Flat ports and Macro

[hyp 115]

Quick question for those more invested in the optical physics side of underwater photography. Do Flat ports just change the FoV of macro lenses (I think about 30% compared to on land?) or does magnification get changed too? Basically, will the same macro lens behind a dome port produce less magnification or have a different working distance, compared to on land. Asking because I'm interested in trying the 4" semidome for my 12-50mm lens.

[Interceptor121 843]

Quick question for those more invested in the optical physics side of underwater photography. Do Flat ports just change the FoV of macro lenses (I think about 30% compared to on land?) or does magnification get changed too? Basically, will the same macro lens behind a dome port produce less magnification or have a different working distance, compared to on land. Asking because I'm interested in trying the 4" semidome for my 12-50mm lens.

A flat port increases magnification and working distance resulting in exactly the same magnification that you have on land
With a dome port assuming all is correct you will get the same situation at the land working distance
Hopefully this was clear enough


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[hyp 115]

13 minutes ago, Interceptor121 said:

A flat port increases magnification and working distance resulting in exactly the same magnification that you have on land

This is not quite clear to me. You say it increases magnification resulting in the same as on land. Do you mean it increases working distance, but magnification stays the same?

[Interceptor121 843]

This is not quite clear to me. You say it increases magnification resulting in the same as on land. Do you mean it increases working distance, but magnification stays the same?

The apparent focal length increases but the working distance also increases so you get the same magnification from further away
With a dome port you are closer but the field if view is the same as topside
Magnification doesn’t change but with the flat port you are further away
Generally for true macro you don’t want to be closer but for a zoom lens that is not a macro lens where you could be at half a meter a dome may help
Your position changes not the maximum magnification you can get


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[hyp 115]

Thank you, now it is clear.

[Interceptor121 843]

Thank you, now it is clear.

Magnification in photographic terms is the ratio of the frame size in the image and the sensor size
If you take your macro lens on land and go as close as you can to a ruler and take a shot then put that macro port underwater go as close as you can you will get the same frame size but from further behind
The photographic magnification didn’t change but the apparent magnification standing at the same distance did
This however is irrelevant to your objective as photographer in terms of frame size and photographic magnification


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