Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens Review

What if you could create Stereoscopic 3D VR video content that immerses the viewer into a scene with the camera system you already understand? Just as the Canon RF 5.2mm F2.8 L Dual Fisheye Lens enabled that dream for select full-frame EOS R-series cameras, the Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens enables the dream but scales the affordability down to select APS-C models, initially the EOS R7 (with firmware 1.5.0 or higher).

The "RF-S" in the name reflects the smaller (yet still big) APS-C image circle provided by this lens, and the "F3.5" refers to the also smaller aperture opening (vs. F2.8 in the RF 5.2). Smaller x2 results in a $900.00 lower price, and the lower cost of an APS-C camera further impacts system affordability, a goal for this lens.

Like the RF 5.2mm F2.8 L Dual Fisheye Lens, the RF-S 3.9mm F3.5 STM Dual Fisheye Lens is not a normal lens.

The RF 5.2 was the world's first digital interchangeable dual fisheye lens capable of shooting stereoscopic 3D 180° VR imagery to a single image sensor. "The complexities of virtual reality production and the ability to view the content in full capacity are greatly streamlined for seasoned professionals and newcomers to the craft." [Canon]

Canon's APS-C field of view crop factor is 1.6x. 1.6 times the 3.9mm focal length is 6.24mm, the full-frame equivalent angle of view. That number is slightly narrower than the full-frame sibling's 5.2mm, and thus, the RF-S 3.9 gets a specified 144° angle of view (from both lenses), vs. 190°. Still, 144° still takes in a vast amount of its surroundings.

The RF-S 3.9mm lens is primarily designed for delivering Stereoscopic 3D VR video content. The VR viewing format can be experienced in 3D with a compatible VR headset or in 2D via desktop or mobile VR viewing platforms. While shooting VR content utilizes traditional video capture skills, it extends to new and interesting capabilities.

"Overall, the 3D Marketplace has seen incredible growth, and due to a substantial amount of content being CGI-based, there is high demand for high-quality "Live Action" content captured by a camera – meaning opportunity for someone looking to reach new viewers or share a story in a new way. This is an extremely powerful creative tool, and we know it will empower new stories and content to be shared ... so we're excited to see what the market will create with it." [Brandon Chin, Canon USA]

Dive into this exciting and growing genre of photography, producing content that differentiates itself.

Overall, this easy-to-use lens creates excellent image quality.

Focal Length

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The focal length range (or individual focal lengths for prime lenses) is a primary consideration for a lens purchase or selection for use, and few lenses have focal lengths that limit their uses as much as this one does. As you likely already realized, this lens — or more accurately, these two lenses — see a super-wide 144° angle of view (though still short of 180°) and create a double circular image that is amusing but otherwise useless without further processing.

The double-round image is not intended to be the final result, with significant cropping and distortion correction expected to create the final result. This processing creates a normal-appearing image, albeit with significantly lower resolution (using high-resolution still and video formats is advised).

Virtual reality processing is where this image gains extraordinary value. VR processing enables the viewer to see through a smaller viewport, with the ability to look around the larger image, much as our eyes see the world. VR stills and movies can be viewed on a computer display or similar device, allowing panning around a scene, but only a flat 2D view is available.

Just as our eyes enable a stereoscopic view of life, "This lens has two optical paths with a 60mm interpupillary distance ... that simulates human vision." [Canon]

The dual images recorded to a single frame make virtual reality production considerably easier vs. piecing separate videos from different cameras together. Note that the right lens's image shows on the left side of the frame, and the left lens's image shows on the right.

Here is a comparison showing an image from each side:

Load Comparison Images

Notice how the left and right images vary considerably less as the distance increases? Utilize that knowledge when selecting a subject and scene for this lens.

Note that critically framing a scene requires finding center, balancing the difference between the two images.

VR movies come to life when using a VR headset, and the edited format must be compatible with the selected model. The Oculus Quest 2 Advanced All-in-One VR Headset is the most popular at review time. Pimax models have extremely high resolution, and B&H has other models available.

When this lens is mounted on a compatible camera, a VR central resting position magic window compositional aid is available (press the info button) to delineate a normal angle of view (RF 5.2mm image is illustrated). The image can be magnified at 5x and 10x, with MF Peaking available at magnification (a new feature).

Keeping non-subjects out of the 144° useful frame may be more difficult than keeping subjects in the frame, and I often find my feet in the frame.

Note that "When viewing content created using EOS VR System with a compatible head mounted display, camera shake, and certain movements can be disorienting to the viewer." [Canon]

Tripods are the first choice for steadying a camera, but unless anchored, a tripod requires at least one leg forward of the camera to remain balanced. With the RF 5.2's 190° angle of view, everything forward of the lens on a level camera will be in the final result, and the legs of a balanced tripod are going to show in the frame. The RF-S 3.9's narrower 144° angle of view makes conventional tripod use considerably easier, but a downward camera angle is still likely to include them in an image.

Next, consider how you will light the scene. Ambient lighting is usually a good option.

What are the applications for the Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens? You be the creator. Start imagining how 3D VR viewer immersion can be implemented within your scope of interest — or branch out to something completely new.

Remember, if there is no movement in a scene, a still image is optimal. Thus, VR movies will incorporate something in motion, potentially the camera. But also remember that too much motion may induce motion sickness in viewers.

The 3D VR effect is optimal at a close subject difference, where the perspective differences between the lenses are greatest. Far subjects do not take advantage of the difference, and subjects that are too close will take on an awkward appearance.

The real estate and music video industries are among those adopting VR.

What is the VR Workflow?

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Including information from Canon USA and Europe:

This lens greatly simplifies the VR workflow by eliminating the need to sync and stitch multiple video files (the RF 5.2mm lens is shown in the above image). Canon's EOS VR Utility software converts dual fisheye footage to an equirectangular file that can be exported in various file formats and resolutions. For Adobe users, the EOS VR Plug-in allows for equirectangular conversion to be done within the Adobe Premiere Pro application. Now, conversion, editing, and color grading can be done without leaving the Adobe ecosystem.

While the use of Canon’s dedicated software is not a requirement, it is highly recommended for most VR creators. The basic workflow of the Canon VR system is:

Capture your footage with a compatible camera, which is currently the EOS R7 camera with updated firmware version 1.5.0 or greater. For the highest image quality, select 4k 30p (HDR PQ is disabled with this lens).

After recording, the files are brought into either the Canon EOS VR Utility application or into Adobe Premiere Pro with the Canon EOS VR Plug-in installed. The software is free to download and use for still image processing, but a paid subscription is required to process movie clips exceeding 2:00 minutes in length.

If using EOS VR Utility, choose whether you are working with stills or movies, then open the folder on your computer where your VR files are saved. After choosing a file, a corrected equirectangular image is displayed. You can choose clip start and end points, adjust parallax and horizontal correction, apply a LUT, preview the conversion, and export the clip to various resolutions and file formats.

To properly experience the VR footage or still image through a VR headset, the order of the left and right eye images must be switched and an equirectangular conversion of the two circular fisheye images must be performed. This equirectangular conversion requires the use of Canon’s EOS VR Utility and effectively 'de-squeezes' the two circular fisheye images into two side-by-side 'square' images (a standard format for VR image files), ready for viewing on a VR headset or editing in a compatible software application or NLE system.

If using the EOS VR Plug-in for Adobe Premiere, simply import the file into your project. The file will automatically convert to equirectangular. Then, drag it into your sequence. From here, you can edit and grade your timeline like any other video.

EOS VR Plug-in for Adobe Premiere Pro supports .JPEG stills and .MP4 video files, while EOS VR Utility supports .JPEG Stills, .MP4 Video files, and .CRM RAW files.

Max Aperture

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The aperture is measured as a ratio of lens opening to focal length, the focal length must be considered when assessing how wide a lens's aperture can open. For a 3.9mm lens, f/3.5 is a tiny opening.

Wide apertures are not always needed, especially in the ultra-wide-angle focal lengths. While disadvantageous for blurring the background, the tiny focal length is advantageous for keeping everything in the frame sharp, even at wide apertures, and the uses for this lens favor the everything-sharp objective.

This image illustrates the maximum background blur this lens is capable of:

Image Stabilization

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This lens does not have image stabilization, and the Canon EOS R7's IBIS feature is disabled when this lens is mounted. A 3.9mm lens renders all but extremely close details small in the frame, significantly reducing the need for image stabilization.

Image Quality

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When cropping deeply into an image for the normalized viewport, significant resolution is lost. Thus, it is paramount that the remaining pixels be critically sharp. Fortunately, the Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens meets that requirement.

Circular fisheye lenses don't play well with the studio's test charts, but real-world testing quickly proved that this lens is sharp throughout the entire image circle at f/3.5. Little improvement is seen through f/5.6, and none is needed.

Here is a center-of-the-frame 100% resolution crop example. This image was captured using a Canon EOS R7, with RAW files processed in Canon's Digital Photo Professional (DPP) using the Standard Picture Style with sharpness set to 1 on a 0-10 scale.

That image looks great.

Next, we'll look at a 100% resolution extreme top left corner crop captured and processed identically to the above image. The lens was manually focused in the corner of the frame to capture these images.

Count on samples taken from the outer extreme of the image circle, full-frame corners, to show a lens's weakest performance. That said, I don't see a weakness here. This result is great.

The review lens does not render the two image circles completely centered on their sides of the frame. The left circle is slightly left and low.

This lens produces a modest amount of peripheral shading at f/3.5. The shading clears through f/8.

Lateral (or transverse) CA (Chromatic Aberration) refers to the unequal magnification of all colors in the spectrum. Lateral CA shows as color fringing along lines of strong contrast running tangential (meridional, right angles to radii), with the mid and especially the periphery of the image circle showing the most significant amount as this is where the most significant difference in the magnification of wavelengths typically exists.

The image below is a 100% crop from the extreme top edge of an R7 frame showing black and white details.

Little lateral CA is shown in this image.

Bright light reflecting off lens elements' surfaces may cause flare and ghosting, resulting in reduced contrast and sometimes interesting, usually objectionable visual artifacts. The shape, intensity, and position of the flare and ghosting effects in an image are variable, dependent on the position and nature of the light source (or sources), selected aperture, shape of the aperture blades, and quantity and quality of the lens elements and their coatings. Additionally, flare and ghosting can impact AF performance.

This RF-S 3.9 is the first non-L series lens to feature Canon's ASC (Air Sphere Coating), an ultra-low refractive index coating consisting of air and silicon dioxide, to combat flare and ghosting. Even with the sun at the edge of the image circle at f/16, this lens produced almost no flare effects.

It's a fisheye lens, so it is expected to have extreme barrel distortion, and it does.

As seen earlier in the review, it is easy to illustrate the strongest blur a lens can create, and wide-angle lenses are inherently disadvantaged in this regard. Due to the infinite number of variables present among available scenes, assessing the blur quality, bokeh, is considerably more challenging. Here is an f/11 (for diaphragm blade interaction) example.

Ultra-wide-angle lenses are not known for their bokeh.

The design of this lens, including 2 UD elements, is illustrated above.

The Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens is a remarkably sharp lens.

Focusing

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Accurate focusing is critical to optimizing camera and lens image quality. The manual focus only Canon RF 5.2mm F2.8 L Dual Fisheye Lens leaves that task up to you. While the RF-S 3.9 lens's deep DOF makes accurate focusing easy, especially with the aid of focus peaking, it gets an STM AF system in each lens.

Note that servo AF is not supported for stills or movies, but focusing before recording starts is still quite helpful, and the significant depth of field means servo AF is often not needed.

This lens's AF locks quickly, even during a large distance change. If servo AF was supported, the camera's mic would pick up the modest focusing noise during audio recording.

Low light scenarios challenge this lens's AF system

This lens features a combination control and MF ring. The slim, non-clicked, knurled plastic ring turns smoothly and has an ideal resistance and adjustment rate for focusing.

This lens does not have an AF/MF switch, requiring this frequently used camera setting to be changed via the menu system or via a switch on some camera models, including the R7.

It is normal for the scene to change size in the frame as the focus is pulled from one extent to the other. This effect is focus breathing, a change in focal length resulting from a change in focus distance. Focus breathing impacts photographers intending to use focus stacking techniques, videographers pulling focus (without movement to camouflage the effect), and anyone critically framing while adjusting focus.

This lens produces a moderate change in subject size through a full-extent (worst-case) focus distance adjustment.

Load Comparison Images

Like its 5.2mm sibling, the RF-S 3.9mm lens has a minimum focus distance of 7.9" (200mm) and a 0.03x maximum magnification spec. Those lens's max magnification numbers are less than half of the next-lowest spec in the site's database of over 500 lenses.

Model	Min Focus Distance "(mm)		Max Magnification
Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens	7.9	(200)	0.03x
Canon RF 5.2mm F2.8 L Dual Fisheye Lens	7.9	(200)	0.03x
Canon EF 8-15mm f/4L USM Fisheye Lens	5.9	(150)	0.39x
Canon RF-S 10-18mm F4.5-6.3 IS STM Lens	5.5	(140)	0.23x
Canon RF 10-20mm F4 L IS STM Lens	9.8	(250)	0.12x
Canon EF 11-24mm f/4L USM Lens	11.0	(280)	0.16x
Canon RF 14-35mm F4 L IS USM Lens	7.9	(200)	0.38x

Making subjects large in the frame is not what this lens is useful for.

This lens is not compatible with Canon extenders.

Design & Features

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The Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens has an intriguing design.

This fixed-size lens has a high-quality build with excellent fit and finish.

When moved rearward, the adjust switch enables the lenses to be focus coordinated.

"If the right lens focus goes notably out of range while correcting for focus differences in the left and right lenses, slide the Left-right focus difference adjustment mode switch back and forth three times within 6 seconds, starting from the ADJUST side. This will reset the right lens position to its initial setting. After that, check and adjust the left and right focus again." [Canon]

When its function is enabled (not in use as an MF ring), the control ring is configurable for fast access to camera settings, including aperture, shutter speed, ISO, exposure compensation, AF area, and more.

This lens is not dust and moisture sealed.

The front lens element does not have a fluorine coating to repel fingerprints, dust, water, oil, and other contaminants and for easier cleaning.

The RF-S 3.9 is light, short, and narrow in one dimension. The flared sides, required to fit two lenses into the design, create a relatively wide dimension that encroaches on grip space. While I have not found the lack of space to be an issue, my fingers do sometimes inadvertently touch the lens.

Model	Weight oz(g)		Dimensions w/o Hood "(mm)		Filter	Year
Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens	10.2	(289)	4.4 x 2.1	(112.0 x 53.0)	n/a	2024
Canon RF 5.2mm F2.8 L Dual Fisheye Lens	12.4	(350)	4.8 x 2.1	(121.1 x 53.5)	n/a	2021
Canon EF 8-15mm f/4L USM Fisheye Lens	19.1	(540)	3.1 x 3.3	(78.5 x 83.0)	n/a	2010
Canon RF-S 10-18mm F4.5-6.3 IS STM Lens	5.3	(150)	2.7 x 1.8	(69.0 x 44.9)	49	2023
Canon RF 10-20mm F4 L IS STM Lens	20.1	(570)	3.3 x 4.4	(83.7 x 112.0)	n/a	2023
Canon EF 11-24mm f/4L USM Lens	41.7	(1180)	4.3 x 5.2	(108.0 x 132.0)	n/a	2015
Canon RF 14-35mm F4 L IS USM Lens	19.1	(540)	3.3 x 3.9	(84.1 x 99.8)	77	2021

View the complete Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens Specifications using the site's lens specifications tool for many more comparisons.

Here is a visual comparison:

Positioned above from left to right are the following lenses:

Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens
Canon RF 5.2mm F2.8 L Dual Fisheye Lens
Canon RF-S 10-18mm F4.5-6.3 IS STM Lens

Use the site's product image comparison tool to compare the Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens to other lenses.

Fisheye lenses do not have front filter threads, but this lens has 30.5mm filter threads (narrow, but an uncommon size) in a bayonet mount rear filter holder, supporting standard threaded filters within the thickness limitation.

Cut gel filters are also supported.

Like the RF 5.2, the RF-S 3.9 gets a unique lens cap, with fitting three-dimensionality.

When the top and bottom releases are squeezed, four hooks retract from groves in the top and bottom of the lens, releasing the cap.

Significant structure, including four protective pads, is visible in the back view.

This lens's angle of view precludes the viability of a hood, and such is not available.

As a rule, Canon includes a case only with L-series lenses. The Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens is not an "L", and my lens did not come with a case. However, Canon says the Lens Case LS1014 is included in the box. I looked through the box three times and asked my rep twice. I didn't get a case, but the case inclusion was affirmed. As this review goes live, B&H still says the case is included, but the Canon USA store does not include it in the "In The Box" list.

The LS1014 drawstring pouch will protect from scratches and dust, but only the bottom is padded against impact.

Price, Value, Compatibility

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The RF-S 3.9 has a moderate price. If we consider that it is really two lenses, the price per lens is reasonable. Those serious about creating VR movies will find this lens a great value, especially considering the eased workload.

Canon RF-S lenses mount on all Canon EOS R-series cameras, including full-frame and APS-C models. Full-frame imaging sensor camera models will automatically switch into APS-C mode when an RF-S lens is mounted. However, this lens is technically compatible with a limited number of models, initially only the Canon EOS R7. Mounting the RF-S 3.9 on the Canon EOS R5 Mark II results in a firmware upgrade required message and AF is not supported, but the camera and lens capture the expected photo.

Canon USA provides a 1-year limited warranty.

The reviewed Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens was retail sourced.

Alternatives

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If shooting 3D virtual reality on an APS-C platform, get the Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens. There is no alternative lens at review time.

If shooting 3D virtual reality on the full-frame platform, get the Canon RF 5.2mm F2.8 L Dual Fisheye Lens.

Aside from the image circle and focal length, what are the differences between the Canon RF-S 3.9mm F3.5 STM and RF 5.2mm F2.8 L Dual Fisheye Lens? The RF-S lens is slightly smaller and lighter, has AF (one shot only), and costs considerably less. The RF 5.2 has a considerably wider angle of view, 190° vs. 144°, and has weather sealing.

If looking for an extremely wide fisheye view for normal still and video use, get the Canon EF 8-15mm f/4L USM Fisheye Lens. R-series cameras require the Canon Mount Adapter EF-EOS R for EF lens compatibility.

Use the site's tools to create additional comparisons.

Summary

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The Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens is creativity inspiring.

As I said in the RF 5.2mm VR lens review, this lens has niche capability, but that niche has the potential to go big. Are you ready to jump in?