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3ricj

Member Since 11 Sep 2012
Offline Last Active Mar 31 2014 08:02 AM
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Posts I've Made

In Topic: Dome calculations - how to increase your near focus behind a dome

31 March 2014 - 08:05 AM

How do I adjust the calculations of a virtual image on a dome port based on having a different position of the exit pupil on a lens?   Is it time for some real optical modeling? 


In Topic: Dome calculations - how to increase your near focus behind a dome

31 March 2014 - 08:00 AM

Thanks for the feedback.   Maybe the right answer is to contact nauticam. 

 

I was thinking that maybe they just forgot to tell me I needed a diopter. :) 

 

Anyway, I've just posted two photos for conversation.  They are both bad photos, but posted for conversation.  Incidentally, the first shaggy mouse nudi' I've seen. 

 

The shot I wanted: (well, honestly, I really wanted a macro lens, but maybe I should say "the shot I was expecting this lens to be able to handle")

http://www.flickr.co...cj/13540155013/

 

The closest I could focus: (I was at least one full body length off the bottom, so .. 6'? plus fins? )

http://www.flickr.co...cj/13540388354/

 

I was hoping that the sony would report the focal distance  -- my 5d did this, but I can't seem to spot it in the exif data. 


In Topic: Dome calculations - how to increase your near focus behind a dome

31 March 2014 - 07:08 AM

I may misunderstand your values but if I look at dome port theory with a dome of 4" diameter you should be looking at an external radius of 2" which is not on the scubageek tables.

If your dome thickness is really 0.125 (seems very thin to me) then you are looking at 7.6" curvature point to secondary focus point and assuming your centre of curvature is aligned with the dome (or otherwise you need an extension ring) you are looking at 5.15 diopters correction for an infinity focus if your lens can't focus at 7.6"

generally the theory helps only to an extent as the centre of curvature may or not be accurate and the back-focal distance may be unknown so there is still a lot of trial and error

I would be really surprised if you bought something out of nauticam port system and is not focussing

Excellent catch!  Thank you.   But now I'm confused, as my lens shouldn't have been able to focus at 7.6".  But I *was* able to get photos in focus (using autofocus) but only if I got VERY far away from my subject.  I started down this path after having really poor results - - but results!  It seems that my lens isn't very close to the dome, so this may be impacting things - -  But yes, I'm using the Sony A7r, 35mm F2.8 FE lens and the 37122.4 port.  This system (and port) is very new, I'm suspecting it has been tested much underwater.  Nauticam has not shared specifications on the dome, so I had to measure it.  The thickness was determined by measurement, I confirmed it was a simple radius (not some parabolic whatsit), and material I determined by using my highly calibrated index of refraction measurement tools (my eyeballs, who deal with acrylics and glass frequently, but could have easily made a mistake). 


In Topic: FS: Ikelite housing for Nikon D600, Ikelite ports for Nikon, and Ikelite D161...

30 July 2013 - 07:51 PM

I'm interested in the following: 

 

5510.22  port body

5510.16 port body

 

4067 spare Li-Ion battery pack  (do you have two? )