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Sigma 100-400mm F5-6.3 DG DN OS (X-Mount) Review

Dustin Abbott

September 5th, 2023

For the second time in about a month, I am working on a review of a lens that was designed on full frame but is being ported over to the APS-C only Fuji X-mount.  Tamron determined that its full frame 150-500mm VC lens was compact and competent enough to work on Fuji (where there are few telephoto options).  The result is (for the most part) successful, as I detailed in my review here.  But Sigma also has an excellent candidate for this converter – a direct competitor to the Fujinon XF 100-400mm OS (my review here)in the form  Sigma 100-400mm F5-6.3 DG DN OS (we’ll call it the 100-400X in this review for brevity).  The 100-400X is going to be a bit of disruptor on X-mount for a couple of reasons.  The first is that it is a very competent lens in terms of performance.  The second is that is going to be a huge value alternative at $950 vs $1900 USD for the Fuji.  The 100-400mm zoom range is one of the most popular for those who want some serious reach for birding, wildlife, or sports but don’t want the larger size that comes with longer focal lengths.  When you consider Fuji’s 1.5x crop factor on X-mount cameras you get a focal length equivalence of 150-600mm on full frame, which is obviously incredibly useful, going from this at 100mm:

to this at 400mm:

I have the original Sigma 100-400mm DN a positive review on Sony E-mount in mid 2020.  It was the first of the third party telephoto lenses to come to Sony E-mount, and it was very welcome because it was along about a third of the price (though you had to buy the tripod collar separately if you wanted one) while providing most of the features and performance of the Sony 100-400mm G Master lens.  I suspect that it can serve a similar role here on Fuji, mostly because it can create images like this…

…for under a thousand bucks.  The fact that Fuji’s own 100-400mm is getting a little long in the tooth won’t hurt, either, though there are still a couple of areas where the Fuji has the advantage (compatibility with teleconverters, for example).  So, does using a lens designed for full frame on an APS-C only system make sense?  We’ll try to unpack that in this review.  If you prefer to watch your reviews, just click the video below.



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Thanks to Gentec (Sigma’s Canadian Distributor) for sending me a pre-release review loaner of this lens. As always, this is a completely independent review. I’m doing this review on a 40MP Fujifilm X-H2 camera.

Sigma 100-400X Build and Handling

The Sigma 100-400mm is mostly similar in Fuji X-mount build to the Sony E-mount and Leica L-mounts before, though with a few minor feature changes due to the unique market positioning on Fuji. The lens continues to be lighter than the competition despite being designed for a larger sensor.  While the Fuji 100-400 OSS weighs in at 1375g (right over 48 oz), the 100-400X tips the scales at a relatively svelte 1135g (40 oz), a nearly 250g weight savings.  This is without the tripod collar, obviously (as this is an optional accessory for the Sigma), which will add another 123g.  (Nala really wanted to join this product photo session!)

The Fuji is 94.8mm in diameter and 210.5mm in length (3.73 x 8.29″), while the Sigma is thinner and shorter at 86 x 199.5mm (3.4 x 7.9″).  Not a major difference, obviously, but enough to be noticeable.  The front filter thread is also smaller at 67mm vs the 77mm standard for the Fuji.

Part of the reason for this difference is the fact that the Fuji lens does have an aperture advantage throughout the zoom range.  It starts at F4.5 and doesn’t hit F5 until a little before 200mm.  At 300mm, it’s f/5.2, and from 350mm on it is f/5.6.  The 100-400X performs much worse in this regard, as, while it starts at F5 at 100mm, it reaches F5.6 by 113mm where it remains until it hits F6.3 at 235mm.  What this means is that the Sigma is going to require more light (either slower shutter speed or higher ISO) than the Fuji in identical conditions regardless of the focal length.  

While the Sigma 100-400mm DN lenses are compatible with teleconverters on Leica L-mount, Fuji X-mount shooters are in the same boat as Sony E-mount – there are no TCs that can be used on the lens.

Sigma has made a few changes to the controls to accommodate the difference in Fuji’s protocols.  There are four switches and buttons on the side, but these have been slightly changed on X-mount.  Instead of an AF/MF switch, there is an AF-L/AF switch instead.  The Sony-style “Focus Hold” button has been rebranded as AF Function.  When AF-L is selected, you can use the button to either lock focus or reactivate autofocus afterwards.  So yes, we’ve got reduced function here compared to the Sony version.  The loss of a direct AF/MF switch is because Fuji lenses don’t come with this function (typically AF/MF is controlled from a dial on the camera).  The loss of more function on the “Focus Hold” button is due to the simple fact that unlike Sony or L-mount cameras, Fuji has no option to assign different values to this button in camera.

Other functions here include a 3 position focus limiter (FULL | 6M to infinity | Under 6M) and a three position switch for the OS (Mode 1 [Standard] | Mode 2 [Panning] | OFF).  

The OS (Optical Stabilizer) has gotten an updated tuning here and is now rated for 5 rather than 4 stops, which puts it on equal footing with the Fuji 100-400mm, which is also rated at 5 stops.  The first shot of Nala below was shot at 100mm and 1/7th of a second shutter speed, while the shot of the woodpecker is at 400mm and 1/20th of a second.

Both lenses have a standard zoom lock that locks the lens at 100mm and keeps it from extending.  The lens barrel will extend out a fair bit when zoomed to the telephoto end of the zoom range on both lenses, as these are externally zooming designs.

While these lenses have mostly similar controls, I prefer the layout and feel of the Sigma controls.  They are organized more logically and feel better to the touch.  I do have one practical complaint, however.  While hiking with the lens on a strap I would sometimes pull the lens up for a shot and it wouldn’t focus.  I would look, and the focus limiter would have moved to close focus position (furthest to the right), limiting focus.  I’ve not had this problem previously, so it does indicate in some carrying positions the switches can be inadvertently moved.

One feature the Fuji has that the Sigma does not is an aperture ring.  Aperture rings are fairly ubiquitous on Fuji lenses, but obviously this redesign by Sigma for X-mount didn’t extend quite that far.

Another minor difference is with the lens hood.  The Fuji lens features a little window in the hood to allow one to rotate a circular polarizer without reaching down into the hood.  The Sigma lacks this feature, though it does have a relatively small 67mm front filter thread and a nice flare in the lens hood at that point which allows one to reach in to rotate a C-PL fairly easily.  The lens hood also has a textured portion near the front for one to grasp as the 100-400 DN is designed to function as either a typical “twist” zoom or a “push-pull” design where one simply grasps the front of the lens hood and pushes or pulls the lens to the desired focal length.  Something for everyone here.

The 100-400 DN is a very nicely made lens, using a mixture of premium materials, including a brass lens mount, magnesium alloy in the first section of the lens, and then engineered plastics over a metal frame.  I didn’t get the feel that the Fuji lens was superior in materials.  The 100-400X is a good looking lens that feels very sturdy and well made.  It looks and feels more modern in design than the older Fuji option.

As noted already, the lens does not ship with a tripod collar (many people do not use one on a lens like this).  It comes with a rubber sleeve that covers the screws where the tripod collar attaches.  It has 100-400 stamped on there and makes for a cleaner finish when no tripod collar is attached.

The optional tripod collar is the TS-11. The tripod foot is nicely made, and, unlike the Sony tripod foot, it is ARCA compatible (meaning you can attach it right onto most tripods without the need for a quick release plate.  You can freely rotate and lock it in any position.

Using the tripod collar and foot makes a significant difference when using the lens on a tripod.  While the lens is on the lighter side of its class, it is still too heavy to easily balance on a tripod.

We have got a thick rubber gasket at the lens mount, but Sigma’s language does not specify other seal points in the lens itself, so that is likely another area where the Fuji lens is a little more robust.  Thus far Sigma’s “Contemporary” branded lenses (like this one) have only had sealing at the lens mount.

The 100-400 DN sports a useful magnification figure at 400mm of 1:4.1 (0.24x), which actually bests the Fuji’s 0.19x .  Minimum focus distance is 1.6m (5.25ft), which also best Fuji’s 1.75m.  Here’s what the Sigma’s MFD looks like:

You can really compress the background at close distances, and the bokeh is quite beautiful.  One could add an extension tube to allow for closer focus and higher magnification.  One thing is clear:  at minimum focus distance your backgrounds will completely blur out beautifully.  

The overall build quality is familiar to those who have used the lens elsewhere, but, for the most part, the 100-400X holds up pretty well when compared to the Fuji competition.

Sigma 100-400mm DN Autofocus Performance

This is an area that has historically been challenging for Fuji in general and even more so for third party lenses being adapted to the platform.  This is definitely the area where I experience my greatest frustrations with the 100-400x.  Sigma’s most recent telephoto lens on Sony received a new focus system (called HLA), but unfortunately we don’t get that here.  That means that we are working with an older STM motor that was in the original Sony design over 3 years ago.  There are moments when it works great, and other moments where it is pretty frustrating…and that’s on the X-H2, which has one of the most robust focus systems available on Fuji at the time of this review.  At times, autofocus was great, allowing me to effectively track and photography birds in rapid flight.

In other situations, just trying to focus on a slightly closer subject (but further than the minimum focus distance) would be impossible.  Focus would only go to the background, and even trying to choose a more obvious focus choice would not motivate focus movement.  Here’s what autofocus gave me in a shot that I wanted:

…and here’s what manual focus gave me.

I think we can all agree the latter is the much nicer shot.  The optics on this lens are really quite good, but there are definitely moments when the autofocus experience holds it back.  In the scenario above, there were a few minutes of trying to get autofocus to work, then another few minutes of trying to manually focus (a very slow process as it takes many full rotations to go through the focus possibilities ).  I estimate I had about six minutes invested in trying to get two very easy photos that should have taken a couple of seconds each.


And these subjects weren’t going anywhere.  In another instance I had a great shot of a dragonfly about 10 feet away.  By the time I went through all the effort to get focus to the proper place, I got this:

You’ll notice there are no dragonflies on this pine bough.  The dragonfly patiently waited for a minute or so, but then moved on.

There were other situations where focus worked just fine.  About fifteen minutes after the dragonfly episode I got a nice series of well focused images of a butterfly flitting around wildflowers.

About five minutes later I saw a pileated woodpecker through the trees, and tried to react quickly to get the shot.  At first, this is all autofocus gave me.

It just refused to focus.  I maneuvered around a bit to allow eye detect to focus on the eye, and even with some foreground obstructions, I got a well focused result.

My observation has been that the current iteration of Fuji autofocus is that focus is quite good if the AI has a detectable subject to track, but it’s not nearly as good if there is no trackable subject and the core autofocus system (which hasn’t changed much in years) has to do the heavy lifting.  This shortcomings are magnified by a long focal range and a fairly slow maximum aperture of F6.3 on the long end.  I’m pretty spoiled by the autofocus capabilities of my long glass on either Sony or Canon, so I do find all of this somewhat frustrating.

In long tracking sequences with the X-H2 and the 100-400x, I found that tracking was okay if I started the burst with a focus lock.  There were some dips in and out, but probably about a 70% keeper rate.

If I started the burst without a good lock, the camera and lens never did achieve proper focus.  I could follow the action of the bird for dozens of frames without focus ever locking on, which is rather disappointing for 2023.  

Most of the time autofocus would grab the eye of the bird quickly, and I could get some great reactive shots.

Other times it just wouldn’t want to grab on at all.  I can’t really tell you why…because other times focus would lock well even with the subject’s back turned to me.

I shot long bursts at 15FPS with the mechanical shutter on the X-H2, and, while I got some shots during the session that I really liked, I also had a lot more castoffs than usual.  I would say that my overall keeper rate for the session was no better than 60%.

If you plan on doing a lot of BIF work or tracking a lot of fast paced action, you might want to spend a bit more for one of the Fuji options, though, to be fair, there isn’t really a “slam-dunk” option on the platform outside of the hugely expensive 200mm F2.  I think most able photographers will be able to get the Sigma 100-400X to work just fine, but just realize that you won’t be getting anything like a 90% hit rate for action work.  But I came away with dozens of great looking shots from just a 20 minute session of tracking gulls, so there is value here for birders or wildlife photographers.

On the video front I found that at 100mm (the easiest focal length to frame and typically fastest autofocus speed) focus pulls were reasonably successful, though with some obvious stepping.  Focus breathing was fairly minimal, however, so that’s a plus.  My “hand test” where I alternatively block the view of my face with my hand and then remove it went well, however, with good transitions from my eye to my hand.  In another clip, focus picked up my face quickly when I stepped into frame.

On a more negative side, I shot a clip of flowers in the morning sun and focus was initially good, but then focus racked forward to where nothing was in focus and didn’t return for at least five seconds.  

The footage itself looked good, with nice detail even when shooting at 8K on my X-H2.  I wouldn’t buy this lens for video work if that work required sophisticated autofocus, but if you want to augment your footage with some long shots, it certainly provides the least expensive way to get that kind of reach…and the footage looks great.

There is obviously room for improvement on the autofocus fronts.  I’m hoping that at least some of my complaints can be fixed via firmware updates, and perhaps the lens will also benefit from growth in Fuji’s autofocus systems in the future.  Some of these frustrations are Fuji frustrations in general, but there’s no question that I had fewer complaints when using Fuji’s own telephoto options and even the Tamron 150-500mm faired better in my tests.

Sigma 100-400 DN Image Quality

The Sigma 100-400 DN has a moderately complex optical formula with 22 elements in 16 groups.  This includes one FLD element (a low dispersion glass) and four SLD (special low dispersion element) to help with aberrations and distortion.  I was quite impressed with this lens on its native full frame when I reviewed it on a 42MP Sony a7RIII years ago, but the standard of Fuji’s 40MP APS-C sensor is much more demanding.  That many pixels on a smaller sensor is the equivalent of 90+MP on full frame, which requires a lens to be really strong optically to resolve the sensor.  Fortunately that is an area of strength for the 100-400x, as the optical performance is very competitive with the more expensive Fuji options.

This is a lens capable of producing really great looking results even on the high resolution Fuji sensor.

The Sigma gives a very strong showing when it comes to vignette and distortion.  What distortion is there is a very mild pincushion distortion that grows from a -1 to correct to a maximum of -3 to correct at 400mm (essentially 1,2,3), but at any point in the zoom range you could leave the distortion uncorrected and never even notice it.  Likewise vignette is at one stop or less throughout the zoom range, and you could easily leave it uncorrected as well.  You can see the uncorrected and then corrected results at 100, 200, and 400mm below.

You may have already figured out why these figures are so much lower here than what we saw on Sony – you are putting a full frame lens on a much smaller APS-C image circle, which means that the majority of the vignette and even distortion have been cropped off (they fall outside the APS-C image circle).  This is the area where a full frame lens is most advantaged by using it on a smaller sensor.  The Sigma does have full support of Fuji’s in-camera correction profiles for JPEG and Video as well, and RAW files will be corrected via the available correction profile in your favorite software.

I also saw minimal issues with Longitudinal Chromatic Aberrations (LoCA), which means that you should see little fringing in your shallow depth of field shots:

I also saw next to no Lateral CA near the edges of the frame.

All good thus far.  The harder test is coming, however, as the 100-400x must now face a much more pixel dense sensor than it was initially designed for.  The highest resolution E-mount or L-mount camera in 2020 was a 42MP full frame sensor; this pixel density is vastly higher.  That can be the area where full frame lenses on high resolution APS-C sensors can struggle. My resolution torture test is done on the 40MP Fujifilm X-H2 and results are examined at a very high 200% magnification.  Here’s a look at the test chart:

And here are the nearly 200% crops at 100mm, F5 from the center, mid-frame, and corners:

That’s an excellent result with very consistent sharpness across the image frame.  It also compares very favorably to the much more expensive Fuji XF 100-400mm, both in the center:

and in the corners:

The Sigma is the clear winner here, particularly in the corner, where it probably benefits from having the weakest performance from the lens cut off by the crop.

And yes, the Sigma has a slower aperture here (F5 vs F4.5), but if I stop both lenses down to F5.6 and compare at 100mm, the Sigma is still the clear winner all across the frame.  Impressive.

Stopping down to F5.6 or even F8 makes little improvement, if any, so you can be confident that you are getting close to peak performance wide open, which is really important on the 40MP Fuji bodies because diffraction arrives so early.  Real world results look good as well:

Diffraction arrives early on these bodies, so while the minimum aperture is F22, I would avoid using it because diffraction really robs away sharpness and contrast progressively after F8:

100mm is the high water mark for the lens performance, however, so while 200mm is good, it isn’t quite as good as what we’ve seen at 100mm (though very, very close):

Maximum aperture is F5.6 at 200mm, so stopping down to F8 brings no advantage because diffraction has started to very slightly soften the image.  Fortunately I think that most people will find real world results in and around 200mm at F5.6 very usable:

Image quality is weakest at 400mm, though it still exceeds what I saw from the older Fuji 100-400mm lens:

As before, the image quality is fairly consistent across the frame.  There’s good sharpness there to begin with, and the weakest part of the image gets cut off by the crop factor, leaving still strong corners.  When focus is nailed, you can get good results wide open at 400mm:

I don’t find contrast “off the charts”, but, to be fair, the only telephoto lens that I’ve been really impressed with on this high resolution sensor is the very expensive Fujinon XF 200mm F2 OIS (my review here).  I haven’t really seen better performance than this from any of the zoom competitors.  The Fuji 100-400mm has a slightly faster aperture of F5.6 at 400mm, but the more expensive XF 150-600mm is slightly slower (F7.1), and the Sigma results are as sharp as what I saw when testing that XF 150-600mm.  Bottom line is that this is about as good of image quality you are going to get at 400mm on the Fuji platform at the moment:

F6.3 isn’t incredibly fast (even at 400mm), but remember that the compression of the focal length is equivalent to 600mm on full frame, meaning that you can really defocus a background.  You can see from the image below that the quality of the bokeh doesn’t look like a $10,000 F4 prime (there is some nervousness to some of the textures), but also the background is strongly blurred.  At closer focus distances you can really defocus the background and get very creamy results with nice subject isolation:

Obviously I prefer the images with greater compression, as the creamy backgrounds look great.  But even in this image where the background is only mildly defocused, I still think the nature of the blur isn’t bad.

How about flare resistance?  I replicated the results from Sony here, as they are representative for the behavior on Fuji, too.  Flare is typically less of an issue with a lens like this, as the angle of view is so narrow (particularly on the long end), that you rarely point it at the sun.  Still, however, the results aren’t bad here.  There are six tests shown below.  The first series (of four) is of the lens at 100mm where the sun is most likely to be in the frame.  We’ve the sun centered in the frame wide open, then in the upper right corner, then with those results repeated at F11.  There’s a mild flare pattern that doesn’t worsen when the lens is stopped down.  Pretty good.

The final two images show the lens at 400mm with the lens wide open and then stopped down to F11.  There’s a little most veiling and loss of contrast here, though this will probably rarely be a real-world factor.

I ended my section on the autofocus with many reservations, but I’ve got no such reservations here.  The image quality stands up very well to the Fuji competition that will cost twice as much.  If you’d like to see more photo samples, I would recommend that you visit the image gallery here.


The 100-400mm focal range is popular for a reason.  By designing a variable aperture lens, lens makers are able to fit a fairly high performing long telephoto lens into a body roughly the size of a typical 70-200mm F2.8 zoom.  The end result is a a very flexible tool that can meet most anyone’s telephoto needs without breaking their backs in terms of the weight.  The Sigma 100-400mm F5-6.3 DG DN OS takes that to the next level, as it also won’t break the bank at a price point of right under $1000 USD.   

Fuji has been a bit of a wasteland for telephoto options, with only two lenses reaching beyond 300mm from Fuji.  The release of the Tamron 150-500mm VXD added a third lens, and this Sigma provides a welcome fourth option.  But the Tamron and Sigma lenses are actually full frame designs, but their reasonably compact size allows them to work on this smaller platform.  Like the Tamron, the biggest limitations include the lack of compatibility with teleconverters and the simple fact that autofocus isn’t as effective as what we’ve previously seen on Sony.

The difference in price between the Sigma and the Fuji options will probably mean that there are plenty of people who would be willing to do deal with a few more autofocus frustrations to get a quality telephoto lens that they can afford.  The fact that the Sigma 100-400X actually bests the Fuji competition optically won’t hurt, either.  The Sigma 100-400mm F5-6.3 DG DN OS is a perfect example of the role that Sigma can and should play in the Fuji marketplace – a quality mid-tier option that offers 90% of the first party lens at a much cheaper price.  


  • Nice build quality including some weather sealing and premium materials
  • Slimmer and lighter than competing lenses
  • Fairly good tracking results for birding or fast action
  • Excellent image quality…particularly at the very important 400mm position
  • Nicer bokeh than many variable aperture zooms
  • Almost no vignette or distortion
  • Excellent chromatic aberration control
  • Improved optical stabilizer (5 vs 4 stops)
  • Good magnification and close focus results.
  • Fantastic price


  • Autofocus can be frustrating at times
  • Tripod collar a separate purchase
  • Variable aperture zoom reaches smaller apertures very quickly
  • No TC options available on Fuji




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