I used the Marlex R5 and purchased an RF 7-14 lens. The official recommendation is a 30mm extension ring, but I saw many people on the forum saying that its best optimal length is 35mm. Has anyone tested it? (I currently only have one 40mm extension ring, and testing has found significant black edges)

Additional, if I carry an additional RF 35 1.8 or 501.8 as a supplement, will the image quality significantly decrease behind the 140 dome? （I just want to carry one dome）

Edited July 19Jul 19 by Davide DB
Typo

In addition, after testing, rf 1.4TC can’t be used together, even if the rear filter is removed, it is too long. But the color filter and rear filter are a good match. Even when magnified multiple times, there is no decrease in image quality

Edited July 19Jul 19 by yiheng

I don't recall any detailed discussion on extensions for this lens on the forums as the lens is so new. SO far it seems only Nauticam has it on port charts where it uses 10mm less extension than the EF 8-15. It is likely it also uses 10mm less on Marelux, but needs to be confirmed as it is not on the port chart yet. There was a lot of discussion on the optimum extension for the 8-15 lens but it was rather inconclusive , the samples provided IMO showed no improvement for the longer extension. Nothing so far on the 7-14 I recall. Have you tested with 30mm extension at the 7mm end?, due to the 190 field the lens needs to be placed further forward to prevent vignetting, which is probably why Nauticam use 20mm. I would expect the 7-14 to vignette at 7mm with a 35mm extension, but it needs to be tested.

Regarding a 1.4x it seems it's currently not possible to use a 1.4x, as you note the nose is too long. Also I believe the mount is keyed to prevent mounting it even if the nose was shorter. Kenko 1.4x is not available in RF mount so out of luck to use a 1.4x. Currently the EF 8-15 lens is the only way to get a fisheye plus 1.4x in combination with Kenko 1.4x and some people have used the RF 1.4x with the nose inside a Comcast RF-EF adapter that has been enlarged by filing it out and reported good results.

On the 35mm f1.8, Marelux recommend the 140mm dome, the 50mm would be fine in that dome I think but you would need to test if it focuses well UW as the 50mm has a long 30cm min focus distance.

Dear Yiheng,.. I think I reported back on the 15mm + 20mm a while ago, beeing slightly sharper, but that was with the Canon EF 8-15mm not to confuse with the new 7-14mm fisheye.

About the RF35mm - yes it works great and there has been a forum post about it. You will be able to enhance its AF performance by using a diopter behind the small 140mm marelux dome.

46 minutes ago, Chris Ross said:

I don't recall any detailed discussion on extensions for this lens on the forums as the lens is so new. SO far it seems only Nauticam has it on port charts where it uses 10mm less extension than the EF 8-15. It is likely it also uses 10mm less on Marelux, but needs to be confirmed as it is not on the port chart yet. There was a lot of discussion on the optimum extension for the 8-15 lens but it was rather inconclusive , the samples provided IMO showed no improvement for the longer extension. Nothing so far on the 7-14 I recall. Have you tested with 30mm extension at the 7mm end?, due to the 190 field the lens needs to be placed further forward to prevent vignetting, which is probably why Nauticam use 20mm. I would expect the 7-14 to vignette at 7mm with a 35mm extension, but it needs to be tested.

Regarding a 1.4x it seems it's currently not possible to use a 1.4x, as you note the nose is too long. Also I believe the mount is keyed to prevent mounting it even if the nose was shorter. Kenko 1.4x is not available in RF mount so out of luck to use a 1.4x. Currently the EF 8-15 lens is the only way to get a fisheye plus 1.4x in combination with Kenko 1.4x and some people have used the RF 1.4x with the nose inside a Comcast RF-EF adapter that has been enlarged by filing it out and reported good results.

On the 35mm f1.8, Marelux recommend the 140mm dome, the 50mm would be fine in that dome I think but you would need to test if it focuses well UW as the 50mm has a long 30cm min focus distance.

Yes, there isn't much information.

My friend has already used this lens on the Marelux R52, using a 30mm extension ring and obtaining images at aperture F8. I think there is some blurring in the corners, which may not have fully realized the potential of the lens

4 minutes ago, Adventurer said:

Dear Yiheng,.. I think I reported back on the 15mm + 20mm a while ago, beeing slightly sharper, but that was with the Canon EF 8-15mm not to confuse with the new 7-14mm fisheye.

About the RF35mm - yes it works great and there has been a forum post about it. You will be able to enhance its AF performance by using a diopter behind the small 140mm marelux dome.

15 minutes ago, Adventurer said:

亲爱的易恒，……我想我之前已经汇报过 15mm + 20mm 镜头的锐度略有提升，但那是用佳能 EF 8-15mm 镜头测试的，不要和新的 7-14mm 鱼眼镜头混淆。

关于 RF35mm 镜头——是的，它的确很好用，论坛上也有人讨论过。在 140mm 的小型 Marelux 球形罩后面加装一个屈光度镜，可以提升它的自动对焦性能。

Thank you for sharing. What brand of diopters do you use?

1 hour ago, yiheng said:

Yes, there isn't much information.

My friend has already used this lens on the Marelux R52, using a 30mm extension ring and obtaining images at aperture F8. I think there is some blurring in the corners, which may not have fully realized the potential of the lens

I recall most people using full frame tend to stop down to f11-13 range with the 8-15 fisheye, you might try that. If you have a 20mm extension you could try that as well. Nauticam list a 20mm extension with the 7-14, while both Nauticam and Marelux list a 30mm extension for the EF 8-15, suggesting that 20mm may work on Marelux. I would not suggest buying a 20mm extension yet until you see a recommendation from Marelux.

Perhaps @Phil Rudin may see the thread and comment?

1 hour ago, Chris Ross said:

我记得大多数使用全画幅相机的人搭配 8-15mm 鱼眼镜头时，光圈通常会收缩到 f/11-f/13，你可以试试。如果你有 20mm 的增距镜，也可以试试。Nauticam 的产品目录里列出了 7-14mm 镜头搭配的 20mm 增距镜，而 Nauticam 和 Marelux 都列出了 EF 8-15mm 镜头搭配的 30mm 增距镜，这表明 20mm 增距镜可能也适用于 Marelux 镜头。不过，在 Marelux 给出推荐之前，我建议你暂时不要购买 20mm 增距镜。

也许@Phil Rudin可能会看到这个帖子并发表评论？

Yes, a smaller aperture definitely helps with the picture quality. I don't have a 20mm extension ring, plan to purchase a 15+20mm extension ring

If you are using the 7-14 fisheye with a 140mm dome port then it should work with the 20mm extension for best results. Marelux has not yet released a zoom gear or port and extension recommendations for Canon RF 7-14mm fisheye.

I rented one and used it with the 30mm extension - see comments and images here:

I did not try the 20mm. There was no obvious vignetting with the 30mm extension. the 7-14 and the 8-15 are very close to the same length after you add the EF-RF adapter to the 8-15. Would be nice if it was even better with a 20 vs the 30! Solid lens.

To your other point - I have never put another lens behind the 140mm dome. Not sure when I would use the 50 or 35 underwater - although I do bring the 24mm macro to use when I want simplicity (but don't love any of those focal lengths underwater...) but I use that with the 180mm port.

On 2026/7/20 at AM5点29分, Phil Rudin said:

如果您使用 7-14mm 鱼眼镜头搭配 140mm 球形罩，那么搭配 20mm 延长管可以获得最佳效果。Marelux 尚未发布适用于佳能 RF 7-14mm 鱼眼镜头的变焦齿轮或球形罩和延长管推荐方案。

Thank you Phil. I just got the Marelux 140 dome and tested it with a 40mm extension ring. It has distinct black edges, I guse 35mm will be ok.

You mentioned that 20mm is the most suitable, I'd like to know the reason for this setting. Because I obtained that 32-36mm is the best optical distance through the theoretical calculation method in the forum (the entrance pupil distance of rf7-14 comes from the Internet, and other parameters are actually measured by me)

On the Canon RF port chart Marelux has 30mm's of extension recommended with the Canon EF 8-15mm and adapter. They introduced the 140mm dome with the bayonet shade for this lens which must be removed when at the 8mm circular fisheye end.

For the new Canon RF 7-14mm I suggested 20mm's because Nauticam RF charts show 20mm for RF and they were also at 30mm for ef 8-15mm.

I have ask Marelux to update the RF port charts for 7-14mm but they have not gotten to a zoom gear or extension size yet.

On 8/2/2026 at 10:59 AM, yiheng said:

Thank you Phil. I just got the Marelux 140 dome and tested it with a 40mm extension ring. It has distinct black edges, I guse 35mm will be ok.

You mentioned that 20mm is the most suitable, I'd like to know the reason for this setting. Because I obtained that 32-36mm is the best optical distance through the theoretical calculation method in the forum (the entrance pupil distance of rf7-14 comes from the Internet, and other parameters are actually measured by me)

This may be the "correct" position according to placing the entrance pupil at the centre of curvature of the dome, however I believe the 140mm domes are not quite 180° domes. The Canon 8-15 I believe is 175° across the diagonal at 15mm, while the 7-14 is quoted to be 180° at 14mm and have a 190° field for the circular fisheye at 7mm. What this means is likely the 8-15 can sit right at the centre of curvature and the 7-14 will need to be slightly forward to avoid vignetting by the dome. At 7mm it will need to even further forward to avoid vignetting of the circular fisheye image.

Based on this it might be OK with a longer extension at 14mm but need the 20mm extension for circular fisheye images at 7mm. The calculation you quote doesn't take vignetting into account, this happens for a number of lenses, including for example using lenses wider than 16mm in the Nauticam 180mm dome.

You can test for vignetting on land, just setup the housing and dome and you can pull the camera in and out of the housing to zoom and replace it to check. If you are not interested in using the 7mm end the longer extension you calculated might work for you.

2 hours ago, Chris Ross said:

If you are not interested in using the 7mm end

I think this is an important point. Most of us only use this (and the 8-15) as a 14/15 prime. So the extension may be different if you want to get that 180 look at 7/8mm or just want the sharpest corners at 14/15mm.