Lense port and air gap question

[Hans Dahle]

Hi.. 

 

Have a somewhat theoretical question regarding ports and distance between front element and glass. 

 

When I upgraded my camera to mirrorless, I had a 60mm nikkor and sigma 105mm and got suggested the macro 60 port for the 60mm and a 30mm extension which allowed the sigma lense to be used. 

I now want to upgrade to the Z 105, but on the port chart it macro 60 and a 20mm extension..

 

Is there any noticeable differece in image quality with a 10 mm difference.. I guess there will be more bouancy, but more interessted in optical effects and operational effects, like focusing etc. 

The reason for upgrade is also a step on the way to invest in the EMWL. Would that add more precice requirement to it? Should I also plan for buying a 20mm extension or even just the port without using extensions?

 

Any insights, comments or recommendations?

[TimG]

Hey Hans

 

I've switched between a 105mm and 60mm using the same port with an extension ring (EXR) to provide the extra length required by the 105mm. 

 

My experience is that the only issue to look out for is vignetting if the EXR is too long. Other than that, no issues. No optical impact. 

[Hans Dahle]

Nice, thanks. 

 

So vignetting is mostly the consequence to consder.. I guess for the 105mm 10mm should not really impact then. Is this amplified with diopters? But i guess I will just try using the current combination and then buy new if it is an issue.. Different budget when buying later 🙈🤣🤣

[TimG]

Yep, my experience has been that vignetting is the only issue. Diopters shouldn't make any difference.

 

Test out what you have and you'll see if there is an issue immediately.  As you say, if there's then a problem, get the credit card out.... 😝

[Chris Ross]

Diopters don't work as well if there is too much gap between lens and port.  You could probably just use what you have now and get the right port to go with the EMWL when you go that way - The wide angle of the EMWL will probably impact that more so and getting the right port more critical.  The other impact of course if the port is too long is that you lose that much working distance.

[Hans Dahle]

I guess if one first have bought the EMWL and discover the port reduce the quality, there are not that many relevant arguments for not buying the correct port combination 😉 

 

I kind of assumed that the working distance was the same if it was air in front of the port or water after the port.. But ofc if the air gap causes the the working distance to be "on the inside" it would ofc be not optimal.. maybe i'm mistaken here? 

[Chris Ross]

19 minutes ago, Hans Dahle said:

I guess if one first have bought the EMWL and discover the port reduce the quality, there are not that many relevant arguments for not buying the correct port combination 😉 

 

I kind of assumed that the working distance was the same if it was air in front of the port or water after the port.. But ofc if the air gap causes the the working distance to be "on the inside" it would ofc be not optimal.. maybe i'm mistaken here? 

I'm not sure exactly what you are saying with regards to a larger air gap between the port glass and lens, but basically the point in focus at 1:1 is a constant distance from the sensor and if the port is longer this eats into the distance so at 1:1 (for example) you have less space between the end of the port and the subject if the port is too long.

 

Looking at the EMWL another way, if you've spent all that money why compromise to save the price of an extension ring?

[Hans Dahle]

I guess the question there is:
The minimum focusing distance for the 105 is 29cm. Is this 29cm from the sensor regardless of how much air is in front of the port glass. 1 cm in air is the same as 1 cm in the water.. Maybe a stupid question 😉 Know that the focusing is different for domes with the dome diameter comming into play and the virtual image etc..  I guess what you are pointing at with th 1:1 is that if the port extends beyond the minimum focusing distance you will not be able to achieve the 1:1 magnification?

 

The EMWL thing. I guess that the essence of my though as well. However I try to not just buy stuff i not need, as that is money that can rather be directed at a new lense or different thing that is needed 😉 

[Chris Ross]

I don't think there is any danger of losing 1:1 just working distance.  Flat ports don't have a virtual image in the same way dome ports do, the impact of the virtual image is basically to just magnify the subject so it looks closer but they also need to focus closer than the subject on that virtual image.  With the nikon Z the working distance is 290-140-16 = 134mm.  You can use this calculator to see how much closer the focal point is:   https://oceanity.com.au/tools/flat-port-virtual-image-visualiser

 

with this situation with the virtual image at 290mm, the subject distance from the focal plane is 400mm so you according to the calculator the working distance would 254mm at 1:1.  I think I've interpreted that correctly....   And you lose 10mm of that working distance.