In the past, Alex Mustard recommended trying a Nikon 5T dry diopter on the front of the Sony 90mm macro lens for slight magnification and a more useable focus range. This is largely consistent with what the new Nauticam MFO-1 wet lens is advertised to do, but I was curious how they compared with regards to working distance/magnification (not looking at image quality).

 

In order to test this, I measured min/max focus distance and magnification ratios underwater for various wet lens combinations, both with and without the 5T dry diopter. I tested using my Sony A1 + 90mm macro in a Nauticam housing and the standard Nauticam N100 Macro Port 105. For the 5T diopter I added a custom 14mm extension ring.

 

The results below show 4 values for each combination of lenses, both at minimum and maximum working distance: working distance from the front of the wet lens or port, working distance from the front of the camera housing (where the port attaches), magnification ratio, and frame width at this magnification. 

 

Working distance is traditionally measured from the sensor plane of the camera, but rather than determining the location of the sensor plane within the housing I chose to measure from the front of the main housing for consistent comparison. Working distance from the front of the wet lens/port is also included, as this is easier to estimate when shooting underwater and is closer to how Nauticam publishes the values. 

 

The MFO-1 and 5T diopter have very similar working distance and magnification ratio characteristics, with the MFO-1 having slightly more max working distance (less magnification).

 

SMC3 and SMC1 characteristics are very similar to each other (as expected), with the SMC3 having a bit broader magnification range (1.05 to 2.32 vs 1.22 to 2.26). Notably, you don't gain anything by stacking the SMC3 or SMC1 on top of the Nikon 5T - magnification ranges for these lenses were better without it.

 

Sony A1 + 90mm	Minimum Focus Distance (mm)				Maximum Focus Distance (mm)
w/ 5T Diopter	From Lens	From Housing	Ratio at Min	Min Width (mm)	From Lens	From Housing	Ratio at Max	Max Width (mm)
None	118	252	1.21	29.7	1030	1164	0.12	302.0
MFO	86	243.3	1.33	26.9	484	641.3	0.25	145.4
SMC3	42	205	2.31	15.5	92	255	1.16	31.1
SMC1	39	218.7	2.19	16.4	86	265.7	1.28	28.0
w/o 5T Diopter	From Lens	From Housing	Ratio at Min	Min Width (mm)	From Lens	From Housing	Ratio at Max	Max Width (mm)
None	157	277	1.02	35.1	Inf	Inf
MFO	118	261.3	1.18	30.5	1103	1246.3	0.11	315.5
SMC3	51	200	2.32	15.5	106	255	1.05	34.1
SMC1	49	214.7	2.26	15.9	98	263.7	1.22	29.4

null

 

-Ross

I also did similar work on a sample of macro lenses of various brands and with 2 Canon R7 cameras with 60 and 100mm and Sony A1 with 90mm. By March I should complete the article I am writing.
I have slightly different values from yours with the SMC3 with the 90 minimum working distance from the lens 50.73mm and max distance 104.73mm, all tests were taken in seawater.
I still have difficulties with the calculation of the magnification ratio, I used a sheet of graph paper for the shot.

 

I would like to understand how you performed the calculation. 

 

I attach a shot with Sony A1 + 90macro + SMC3 minimum distance

 

Your values are very close to mine - within 1.5%, which is within the margin of error for how I made my measurements. I don't know how you're measuring the working distance to get 0.01mm precision; my values certainly have a greater margin of error than this. My measurements were taken in fresh water rather than salt water, and possibly the distance the diopter is mounted in front of the lens could have some small effect as well. 

 

For measuring magnification ratio, I took photos of a similar target to yours. I then measured the number of pixels across multiple parts of the photo (5mm, 10mm, 15mm, etc) and used this to calculate an average px/mm for the photo (let's call this Rphoto). The sony A1 sensor is 8640px and 359mm wide, so 2406.7px/mm (we'll call this Rsensor). Divide the photo px/mm ratio by the sensor ratio to get the magnification factor: mag = Rphoto/Rsensor.