Hi everybody,

while well served at the super wide end with the Canon EF 8-15mm fisheye + Teleconverters (FCP at a more compact size and reasonable price) and having the currently best full frame Macro in the industry with the Canon RF100 USM; I was looking into a mid-range flex lens in the middle for that little kick of flexibility.

I was even looking into buying an old SIGMA 17-70mm for EF mount, which had this amazing close focus an Macro ability in the DSLR era and was used by many shooters behind a dome.

While researching options I stumbled across Canon‘s very own RF 24-105mm F4-7.1 IS STM that was launched + bundled together with the RF mount R6 cameras a while ago. Compared to it‘s much more expensive sister the RF 24-105mm USM which is not really attractive for underwater use it features dent sharpness and much less travel weight on land.

So I bought myself one and also tested it heavily against the widely for UW shooters recommended RF 24-50mm STM shard by Canon.

The winner is certainly the RF 24-105 STM which offers very decent close focusing distance and even some macro capability.

You can use this behind very large 9 and 8 inch domes, but also it is a very interesting candidate for water contact optics.

Behind my Ivanov Optic I can use it from 24-75mm or 32-85mm depending how I set up the extension rings. This might not be useful information for others,… as this underwater lens is simply not available for sale anymore,… but,…

I think it has high potential for Canon RF underwater contact optics use, when you are willing to ditch the 24-27 zoom range and start using it at the 28mm focal length. With water contact optics, I am referring to the Nauticam lineup and the shortly available Marelux Aquista 100 and Marlux Aquista 120.

The sharpness Sweet spot of that lens in land tests is at F8.

I wonder why this baby has not made it into many manufacturers port charts.

Hopefully we can bring this up on the radar of gear makers.

PS: zoom gear of the RF15-30 STM fits also this lens 🫶✅

But to avoid people using the 24-27mm range or extruding the lens too far out, housing makers might want to produce a gear with Zoom-limiter to perfectly match their water contact optics best results.

Edited September 11, 2025Sep 11 by Adventurer

I had both the L series and the f4-7.1 versions for a brief time when I was contemplating switching back to Canon from Sony and Olympus. I liked the portability of the less heralded lens, despite being slow on the long end. It was also sharp enough. I never used it underwater, though.

I think if shooting with strobe(s) which I do and don't do depending on my mood many shooters dismiss slower and less "PRO" labeled lenses without trying them.

At f8 being a sweet spot and modern cameras being so much better at ISO400 and above lightweight mid-zoom or "kit lenses" should be given serious consideration IMHO.

Lighter weight and lower cost make many a good choice and I've used many successfully over decades.

If you're a full frame shooter the mentioned Canon 24-105mm slower lens might be worth picking up!

David Haas

Here's a couple over 20 year old shots. I used a Canon Digital Rebel XT or XTi, Canon 18-55mm IS lens in an Ikelite housing with 6" dome port and a single Ikelite DS125 strobe.

First pic might have been with a Canon 10-22mm EF-S lens....That shark had likely been hooked via a long line and broke free. Bite marks might have made it prey to other sharks (just guessing???)

Edited September 12, 2025Sep 12 by dhaas

On 9/10/2025 at 11:43 PM, Adventurer said:

You can use this behind very large 9 and 8 inch domes, but also it is a very interesting candidate for water contact optics.

I'm interested :) Have you used the 24-70? If so, how would you compare the two. And how is the 24-105 autofocus performance underwater? What extension(s) did you use?

1 hour ago, JayceeB said:

I'm interested :) Have you used the 24-70? If so, how would you compare the two. And how is the 24-105 autofocus performance underwater? What extension(s) did you use?

If memory serves, both extend when changing focal lengths, so that’s a consideration. Above water I really did like the slower Canon 24-105, mostly for its portability, handling and close focusing. Sigma just came out with a 20-200, which has 1:2 close-focusing ability, but again, an extending lens barrel when zooming (L and E mount).

Here are specs on the old 24-105mm f/4-7.1:

https://www.dpreview.com/products/canon/lenses/canon_rf_24-105_4p0-7p1_is_stm