The teleconverter is both lightweight and short (i.e. it doesn't add much to the lens length). It works very well with my Fujinon 70-300mm zoom. There is not much loss of f-stops in photographing wildlife 3-20m away - I can still hand hold my camera. Seems expensive for such a small item but so farI think it has been worth it.

A tale of two (overpriced) converters

First thing to note is that this teleconverter yields different results depending on the lens it is used with. I have and actively use both the 55-140 f/2.8 and the 100-400 f/4.5-5.6 and I have tried this out on both of them. This review is based on my experiences shooting roughly 300 shots with the converter through the 55-140 and about 2,000 through the 100-400. I primarily use this for birding pics - but I tried some action shots as well with cyclists riding. Camera is the X-T3 plus a handful of shots on a rented X-Pro3.The 55-140 is an oddity. I have found the converter doesn't have much of an effect on autofocus performance. It may be a bit slower, but nothing that is pronounced. The image quality stays nice as well. The converter doesn't add a lot of weight ... MoreFirst thing to note is that this teleconverter yields different results depending on the lens it is used with. I have and actively use both the 55-140 f/2.8 and the 100-400 f/4.5-5.6 and I have tried this out on both of them. This review is based on my experiences shooting roughly 300 shots with the converter through the 55-140 and about 2,000 through the 100-400. I primarily use this for birding pics - but I tried some action shots as well with cyclists riding. Camera is the X-T3 plus a handful of shots on a rented X-Pro3.The 55-140 is an oddity. I have found the converter doesn't have much of an effect on autofocus performance. It may be a bit slower, but nothing that is pronounced. The image quality stays nice as well. The converter doesn't add a lot of weight nor does it tack on a lot of length - so really not a lot of compromise. Just added focal length. The oddity is that the added focal length to 196mm is not a generally useful range for me (and of course the fact that 1.4x means the lens itself covers much of the range with the ability to use a lower aperture). In full frame terms it yields a field of view of roughly 297mm (using the 1.52 crop) and this is too short for birding under normal circumstances. It is also too long as a rule for immersive sports action and not long enough for field sports. I found myself backing up a lot or zooming out to the sub-140mm range. If I was shooting birds it was a guarantee I was cropping below the 16MP size requested for most salable pics. I guess from my experience using it with the 55-140 it is a high priced 5 star converter that is in search of a use case. If you enjoy this focal range and can get it at a good price then go for it.Using this with the 100-400 is a very different experience. I will note up front that I shot around 800 shots with the shipping lens FW and a bit more than 1,200 with the updated 1.20 FW. There may be slight reductions in issues with the change, but there are still issues.I have a focus recipe I use for BiF (birds in flight) with the 100-400 and while it doesn’t get me Nikon or Sony hit rates it does get me to where I was with my G9+Pana-Leica 200 combo with much better high ISO performance. The high ISO performance is one of the reasons I felt comfortable adding the converter as the Leica with a 2X is still at 5.6 versus the F8 on the Fuji (the Fuji at ISO 4000 is as clean than the Panasonic at 1000 so the extra stop is doable). My lone area where I approve of the converter and 100-400 is image quality wide open at F8. More than acceptable given the extra range.That is where the approval ends. This converter kills autofocus at any long ranges. I find the lens just will not focus and lock on at longer ranges. I missed out on a juvenile Bald Eagle chasing an Osprey due to the awful autofocus (+ Fuji’s bad ergonomics making a quick shift to manual focus impossible). Beyond frustrating. I also found that my BiF hit rate suffers in a major way even at closer ranges. It simply takes the camera longer to focus. I tried numerous changes to my AF recipe, but ultimately my best hit rates came with my original recipe.I also noticed when I shift from shooting BiF to more stationary subjects that my contrast doesn’t appear to be as solid and that the quality of my backgrounds is lessened under some circumstances. If the background is relatively uncluttered and far away it is basically turned to beautiful mushy swirls. But if there is any solid objects within a few feet the bokeh is not attractive. It also diminishes subject/background separation which is critical for perching birds.Ultimately I was unhappy after leaving Nikon for Lumix due to the truly awful performance at ISOs over 1000. I am happy overall with the 100-400 on the X-T3, but this converter needs some more work to be usable. Even with purposefully shooting way more than normal to “try it out” my ratio of keepers and salable shots was abysmally low and my missed opportunities was unacceptably high. 1 star with the 100-400.Hey Fujifilm - if you are reading reviews where is the 400mm F/4 that many of us are waiting on? Give me that with a camera with the ergonomics of a Panasonic G9 and you have a long-term customer.

Excellent optical quality

There is no loss of image quality whatsoever, except of course the resolution reduced by a factor 1.4. Not visible when using a top quality lens. I thought it was calculated for lenses with a maximum aperture of f/2.8, but it works very well down to f/1.8 also. I am using it mostly with adapted Canon EF and Nikon AF-S lenses, on a Fujifilm X-T5 camera.

High quality component that performs very well. Highly recommeded.

Teleconverters are much maligned by people who seem to expect too much from them but if used in the right combination with a lens of equal quality that was designed and even manufactured by the same company then they can be a wise choice. I have purchased this to use with the Fujifilm 70-300 telephoto lens and from my initial observations it is a fantastic combination. These are not cheap components but ... "you get what you pay for" and I would recommend this combination without hesitation.

Must have accessory for the 100-400 Zoom

I had a bit of a struggle making the choice between the 1.4tc vs the 2.0tc. The 1.4 extends the focal length of 100-400 to 560mm on the long end. The loss of F stop is easily accomidated with the Optical Image Stablization and the relativley low noise of noted with higher ISO settings.The optical image quality loss is not noticeable even when the image is enlarged to pixel peeping levels. ON the low end of the lens focal lenght, 140mm with the 1.4tc attached the image quality is still very good.The shot below of a Green Herons eye is an extreme crop of an image shot using the 100-400 + 1.4tc.

Release knob is defective

I've used this lens for about 4 years on numerous lenses. The image quality is very good. My negative comment is that the release knob is poorly designed and subject to breakage. Then when you break this part (probably costs about $.25) that Fujifilm designed poorly, they tell you that a swap is the only thing that they will do and they charge about $360 plus tax plus freight for the swap. They give you a used lens, probably in good condition, and give you a 6 month warranty. When you try to get it repaired elsewhere the other repairers tell you that Fuji won't sell them the part. I like most things about Fuji and have lots of their equipment, but this was a disturbing encounter. I'm going to buy a new one with a one year's warranty for just slightly more than the ... MoreI've used this lens for about 4 years on numerous lenses. The image quality is very good. My negative comment is that the release knob is poorly designed and subject to breakage. Then when you break this part (probably costs about $.25) that Fujifilm designed poorly, they tell you that a swap is the only thing that they will do and they charge about $360 plus tax plus freight for the swap. They give you a used lens, probably in good condition, and give you a 6 month warranty. When you try to get it repaired elsewhere the other repairers tell you that Fuji won't sell them the part. I like most things about Fuji and have lots of their equipment, but this was a disturbing encounter. I'm going to buy a new one with a one year's warranty for just slightly more than the cost of the swap.

Solid and heavy as a little rock - top optics - no protection case included.

Heavy duty construction. Top performance optics. When unpacking the first thing I noticed : Small and Heavy. In use: Extremely precise fit bayonet - the protruding optic that goes into the lens is rubber coated to avoid lens damage. Optical performance: I'd say 98% as good as my XF 100-400 Pro - some times a tiny bit of chromatic aberrations - too easy to remove in post process. But dear Fuji: Why not include a sold protection case for that money ? As it is a premium price to pay - almost 30% more as the Olympus equivalent. Photo: An Australian Monitor Lizzard / Goanna in my garden. XF 100400 Pro + 1.4 tele converter. Processed in capture 1 - moderate sharpening.

Started with the 2x dialed back to the 1.4x - very pleased

I used this in Scotland with my 100-400mm + X-Pro 2 and got fantastic compression results like the attached photo. I should be clear - I'm not a birder in any way shape or form. I just like judicious use of hyper compressed flattening-the-background perspective. I used the combo maybe 10% of my shots...but the ones I did definitely show it in a good way. I originally started with the 2x, but I wasn't happy not having the phase detection - B&H cheerfully exchanged for the 1.4x and this Teleconverter maintains all communication with the camera.... I can say that other than the slight softening on the 400mm end (which is a function of the lens and not the tele) and the 1 stop drop, the 1.4x might as well be built into the lens - it's awesome. Wish I had this combo when ... MoreI used this in Scotland with my 100-400mm + X-Pro 2 and got fantastic compression results like the attached photo. I should be clear - I'm not a birder in any way shape or form. I just like judicious use of hyper compressed flattening-the-background perspective. I used the combo maybe 10% of my shots...but the ones I did definitely show it in a good way. I originally started with the 2x, but I wasn't happy not having the phase detection - B&H cheerfully exchanged for the 1.4x and this Teleconverter maintains all communication with the camera.... I can say that other than the slight softening on the 400mm end (which is a function of the lens and not the tele) and the 1 stop drop, the 1.4x might as well be built into the lens - it's awesome. Wish I had this combo when I was on Safari in 2015, but them's the breaks. The other minus - dang, that's an expensive teleconverter, Fuji. But I guess that's true of all their superior optics :) No regrets. Go forth and shoot.

Works pretty well

I use the 1.4 teleconverter with the 70-300 lens and the X-T4 and works pretty well, with almost no loss of sharpness. I appreciate the long reach that helps with birds and wildlife photography and even when you use as a macro lens works pretty well.The only cons is that 1 f stop missed, because without the teleconverter and at 300, the lens is at f5.6, but with the teleconverter becomes f8, which means if you are inside a forest or in a cloudy day near in late afternoon, you need to go pretty down with the shutter speed, which increases the blurriness of the photo. But when you have good light (most of the time), the 70-300 with the 1.4 teleconverterworks very well.I think if you have the extra dollars, you should go for the fujinon 100-400 f4.5-5.6, because you ... MoreI use the 1.4 teleconverter with the 70-300 lens and the X-T4 and works pretty well, with almost no loss of sharpness. I appreciate the long reach that helps with birds and wildlife photography and even when you use as a macro lens works pretty well.The only cons is that 1 f stop missed, because without the teleconverter and at 300, the lens is at f5.6, but with the teleconverter becomes f8, which means if you are inside a forest or in a cloudy day near in late afternoon, you need to go pretty down with the shutter speed, which increases the blurriness of the photo. But when you have good light (most of the time), the 70-300 with the 1.4 teleconverterworks very well.I think if you have the extra dollars, you should go for the fujinon 100-400 f4.5-5.6, because you have the same range, but with more light possibilities.

Worth it for Wildlife

Purchased for a recent trip to Alaska, where there was plenty of opportunity for photographing wildlife, especially marine mammals (whales, otters, sealions). I have the XF50-140mm f2.8 lens; note that this teleconverter is currently only compatible with this and three other Fuji lenses, so take care before purchasing!It's a teleconverter, so there's not much to say about use... there are no adjustments or settings, just attach and start shooting. The zoom range of my lens changes from 70mm to 196mm, and the effective change in aperture is shown in the viewfinder, e.g. if you have f8 selected on the lens, f11 appears in the viewfinder.There are front and rear caps, and a soft drawstring bag for storage.I'm happy with the end results. The XF50-140mm lens has ... MorePurchased for a recent trip to Alaska, where there was plenty of opportunity for photographing wildlife, especially marine mammals (whales, otters, sealions). I have the XF50-140mm f2.8 lens; note that this teleconverter is currently only compatible with this and three other Fuji lenses, so take care before purchasing!It's a teleconverter, so there's not much to say about use... there are no adjustments or settings, just attach and start shooting. The zoom range of my lens changes from 70mm to 196mm, and the effective change in aperture is shown in the viewfinder, e.g. if you have f8 selected on the lens, f11 appears in the viewfinder.There are front and rear caps, and a soft drawstring bag for storage.I'm happy with the end results. The XF50-140mm lens has stellar image quality, so you really just want an accessory lens like this to stay out of the way and be as transparent as possible. Without pixel-peeping (ugh!) I think the XF1.4x TC WR delivers.Why not five stars? IMO this accessory is very expensive, and offers marginal value for money.