Use this 31170 Focus Gear from Sea & Sea to control manual focusing with your Canon EF 17-40mm f/4L USM lens in a compatible lens port, which mounts onto a Sea & Sea MDX underwater camera housing. The gear mounts onto the focus ring of the lens and is controlled via the required extension ring with focus knob. It does not work with the focus/zoom dial on the housing. It is constructed from a corrosion-resistant aluminum alloy.

Mounts onto Focus Ring of Lens    Rotate Knob to Adjust Focus with Lens

Related Questions and Answers

Q: 1. When using a screw-in filter on a full-frame camera, will I be likely to see the edges of the filter at wider angles?

A: Yes, depending on the thickness of the filter ring. Some of the highe quality filter manufacturers (Tiffen, Schneider, etc.) make thin filters rings specifically to address this issue.

Q: 2. Can I use the EF 17-40 f/4L on my 5D SR (with tripod) for Astrophotography?

A: The Canon EF 17-40mm f/4L USM Lens is fully compatible with the Canon EOS 5DS R. This is a good wide angle lens option for astrophotography.

Q: 3. Is this lens parfocal?

A: Yes, the 17-40 is considered a Parfocal lens. And note that Parfocal zooms in the Canon EF lens line-up are essentially limited to the fixed-aperture L-series category and front-focusing zoom lenses.

Q: 4. Is this a good zoom lens for a Canon Rebel t5i camera shooting in limited light like an auditorium or in a movie theater without a flash where the lights have been dimmed?

A: I would recommend purchasing the brightest lens possible for your stated usage needs. Of the options we carry with a similar focal length and compatible for use on the Canon EOS Digital Rebel T5 DSLR camera, I would recommend the Sigma 18-35mm f/1.8 DC HSM Art Lens for Canon EF, B&H # SI183518DCC, for your usage needs. The constant f/1.8 aperture is 2.3 f-stops brighter than the f/4 aperture used on the Canon EF 17-40mm f/4L USM Lens. As an example, if your shooting conditions require you to have an exposure of f/4 at 1/13 sec. to get a properly exposed image, and there is a chance you can get blurred images due to a slow shutter speed, the Sigma lens would give you the ability to shoot an equivalent exposure of f/1.8 at 1/60 sec., which is much faster to hand-hold this lens at any of its focal lengths with minimum blur from hand movement. You may further use a higher ISO setting to assist in obtaining an exposure with a shutter speed fast enough for your specific lighting conditions. However, do note that the lighting conditions you list above are extreme, so you may need a higher-than-normal ISO setting, and which is why the brighter Sigma 18-35mm f/1.8 DC HSM Art Lens for Canon EF would be a better option for your indicated usage needs.

Q: 5. Is this a good zoom lens for shooting in limited light, such as an auditorium or in a theater without a flash?

A: I would recommend purchasing the brightest lens possible for your stated usage needs. Of the options we carry with a similar focal length and which would be compatible for use on the Canon EOS Digital Rebel T5i DSLR camera, I would recommend the Sigma 18-35mm f/1.8 DC HSM Art Lens for Canon EF, B&H # SI183518DCC, for your usage needs. The constant f/1.8 aperture is 2.3 f-stops brighter than the f/4 aperture used on the Canon EF 17-40mm f/4L USM Lens. As an example, if your shooting conditions require you to have an exposure of f/4 at 1/13 sec. to get a properly exposed image, and there is a chance you can get blurred images due to a slow shutter speed, the Sigma lens would give you the ability to shoot an equivalent exposure of f/1.8 at 1/60 sec., which is much faster to hand-hold this lens at any of its focal lengths with minimum blur from hand movement. You may further use a higher ISO setting to assist in obtaining an exposure with a shutter speed fast enough for your specific lighting conditions. However, do note that the lighting conditions you list above are extreme, so you may need a higher-than-normal ISO setting, and which is why the brighter Sigma 18-35mm f/1.8 DC HSM Art Lens for Canon EF would be a better option for your indicated usage needs.

Q: 6. Will I be able to use a filter on the lens ?

A: Yes, but I've only been able to use one at a time. More than that and I start to see the edge of the filter when shooting at 17mm.

Q: 7. Has anyone used this lens on a crop sensor like the 80D for video and if so how did you like the results?

A: Hi, I have bought this lens originally for my 7D, and it works great as a walk around lens. Due to the cropped sensor, it behaves more like a 24-70mm on a full-frame. For video, I have shot several travel videos and product videos with the lens. Picture quality and color is top-notch. The zoom is smooth. In my opinion, having a cropped sensor on this lens is better for video, as it crops out the edges where lines are distorted. Hope this helps.

Q: 8. How is this lens compared to the Canon EF 16-35mm f/4L IS USM Lens? Also considering that it is cheaper?

A: It is older, but still a very good option for a wide angle zoom. It is also lighter and smaller too.

Q: 9. does focus changes alot when you zooming?

A: The EF 17-40mm f/4L USM is a parfocal lens.

Q: 10. can it be use on t3i ?

A: Yes, the lens is compatible with both Canon APS (crop sensor) and full frame cameras. It's a great L lens for a reasonable price!!