Long pass filters vs dichro's

[astatic]

Hi,

I've seen Planters talked about Long pass filters once in a topic about dichro's before, that they will be "the solution" for loss with dichro's.
They are more expensive as dichro's but when they have a loss of less then 1% then it maybe is worth the extra amount of $$.

I'm not doubt planters is wright, but i want to know more about the long pass filters before i decide to buy them or just choose for dichro's?
When i believe Planters the projector setup should be Red - Green - Blue - Scanners to get these to work.
Can someone who knows how these work explain me?

Thanks!

[badger1666]

I too wish to learn more on these, but for me the order of color would need to be
Green / blue / red scanners or blue/green/ red scanners , but then if the losses are that small with these filters
I dont suppose it matters what order they are ,and would more likely down what filters are available to dictate the order.
It would be great if some one could do a group buy on this sort of thing.
I am not happy with the losses i keep getting with green going through two dichros loosing hundreds of mw off some,
Though i did find using a waveplate did improve this loss ,but would like to find a better solution like these filters

[astatic]

Hi badger1666,

This is the topic i talked about where Planters talks about the long pass filters.
He talks about Red/Green/Blue/scanner.
Only what i see is that the tolerance is very narrow with the edmund's which makes me doubt if they will be the right choice without tec (colourshift wavelenght).

[svandescheur]

very interesting thread astatic ! I'll keep an eye on this one...
my dichro's from laser-wave do also have much power losses...

[astatic]

I've send Planters a PM to ask what kind of Long Pass Filters he was talking about because i contacted Edmunds optics and they told me there filters are not build for operating under 45° but to operate at 0°.
Planters gave me a link to the right filters.
I'm going to contact Edmunds again and order 2 filters to test with, if these work like Planters told i'll be happy and will use them in my projector.
I'll come back as soon as i got them.

[mixedgas]

You can use a normal longpass. You just have to remember that the wavelength shifts as the cosine of the angle. Not everything has to be at 45 degrees. In fact, we used to lay the projector out for the peak angle of the dichro after tests. Often dichroic longpass filters show up on Ebay, and it does not hurt to buy one once in a while for the stockpile.
Or you can ask the vendor to select one from stock for you at 45'.

Steve

[astatic]

Thank you Steve for the info.

@Badger1666,
The color setup should be like Planters said (Red 638, Green 532, Blue 445) because the filters reflects on the lowest wavelength, it always has to pass the beam which comes from the left (left hand entry scanner setup).

Because the filter will be in an angle of 45° the width of the beam will be critical with the 1/2" sized, i've asked Edmunds what the max width of the beam may be because it also has a mounting ring.