How do you make eye glasses look real?

In my latest render I put a pair of glasses on my character, but they came out semi-transparent rather than clear like real glasses.

Does anyone have any tips please?

i don't know if your model is capable of good results with this, but using refraction will add the effect of glasses "bending light". add a bit of reflection to it as well, and possibly specularity depending on previous results. 

basicly look up realistic glass shaders, or read the recent thread about gems. glass and gems effect like in the same way, just need a different refraction index, to get decent results. unless you plan to go for extreme realism, which i won't go into, lots more work :) but this should get you started

Glass is a refractive material. To get real looking glass, you'd best plug a Fresnel node into the Refraction input of the root material node. Refraction index of glass is about 1.45.

There's a bit of a problem though. Refraction in Poser requires that the refractive object does NOT cast a shadow, and that it is NOT transparent. The frame of your pair of glasses won't be transparent, but you probably want it to cast shadows!

The solution is to make the glasses a two-part prop: the frame (parented to the head) and the lenses (parented to the frame). 

Also, for refraction to work, Poser requires a minimum of 2 raytrace bounces. Since the light rays enter the glass from one side, leave it on the other side, hit the face and bounce back through the lens again, you'll need 4 raytrace bounces.

I hope the glass portion is modeled as a double sided lens, and not as a simple one-sided flat shape. If it is, you can get "real" reflections/refractions from the lens. If not, you can make it a double sided lens shape by creating an extra prop from the glass material using the Grouping Tool. Flip the normals of the spawned glass, it'll be the "inside" of the lens.
Use magnets to shape the two glass parts into lens shape. Then it should work.

It'll take a lot of test renders to get things right. But you'll be basing your work on physical reality, which (hopefully) can lead to a high degree of realism.

Good luck!

It largely depends on the "glass" that is used in the lenses.

If the glasses allow me to change the material for the lenses, I usually use the glass material from templargfx's car materials freebie.

Make sure you have raytracing turned on. 4 bounces is the usual.

http://www.renderosity.com/mod/freestuff/index.php?username=templargfx

on a side note, could also plug a "slight domed shaped" pattern into the displacement for the lens, to get the bulge and easily edit the curve shape to what is desired. i do this approach for the ease of changing the curve, but if you aren't good in mat room, or the lens glass isn't uv mapped right, it can easily turn out very wrong

Thanks for the tips.

Raytracing was turned on, with 4 bounces, but I will have a play with the other suggestions, thanks.