calculating diopter effects

I am considering going from DX format to 1" sensor format to reduce size and weight of my gear.  I own a Sony RX100 vi so considering getting a housing for it.

As I am learning, this camera has up and down sides.  I like the LED screen magnifier and back button arrangement of the Fantasea housing but not the 66mm max focal length.  I like the option of having a short and long port for moving between wide angle and macro work of the Ikelite housing but not the button layout or lack of an LED screen magnifier.

I want to know how the magnification and working distance will compare to what I am used to.  I use a Nikon 105mm micro in DX format now.  Its great, as you all know.

The RX100vi has a 1 meter close focusing distance at 200mm focal length, according to Sony.  From what I read online, if I use my Subsee +5 then the close focus distance on the lens would be 1/5th of of a meter or 20 cm or about 8 inches.  Wondering what magnification I would be getting on the sensor.  With the 105mm lens, you can get as much as 1:1 at 12 inches (or maybe 1.5:1 in DX format). 

Anyone good enough at math to be able to calculate what magnification one would get with the Rx100 vi with the +5 diopter in the working range of 12 inches, more or less?

I want to be able to shoot gobies and blennies. Below are examples of photo's I like to take of those macro buddies.

Blenny photo

Goby photo

I would suggest that for photos of small fish , working distance is probably the most important factor.  The Nauticam port chart for compact housings gives you an idea of what you could expect with various Nauticam lenses.  for example the RX100VI with the short port and a CMC-2 will give a working distance of 50-160mm and at 50mm it will cover 48 x 32mm.  here is the port chart: 

https://drive.google.com/file/d/1HM8Jlvdbb8MLCLDIYeVSV2tBnZQv-I6f/view

This indicates to get decent magnification you are in very close.  While you can do macro using the wet diopters it is more fiddly than using a macro lens because your working range is very limited.  Ultimately to get working distance you need more focal length and as the focal length on the RX-100VI is only 75mm at maximum it means you will always be closer than you would with a 105mm macro lens.  You can see the magnification range of this camera in this page:

https://www.dpreview.com/forums/thread/4296544

5 minutes ago, ChrisRoss said:

Ultimately to get working distance you need more focal length and as the focal length on the RX-100VI is only 75mm at maximum it means you will always be closer than you would with a 105mm macro lens.

I think you're misreading the chart. The short port is primarily there for WWL-C/WWL-1, with a secondary macro capability. If you use the bundled rectangular port, you cannot mount a WWL, but you have access to the full range of zoom (24-200mm equivalent - this is the model six with the long lens, not the earlier ones with 24-70mm or 28-100mm) and you can add a flip diopter holder, which, with an SMC-2, can get you down to frame size of just 7.5x5mm - on a full-frame camera, that'd be 5x magnification supermacro.

I,m deliberately not looking at the long port part because the long port chart gives such high magnifications it has very small working distances which would be unusable for shooting gobies and blennies as they would likely leave if approached so closely.   So the point is that while you can achieve high magnifications easily you get small working distances.  You are looking at obtaining about 0.5x  for example to fill the frame with a 25mm long subject (0.5x on a 12.8mm long axis sensor).  the working range is only 10mm with the SMC-1 so not much chance of backing off.  you could zoom out of course.  if you are looking for more moderate magnifications and more working you would be zooming out anyway.

The calculator on the subsee page would allow you to estimate performance as you zoom out with their diopters.  you would need estimate the magnification of each focal length of interest.  You can focus closer as you zoom out so you could work out where you would be working.  The problem of course as you zoom out is the focal length reduces and you need to get closer. 

The Backscatter review of RX100 VI is illustrated with photos of blennies taken with an SMC-1, so evidently it's possible. I wonder why Nauticam's port chart doesn't include CMC-1/CMC-2 on the long port; that should give a decent working range.

30 minutes ago, Barmaglot said:

The Backscatter review of RX100 VI is illustrated with photos of blennies taken with an SMC-1, so evidently it's possible. I wonder why Nauticam's port chart doesn't include CMC-1/CMC-2 on the long port; that should give a decent working range.

yes possible is different to "easy" the following paragraph in the review they talk about the caveats,  while you can do it with a diopter and compact using a dedicated macro lens is way more convenient and quite a different experience.   When photographing shy subjects working distance makes life so much easier.  If I'm not mistaken the CMC is a little more powerful for use with shorter focal length lenses.