Hi All, I've just invested in an SMC3 after having used the SMC1 for a number of years. I've only been able to use it on 3 dives so far, but I have a question for those familiar with both lenses used in front of a sony FF and 90mm macro.

My question is... for any given fstop, does the SMC3 have a narrower DOF than the SMC1?

The DOF is razor thin anyway, but is it thinnerer on the SMC3? Maybe there's a mathematical answer and an answer from the gut.

I'm only using my gut after 3 dives, so have nothing scientific to back its churning feeling, but I feel like the SMC3 has less DOF.

In general terms depth of field varies with magnification at the same f stop. Focal length does not impact DOF apart from changes it makes to the magnification achieved. The background blur does change with focal length at the same magnification with shorter focal lengths showing more detail for want of a better word in the out of focus background, while a long focal length produces a smoother backgroud. However when talking about macro lenses with diopters the only real variable if magnification once you have selected your f stop as the focal length doesn't move very much.

It appears that some wet optics can produce less depth of field with a specific example being the fisheye conversion port, likley related to how it interacts with the virtual image. A Diopter however basically just allows a lens to focus closer and the SMC lenses have optics to correct distortions caused by the air-water interface, but this is a fairly monor adjustment and I can't see it impacting depth of field.

Thanks @chris, It could be that I was just shooting at the inner limit of the working distance, instead of the outer limit, compressing that DOF.

I definitely saw an improvement in the camera's ability to lock and hold focus when I stopped down from f11 to f16.

Hi @foetusmachine

I'm using a SMC1.. you made the swith to the 3... what are after 3 dive the improvments (If they are ;) )

Thanks

I havent reviewed the images on a screen yet. I'm also new to the nauticam housing (used the smc1 on a seagrogs housing). But can offer:

It is smaller and lighter.

The lens itself brings the bulk of the housing closer to the macro subject. The smc1 might actually be able to get into a tighter spot.