Albireo with an UHC filter

I just got the filter (Lumicon) and was playing with it a few nights ago. It's mounted in a Van Slyke filter slider system which makes it possible to view with and without the filter with a push of the slide. Just for the heck of it I looked at Albireo and was surprise with a fairly dramatic change it its appearance. With the UHC the yellow star becomes dimmer but sharper and the blue component becomes the richest blue I've ever seen thru a scope -- pretty spectacular, I thought. Give it a try and let me know what you think.
Can anyone explaing what's going on?
Thanks.

Bob Polcyn

Any colour filter (wideband or narrowband) will let parts of the colour spectrum through while reducing other parts. A blue filter will strongly reduce yellow colour, most probably also red and green, while blue passes more or less unfiltered. Assume you have two light sources appearing equally bright to your eye, one yellow and one blue. If you look at these light sources through a blue filter, the light from the blue light source will be much less reduced than that from the yellow light source. In many cases a narrowband filter will make a virtually invisible object stand out while pretty bright stars are strongly reduced in brightness.

I don't have a UHC filter, but an O-III. It is not suited for viewing bright objects (tends to produce double images), but it performs wonders on planetary nebulae and particularly the Veil nebula.

I've exchanged emails with Dale Mais who is seriously into spectroscopy. He thinks that the sharper looking yellow component is likely to be related to narrowing the view to more of the H-alpha region of its spectrum.
The change in blue would be related to good transmission at H-beta and O-II regions.
His thoughts match the published transmission characteristics of the UHC very well.
Fascinating stuff, this. I recommend that you look for yourselves when opportunity allows -- a big change and very pretty view.

Bob Polcyn