Go

[sphelps]

Originally Posted by SeaHorse_Fanatic

When I was doing my Master's thesis work, we videoed salmon using an underwater camera with a bowed lense. It took a special program to digitally "un-bow" the images or to flatten them out so another program would allow us to use the computer mouse to help size the fish without physicall handling them. I don't think that such a program is commercially available but for someone who was reallllllllly determined to do this, it may be possible. You would have to capture images of a grid with known spacing, then click the mouse on each intersection of the lines. Then through trial and error in programming the right algorythm, you could try to find one that spreads out the image until the grid is again flattened digitally. Simple, no?

I think the lining up the camera lense to the plane of the glass is by far the better method than trying to digitally flatten the image using geometry or computer programming

It's actually much more complicated than that and still not possible to correct for the distortion resulting from a bow front.

All camera lenses are actually curved, especially fish eye lenses which are often added with another glass lens to many underwater housings for cameras. This allows for a wider viewing angle and more light intake. The difference though relates to how these lenses are curved and sized.

A simple curved lens will create distortion and blurring effects, often called aberrations, which get worse as you move closer to the edge. The difference is camera lens curvature, including those placed externally on housings or wide angle additions, is not constant but rather aspheric which vary like the shape of a parabola. This combined with setting the proper distance between elements and the lens size, type and radius reduces the effect of aberrations. What you are still left with is simple lens distortion which is easily fixed with various programs including photoshop.

Bow front tanks have constant curvature and a radius or shape which isn't designed for photography in anyway so even if you figured out the correct distance you wouldn't be able to eliminate the major aberrations which cause the blurring effects.

[OceanicCorals-Ian-]

Also, the further the subject is away from the glass the more distortion. The curved glass and water will distort the image unless you position your lens as close to the subject as possible. Have the corals almost touch the glass and you will find that there is less distortion.

Having said that, the lighting will be different as well if your lights aren't fully covering the front part of the tank.