Glass for ports...

Hello all!

I don´t like that my hugy flat port "glass" is make out of plastic and gets scratches very easily. So I thought to change it for a glass one but the question is:

Is there any specification I should take into account when choosing the glass? do you order "optic glass" (whatever that means) or that name doesn´t exist straightforward?

Thank you very much!!

actually hugyfot offers their ports also with optically coated glass on request.

greets, serge

Actually all the manufacturer who have glass port in their catalog use optical grade glass.

Acrilyc port do have a positive feature, being close in density to water, external minor scratches will basically disapear from view once the port is immersed, so the question of the day is... take a long look at your port, is it still usable underwater ? if yes then consider this, a glass port would be useless by then and would need to be replaced.

Glass is harder to scratch but when scratched it usually end up fatally wounded. Can't have your cake and eat it too

Acrilyc port do have a positive feature, being close in density to water, external minor scratches will basically disapear from view once the port is immersed...

I am curious about this statement, which I have heard from many sources. It isn't the density of the plastic or glass that matters. The amount of light that reflects from a material (or scatters from a scratch) depends on the index of refraction difference between the material and seawater.

As a simply approximation you can compute the Fresnel reflectivity of the surface R=(n1-n2)^2/(n1+n2)^2. The index of refraction of BK7 borosilicate glass is around 1.52. The index of refraction of optical grade polycarbonate is varies from 1.583 - 1.59 (www.matweb.com). I will assume the low end of 1.583

The index of seawater varies with temperature and salinity, but it is around 1.34. Therefore the R_glass_water = 4.0% and R_plastic_water = 6.9% The conclusion is that, all things being equal, a scratch in polycarbonate would scatter MORE than an equivalent scratch in glass. Moreover, since polycarbonate is soft, scratches tend to be deeper, which just makes things worse. Of course, being soft, you can polish them out much more easily.

Another disadvantage of plastic that is not often mentioned is that it picks up a strong static charge when rubbed. This acts as a magnet for dust particles. I find it painful to get all of the dust off of my polycarbonate ports, and they don't stay clean for very long. I am planning to change my flat port to glass as soon as possible, especially since Aquatica has made the replacement glass reasonably priced. I will probably not change out my dome port because the glass one is very expensive!