Upgrading from compact, undecided between Canon R3 and R5

Been diving with my compact Sony Rx100 (first edition) 

it still shoots. But I’ve been meaning to upgrade. Mainly taking underwater macro photography. And the working distance with a wet lens just doesn’t work for me.

I don’t dive that many times a year. A good year precovid would be maybe two week long dive trip. But the lack of a working distance for things like hairyshrimp and Pygmy seahorses kills me. 

I have access to a canon 5d mkii but I’ve been looking at the R5 and the R3 as well. 

Was hoping I’d be able to get some feedback from other users here. 

What would you use to take photos of things like hairy shrimp, skeleton shrimp, nudis, Pygmy cuttlefish, and seahorses?

If you are shooting macro, the R series Canons may not be your best option as the RF 100mm macro has issues, it has focus shift which means that the focal point shifts as the lens stops down, apparently Canon are trying to call that a feature.  What happens is the lens does AF wide open then when it stops down the take the shot, the focus point shifts -  A problem mostly when working in close where depth of field is shallow.  See this post and scroll to the end for this issue: 

View archived post in: Any UW experience with Canon RF 100mm macro ?

An adapted EF 100mm is also not great as the AF on the adapted lens is reported to be rather poor. 

As to what to use, I would ask if you really need full frame the expense of taking full frame underwater can be significantly higher, though for macro only it's not as bad as only the housings are more expensive, assuming some version of aluminum housing.  The travel weight can also be significant, though again if only shooting macro not so bad.  Consider though that you may like to do some wide angle macro or CFWA in the future. 

I use m43 and I've been quite happy with that choice using an Olympus EM-1 MkII  and the 60mm macro.  There is a new 90mm macro coming which does 2x without accessories.    The full olympus kit with 3 lenses, ports and strobes can be carried in a carry on legal size back pack.  You could also look at a Nikon D500 setup.

I'll give my Nikon options, but I'm not sure if there is an equivalent Canon option.

I used to shoot an RX100 II, but I got frustrated with poor autofocus speed.  I too was frustrated with wet lenses and working distance.

I went full frame, taking my D810 under in a Nauticam housing.   I shot macro using the Nikkor 105mm macro lens and (briefly) the 60mm macro.  I later upgraded to the D850 (amazing autofocus), with the same 105mm lens.   During the time I shot those cameras (2016 to 2022) I did a lot of macro shooting, and I determined that 105mm was a bit short for full frame.   I was constantly cropping, often to about a DX/APS-C area.   For that lens, a Nikon D500 might be perfect.   But for me, there was a certain distance I could approach animals, and closer than that led to the animal fleeing.  Based on my cropping, I figured a 150mm macro would work the best.  And indeed it did - I put a 1.4TC on the 105 macro to give me 150mm, and I was then able to fill the frame at my normal approach distances.

However, I did not like the slight degradation in sharpness, along with slowing of the autofocus speed, so I took off the TC and never used it again.  I try to get closer, and I just crop as needed.

For the REALLY small stuff, I have no answer yet.   I have thought about add-on wet lenses like the SMC-1 or CMC-1, and I think if you are going to shoot creatures of the size of Wire Shrimp and smaller, you're going to need some way to get to 2X or more, possibly along with a tripod.

When it gets down to it, underwater photography is quite challenging.   I think that's what makes it so fun when you get a good shot from your efforts.  It actually takes effort, skill and good equipment to do well, though the definition of 'good equipment' can vary widely in price.