Help identifying eyepiece / camera filters

[Jonk]

I have these 2 filters in my odds n sods box, which came with the bundle I bought last year.

There's no writing on either of them so I don't know what they are.

Can anyone tell me please?

Thanks

[michael.h.f.wilkinson]

They look like dielectric yellow and green filters respectively (probably intended for planetary work). A dielectric filter reflects the unwanted wavelengths rather than absorbing them (like dye-based filters). This explains the reflected light is the complement of the transmitted

[Jonk]

Hmmm...I've not heard of dielectric filters...I'll look them up.

 

So presumably only for planets, and perhaps the moon...not DSOs?

[michael.h.f.wilkinson]

They might be DSO filters, difficult to tell. The greenish one could be an O-III I suppose, the other might perhaps be an LPR filter, but those usually reflect more yellow (for sodium lights)

[Jonk]

I've shined a red torch through the green one and it reflects most of the red light, only letting through a small amount of red.

A red torch through the yellow one reflects a tinge of purple.

[Jonk]

Could they be same / similar to these?

http://www.firstlightoptics.com/rgb-filters-filter-sets/dichroic-rgb-filters-uvir-cut.html

[michael.h.f.wilkinson]

I've shined a red torch through the green one and it reflects most of the red light, only letting through a small amount of red.

A red torch through the yellow one reflects a tinge of purple.

Best think to do is to try the green one out on e.g. M42 (or the Eskimo Nebula). If the contrast increases it is probably some kind of DSO filter. The same could be done with the other. You could also try to look through the other filter at a sodium lamp (the older pure yellow street lights) or a mercury lamp (greenish white, also being phased out in many places). If these lamps nearly disappear, but objects like M42 still stand out, it should work as an LPR filter

[michael.h.f.wilkinson]

Could they be same / similar to these?

http://www.firstlightoptics.com/rgb-filters-filter-sets/dichroic-rgb-filters-uvir-cut.html

Yes, this type of dielectric filter is more usually called a dichroic

[Jonk]

Pointing at a streetlamp will be easy - good idea.

Getting a clear sky might be a bit harder!

Thanks for the advice.

[Jonk]

Here's a camera phone photo of the street light opposite, through a window.

I've put the 2 filters across the phone camera and taken 2 more photos.

The 'yellow' filter didn't appear to make much difference, although you can see some reflected light from the filter reflect back off the window.

The 'green' filter appears to have reflected most of the orange light back.

Does this <ahem> shed any light on these filters?