Variable Polarizing Filters. (Moon) ?

[Daz Type-R]

Hi guys and gals, wondering if anybody can help?

 

I`m not 100% sure but I may of posted this a while ago (can't find the post so maybe not).

 

Quite a while ago, I was given a 2" variable polarizing moon filter, all seemed great, it was in a case, no scratches etc, came to use it a week or so ago for the first time (the moon doesn't really float my boat but I want to start getting into it) and nothing happened, it did not dim the brightness at all, I turned it all the way, then back again, nothing, the moon stayed the same constant brightness.

 

Took it out the EP, pointed it at the Tv and I could not see a thing, so it blocks the light from the TV but not the moon, any body got any ideas at all????

 

Like I say it was free, given to me by somebody so have no issues with binning it, just thought I would ask.

 

Hope somebody can help?

[Brantuk]

If it's a polarising filter then I would guess it has to be turned to the correct orientation to be effective. Like polaroid sunglasses - if you put on one pair and hold another pair against them - then turn the second pair through 90 degrees - it completely blocks out the light. It acts a bit like a blind shutting out horizontal light - the second turned pair shut out the vertical light.

 

Try rotating the filter gradually till you get a dimmer view (rotate the eyepiece in the focuser tube - don't need to touch the filter). You probably had it in the correct orientation by chance when you looked at the TV.

[Tweedledee]

A variable polarising filter is, as Kim says, two polarising filters which can be rotated relative to each other to vary the brightness.

Sometimes people lose one of the polarisers by unscrewing them too far.

Are you sure that you don't just have one half of a variable polarising filter. That could explain why nothing changes when you rotate it.

Edited June 26, 2013 by petersull

[Tweedledee]

If you only have one half, you can usually pick up the other half very cheaply from Astroboot.

[xanthic]

If it's a circular polariser, it will behave differently if viewed from the back to the front

[Tweedledee]

 

Took it out the EP, pointed it at the Tv and I could not see a thing, so it blocks the light from the TV but not the moon, any body got any ideas at all????

 

I gather that LCD screens give out polarized light. Not sure whether it is horizontal or vertical. Therefore, if you look at a screen through a polarizing filter it should dim the view and the dimming can be varied depending on the rotation of the filter, usually between about 40% and 2%.

 

[Daz Type-R]

Thanks for all the reply's guys, next time the scope is out and the moon is up I will give it a go, never really thought about how these things work but all the explanations make sense.

 

Thank you very much.