Improving macro images using Inon lenses and Canon Housings
Guido Zsilavecz
Cape Town, May 2006
Inon bracket, close-up lens and diffuser
Inon bracket, close-up lens and diffuser
Using Inon diffuser
Using Inon diffuser
Custom diffuser
Custom diffuser
Custom diffuser
Using custom diffuser
Using custom diffuser
Using custom diffuser underwater
Reflection in the eye

Introduction

Inon produces some excellent add on lenses for underwater use. Both wide-angle and macro lenses are available. Using a mounting bracket which differs from housing to housing, the same lenses can be re-used, mating to the bracket using a bayonet mounting. I use the Canon A70 and A75 cameras in their Canon housings, and while the macro of these cameras is quite acceptable, use of Inon macro lenses (UCL-165 AD) allows the photographer to get closer - you can even stack two lenses for more detail.

The problem is getting light on your subject. I tried using the external strobes (see the other articles on this site), but found that I could not get the right angle, that is, I was lighting too much from the top. I also had some problems reducing the output from the Nikonos SB105 strobe, and found that the reddish bias of the Canon cameras, and the warm light from the Ikelite DS125, simply burned out reds.

Given the short distance from subject to lens I decided that using the built-in flash would be quite acceptable, as backscatter would generally not be a problem. When using the Inon lens mouting bracket the diffuser on the Canon housing must be removed, which is easy, as it is held in place by two screws. Thanks to Canon for making it removable, as it allowed Inon to make the bracket. Why Canon then decided to make a non-circular lens port on the housing for the A620 is utterly inexplicable, as Inon must still be scratching their head trying to figure out how to get around that problem.

The INON diffuser

The bracket comes with a diffuser, which can also be removed. Image 1 shows the housing with the Inon bracket, a close-up lens, and the diffuser. The problem, as image 2 clearly shows, is that the distance between diffuser and the end of the lens is quite large, and the diffuser quite small. This results in the lens blocking the light, causing a bad shadow, which gets worse as one moves closer to the subject. This is shown in the first two photos of the car, images 3 and 4.

Custom diffuser

After experimenting a bit I finally came up with a working diffuser. It was made from milk-glass perspex, bent using a hot air gun. The design is such that the front of the diffuser is exactly in line with the macro lens, as images 5, 6 and 7 show. It is attached to the housing using the two screw mounting points used for the standard Canon housing diffuser. This requires some careful bending of the lower mounting point, and it is a weak point - so be careful - you might snap off that mounting point, either on the diffuser, or worse, on the housing!

Although it is a tight fit, the macro lens can be removed. With it removed the diffuser now extends beyond the housing, but this has no adverse impact on photos - that is, it neither reflects light back into the lens, nor is it visible even when the lens is set to its widest angle. It is recommended to keep the macro lens on when entering or exiting the water, as it stabilizes the diffuser - without the lens it is easy to move the diffuser, and with it the possibility of destroying the mounting points!

The diffuser is large enough to light up subjects when using the second macro lens stacked on the first one. The Inon wide angle (UWL-105 AD) lens can be mounted very easily with the diffuser in place, and the diffuser actually works quite well with that lens too. Due to it being opaque the flash power is reduced quite substantially however, and it can only be used for close-up wide angle work.

Images 8 and 9 show how well the diffuser works: both images are lit quite evenly all over, and that nasty shadows shown in images 3 and 4 are completely gone.

As I still like to use an external strobe for wide-angle or other shots, and have modified the diffuser by adding a slot which allows me to insert a black piece of plastic to block the flash - this is not shown. I have also used black masking tape to darken out the top and sides of the diffuser, as I found the bright light of the flash to be a bit annoying. It has no impact on the image, in fact, I think that the top and sides now act more as a mirror, creating more even light. Note, I think this, and I have not empirically tested this.

Making the custom diffuser

Image 10 (right) shows the outline of the diffuser, for the A75 housing, from the front. The A70 housing has slightly different mounting points, but it should be compatible. For other housings I would recommend to start with this design, and create it out of cardboard first, to make sure it works. To make the diffuser from this drawing keep the front (the part with the lens cut-out) flat and bend the side and top down. I drew the outline on the perspex, with a waterproof pen, and then rubbed it out afterwards. The red lines shown are only for distances - the black lines are the diffuser.

The odd rectangle on the bottom right is for the lower housing mounting. You need to cut along the upper line until the corner, and bend along the vertical line (the one that says "10mm" at the bottom.) First bend, then add the hole for the screw, as it is often dificult to bend exactly along the line.

To bend, I found it easiest to place the plastic on a piece of wood with a sharp edge, with the edge to be bend exactly on the line. Using the heat gun heat up along the edge until it starts drooping slightly, then using another piece of wood apply pressure evenly. This creates a clean, sharp bend of 90 degrees. Do note that you need to bend beyond 90 degrees, but once you have the first bend, going slightly further is easy. It is easiest to bend both side and top by 90 degrees, so you can see easily how much further to bend, as they must meet at the edge. As the perspex stays hot some time after using the heat gun, you can speed matters up by dunking the diffuser into water. Do not do this immediately, but let the edge set first, as otherwise it straightens out again!

The notch at the top left is required by the housing design. The housing has a flat edge where the standard diffuser is mounted, and this is best replicated, as image 5 shows, by bending a narrow strip slightly upwards. This allows the diffuser to sit more firmly.

The hole for the lens is quite exact, and you may find it dificult to remove the lens if it is tight - scrape the edge of the cut-out with a sharp knife to get a better fit.

Actual results

Photo 11 was taken with a single macro lens using the diffuser. The image is well lit (I explicitly under-exposed slightly to get warmer colours). One does get an odd reflection in the eye from the shape of the diffuser as image 12 shows. This can also be seen in image 8 and 9, on the fender. There is nothing you can do about that, but thankfully is not that obvious most of the time.
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