The new digital revolution has added problems for the photographic community. Digital offers many features on the fly that film cameras cannot. Film cameras have one great advantage for the underwater photographer, the ability to take wide-angle images. We commonly use 14mm, 15mm, 18mm, 20mm and 24mm wide lenses with our 35mm film cameras. Using wide-angle lenses is paramount to underwater photography. We use it to get close to large subjects to maintain saturated color and perspective.
Unfortunately, digital cameras have a problem supporting very wide lenses, especially for cameras that use interchangeable lenses. A lens with a wide angle of view has to be factored to fit the size of the smaller digital chip. The CCD and CMOS chips are smaller than the traditional a 35mm film area. This factoring will convert a standard 28mm lens convert into a 42mm lens. Nikon developed a 12-24 zoom lens that most of us looked forward to as an answer for some of the wide-angle issues. Using the12mm setting and a D100 seemed to solve some of the wide-angle issues by giving us an effective focal length of 18mm. This is a respectable focal length.
We were elated when we got the first lens to test. Al Bruton grabbed the lens along with his Subal D100 housing, a SWB dome port and a 30mm-extension ring. He went to the pool to shoot his test chart. It was a disaster. The lens wouldn’t focus close enough and the image suffered from pincushion with a +4 diopter on it.
In an attempt to correct this Al added a + 3 diopter to the lens to make it focus closer behind the SWB dome. This is all we had to test at the time and it was disappointing. Later we obtained a bigger dome that the SWB and the lens worked better with. (Sorry, I don’t have the images to show you at this time). There are quite a few photographers getting great images with this lens now that the domes are available to meet the demand by the lens.
The pincushion was worse, but the edge sharpness was better. Without having the right dome set-up Al could not get satisfactory results. He continued to test several options with different extension rings and diopters, but the best was the 30mm extension ring and +3 diopter. With a +3 diopter Al was able to focus to 3″ inches in front of the dome. When we tested the lens above water with the +3 diopter we discovered that the pincushion was just as severe. The Nikon lens design set the wide-angle image to compensate for the chip size and made a lens with the nodal point set far forward from a standard lens.
The result is that any glass filters added to the lens caused optical distortion. This included the addition of a glass dome port to some extent. If you put the 12-24 behind a flat port you will not have an effective 18mm lens but a 24mm lens due to the refraction index of water and a flat port. Al has decided that this lens is not good for underwater use and will continue to use it for topside photography where it performs very well. If he is going to use this lens underwater, he will have to fork out some money for a bigger dome that helps place the lens in the right nodal point and the need for the diopter will be unnecessary. The problem for acceptable wide-angle lens use underwater is still haunting photographers. However, the future is getting brighter. Jim Hellemn is using the Nexus D70 housing with a 40mm extension and the 170 dome for the 12-24 lens to shoot his underwater panoramas where he has to over lap the exposures and stitch them together with software. The best optical setting was found to be at the 17mm focal length for his use.
|4″dome with 15mm Sigma lens||WP7 dome with Sigma 15mm lens|
|12-24 Zoom /Subal SWB +30mm extension, +3 diopter||In an attempt to correct this Al added a + 3 diopter to the lens to make it focus closer behind the SWB dome.|
|Jim Hellemn testing the 12-24 in a Nexus D70||Sigma 15- aread covered at the closest focus was 5″ inches wide.|
Meanwhile, Nexus sent me their new special 4″ inch port for the Sigma 15mm fish eye lens to test with their D100 housing. Like the Nikon 16mm, the Sigma has the 180-degree angle of view. These lenses have a barrel distortion in the design and do not keep a linear line straight. The chip factor of the D100 reduces these lenses from 180 degrees of coverage to 120 degrees. The Sigma lens will focus down to 5.4 inches in front of the lens and the Nikon will focus to 10.5 inches. Nexus chose the Sigma lens over the Nikon because it will focus closer and diopters cannot be added to the front of these lenses.
The 4″ dome created a wider view of about 8 degrees over the 7″ dome.
Notice that there is some barrel distortion, but the target on the side of the pool is actually curved because it is resting at an angle on the side of the pool.
The 15mm in the WP7 was at 48″ from the target to get full coverage. The 15mm in the 4″ dome was at 39″ from the target to get the same coverage. The angle of view is wider but the barrel distortion is more. Minimum focus in the front of the small dome is 3″ inches and 5″ inches with the WP7. Nikon’s 16mm lens could only focus to 9 inches.
The area covered at the closest focus was 5″ inches wide.
Conclusion: Wide-angle photography is still a problem for the digital cameras that use standard 35mm lenses. The only camera that won’t have this problem is the Canon 1Ds and Kodak 14n. They have full frame 35mm sensors and the standard wide angle lenses work fine with these cameras. They are very expensive and there are few housings that support these cameras. SeaCam and Sea & Sea have introduced housings for these cameras. The cost for a camera, port, lens, and housing is about $18,000.00. A D100 housing and camera and port will cost about $4,600.00.
Is it worth it to have the standard wide-angle capability? We have shown that the cameras with the smaller chip area have difficulty providing good wide-angle coverage without some lens distortion. The 12-24 is a compromise with pincushion distortion unless you use a larger dome and have it set at the critical nodal point. The 15mm and 16mm lenses will give 120 degree coverage with some barrel distortion. Software like PanoTools has the ability to straighten out the curvature in the images in a post production computer process so you will have perceptively corrected images in the final out put. It seems that cost is the biggest hurdle to get wide angle with digital cameras. The alternative is less costly and with postproduction software you will have good wide-angle images.
Nikon has announced that they are making a 10.5mm fisheye lens for their D100 camera. We just tested this lens in the Nexus housing for the D70 and it works very well. The 15mm Sigma and Nikon 16mm do a fine job at 120-degree angle of view. The 10.5mm fisheye is a true 180-degree wide lens for the D100 and D70.
A lot of us are making the jump into digital photography. We are also keeping our 35mm systems so we have alternative wide-angle capability. Soon there will be a single system that does it all. It may be a few more years before this is cost effective and available to us.
Al Bruton opted not to use his 12-24, but a lot of others are having success with it. Sigma has their 12-24 out now but I have yet to test it. Maybe it will work for my Canon Rebel Digital. So far I like the results with the Sigma 15 in the Nexus dome. The Nikon 10.5 for the fish eye and the 12-24 works for me in the bigger domes. I hope Canon starts to offer lenses like the 12-24 and 10.5 since I am a Canon system user. I have the Canon 1Ds with full frame coverage, but the housings is a beast. After shooting with the Rebel Digital and the Nikon D100 and D70 in different housings I can say that the D70 in a small housing is much better to use underwater.