from the sensor, and the lens is 2.9 inches, you can have your focus 2 inches away from the front of the lens.

The Tamron 17-70 f/2.8's minimum focusing distance is 7.5 inches, and the lens is 4.7 inches, so your subjects can be 2.8 inches away from the front of the lens.

I wouldn’t say either of these work as well as a traditional macro lens, but are capable of giving you macro-like shots.

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Focus Breathing

Since both of these lenses are third party lenses, they’re not compatible with Sony’s lens breathing compensation. Wide open, when looking at the Sigma’s focus breathing at the 18 and 50mm, I’m notice some focus breathing at 50mm and less at 18. But still not terrible.

The Tamron 17-70 f/2.8 is a similar story here, minimal to no focus breathing at 17, but some more noticeable shifting of the frame at 70. In my opinion, both of these lenses have focus breathing but not enough to be distracting. You may not even notice it, especially for third party lenses at this price point.

Image Stabilization

When it comes to image stabilization, things are weird here.

The Tamron 17-70 f/2.8 does have image stabilization built into the lens, and the Sigma 18-50mm f/2.8 does not. However, in the Sony FX30, I sometimes get strange frames jumping on Tamron lenses with internal stabilization. Especially while manual focusing. I go over this more in my Budget FX30 lenses video that I’ll leave it at the end of this video.

So, when I was using the Sigma, I could leave the internal active stabilization on at all times on my FX30. When I was using the Tamron, I would only use standard stabilization. If I’m on a tripod, I’d turn the stabilization off altogether.

If you’re moving the camera while using these lenses, I’d recommend using a gimbal to get the best results possible.


Both of these lenses have their pros and cons.

If you want the sharper lens, with the widest focal length, go with the the more expensive and larger Tamron 17-70 f/2.8. However, if your camera has internal stabilization, you’ll be limited to standard stabilization only.

If you don’t mind the lens being softer on the wider end and having more distortion, the smaller and cheaper Sigma 18-50mm f/2.8 lens is a great option. The focus ring sits flush with the body, so that can be a bit annoying. But you can use the Sigma with active stabilization to help with handheld shake. But if you’re walking with either of these lenses, you’ll need a gimbal to smooth out shakes from walking.

If you’re prioritizing a small kit, the Sigma 18-50mm f/2.8 wins. If you’re prioritizing the best image quality, the Tamron 17-70 f/2.8 wins. 

Personally, I think the Tamron 17-70 f/2.8 is worth the extra $150.

About Keith Knittel

I'm a designer from Cleveland, Ohio and love to shoot photos & videos. I made my first website in 2004 to show friends photos & videos (before YouTube/Flickr/Instagram were things) and have been shooting and designing ever since! I have a deep passion for making and helping others create.

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