Canon RF-S 7.8mm F4 STM Dual Lens Review

The Canon RF-S 7.8mm F4 STM Dual Lens provides stereoscopic 3D dual image capture to a single imaging sensor, creating a unique still image or movie for use in VR content.

What has now become a series of RF VR content creation lenses started with the Canon RF 5.2mm F2.8 L Dual Fisheye, a fantastic but expensive lens that was supported only by expensive camera models. The RF-S 3.9mm F3.5 STM Dual Fisheye was next, bringing much of the predecessor's capabilities and a price scaled down to the APS-C format. While the RF-S 7.8mm F4 STM Dual Lens does not have the extreme wide-angle field of view of its predecessors, it features a simpler APS-C optical design, enabling a more compact overall size and reducing the cost to less than half that of the RF-S 3.9, making it even more accessible.

The tiny, ultralight RF-S 7.8mm F4 STM Dual Lens provides an inexpensive entry into the exciting and growing genre of VR, producing content that differentiates itself.

Focal Length

Back to Top

As our eyes enable a stereoscopic view of life, and so does this lens. The dual 7.8mm lenses (with an 11.8mm inter-pupillary distance) each see a natural-apearing 63° angle of view, and the result is a double circular image that is amusing but otherwise useless without further processing.

However, a single lens and imaging sensor recording complete 3D content makes camera setup and further processing dramatically easier than the traditional approach of merging multiple camera output.

3D processing creates a normal-appearing view, albeit with significantly lower resolution (high-resolution still and video formats are advised), for use in compatible VR headsets.

The RF-S 7.8 creates this image in the viewfinder and the imaging sensor:

Here is another look:

Those images are mostly worthless without further processing, and 3D virtual reality processing is where this image gains its value.

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 the image from the referenced lens:

Load Comparison Images

The left and right lens images vary considerably less as the distance increases. Utilize that knowledge when selecting a subject and scene for this lens. The optimal RF-S 7.8 subject distance is 5.9-20" (150-500mm), and a distant background is advantageous.

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.

When this lens is mounted on a compatible camera, square magic window compositional aids are available (press the info button) to delineate the capture area (the curved RF 5.2mm image view is illustrated above). The image can be magnified at 5x and 10x, with MF Peaking available at magnification (a feature not usually availed by Canon cameras).

What is the Canon VR Workflow?

Back to Top

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 the latest firmware. 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 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.

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

Back to Top

An ultra-wide focal length creating small image circles facilitates a moderately wide f/4 aperture despite the tiny lens size.

This example illustrates the maximum blur this lens can create:

Image Stabilization

Back to Top

This lens does not feature image stabilization, and the EOS R7's IBIS is disabled when this lens is mounted. A 7.8mm lens renders all but extremely close details small in the frame, significantly reducing the need for image stabilization.

Image Quality

Back to Top

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 7.8mm F4 STM Dual 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 image circle at f/4. Little improvement is seen at f/5.6, and none is needed.

Next up is a series of center-of-the-frame 100% resolution crop examples. These images were captured in RAW format by a Canon EOS R5 and processed in Canon's Digital Photo Professional (DPP) using the Standard Picture Style with sharpness set to 1 on a 0-10 scale. Note that images from most cameras require some level of sharpening, but too-high sharpness settings are destructive to image details and hide the deficiencies of a lens.

Load Comparison Images

These results are sharp.

Next, we'll look at a series of comparisons showing 100% resolution crops from the image circle periphery.

Load Comparison Images

These results are also sharp, though peripheral shading is impacting the brightness and contrast of the f/4 samples.

When used on a camera that utilizes its full image circle, a lens is expected to show peripheral shading at the widest aperture settings.

Load Comparison Images

The shading impact is strong at f/4. For this reason, stopping down will often be a good idea.

Lateral CA, color blur, and flare are well controlled. This is a "Dual Lens", not a "Dual Fisheye Lens", and geometric distortion is corrected. Bokeh appears normal.

The design of this lens is illustrated above.

Premium optics include 2 UD elements, and Super Spectra Coating is used.

Focusing

Back to Top

The Canon RF-S 7.8mm F4 STM Dual Lens features dual STM (Stepping Motor) AF systems, one for each lens.

AF coverage is available throughout most of the magic window, but AF point selection is not limited to the functional area and the camera doesn't tell you why AF is not locking focus when the point is outside of that area.

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.

The AF speed and smoothness are good. A buzz and clicks are heard during long focus distance adjustments. If servo AF was supported, the camera's mic would pick up the modest focusing noise during audio recording.

This lens autofocuses in moderately dark environments.

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 a switch on some camera models, including the supported R7.

Despite this lens's close minimum focus distance of 5.9" (150mm), it generates a super low 0.07x maximum magnification spec.

Model	Min Focus Distance		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 RF-S 7.8mm F4 STM Dual Lens	5.9	(150)	0.07x
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

Design & Features

Back to Top

The Canon RF-S 7.8mm F4 STM Dual Lens appears to be a typical but tiny lens.

Viewing it from the front shows that it is atypical.

Load Comparison Images

This fixed-size lens has a nice build quality.

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.

The lens mount is plastic.

This lens is not dust- and moisture-sealed, and 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 7.8 is tiny and light. You will barely know it is in your bag or on your camera.

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 RF-S 7.8mm F4 STM Dual Lens	4.6	(131)	2.7 x 1.6	(68.6 x 40.6)	58	2024
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 7.8mm F4 STM Dual 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 Canon lenses:

RF-S 7.8mm F4 STM Dual Lens
RF-S 3.9mm F3.5 STM Dual Fisheye Lens
RF 5.2mm F2.8 L Dual Fisheye Lens

Use the site's product image comparison tool to visually compare the Canon RF-S 7.8mm F4 STM Dual Lens to other lenses.

An RF-S 7.8 advantage over its Canon VR counterparts is the ability to use threaded front filters vs. rear gel filters, and 58mm filters are small, light, affordable, and common.

A lens hood is not available for this lens. The optional Canon LS1014 drawstring pouch will protect from scratches and dust, but only the bottom is padded against impact.

Price, Value, Compatibility

Back to Top

The RF-S 7.8 has a low price. Those interested in spacial imaging, 3D capture, 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 and functionally compatible with a limited number of models, initially only the Canon EOS R7, which has the imaging sensor pixel density to support the significant crop. Mounting the RF-S 7.8 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 7.8mm F4 STM Dual Lens was retail sourced.

Alternatives

Back to Top

Though it costs more, the Canon RF-S 3.9mm F3.5 STM Dual Fisheye Lens provides a considerably wider angle of view with greater VR capabilities.

It all started with the Canon RF 5.2mm F2.8 L Dual Fisheye Lens, and this lens provides considerably higher VR capabilities. This lens and the full-frame camera supporting it significantly raise the cost of entry.

Summary

Back to Top

I often comment that a lens near the top of the best sellers list. In this case, the Canon RF-S 7.8mm F4 STM Dual Lens is nearly at the bottom of that list.

In part, that means you will have less competition for the unique results it can create.