The choice between these two lenses is truly a matter of your specific needs. They are as much different as they are similar. Both have f/2.8 constant apertures but the Tamron has IBIS and a longer focal range, while the Sigma is lighter and more compact for travel.
Some would argue, "Why do we need another standard zoom?" Fujifilm has two others in their lineup which are both popular in their own right. The pro 16-55mm f/2.8 and travel friendly uber kit lens 18-55mm f/2.8-4. They are as much different as the Tamron and Sigma for their respective size and image stabilization features.
Having choices is good and ultimately provides value to every type of photographer/videographer. And we ultimately benefit the most so take your pick. Or do like I did and get both.
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Although I prefer prime lenses, standard zooms are some of the most useful lenses for any camera system, especially a constant f2.8. The most used focal lengths are all covered in each lens.
I love to use a zoom when I don't want to carry multiple lenses and have the versatility at events. Being able to adjust and react to situations and use the right focal length without changing lenses is what most pro photographers value.
Below I discuss a few key points that might help you make a decision on what lens might be your ultimate choice. It's based on my experience so keep that in mind when reading.
Tamron 17-70mm f/2.8 vs Sigma f/2.8 | Fujifilm Standard Zoom Lens Video
Size and Weight
The Sigma 18-50mm is extremely compact for a lens with a constant f/2.8. At 285g it is not much heavier than a Fujifilm f2 prime lens and less than the Fuji 18-55mm.
This makes it a great lens for street photographer but can also be used for events. The knock that I had on the Fuji 18-55 is the maximum aperture at F4 on the telephoto. That is quite useful in good light but not when doing events. It doesn't provide the flexibility I needed when I didn't want to use a flash.
As the obviously larger lens its clear that the weight of the 17-70mm at 525g is nearly double weight of the Sigma and much longer due to the reach. Extra weight and reach can give a more professional look with bigger Fujifilm bodies like the X-H series. When I used this with the X-H1 it felt really balanced and gave a feeling of workhorse. If that matters to you it will suit the big bodies well.
Size is relative to the use and some may value that the Tamron is larger and therefore feels more professional. However, I value size and portability and feel the Sigma is much better for my needs if I had to choose one. If you use a Fujifilm camera with IBIS than the Sigma may be a better fit. If you need the extra reach than the Tamron will be the choice.
My Real World Use
One thing to note is I'm not a pixel peeper nor a technical reviewer. I use cameras and lenses in the real world. I don't do test chart or care much for specs out of the box. There is nothing more important than putting the lens on the camera, going out and using it in various scenes to judge for yourself how the performance meets your expectations.
I used the 18-50mm primarily as a prime lens replacement. It really suits the size to do that. Its small but useful due to the zoom range. It covers a good focal range which includes almost all the Fuji prime lenses I own (16, 23, 35, 50). Some would have liked to have started at 16mm but I think that's the point where you need a larger front element to achieve the wide angle. I like the 18mm which is a 27mm equivalent and think for most it will be fine.
I did a family portrait session outdoors and some street photography around my city. It doesn't have image stabilization but being outdoors in good light it wasn't much of a factor. I think most will enjoy it for these purposes and It doesn't weigh down any of the Fuji bodies that I used with it. I used it with the Fuji X-T2, Xpro2, and X-S10. It balances really well on each.
I found the image quality to be sharp with good contrast. The best results came at F4 but F2.8 is still very usable. The best part of the lens is the center, which was perfect for me at any focal length.
Autofocus is really quick, silent, and seems to never miss a shot. I shoot in RAW+JPG and when doing pro work I also edit my photos. When looking at the JPGs straight out of camera I have no complaints. Colors are accurate also.
Overall, the standout features for this lens is the size, weight, and constant f/2.8. That's the true benefit and the sole reason why I purchased it. Its a good travel lens and a slight upgrade to your Fujifilm 18-55 f2.8-4 depending on your needs.
With a stellar zoom range of 17-70mm and included image stabilization I purchased this lens with the intent to be my professional lens workhorse. In my opinion this is meant to be a "do it all" lens and that's exactly how I used it. It's the natural alternative to the Fujifilm 16-55mm f2.8 or Fujifilm 16-80 F4. It has a longer reach than the 16-55mm and constant f2.8 that the 16-80 doesn't.
I used it for events, portraits, and travel in varying lighting conditions. I mostly paired this with my Fujifilm X-T2 with the battery grip attached. The Tamron isn't a particularly heavy lens but it is long and can be awkward on smaller bodies. For instance, I wouldn't use it on my X-E3. Therefore, I reserved this lens for more serious shooting scenarios.
In terms of image quality, I think this lens is a bit better overall than the Sigma. Admittedly, I did have it longer and used it in more situations to truly get a feel for it. F2.8 is very good and F4-5.6 is perfect across the focal range. No complaints.
Given that it's a longer reach and has IS it has more going against it to be a worse optic, but it's not. Tamron has put more of the effort in getting image quality to be top notch. Good move since you have to compete with the 16-55 which has a good reputation for excellent image quality.
Standard zooms are popular and both Sigma and Tamron needed to come out of the gate with an offering that is going to be both unique and up to par for the demanding Fujifilm user. The image quality difference is narrow and the biggest different is going to come from your use case, camera it will be mounted on, and your preferred user experience.
Build Quality and Handling
The build quality of this lens is not bad. Its lightweight and is mostly plastic but it doesn't feel cheap. I think it will hold up and it was a good decision for a small lens with an unusual focal range for the size to be plastic. If it were metal it would make it dramatically heavier and that would hurt its potential core user base, travel and street photographers. Event photographers will also appreciate the weight savings.
Saving on weight is a priority and I would say this its really good overall. It does have a rubber gasket on the rear of the lens so it does have some degree of weather resistance but its not marketed that way. I personally don't fall for the weather sealing gimmick and take care of my cameras and lenses no matter the designation. I personally love the minimal look. Its stealthy which suits the size.
Tamron lenses of the past have had a reputation for poor build and sometimes image quality but they have done a lot to change that in the past decade and this is no exception. The lens is built well and for a unique offering its solid. Getting an equivalent 25-105mm, and constant 2.8, with image stabilization is not small task.
Just like the Sigma it does have a small degree of weather resistant. As this lens is likely going to be your alternative to the Fuji 16-55mm it will compete for pro work and possibly travel situations so it makes sense to include it. That's how I've used it and it held up well.
I'll keep this short, sweet, and waste no time. Both lenses are great. If you can afford it, get both. They are both good lenses and have different advantages. If you're on a budget I would first look at what camera you are using and how you shoot. Size is a major difference and so is image stabilization. My choice is the Sigma for the size but your mileage may vary. Good luck and enjoy.
Image samples from the Sigma 18-50mm f/2.8 lens for the Fujifilm X mount
Image samples from the Tamron 17-70mm f/2.8 lens for the Fujifilm X mount
My name is Jason Logan. I'm a photographer and content creator from Jersey City, NJ.
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