Macro close focus questions

I make a test with my D100 in swimming pool and my conclusion is "there is no size-ratio difference between underwater and topside"

60mm at 1:1 (minimum focus) - topside

60mm at 1:1 (minimum focus) - underwater

The only difference is the distance between object and flat port, it's little far underwater than topside (~70mm)

There is no magnitude gain underwater !!!!!

Mauricio

I make a test with my D100 in swimming pool and my conclusion is "there is no size-ratio difference between underwater and topside"

 

60mm at 1:1 - topside

 

60mm at 1:1 - underwater

 

The only difference is the distance between object and flat port, it's little far underwater than topside (~70mm)

 

There is no magnitude gain underwater !!!!!

 

Mauricio

By definition, 1:1 is the same magnifcation underwater or above. The question is can a lens with minimum focus of 1:1 in air do better underwater with a flat port.

Can you do the test again and move in closer and see if it will focus.

If I go closer the object will go out of focus. The test surprises me too but the magnification underwater and topside is the same.

the question is can a lens with minimum focus of 1:1 in air do better underwater with a flat port.

The answer is negative; the lens doesn’t better underwater with a flat port.

Hi James, might as well you bring this one too. as a reference the human eye see's an average of 45 degrees wide. it illustrate in a different way the image circle.

Cheer's

P.S. a pool session up here is called a skating on the pool/ice ring these days

the question is can a lens with minimum focus of 1:1 in air do better underwater with a flat port.

 

The answer is negative; the lens doesn’t better underwater with a flat port.

Thanks. That is interesting!

It is interesting. I played with some simple ray tracing (single thin lens, negligible port thickness ... all the assumptions in the world). The example shows that for these assumptions, the focus does indeed move out such that magnification is preserved (flat port, contrast in "n" across port).

CeeDave

Yeah!

This is what I've suspected but never tested. I still plan to test it when I get the chance and would encourage others to as well.

So, to relate this back to my original question ---- I believe I heard that for a given macro lens, if it is advertised to focus 1:1 at say 8" in air, then underwater you get relatively more working distance underwater, say 10" for 1:1.

So, to relate this back to my original question ---- I believe I heard that for a given macro lens, if it is advertised to focus 1:1 at say 8" in air, then underwater you get relatively more working distance underwater, say 10" for 1:1.

<{POST_SNAPBACK}>

Yeah, that appears to be right, from the tests posted from mandrade and some over-simplified ray tracing. Keep in mind that closest focus distance is usally given from the film plane, so may be VERY close to the front of the port, even with the additional standoff reqiured underwater.

Cheers,

Chris

So, to relate this back to my original question ---- I believe I heard that for a given macro lens, if it is advertised to focus 1:1 at say 8" in air, then underwater you get relatively more working distance underwater, say 10" for 1:1.

<{POST_SNAPBACK}>

You are absolutely right, in water you have more distance between flat and object than topside, and this is a real advantage in macro and super macro shots to work with strobes not magnification.

Mauricio

... and the maximum reproduction ratio is now 1.33:1.

Tom,

I just tested my 105mm/2.8D macro from Nikon in my D300.

I got the same 23.6mm wide picture both underwater and topside.

Got both pics here with me... puzzled.

The lens was locked at minimum focus, and at manual mode.

Any idea why I didn't get the 1.33 factor for the reproduction ratio?

Tom,

 

I just tested my 105mm/2.8D macro from Nikon in my D300.

I got the same 23.6mm wide picture both underwater and topside.

Got both pics here with me... puzzled.

The lens was locked at minimum focus, and at manual mode.

Any idea why I didn't get the 1.33 factor for the reproduction ratio?

The 1.33 magnification factor by a flat port refers to the *same* lens-to-subject distance, in-air and in-water.

Your test didn't keep the distances the same. In air, with the lens at minimum focus, the subject was at distance "x". In water, with the lens at minimum focus, the "apparent subject" was at distance x, meaning the *real* subject was at distance 1.33x. The real subject WAS magnified by 33% by the flat port, but it was also 33% further away. The two effects cancel, so there was NO CHANGE in magnification relative to in-air.

Les

Thanks!!!

I figured that out too late duh!!!

Anyway, we do not get the 1.33:1, maybe with the SubSee Adapter

Thanks!!!

I figured that out too late duh!!!

Anyway, we do not get the 1.33:1, maybe with the SubSee Adapter

I tried my SubSee magnifier/diopter on the Nikkor 105 behind a flat port in air. It greatly shortened the minimum focus distance. It is good to know that I will get back some working distance in water.

Bob