Which way round does the glass go in a PD?

[dmdrewitt]

I have read that you should note which way round the glass comes out of a PD by, for example using a piece of sticky tape.

Is there any way of telling which is the correct side with the film on it? (if it is not noted beforehand with tape)

What are the potential problems if the glass is installed the wrong way round?

dmd

 

[easilyled]

One way I can tell is that there is a faint, circular imprint where the Ti Bezel ring has rubbed against the glass on the outside.

I think the main thing is to try to preserve the AR film (which I believe is on the inside) as it is very fragile on the sapphire windows, so contact with this surface should be avoided as much as possible.

If the AR film is rubbed off it will reduce the amount of light transmittance by quite a considerable amount because the sapphire window without any AR film on it absorbs maybe 12% of the light, wheras with the AR, it may be only about 5%.

Another alternative is to get the new 22.6? mm UCL lens from flashlightlens.com which has more durable AR coats on both sides and a claimed light transmittace of about 99%.

However the UCL lens is more fragile and can crack much more easily.

 

[dmdrewitt]

Thanks easilyled

 

[:)>]

Is it easy to get the lens out? After taking it out, is there some special way to store it to make sure that the AR coating doesn't get hurt?

-Goatee

 

[ouchmyfinger]

theres a nice fingerprint on mine now, so be careful. those lenses aren't cheap.