JayceeB

I always cover ports in/out of the boat, or to/fro shore entry. Just be careful not to lose the cap...they're $132 to replace...don't ask me how I know that 🙂

Thanks, @Adventurer. Let me ponder on the +4 diopter suggestion. Not sure how far I want to pursue this option as I was looking for a lightweight travel setup for Malapascua Thresher Sharks. I have tested the 140mm dome + RF 14-35mm successfully at the 35mm end. I think that will likely be my choice, as AF is fast and reliable. I'll utilize the 50mm for above water use only.

I tested this setup today with the RF 50mm and 140mm dome port with no extension. It did not go well. The lens would not autofocus on subjects less than 20' away. In most cases, when I pushed the back button autofocus, the focus box (Canon R5) would just turn red, and it wouldn't even attempt to focus hunt. The specs on this lens give a minimum focus distance of 30cm. Could it be that the virtual image of the dome is too close to the lens? I'm wondering if adding some extension would solve this. Test shot of a manta I had to back off by 20' to get focus. (Some color correction, but no sharpening)

I picked up a refurbished RF 50mm f/1.8 from Canon for $160 USD. It is tiny. Image sharpness above water is more than adequate by my standards. Autofocus speed above water is average, but I wasn't expecting class leading performance. This lens isn't listed on the Marelux port chart, but they confirmed that the 140mm dome port should work with no extension. I'll post my experience and samples once I get this combination underwater.

Thank you for posting these. It's nice to see some samples from less common lens/dome/port combinations. Glad it worked out for you.

Thank you for sharing your experience!

Folks, Has anyone tested the Canon RF 50mm f/1.8 or Canon EF 50mm f/2.5 Macro + EF/RF adapter in a Flat Port? Looking for feedback on AF and IQ. Thank you!

I was able to test out the 60mm extension on the 140mm fisheye dome. The sun shade appears at top and bottom slightly at 14mm. At 16mm+, the shade does not show in shots. 14mm 17mm

Awesome information! That makes sense now. My camera is already packed for today with the 30mm extension, but I will try the 60mm tomorrow. If the 60mm causes slight vignetting at 14mm, no problem zooming in a bit. The bulk of my shooting will be at the 35mm end anyways with this setup.

I see what you're saying with the Canon 8-15mm. Both the 140mm and 230mm domes require a 30mm extension. Perhaps a bit different with the 14-35mm? The 180mm dome requires a 50mm extension, but the 230mm dome requires a 60mm extension. The test shots I have been making were using the 140mm + 30mm extension exactly as setup for the 8-15mm. I wonder if it would be worthwhile testing the 14-35 + 140mm + 60mm extension, which I have for my 14-35mm + 230mm dome. I don't have a 50mm extension.

Based on that test I'd say you have your solution and it doesn't involve buying anything new. Corners look fine at 35mm, any unsharpness could just be depth of field. Thanks for the feedback, Chris. Yes, I think this will work just fine for my needs, where travel weight is a big stress factor. Also, I don't remember the last time a solution presented itself with zero cost 🙂

14mm Second Set null

So I compared the EF 8-15mm fisheye to the RF 14-35mm, and they’re nearly the same length, so I thought I would try out the 14-35mm with the 140mm fisheye dome port. I set my expectations extremely low, and was hoping it would give acceptable results at the 35mm end. I tested it out on two dives today, and took mainly 35mm shots, but also tried some 14mm shots as well. I was actually pleasantly surprised at how well it performed, at least to my eyes, but I’m not very picky on edge sharpness. I’ve uploaded a few shots to show 35mm and 14mm in case anyone is interested. 35mm first set.

So true. I almost always shoot sharks at 35mm, and usually wished I had more zoom.

I'm running Marelux. Their port chart says to use the 140mm dome with no extension.