Hello everyone, I previously used EVA Marine soft waterproof shell with RF24-70 in freshwater underwater photography. Although the edge image quality is poor, it can obtain some behavioral photos of sensitive organisms. Also, my luggage allowance is very tight, and it's a bit difficult to carry the flat mirror port

I am looking for a medium focal length lens (50-85mm) that can be used behind a spherical mirror (140mm) on the Canon system with my fisheye lens. Currently, the closest focusing distance of Canon's RF50 1.8 and RF85 f2 exceeds 0.3m, and theoretical calculations show that they are difficult to focus with the 140dome without using an extension ring. If combined with a 30mm extension ring, I can‘’t be sure if better image quality can be achieved because there is no parameter for the entrance pupil distance for rf 50 and 85.

Regarding other zoom lenses for RF, it is more difficult to meet the entrance pupil distance as the closest focusing distance is bigger.

Do you have any good recommendations or experience sharing？ Thank you

Doesn't Canon make a 50 macro? That should work fine with a 140 dome. My Sony 50 macro is great with 140 dome.

11 minutes ago, dentrock said:

佳能不是有50mm微距镜头吗？那款应该能很好地搭配140mm球形罩。我的索尼50mm微距镜头搭配140mm球形罩效果就很好。

Marelux and nauticam not recommend use rf 50 1.8，and this lens is external focus design, not like sonny and niko

30 minutes ago, yiheng said:

Marelux and nauticam not recommend use rf 50 1.8，and this lens is external focus design, not like sonny and niko

You could try the 24-105 STM lens , it focuses very close about 0.2m, not sure if it's the same all through zoom range. It does get quite long so might hit the dome at the longest focal length. I seem to recall Adventurer likes it, he's posted about it on this forum.

49 minutes ago, Chris Ross said:

你可以试试 24-105 STM 镜头，它的最近对焦距离很近，大约 0.2 米，但我不确定整个变焦范围内是否都一样。它的焦距比较长，所以在最长焦距下可能会碰到穹顶。我记得 Adventurer 很喜欢这支镜头，他之前在这个论坛上发过帖子。

Thank you for the reminder. I have checked his post. He used Ivanoff Rebikoff in combination with 24-105, not at dome port

I once considered the EF 50 F2.5 macro, based on calculations, it fits perfectly with the 140 dome (telephoto end) without using an extension ring. However, the lens will protrude 22.4mm at macro, which will cause changes in the entrance pupil distance. I don't know if this has a huge impact on the image quality

If measured by the entrance pupil distance, the change in entrance pupil distance for rf 24-105 stm will be greater

EF-S 60mm macro will cover a FF sensor at maximum magnification.

21 minutes ago, Grantmac said:

EF-S 60mm 微距镜头在最大放大倍率下可以覆盖全画幅传感器。

I have a rf 100 macro, basicly efs 60mm in canon r5 apsc = 96mm. That is not I want

3 hours ago, yiheng said:

Thank you for the reminder. I have checked his post. He used Ivanoff Rebikoff in combination with 24-105, not at dome port

I once considered the EF 50 F2.5 macro, based on calculations, it fits perfectly with the 140 dome (telephoto end) without using an extension ring. However, the lens will protrude 22.4mm at macro, which will cause changes in the entrance pupil distance. I don't know if this has a huge impact on the image quality

If measured by the entrance pupil distance, the change in entrance pupil distance for rf 24-105 stm will be greater

Perhaps, but the same can be said for any zoom lens and many people use them happily. IMO the entrance pupil location is most important at the widest setting, you are talking about using at 50mm or greater which would work behind a flat port. As far as I know all the port charts for zoom lenses are based upon positioning everything correctly at the widest setting.

1 hour ago, yiheng said:

I have a rf 100 macro, basicly efs 60mm in canon r5 apsc = 96mm. That is not I want

Run it in FF mode.

4 hours ago, yiheng said:

I once considered the EF 50 F2.5 macro, based on calculations, it fits perfectly with the 140 dome (telephoto end) without using an extension ring. However, the lens will protrude 22.4mm at macro, which will cause changes in the entrance pupil distance. I don't know if this has a huge impact on the image quality

Sony 50 macro extends 25mm. Check out Alex Mustard's curved port video. Sony 50 macro seems very forgiving of dome misalignment compared to other lenses. Don't forget, measure EP at close distance eg 1:3 (not infinity), because this is where the virtual images will be.

1 hour ago, dentrock said:

Sony 50 macro extends 25mm. Check out Alex Mustard's curved port video. Sony 50 macro seems very forgiving of dome misalignment compared to other lenses. Don't forget, measure EP at close distance eg 1:3 (not infinity), because this is where the virtual images will be.

This video is really helpful, ultimately I need to test it myself to find the best extension ring。 Thank you

2 hours ago, Grantmac said:

以快进模式运行。

Running only FF limited to macro feels like losing a lot of opportunities🤣

I've tested the Canon RF20-50mm and RF14-35mm in a 140mm dome as a compact travel setup. Edges will be too soft for some people, but it provided acceptable results for me.

56 minutes ago, JayceeB said:

我测试了佳能 RF20-50mm 和 RF14-35mm 镜头搭配 140mm 球形罩的组合，作为一套便携旅行摄影方案。边缘成像可能对某些人来说偏软，但对我来说效果可以接受。

I have 14 35 with 180 dome use for some time，video is good. But not wide enough for some time. So I change to fish eye

4 hours ago, Chris Ross said:

或许如此，但任何变焦镜头都一样，而且很多人都乐于使用它们。在我看来，在广角端，入瞳位置最为重要，你指的是使用50mm或更长的焦距，这种焦距搭配平面光圈罩效果会更好。据我所知，所有变焦镜头的光圈罩尺寸图都是基于在广角端正确安装所有部件的前提下绘制的。

I have discovered a master who has summarized complex underwater optical problems into easy to understand laws and answered all the questions I mentioned above. I will try according to his method

https://www.youtube.com/watch?v=rcRtbHXMQPs

Edited September 3Sep 3 by yiheng

We know the master and his t-shirt very well 😁

6 hours ago, yiheng said:

I have discovered a master who has summarized complex underwater optical problems

Some good stuff in those clips. But the master hasn't done anything for many months now, and doesn't reply to comments.

Note that if you watch the last video, there is a link to an unpublished extra clip.