Using the Nikon 12-24mm Lens
with the Nexus Housing - Page 17


When Nikon announced the 12-24mm lens for digital cameras, my first thought was "Sweet!" Just what I needed to start taking true wide angle photos underwater. With the Nikon 1.5x lens factor, the 12-24mm lens is an 18-36mm lens with the D100 or D70. What I didn't realize at the time was how much trouble it would be to establish the right combinations of port, port extension and diopters.

The reasons for the testing was that my photos were sharp in the center and soft on the edges. This was not acceptable. An example is shown below:


In this photo, I focused on the center of the rail. If you look in the lower right and left hand side of the photo, it is soft. This shot was taken with a 170mm dome with a 40mm extension and no diopter

The information provided is the result of pool and ocean testing. I want to thank Woody Mayhew of Nexus America for his help in providing ports, extensions and diopters for testing. The testing was done as follows: The D100 was set in aperture priority with an ISO of 200, no strobe, in the shallow end of a swimming pool on a sunny day. I allowed the camera to determine the shutter speed so all exposures were similar. I measured from the back side of the dome port to the sidewall of the pool and shot a series of images at a distance of 2' and then at a distance of 3'. I shot in the jpeg mode and used the standard camera sharpening. I shot one shot at each of the following f-stops: f5, f5.6, f6, f7, f8, f9, 10 and f11. One of the ports that I used is not easily available but Woody and I decided to test it to see if it was better than the 170mm port. The following were the combinations tested:
Port Size Extension Size Diopter
140mm 40mm None
140mm 40mm +2
140mm 40mm +3
140mm 50mm None
140mm 50mm +2
140mm 50mm +3
170mm 40mm None
170mm 40mm +2
170mm 40mm +3
170mm 50mm None
170mm 50mm +2
170mm 50mm +3

After the testing was complete, I looked at the results using Nikon View software


The two combinations that I thought would work were the 170mm dome with the 40mm extension and the 170mm dome with the 40mm extension and a +2 diopter. The two shots that follow are 500 pixel x 500 pixel x 72 dpi cropped sections of the middle right hand side of each photo. Both photos were taken at f5. The cropped photo shows the softness or sharpness easier on the web than showing the entire photo. All the other combinations that I tried were soft in the corners.


The photo above is the 170mm dome with the 40mm extension and no diopter. Look at the left side of the middle of the photo. It is pretty soft.


The photo above is the 170mm dome port with the 40mm extension and a +2 diopter.
It is much sharper than the other example.

The proof is in the pudding. I took this photo on the shipwreck, Tolten, off the coast of New Jersey. My dive buddy, Beth Dalzell, is holding a North American lobster. The photo below is a crop of her bug bag in the lower right hand corner. After looking at the detail, this is the right combination.

The crop above is a 600 x 300 crop from a 1024 x 768 jpeg.

Photo Information : Nikon D100 in a Nexus housing, ISO 200, Nikon 12-24mm lens with a Kenko +2 diopter, Nexus 170mm dome port with a 40mm extension. f9 at 1/10th of a second. One Ikelite 200 strobe (left side) at half power and one Ikelite DS-125 (right side) at full power. I shot in raw format and processed the image using Nikon Capture 4 software.


Diopters: For your information and to help you choose a diopter, there are two types of diopters - single and two element models. The two element diopter is supposed to have better sharpness and better color rendition than the single element. I decided on the two element model because I wanted the best results. I chose a Canon 500D - 77mm diopter. They are not cheap. The price from B & H Photo in New York was about $135.00. I talked to two very good photographers about diopters. One said that he could not see the difference in single and two element models. The other said that there is definitely a difference. I tried to find out the correct way to do this without testing but I could not find anyone who could give me a definitive answer on the right combo. I understand that Nexus is designing a new port for the Nikon 12-24mm and the Nikon 18-70mm lens. Until then, I believe that this is the way to go. Diopter Update - September 3, 2004: I did a pool test on the Canon 500D two-element +2 diopter today with the Nikon 12-24 mm lens and was surprised to see that at 12 mm, the filter blocks the four corners of the image. Although the Canon diopter is top quality, it is not a good choice for this use.


This photo shows the vignetting in the corners of the image
UPDATE - September 27, 2004


A friend of Woody Mayhew's tried a +4 diopter with the 40mm extension and the 170mm port. According to Woody, the results looked great. I purchased the +4 diopter (B & W brand - about $49 USD) and did a pool test. The photo below is a 500 x 500 x 72 dpi crop from the original jpeg photo. The original photo was taken using the same parameters as the tests above:


The results look excellent. The image is very sharp. I think that this combination may be better than the +3 diopter with the 170mm dome and the 40mm extension. I have included another photo below that I took at the same time with the same equipment. It was taken at 12mm at f8 using aperture priority with an ISO of 200. I found the image to be great with excellent sharpness in the corners where I have previously found problems. My next step will be to try this in the ocean. I am getting to the end of the dive season in New Jersey but if I can, I will test before I stop diving for the season. If not, I should be making my annual trip to the manatees in January and I will test then.
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